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  • richardmitnick 12:12 pm on March 23, 2019 Permalink | Reply
    Tags: "This Is Why The Multiverse Must Exist", , , , , , Ethan Siegel   

    From Ethan Siegel: “This Is Why The Multiverse Must Exist” 

    From Ethan Siegel
    Mar 22, 2019

    1
    The multiverse idea states that there are an arbitrarily large number of Universes like our own out there, embedded in our Multiverse. It’s possible, but not necessary, for other pockets within the Multiverse to exist where the laws of physics are different.

    If you accept cosmic inflation and quantum physics, there’s no way out. The Multiverse is real.

    Look out at the Universe all you want, with arbitrarily powerful technology, and you’ll never find an edge. Space goes on as far as we can see, and everywhere we look we see the same things: matter and radiation. In all directions, we find the same telltale signs of an expanding Universe: the leftover radiation from a hot, dense state; galaxies that evolve in size, mass, and number; elements that change abundances as stars live and die.

    But what lies beyond our observable Universe? Is there an abyss of nothingness beyond the light signals that could possibly reach us since the Big Bang? Is there just more Universe like our own, out there past our observational limits? Or is there a Multiverse, mysterious in nature and forever unable to be seen?

    Unless there’s something seriously wrong with our understanding of the Universe, the Multiverse must be the answer. Here’s why.

    2
    Artist’s logarithmic scale conception of the observable universe. Note that we’re limited in how far we can see back by the amount of time that’s occurred since the hot Big Bang: 13.8 billion years, or (including the expansion of the Universe) 46 billion light years. Anyone living in our Universe, at any location, would see almost exactly the same thing from their vantage point. (WIKIPEDIA USER PABLO CARLOS BUDASSI)

    The Multiverse is an extremely controversial idea, but at its core it’s a very simple concept. Just as the Earth doesn’t occupy a special position in the Universe, nor does the Sun, the Milky Way, or any other location, the Multiverse goes a step farther and claims that there’s nothing special about the entire visible Universe.

    The Multiverse is the idea that our Universe, and all that’s contained within it, is just one small part of a larger structure. This larger entity encapsulates our observable Universe as a small part of a larger Universe that extends beyond the limits of our observations. That entire structure — the unobservable Universe — may itself be part of a larger spacetime that includes many other, disconnected Universes, which may or may not be similar to the Universe we inhabit.

    If this is the idea of the Multiverse, I can understand your skepticism at the notion that we could somehow know whether it does or doesn’t exist. After all, physics and astronomy are sciences that rely on measurable, experimental, or otherwise observational confirmation. If we are looking for evidence of something that exists outside of our visible Universe and leaves no trace within it, it seems that the idea of a Multiverse is fundamentally untestable.

    But there are all sorts of things that we cannot observe that we know must be true. Decades before we directly detected gravitational waves, we knew that they must exist, because we observed their effects.

    Gravitational waves. Credit: MPI for Gravitational Physics/Werner Benger

    Binary pulsars — spinning neutron stars orbiting around one another — were observed to have their revolutionary periods shorten. Something must be carrying energy away, and that thing was consistent with the predictions of gravitational waves.

    3
    Binary pulsars via Universe Today

    4
    The rate of orbital decay of a binary pulsar is highly dependent on the speed of gravity and the orbital parameters of the binary system. We have used binary pulsar data to constrain the speed of gravity to be equal to the speed of light to a precision of 99.8%, and to infer the existence of gravitational waves decades before LIGO and Virgo detected them. (NASA (L), MAX PLANCK INSTITUTE FOR RADIO ASTRONOMY / MICHAEL KRAMER (R))

    While we certainly welcomed the confirmation that LIGO and Virgo provided for gravitational waves via direct detection, we already knew that they needed to exist because of this indirect evidence.


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project


    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    Those who would argue that indirect evidence is no indicator of gravitational waves might still be unconvinced that binary pulsars emit them; LIGO and Virgo didn’t see the gravitational waves that came from the binary pulsars we’ve observed.

    So if we cannot observe the Multiverse directly, what indirect evidence do we have for its existence? How do we know that there’s more unobservable Universe beyond the part we can observe, and how do we know that what we call our Universe is likely just one of many embedded in the Multiverse?

    We look to the Universe itself, and draw conclusions about its nature based on what observations about it reveal.

    4
    The light from the cosmic microwave background and the pattern of fluctuations from it gives us one way to measure the Universe’s curvature. To the best of our measurements, to within 1 part in about 400, the Universe is perfectly spatially flat. (SMOOT COSMOLOGY GROUP / LAWRENCE BERKELEY LABS)

    When we look out to the edge of the observable Universe, we find that the light rays emitted from the earliest times — from the Cosmic Microwave Background [CMB] — make particular patterns on the sky.

    CMB per ESA/Planck

    Gravitational Wave Background from BICEP 2 which ultimately failed to be correct. The Planck team determined that the culprit was cosmic dust.

    ESA/Planck 2009 to 2013

    These patterns not only reveal the density and temperature fluctuations that the Universe was born with, as well as the matter and energy composition of the Universe, but also the geometry of space itself.

    We can conclude from this that space isn’t positively curved (like a sphere) or negatively curved (like a saddle), but rather spatially flat, indicating that the unobservable Universe likely extends far beyond the part we can access. It never curves back on itself, it never repeats, and it has no empty gaps in it. If it is curved, it has a diameter that’s hundreds of times greater than the part we can see.

    With every second that ticks by, more Universe, just like our own, is revealed to us, consistent with this picture.

    5
    The observable Universe might be 46 billion light years in all directions from our point of view, but there’s certainly more, unobservable Universe, perhaps even an infinite amount, just like ours beyond that. Over time, we’ll be able to see more of it, eventually revealing approximately 2.3 times as much matter as we can presently view. (FRÉDÉRIC MICHEL AND ANDREW Z. COLVIN, ANNOTATED BY E. SIEGEL)

    That might indicate that there’s more unobservable Universe beyond the part of our Universe we can access, but it doesn’t prove it, and it doesn’t provide evidence for a Multiverse. There are, however, two concepts in physics that have been established far beyond a reasonable doubt: cosmic inflation and quantum physics.

    Inflation

    4
    Alan Guth, from Highland Park High School and M.I.T., who first proposed cosmic inflation

    HPHS Owls

    Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe) Date 2010 Credit: Alex MittelmannColdcreation

    Alan Guth’s notes:
    5

    Cosmic inflation is the theory that gave rise to the hot Big Bang. Rather than beginning with a singularity, there’s a physical limit to how hot and how dense the initial, early stages of our expanding Universe could have reached. If we had achieved arbitrarily high temperatures in the past, there would be clear signatures that aren’t there:

    large-amplitude temperature fluctuations early on,
    seed density fluctuations limited by the scale of the cosmic horizon,
    and leftover, high-energy relics from early times, like magnetic monopoles.

    6
    Inflation causes space to expand exponentially, which can very quickly result in any pre-existing curved or non-smooth space appearing flat. If the Universe is curved, it has a radius of curvature that is at minimum hundreds of times larger than what we can observe. (E. SIEGEL (L); NED WRIGHT’S COSMOLOGY TUTORIAL (R))

    These signatures are all missing. The temperature fluctuations are at the 0.003% level; the density fluctuations exceed the scale of the cosmic horizon; the limits on monopoles and other relics are incredibly stringent. The fact that these signatures aren’t there have an enormous implication to them: the Universe never reached those arbitrarily high temperatures. Something else came before the hot Big Bang to set it up.

    That’s where cosmic inflation comes in. Theorized in the early 1980s [above], it was designed to solve a number of puzzles with the Big Bang, but did what you’d hope for any new physical theory: it made measurable, testable predictions for observable signatures that would appear within our Universe.

    We see the predicted lack of spatial curvature; we see an adiabatic nature to the fluctuations the Universe was born with; we’ve detected a spectrum and magnitude of initial fluctuations that jibe with inflation’s predictions; we’ve seen the superhorizon fluctuations that inflation predicts must arise.

    6
    Fluctuations in spacetime itself at the quantum scale get stretched across the Universe during inflation, giving rise to imperfections in both density and gravitational waves. Whether inflation arose from an eventual singularity or not is unknown, but the signatures of whether it occurred are accessible in our observable Universe. (E. SIEGEL, WITH IMAGES DERIVED FROM ESA/PLANCK AND THE DOE/NASA/ NSF INTERAGENCY TASK FORCE ON CMB RESEARCH)

    We may not know everything about inflation, but we do have a very strong suite of evidence that supports a period in the early Universe where it occurred. It set up and gave rise to the Big Bang, and predicts a set and spectrum of fluctuations that gave rise to the seeds of structure that grew into the cosmic web we observe today. Only inflation, as far as we know, gives us predictions for our Universe that match what we observe.

    “So, big deal,” you might say. “You took a small region of space, you allowed inflation to expand it to some very large volume, and our observable, visible Universe is contained within that volume. Even if this is all right, this only tells us that our unobservable Universe extends far beyond the visible part. You haven’t established the Multiverse at all.”

    And all of that would be correct. But remember, there’s one more ingredient we need to add in: quantum physics.

    7
    (Illustration: Getty Images)

    6
    An illustration between the inherent uncertainty between position and momentum at the quantum level. There is a limit to how well you can measure these two quantities simultaneously, and uncertainty shows up in places where people often least expect it. (E. SIEGEL / WIKIMEDIA COMMONS USER MASCHEN)

    Inflation is treated as a field, like all the quanta we know of in the Universe, obeying the rules of quantum field theory. In the quantum Universe, there are many counterintuitive rules that are obeyed, but the most relevant one for our purposes is the rule governing quantum uncertainty.

    While we conventionally view uncertainty as mutually occurring between two variables — momentum and position, energy and time, angular momentum of mutually perpendicular directions, etc. — there’s also an inherent uncertainty in the value of a quantum field. As time marches forward, a field value that was definitive at an earlier time now has a less certain value; you can only ascribe probabilities to it.

    In other words, the value of any quantum field spreads out over time.

    8
    As time goes on, even for a simple, single particle, its quantum wavefunction that describes its position will spread out, spontaneously, over time. This happens for all quantum particles for a myriad of properties beyond position, such as the field value. (HANS DE VRIES / PHYSICS QUEST)

    Now, let’s combine this: we have an inflating Universe, on one hand, and quantum physics on the other. We can picture inflation as a ball rolling very slowly on top of a flat hill. So long as the ball remains atop the hill, inflation continues. When the ball reaches the end of the flat part, however, it rolls down into the valley below, which converts the energy from the inflationary field itself into matter and energy.

    This conversion signifies the end of cosmic inflation through a process known as reheating, and it gives rise to the hot Big Bang we’re all familiar with. But here’s the thing: when your Universe inflates, the value of the field changes slowly. In different inflating regions, the field value spreads out by randomly different amounts and in different directions. In some regions, inflation ends quickly; in others, it ends more slowly.

    9
    The quantum nature of inflation means that it ends in some “pockets” of the Universe and continues in others. It needs to roll down the metaphorical hill and into the valley, but if it’s a quantum field, the spreading-out means it will end in some regions while continuing in others. (E. SIEGEL / BEYOND THE GALAXY)

    This is the key point that tells us why a Multiverse is inevitable! Where inflation ends right away, we get a hot Big Bang and a large Universe, where a small part of it might be similar to our own observable Universe. But there are other regions, outside of the region where it ends, where inflation continues for longer.

    Where the quantum spreading occurs in just the right fashion, inflation might end there, too, giving rise to a hot Big Bang and an even larger Universe, where a small portion might be similar to our observable Universe.

    But the other regions aren’t still just inflating, they’re also growing. You can calculate the rate at which the inflating regions grow and compare them to the rate at which new Universes form and hot Big Bangs occur. In all cases where inflation gives you predictions that match the observed Universe, we grow new Universes and newly inflating regions faster than inflation can come to an end.

    10
    Wherever inflation occurs (blue cubes), it gives rise to exponentially more regions of space with each step forward in time. Even if there are many cubes where inflation ends (red Xs), there are far more regions where inflation will continue on into the future. The fact that this never comes to an end is what makes inflation ‘eternal’ once it begins, and what gives rise to our modern notion of a Multiverse. (E. SIEGEL / BEYOND THE GALAXY)

    This picture, of huge Universes, far bigger than the meager part that’s observable to us, constantly being created across this exponentially inflating space, is what the Multiverse is all about. It’s not a new, testable scientific prediction, but rather a theoretical consequence that’s unavoidable, based on the laws of physics as they’re understood today. Whether the laws of physics are identical to our own in those other Universes is unknown.

    If you have an inflationary Universe that’s governed by quantum physics, a Multiverse is unavoidable. As always, we are collecting as much new, compelling evidence as we can on a continuous basis to better understand the entire cosmos. It may turn out that inflation is wrong, that quantum physics is wrong, or that applying these rules the way we do has some fundamental flaw. But so far, everything adds up. Unless we’ve got something wrong, the Multiverse is inevitable, and the Universe we inhabit is just a minuscule part of it.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 11:21 am on March 23, 2019 Permalink | Reply
    Tags: "What Was It Like When Life Began On Earth?", , , , Ethan Siegel, The death of the Martian magnetic field caused its atmosphere to be stripped away rendering it solid and frozen, The planet Earth has had life on it in some form or another for nearly as long as it has existed, While Venus and Mars may have had similar chances radical changes to Venus’ atmosphere rendered it a searing hothouse world after just 200–300 million years   

    From Ethan Siegel: “What Was It Like When Life Began On Earth?” 

    From Ethan Siegel
    Mar 20, 2019

    1
    A planet that is a candidate for being inhabited will no doubt experience catastrophes, collisions, and extinction-level events on it. If life is to survive and thrive on a world, it must possess the right intrinsic and environmental conditions to allow it to persist. Here, an illustration of early Earth’s environment may look fearsome, but life somehow still found a way. (NASA GODDARD SPACE FLIGHT CENTER)

    The planet has had life on it, in some form or another, for nearly as long as Earth has existed.

    If you came to our Solar System right after it formed, you would have seen a completely foreign-looking sight. Our Sun would have been about the same mass it is today, but only about 80% as luminous, as stars heat up as they age. The four inner, rocky worlds would still be there, but three of them would look extremely similar. Venus, Earth, and Mars all had thin atmospheres, liquid water on their surface, and the organic ingredients that could give rise to life.

    While we still don’t know whether life ever took hold on Venus or Mars, we know that by the time Earth was only 100 million years old, there were organisms living on its surface. After billions of years of cosmic evolution gave rise to the elements, molecules, and conditions from which life could exist, our planet became the one where it not only did, but where it thrived. To the best of our scientific knowledge, here’s what those first steps were like.

    2
    A micron-scale view of very primitive organisms. Whether the first organisms formed on Earth or predate the formation of our planet is still an open question, but evidence favors the scenarios where life arises on our world. (ERIC ERBE, DIGITAL COLORIZATION BY CHRISTOPHER POOLEY, BOTH OF USDA, ARS, EMU)

    Life as we know it has a few properties that everyone agrees on. While life on Earth involves carbon-based chemistry (requiring carbon, oxygen, nitrogen, hydrogen, and many other elements like phosphorous, copper, iron, sulfur, and so on) and relies on liquid water, other combinations of elements and molecules may be possible. The four general properties that all life shares, however, are as follows:

    Life has a metabolism, where it harvests energy/resources from an external source for its own use.
    Life responds to external stimuli from its environment, and alters its behavior accordingly.
    Life can grow, adapt to its environment, or can otherwise evolve from its present form into a different one.
    And life can reproduce, creating viable offspring that arise from its own internal processes.

    3
    The formation and growth of a snowflake, a particular configuration of ice crystal. Although crystals have a molecular configuration that allows them to reproduce and copy themselves, they do not utilize energy or encode genetic information. (VYACHESLAV IVANOV / VIMEO.COM/87342468)

    All four of these must be in place, simultaneously, for a population of organisms to be considered alive. Snowflakes and crystals may be able to grow and reproduce, but their lack of a metabolism prevents them from being classified as alive. Proteins may have a metabolism and be able to reproduce, but they do not respond to external stimuli or alter behavior based on what they encounter. Even viruses, which are the most debatable organism on the line between life and non-life, can only reproduce by infecting other successfully living cells, casting doubt on whether they’re classified as living or non-living.

    Many organic materials — chemical compounds like sugars, amino acids, ethyl formate, and even complex ones like polycyclic aromatic hydrocarbons — are found in interstellar space, in asteroids, and were abundant on early Earth. But we do not have evidence that life began prior to Earth’s formation.

    4
    The early Solar System was filled with comets, asteroids, and small clumps of matter that struck practically every world around. This period is historically known as the “late-heavy bombardment”, and is thought to have brought many of the ingredients for life, but not living organisms themselves, to Earth. (NASA)

    Instead, the leading thought is that the Earth was formed with these raw ingredients on it, and perhaps many more. Perhaps nucleotides were common; perhaps proteins and protein fragments came pre-assembled; perhaps lipid layers and bilayers could spontaneously arise in an aqueous environment. In order to go from precursors to life to actual life, however, it’s believed that we needed the right environment.

    These three favorable planets — Venus, Earth, and Mars — all likely had a reasonable level of surface gravity, thin atmospheres, liquid water on their surfaces, and these biochemical precursor molecules. The one thing Earth had that the other two planets likely didn’t, however, was a Moon. While all three worlds likely had a chance to form life for the first time, our Moon helped give us chances that the other worlds may not have had.

    5
    The Earth and Sun, not so different from how they might have appeared 4 billion years ago. In the early stages of the Solar System, Venus and Mars may have looked quite similar. (NASA/TERRY VIRTS)

    The amount of water present on these early planets was very likely enough to create oceans, seas, lakes, and rivers, but not enough to completely cover them in liquid water. This means they all had continents and oceans, and at the interface of the two, there were tidepools: regions where water can stably exist on dry land and be subject to all sorts of energy gradients.

    Sunlight, shadow and night, cycles of evaporation and concentration, porous fluid flow in the presence of minerals, and gradients of water activity could all provide opportunities for molecules to bind together in novel and interesting ways. The effects of tides may be enhanced by the Moon, but all these worlds possess tides due to the Sun. However, there’s an additional energy source that the Earth possesses that likely contributed to life’s origin, that may not have been as spectacular on Venus or Mars.

    6
    Tidal pools, like the ones shown here from Wisconsin, occur at the interface of land and large bodies of water, like lakes, seas, or oceans. A pool with the right conditions and precursor molecules is one candidate for where life could have possibly arisen on Earth.(GOODFREEPHOTOS_COM / PIXABAY)

    That latter factor is thermal activity from the interior of the planet. At the bottom of the oceans, hydrothermal vents are geological hotspots that are excellent candidate locations for life to arise. Even today, they are home to organisms known as extremophiles: bacteria and other lifeforms that can withstand the temperatures that typically break the molecular bonds associated with life processes.

    These vents contain enormous energy gradients as well as chemical gradients, where extremely alkaline vent water mixes with the acidic, carbonic-acid-rich ocean water. Finally, these vents contain both sodium and potassium ions, as well as calcium carbonate structures that could serve as a template for the first cells. The fact that life exists in environments like this points to worlds like Europa or Enceladus as potential homes for life elsewhere in the Solar System today.

    7
    Deep under the sea, around hydrothermal vents, where no sunlight reaches, life still thrives on Earth. How to create life from non-life is one of the great open questions in science today. If life can exist down here, at the bottom of Earth’s oceans, perhaps there’s a chance for life in the deep subsurface oceans of Europa or Enceladus, too. (NOAA/PMEL VENTS PROGRAM)

    But perhaps the most likely location for life to begin on Earth is the best of all worlds: hydrothermal fields. Volcanic activity doesn’t solely occur beneath the oceans, but also on land. Beneath areas of fresh water, these volcanically-active areas provide an additional heat and energy source that can stabilize temperatures and provide an energy gradient. All the while, these locations still allow evaporation/concentration cycles, provide a confined environment that enables the right ingredients to accumulate, and allow a sunlight/night cycle of exposure.

    On Earth, we can be confident that tidepools, hydrothermal vents, and hydrothermal fields were all common. While the precursor molecules certainly originated beyond Earth, it was likely here on our planet that the transformation of non-life into life spontaneously occurred.

    8
    This aerial view of Grand Prismatic Spring in Yellowstone National Park is one of the most iconic hydrothermal features on land in the world. The colors are due to the various organisms living under these extreme conditions, and depend on the amount of sunlight that reaches the various parts of the springs. Hydrothermal fields like this are some of the best candidate locations for life to have arisen on Earth. (JIM PEACO, NATIONAL PARKS SERVICE)

    Over time, the Earth has changed tremendously, as have the living organisms on our planet. We do not know if life arose once, more than once, or in disparate locations. What we do know, however, is that if we reconstruct the evolutionary tree of every extant organism found on Earth today, they all share the same ancestor.

    By studying the genomes of the extant organisms found on our world today, biologists can reconstruct the timescale of what’s known as LUCA: the Last Universal Common Ancestor of life on Earth. By time the Earth was less than 1 billion years old, life already had the ability to transcribe and translate information between DNA, RNA, and proteins, and these mechanisms exist in all organisms today. Whether life arose multiple times is unknown, but it is generally accepted that life as we know it today descended from a single population.

    9
    Scanning electron microscope image at the sub-cellular level. While DNA is an incredibly complex, long molecule, it is made of the same building blocks (atoms) as everything else. To the best of our knowledge, the DNA structure that life is based on may even predate the fossil record. (PUBLIC DOMAIN IMAGE BY DR. ERSKINE PALMER, USCDCP)

    Despite the fact that geological processes can often obscure the fossil record beyond a few hundred million years, we have been able to trace back the origin of life extraordinarily far. Microbial fossils have been found in sandstone dating to 3.5 billion years ago. Graphite, found deposited in metamorphosed sedimentary rock, has been traced back to having biogenic origins, and dates back to 3.8 billion years ago.

    10
    Trilobites fossilized in limestone, from the Field Museum in Chicago. All extant and fossilized organisms can have their lineage traced back to a universal common ancestor that lived an estimated 3.5 billion years ago. (JAMES ST. JOHN / FLICKR)

    At even earlier, more extreme times, the deposits of certain crystals in rocks appear to originate from biological processes, suggesting that Earth was teeming with life as early as 4.3 to 4.4 billion years ago: as soon as 100–200 million years after the Earth and Moon formed. To the best of our knowledge, life on Earth has existed almost as long as Earth itself has.

    11
    Graphite deposits found in Zircon, some of the oldest pieces of evidence for carbon-based life on Earth. These deposits, and the carbon-12 ratios they show in the inclusions, date life on Earth to more than 4 billion years ago. (E A BELL ET AL, PROC. NATL. ACAD. SCI. USA, 2015)

    At some point on our planet, in the very early stages, the molecules that are abundant and precursors to life, under the right energy and chemical conditions, began to simultaneously metabolize energy, respond to the environment, grow, adapt, evolve, and reproduce. Even if it would be unrecognizable to us today, that marks the origin of life. In a radically unbroken string of biological success, our planet has been a living world ever since.

    12
    Hadean diamonds embedded in zircon/quartz. You can find the oldest deposits in panel d, which indicate an age of 4.26 billion years, or nearly the age of Earth itself. (M. MENNEKEN, A. A. NEMCHIN, T. GEISLER, R. T. PIDGEON & S. A. WILDE, NATURE 448 7156 (2007))

    While Venus and Mars may have had similar chances, radical changes to Venus’ atmosphere rendered it a searing hothouse world after just 200–300 million years, while the death of the Martian magnetic field caused its atmosphere to be stripped away, rendering it solid and frozen. While asteroid strikes may send Earth-based life off-world, throughout the Solar System and galaxy, all the evidence suggests that we are where it started.

    By 9.4 billion years after the Big Bang, Earth was teeming with life. We’ve never looked back.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 8:35 am on March 15, 2019 Permalink | Reply
    Tags: "How Much Of The Dark Matter Could Neutrinos Be?", , , , , , Ethan Siegel, , Neutrinos are the only Standard Model particles that behave like dark matter should. But they can’t be the full story   

    From Ethan Siegel: “How Much Of The Dark Matter Could Neutrinos Be?” 

    From Ethan Siegel
    Mar 14, 2019

    They’re the only Standard Model particles that behave like dark matter should. But they can’t be the full story.

    1
    While the web of dark matter (purple) might seem to determine cosmic structure formation on its own, the feedback from normal matter (red) can severely impact galactic scales. Both dark matter and normal matter, in the right ratios, are required to explain the Universe as we observe it. Neutrinos are ubiquitous, but standard, light neutrinos cannot account for most (or even a significant fraction) of the dark matter. (ILLUSTRIS COLLABORATION / ILLUSTRIS SIMULATION)

    All throughout the Universe, there’s more than what we’re capable of seeing. When we look out at the stars moving around within galaxies, the galaxies moving withing groups and clusters, or the largest structures of all that make up the cosmic web, everything tells the same disconcerting story: we don’t see enough matter to explain the gravitational effects that occur. In addition to the stars, gas, plasma, dust, black holes and more, there must be something else in there causing an additional gravitational effect.

    Traditionally, we’ve called this dark matter, and we absolutely require it to explain the full suite of observations throughout the Universe. While it cannot be made up of normal matter — things made of protons, neutrons, and electrons — we do have a known particle that could have the right behavior: neutrinos. Let’s find out how much of the dark matter neutrinos could possibly be.

    2
    The neutrino was first proposed in 1930, but was not detected until 1956, from nuclear reactors. In the years and decades since, we’ve detected neutrinos from the Sun, from cosmic rays, and even from supernovae. Here, we see the construction of the tank used in the solar neutrino experiment in the Homestake gold mine from the 1960s.(BROOKHAVEN NATIONAL LABORATORY)

    At first glance, neutrinos are the perfect dark matter candidate. They barely interact at all with normal matter, and neither absorb nor emit light, meaning that they won’t generate an observable signal capable of being picked up by telescopes. At the same time, because they interact through the weak force, it’s inevitable that the Universe created enormous numbers of them in the extremely early, hot stages of the Big Bang.

    We know that there are leftover photons from the Big Bang, and very recently we’ve also detected indirect evidence that there are leftover neutrinos as well. Unlike the photons, which are massless, it’s possible that neutrinos have a non-zero mass. If they have the right value for their mass based on the total number of neutrinos (and antineutrinos) that exist, they could conceivably account for 100% of the dark matter.

    3
    The largest-scale observations in the Universe, from the cosmic microwave background [CMB]to the cosmic web to galaxy clusters to individual galaxies, all require dark matter to explain what we observe. The large-scale structure requires it, but the seeds of that structure, from the Cosmic Microwave Background, require it too. (CHRIS BLAKE AND SAM MOORFIELD)

    CMB per ESA/Planck


    ESA/Planck 2009 to 2013

    So how many neutrinos are there? That depends on the number of types (or species) of neutrino.

    Although we can detect neutrinos directly using enormous tanks of material designed to capture their rare interactions with matter, this is both incredibly inefficient and is only going to capture a tiny fraction of them. We can see neutrinos that are the result of particle accelerators, nuclear reactors, fusion reactions in the Sun, and cosmic rays interacting with our planet and atmosphere. We can measure their properties, including how they transform into one another, but not the total number of types of neutrino.

    4
    In this illustration, a neutrino has interacted with a molecule of ice, producing a secondary particle — a muon — that moves at relativistic speed in the ice, leaving a trace of blue light behind it. Directly detecting neutrinos has been a herculean but successful effort, and we are still trying to puzzle out the full suite of their nature. (NICOLLE R. FULLER/NSF/ICECUBE)

    U Wisconsin ICECUBE neutrino detector at the South Pole


    But there is a way to make the critical measurement from particle physics, and it comes from a rather unexpected place: the decay of the Z-boson. The Z-boson is the neutral boson that mediates the weak interaction, enabling certain types of weak decays. The Z couples to both quarks and leptons, and whenever you produce one in a collider experiment, there’s a chance that it will simply decay into two neutrinos.

    Those neutrinos are going to be invisible! We cannot typically detect the neutrinos we create from particle decays in colliders, as it would take a detector with the density of a neutron star to capture them. But by measuring what percentage of the decays produce “invisible” signals, we can infer how many types of light neutrino (whose mass is less than half the Z-boson mass) there are. It’s a spectacular and unambiguous result known for decades now: there are three.

    Standard Model of Particle Physics (LATHAM BOYLE AND MARDUS OF WIKIMEDIA COMMONS)


    This diagram displays the structure of the Standard Model, illustrating the key relationships and patterns. In particular, this diagram depicts all of the particles in the Standard Model, the role of the Higgs boson, and the structure of electroweak symmetry breaking, indicating how the Higgs vacuum expectation value breaks electroweak symmetry, and how the properties of the remaining particles change as a consequence. Note that the Z-boson couples to both quarks and leptons, and can decay through neutrino channels. (LATHAM BOYLE AND MARDUS OF WIKIMEDIA COMMONS)

    Coming back to dark matter, we can calculate, based on all the different signals we see, how much extra dark matter is necessary to give us the right amount of gravitation. In every way we know how to look, including:

    from colliding galaxy clusters,
    from galaxies moving within X-ray emitting clusters,
    from the fluctuations in the cosmic microwave background,
    from the patterns found in the large-scale structure of the Universe,
    and from the internal motions of stars and gas within individual galaxies,

    we find that we require about five times the abundance of normal matter to exist in the form of dark matter. It’s a great success of dark matter for modern cosmology that just by adding one ingredient to solve one puzzle, a whole slew of other observational puzzles are also solved.

    5
    Four colliding galaxy clusters, showing the separation between X-rays (pink) and gravitation (blue), indicative of dark matter. On large scales, cold dark matter is necessary, and no alternative or substitute will do.(X-RAY: NASA/CXC/UVIC./A.MAHDAVI ET AL. OPTICAL/LENSING: CFHT/UVIC./A. MAHDAVI ET AL. (TOP LEFT); X-RAY: NASA/CXC/UCDAVIS/W.DAWSON ET AL.; OPTICAL: NASA/ STSCI/UCDAVIS/ W.DAWSON ET AL. (TOP RIGHT); ESA/XMM-NEWTON/F. GASTALDELLO (INAF/ IASF, MILANO, ITALY)/CFHTLS (BOTTOM LEFT); X-RAY: NASA, ESA, CXC, M. BRADAC (UNIVERSITY OF CALIFORNIA, SANTA BARBARA), AND S. ALLEN (STANFORD UNIVERSITY) (BOTTOM RIGHT))

    NASA/Chandra X-ray Telescope



    CFHT Telescope, Maunakea, Hawaii, USA, at Maunakea, Hawaii, USA,4,207 m (13,802 ft) above sea level

    NASA/ESA Hubble Telescope

    ESA/XMM Newton

    If you have three species of light neutrino, it would only take a relatively small amount of mass to account for all the dark matter: a few electron-Volts (about 3 or 4 eV) per neutrino would do it. The lightest particle found in the Standard Model besides the neutrino is the electron, and that has a mass of about 511 keV, or hundreds of thousands of times the neutrino mass we want.

    Unfortunately, there are two big problems with having light neutrinos that are that massive. When we look in detail, the idea of massive neutrinos is insufficient to make up 100% of the dark matter.

    6
    A distant quasar will have a big bump (at right) coming from the Lyman-series transition in its hydrogen atoms. To the left, a series of lines known as a forest appears. These dips are due to the absorption of intervening gas clouds, and the fact that the dips have the strengths they do place constraints on the temperature of dark matter. It cannot be hot. (M. RAUCH, ARAA V. 36, 1, 267 (1998))

    The first problem is that neutrinos, if they are the dark matter, would be a form of hot dark matter. You might have heard the phrase “cold dark matter” before, and what it means is that the dark matter must be moving slowly compared to the speed of light at early times.

    Why?

    If dark matter were hot, and moving quickly, it would prevent the gravitational growth of small-scale structure by easily streaming out of it. The fact that we form stars, galaxies, and clusters of galaxies so early rules this out. The fact that we see the weak lensing signals we do rules this out. The fact that we see the pattern of fluctuations in the cosmic microwave background rules this out. And direct measurements of clouds of gas in the early Universe, through a technique known as the Lyman-α forest, definitively rule this out. Dark matter cannot be hot.

    7
    The dark matter structures which form in the Universe (left) and the visible galactic structures that result (right) are shown from top-down in a cold, warm, and hot dark matter Universe. From the observations we have, at least 98%+ of the dark matter must be cold. (ITP, UNIVERSITY OF ZURICH)

    A number of collaborations have measured the oscillations of one species of neutrinos to another, and this enables us to infer the mass differences between the different types. Since the 1990s, we’ve been able to infer that the mass difference between two of the species are on the order of about 0.05 eV, and the mass difference between a different two species is approximately 0.009 eV. Direct constraints on the mass of the electron neutrino come from tritium decay experiments, and show that the electron neutrino must be less massive than about 2 eV.

    8
    A neutrino event, identifiable by the rings of Cerenkov radiation that show up along the photomultiplier tubes lining the detector walls, showcase the successful methodology of neutrino astronomy. This image shows multiple events, and is part of the suite of experiments paving our way to a greater understanding of neutrinos. (SUPER KAMIOKANDE COLLABORATION)

    Super-Kamiokande experiment. located under Mount Ikeno near the city of Hida, Gifu Prefecture, Japan

    Beyond that, the cosmic microwave background [CMB [above] (from Planck [above]) and the large-scale structure data (from the Sloan Digital Sky Survey) tells us that the sum of all the neutrino masses is at most approximately 0.1 eV, as too much hot dark matter would definitively affect these signals. From the best data we have, it appears that the mass values that the known neutrinos have are very close to the lowest values that the neutrino oscillation data implies.

    In other words, only a tiny fraction of the total amount of dark matter is allowed to be in the form of light neutrinos. Given the constraints we have today, we can conclude that approximately 0.5% to 1.5% of the dark matter is made up of neutrinos. This isn’t insignificant; the light neutrinos in the Universe have about the same mass as all the stars in the Universe. But their gravitational effects are minimal, and they cannot make up the needed dark matter.

    THE The Sudbury neutrino observatory, which was instrumental in demonstrating neutrino oscillations and the massiveness of neutrinos. With additional results from atmospheric, solar, and terrestrial observatories and experiments, we may not be able to explain the full suite of what we’ve observed with only 3 Standard Model neutrinos, and a sterile neutrino could still be very interesting as a cold dark matter candidate. (A. B. MCDONALD (QUEEN’S UNIVERSITY) ET AL.,SUDBURY NEUTRINO OBSERVATORY INSTITUTE

    There is an exotic possibility, however, that means we might still have a chance for neutrinos to make a big splash in the world of dark matter: it’s possible that there’s a new, extra type of neutrino. Sure, we have to fit in with all the constraints from particle physics and cosmology that we have already, but there’s a way to make that happen: to demand that if there’s a new, extra neutrino, it’s sterile.

    A sterile neutrino has nothing to do with its gender or fertility; it merely means that it doesn’t interact through the conventional weak interactions today, and that a Z-boson won’t couple to it. But if neutrinos can oscillate between the conventional, active types and a heavier, sterile type, it could not only behave as though it were cold, but could make up 100% of the dark matter. There are experiments that are completed, like LSND and MiniBooNe, as well as experiments planned or in process, like MicroBooNe, PROSPECT, ICARUS and SBND, that are highly suggestive of sterile neutrinos being a real, important part of our Universe.

    LSND experiment at Los Alamos National Laboratory and Virginia Tech>

    FNAL/MiniBooNE

    FNAL/MicrobooNE

    Yale PROSPECT Neutrino experiment


    Yale PROSPECT—A Precision Oscillation and Spectrum Experiment

    INFN Gran Sasso ICARUS, since moved to FNAL


    FNAL/ICARUS

    FNAL Short Baseline Neutrino Detector [SBND]

    Scheme of the MiniBooNE experiment at FNAL

    A high-intensity beam of accelerated protons is focused onto a target, producing pions that decay predominantly into muons and muon neutrinos. The resulting neutrino beam is characterized by the MiniBooNE detector. (APS / ALAN STONEBRAKER)

    If we restrict ourselves to the Standard Model alone, we simply cannot account for the dark matter that must be present in our Universe. None of the particles we know of have the right behavior to explain all of the observations. We can imagine a Universe where neutrinos have relatively large amounts of mass, and that would result in a Universe with significant quantities of dark matter. The only problem is that dark matter would be hot, and lead to an observably different Universe than the one we see today.

    Still, the neutrinos we know of do behave like dark matter, although it only makes up about 1% of the total dark matter out there. That’s not totally insignificant; it equals the mass of all the stars in our Universe! And most excitingly, if there truly is a sterile neutrino species out there, a series of upcoming experiments ought to reveal it over the next few years. Dark matter might be one of the greatest mysteries out there, but thanks to neutrinos, we have a chance at understanding it at least a little bit.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 7:18 am on March 13, 2019 Permalink | Reply
    Tags: "How Much Of The Unobservable Universe Will We Someday Be Able To See?", , Ethan Siegel, SDSS-Sloan Digital Sky Survey,   

    From Ethan Siegel: “How Much Of The Unobservable Universe Will We Someday Be Able To See?” 

    From Ethan Siegel

    Mar 12, 2019

    1
    Our deepest galaxy surveys can reveal objects tens of billions of light years away, but there are more galaxies within the observable Universe we still have yet to reveal. Most excitingly, there are parts of the Universe that are not yet visible today that will someday become observable to us. (SLOAN DIGITAL SKY SURVEY (SDSS))

    SDSS Telescope at Apache Point Observatory, near Sunspot NM, USA, Altitude2,788 meters (9,147 ft)

    As more time passes since the Big Bang, more of the Universe comes into view. But how much?

    Even though it’s been billions of years since the Big Bang, there’s a cosmic limit to how far we can observe the objects that occupy our Universe. The Universe has been expanding all this time, but that expansion rate is both finite and well-measured. If we were to calculate how far a photon emitted at the instant the Big Bang occurred could have traveled by today, we come up with the upper limit to how far we can see in any direction: 46 billion light-years.

    That’s the size of our observable Universe, which contains an estimated two trillion galaxies in various stages of evolutionary development. But beyond that, there ought to be much more Universe beyond the limits of what we can presently see: the unobservable Universe. Thanks to our best measurements of the part we can see, we’re finally figuring out what lies beyond, and how much of it we’ll someday be able to perceive and explore.

    2
    On a logarithmic scale, we can illustrate the entire Universe, going all the way back to the Big Bang. Although we cannot observe farther than this cosmic horizon which is presently a distance of 46.1 billion light-years away, there will be more Universe to reveal itself to us in the future. The observable Universe contains 2 trillion galaxies today, but as time goes on, more Universe will become observable to us. (WIKIPEDIA USER PABLO CARLOS BUDASSI)

    The Big Bang tells us that at some point in the distant past, the Universe was hotter, denser, and expanding much more rapidly than it is today. The stars and galaxies we see throughout the Universe in all directions only exist as they do because the Universe has expanded and cooled, allowing gravitation to pull matter into clumps. Over billions of years, gravitational growth has fueled generations of stars and the formation of galaxies, leading to the Universe we see today.

    Everywhere we look, in all directions, we see a Universe that tells us the same cosmic story. But part of that story is the fact that the farther away we look, the farther we’re looking back in time. The Universe hasn’t been around, forming stars and growing galaxies, forever. According to the Big Bang and the observations that support it, the Universe had a beginning.

    Inflationary Universe. NASA/WMAP


    Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe) Date 2010 Credit: Alex Mittelmann Cold creation


    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey

    In the early stages after the Big Bang, the Universe was filled with a variety of ingredients, and it began with an incredibly rapid initial expansion rate. These two factors — the initial expansion rate and the gravitational effects of everything in the Universe — are the two head-to-head players in the ultimate cosmic race.

    On the one hand, the expansion works to push everything apart, stretching the fabric of space and driving the galaxies and the large-scale structure of the Universe apart. But on the other hand, gravitation attracts all forms of matter and energy, working to pull the Universe back together. Normal matter, dark matter, dark energy, radiation, neutrinos, black holes, gravitational waves and more all play a role in the expanding Universe.

    3
    The relative importance of different energy components in the Universe at various times in the past. Note that when dark energy reaches a number near 100% in the future, the energy density of the Universe (and, therefore, the expansion rate) will remain constant arbitrarily far ahead in time. Owing to dark energy, distant galaxies are already speeding up in their apparent recession speed from us, and have been since the dark energy density was half of the total matter density, 6 billion years ago. (E. SIEGEL)

    The expansion rate began large, but has been decreasing as the Universe expands. There’s a simple reason for this: as the Universe expands, its volume increases, and therefore the energy density goes down. As the density drops, so does the expansion rate. Light that was once too far away from us to be seen can now catch up to us.

    This fact carries with it a huge implication for the Universe: over time, galaxies that were once too distant to be revealed to us will spontaneously come into view. It may have been 13.8 billion years since the Big Bang occurred, but with the expansion of the Universe, there are objects as far away as 46.1 billion light-years whose light is just reaching us.

    4
    An illustration of how redshifts work in the expanding Universe. As a galaxy gets more and more distant, it must travel a greater distance and for a greater time through the expanding Universe. In a dark-energy dominated Universe, this means that individual galaxies will appear to speed up in their recession from us, but that there will be distant galaxies whose light is just reaching us for the first time today. (LARRY MCNISH OF RASC CALGARY CENTER, VIA CALGARY.RASC.CA/REDSHIFT.HTM)

    All told, if we were to add up all the galaxies that exist within this volume of space, we’d find there are a whopping two trillion of them within our observable Universe. As enormous as this number is, it’s still finite, and our observations don’t reveal an edge in space in any direction we look.

    The amount of time that’s passed since the Big Bang, the speed of light, and the ingredients in our Universe determine the limit of what’s observable. Any farther than that, and even something moving at the speed of light since the moment of the hot Big Bang will not have had sufficient time to reach us.

    But all of this will change in time. As the years and aeons tick by, light that was unable to reach us will finally catch up to our eyes, revealing more of the Universe than we’ve ever seen before.

    You might think that if we waited for an arbitrarily long amount of time, we’d be able to see an arbitrarily far distance, and that there would be no limit to how much of the Universe would become visible.

    But in a Universe with dark energy, that simply isn’t the case. As the Universe ages, the expansion rate doesn’t drop to lower and lower values, approaching zero. Instead, there remains a finite and important amount of energy intrinsic to the fabric of space itself. As time goes on in a Universe with dark energy, the more distant objects will appear to recede from our perspective faster and faster. Although there’s still more Universe out there to discover, there’s a limit to how much of it will ever become observable to us.

    5
    The different possible fates of the Universe, with our actual, accelerating fate shown at the right. After enough time goes by, the acceleration will leave every bound galactic or supergalactic structure completely isolated in the Universe, as all the other structures accelerate irrevocably away. We can only look to the past to infer dark energy’s presence and properties, which require at least one constant, but its implications are larger for the future. (NASA & ESA)

    Based on the expansion rate, the amount of dark energy we have, and the present cosmological parameters of the Universe, we can calculate what we call the future visibility limit: the maximum distance we’ll ever be able to observe [The Astrophysical Journal]. Right now, in a 13.8 billion year old Universe, our current visibility limit is 46 billion light-years. Our future visibility limit is approximately 33% greater: 61 billion light-years. There are galaxies out there, right now, whose light is on the way to our eyes, but has not had the opportunity to reach us yet.

    If we were to add up all the galaxies in the parts of the Universe that we’ll someday see but cannot yet access today, we might be shocked to learn that there are more yet-to-be-revealed galaxies than there are galaxies in the visible Universe. There are an additional 2.7 trillion galaxies waiting to show us their light, on top of the 2 trillion we can already access.

    6
    The observable Universe might be 46 billion light years in all directions from our point of view, but there’s certainly more unobservable Universe, perhaps even an infinite amount, just like ours, beyond that. Over time, we’ll be able to see a bit, but not a lot, more of it. (FRÉDÉRIC MICHEL AND ANDREW Z. COLVIN, ANNOTATED BY E. SIEGEL)

    Compared to what the future holds for us, we’re presently only seeing 43% of the galaxies that we’ll someday be able to observe. Beyond our observable Universe lies the unobservable Universe, which ought to look just like the part we can see. The way we know that is through observations of the cosmic microwave background [CMB] and the large-scale structure of the Universe.

    CMB per ESA/Planck


    ESA/Planck 2009 to 2013

    If the Universe were finite in size, had an edge to it, or its properties began to change as we looked to greater distances, our measurements of these phenomena would reveal it. The observed spatial flatness of the Universe tells us that it is neither positively nor negatively curved to a precision of 99.6%, meaning that if it curves back on itself, the unobservable Universe is at least 250 times as large as the presently visible part.

    7
    The magnitudes of the hot and cold spots, as well as their scales, indicate the curvature of the Universe. To the best of our capabilities, we measure it to be perfectly flat. Baryon acoustic oscillations and the CMB, together, provide the best methods of constraining this, down to a combined precision of 0.4%. (SMOOT COSMOLOGY GROUP / LBNL)

    We will never be able to see anything close to those extraordinary distances. The future visibility limit will take us to distances that are presently 61 billion light-years away, but no farther. It will reveal slightly more than twice the volume of the Universe we can observe today. The unobservable Universe, on the other hand, must be at least 23 trillion light years in diameter, and contain a volume of space that’s over 15 million times as large as the volume we can observe.

    8
    The simulated large-scale structure of the Universe shows intricate patterns of clustering that never repeat. But from our perspective, we can only see a finite volume of the Universe, which appears uniform on the largest scales. (V. SPRINGEL ET AL., MPA GARCHING, AND THE MILLENIUM SIMULATION)

    At the same time that we ponder the Universe beyond our observational limits, however, it’s worth remembering how little of that Universe we can actually access or visit. All that we’re looking forward to viewing is based on light that was already emitted many billions of years ago: close to the Big Bang in time. As it stands today, even if we left right now at the speed of light, we wouldn’t be able to reach nearly all of the galaxies throughout space.

    Dark energy is causing the Universe to not only expand, but for distant galaxies to speed up in their apparent recession from us. Although there are a total of 4.7 trillion galaxies that we will someday be able to observe out to a distance of 61 billion light-years, the limit of what we can reach today is much more modest.

    9
    The observable (yellow, containing 2 trillion galaxies) and reachable (magenta, containing 66 billion galaxies) portions of the Universe, which are what they are thanks to the expansion of space and the energy components of the Universe. Beyond the yellow circle is an even larger (imaginary) one containing 4.7 trillion galaxies, the maximum portion of the Universe that will be accessible to us in the far future. (E. SIEGEL, BASED ON WORK BY WIKIMEDIA COMMONS USERS AZCOLVIN 429 AND FRÉDÉRIC MICHEL)

    Only those galaxies within approximately 15 billion light-years, or a quarter of the radius at the future visibility limit, can be reached today, which equates to about 66 billion galaxies only. This is only 1.4% of the total number of galaxies that will ever become visible to us. In other words, in the future, we will have a total of 4.7 trillion galaxies to view. Most of them will only ever appear to us as they were in the very distant past, and most of them will never get to see us as we are today. Of all those galaxies we’ll someday see, 4.634 trillion of them are already forever unreachable, even at the speed of light.

    You might notice an interesting occurrence: the future visibility limit is exactly equal to the reachable limit (of 15 billion light-years) added to the current visibility limit (of 46 billion light-years). This no coincidence; the light that will ultimately reach us is right at that reachable limit today, after journeying 46 billion light-years since the Big Bang. Someday far in the future, it will arrive at our eyes. With each moment that passes, we come ever closer to our ultimate cosmic viewpoint, as the light from the last galactic holdouts continues on its inevitable journey towards us in the expanding Universe.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 1:14 pm on March 5, 2019 Permalink | Reply
    Tags: "This Massive Black Hole Is Mysteriously Quiet and Astronomers Don’t Know Why", , , , Both galaxies pull on each other funneling gas onto each central black hole, , Ethan Siegel, Excessive emission isn’t present in these cores; the galactic centers are even outshone by outlying neutron stars, Exploring higher energies NuSTAR still showed the same missing X-ray problem, Further research is needed; the mystery remains unsolved for now, Galactic mergers should push gas and dust into the centers of galaxies. So why are these two so quiet?, Messier 51 the Whirlpool Galaxy is one of astronomy’s most spectacular objects, Prior studies with NASA’s Chandra X-ray telescope showed fewer X-rays than expected, Scientists have studied the closest largest brightest galaxies to Earth for centuries., Such mergers trigger new waves of star formation and create grand spiral arms and activate supermassive black holes, The small object alongside it the galaxy NGC 5195 is interacting and merging with the Whirlpool galaxy, These results imply black holes flicker on and off more rapidly than anticipated, This enormous face-on galaxy was the first one ever to reveal its spiral structure, This is problematic according to lead author Murray Brightman: “Galactic mergers are supposed to generate black hole growth and the evidence of that would be strong emission of high-energy X-rays. B, This matter then accelerates and gets ejected along powerful jets producing X-ray emissions   

    From Ethan Siegel: “This Massive Black Hole Is Mysteriously Quiet, And Astronomers Don’t Know Why” 

    From Ethan Siegel
    Mar 4, 2019

    Galactic mergers should push gas and dust into the centers of galaxies. So why are these two so quiet?

    1
    The Whirlpool galaxy, Messier 51, is merging with its smaller neighbor, NGC 5195. It’s expected that mergers like this will cause the black holes at the center to become active, but both black holes are much quieter than anticipated. (NASA, ESA AND THE HUBBLE HERITAGE TEAM (STSCI / AURA))

    NASA/ESA Hubble Telescope

    Scientists have studied the closest, largest, brightest galaxies to Earth for centuries.

    2
    Located close to the edge of the handle of the Big Dipper, the Whirlpool galaxy, Messier 51, is a classic example of a close, bright, nearby spiral galaxy. (JEAN-DANIEL PAUGET / FLICKR)

    Messier 51, the Whirlpool Galaxy, is one of astronomy’s most spectacular objects.

    3
    This sketch from the mid-1840s is the first ever one to reveal the spiral structure of any nebula in the night sky. Now known to be a spiral galaxy, Messier 51, the Whirlpool Galaxy, is one of the most well-studied galaxies beyond our Milky Way. (WILLIAM PARSONS, 3RD EARL OF ROSSE (LORD ROSSE))

    This enormous, face-on galaxy was the first one ever to reveal its spiral structure.

    4
    Modern observations can reveal gas, dust, and stars in the optical, ultraviolet, and near-infrared from most observatories on Earth. Both Messier 51 and its companion display fascinating extended properties. (ADAM BLOCK / MOUNT LEMMON SKYCENTER / UNIVERSITY OF ARIZONA)

    U Arizona Mount Lemmon Observatory on Mount Lemmon in the Santa Catalina Mountains 17 mi northeast of Tucson, Arizona ,US. Altitude 2,791 meters (9,157 ft)

    The small object alongside it, the galaxy NGC 5195, is interacting and merging with the Whirlpool galaxy.

    5
    This ultraviolet image of Messier 51, taken by GALEX, reveals the hottest, youngest, most newly-formed stars found in the merging system of the Whirlpool galaxy and its smaller companion. Note how the gas-rich spiral galaxy forms new stars, but the gas-poor companion does not.(NASA / JPL-CALTECH / GALEX)

    NASA/Galex telescope

    Such mergers trigger new waves of star formation, create grand spiral arms, and activate supermassive black holes.

    6
    The gas and dust radiates at much cooler temperatures than the stars, and can be imaged by an infrared observatory like NASA’s Spitzer. Note how much rich gas is present in the central regions; that gas should be feeding the central, supermassive black holes. (NASA / JPL-CALTECH / SPITZER SPACE TELESCOPE)

    NASA/Spitzer Infrared Telescope

    Both galaxies pull on each other, funneling gas onto each central black hole.

    7
    When material gets accelerated and funneled into the enormous magnetic field surrounding a supermassive black hole, it can get ‘beamed’ in a particular direction. When those beams arrive at our eyes, we see a tremendous increase in flux. Galaxies undergoing mergers are expected to have their black holes activated. (KIPAC / SLAC / STANFORD)

    This matter then accelerates and gets ejected along powerful jets, producing X-ray emissions.

    8
    The jet of the active galaxy Pictor A, with X-rays in blue and radio lobes in pink. When galaxies merge together, they’re expected to activate similarly to how this one has. (X-RAY: NASA/CXC/UNIV OF HERTFORDSHIRE/M.HARDCASTLE ET AL., RADIO: CSIRO/ATNF/ATCA)

    NASA/Chandra X-ray Telescope

    CSIRO ATNF Mopra Telescope located near the town of Coonabarabran in north-west New South Wales.

    CSIRO Australia Compact Array, six radio telescopes at the Paul Wild Observatory, is an array of six 22-m antennas located about twenty five kilometres (16 mi) west of the town of Narrabri in Australia.

    Prior studies with NASA’s Chandra X-ray telescope showed fewer X-rays than expected.

    9
    The galaxy Messier 51, observed in the X-ray, shows point sources and extended emissions that correspond to neutron stars, black holes, and very hot gas. The central regions are far fainter than expected for merging galaxies with supermassive black holes, so it was anticipated that the energy would be found with higher-energy X-ray observatories.(NASA/CXC/WESLEYAN UNIV./R.KILGARD ET AL.)

    Exploring higher energies, NuSTAR still showed the same missing X-ray problem.

    NASA/DTU/ASI NuSTAR X-ray telescope

    10
    Bright green sources of high-energy X-ray light captured by NASA’s NuSTAR mission are overlaid on an optical-light image of the Whirlpool galaxy (the spiral in the center of the image) and its companion galaxy, Messier 51b (the bright greenish-white spot above the Whirlpool), taken by the Sloan Digital Sky Survey.

    SDSS Telescope at Apache Point Observatory, near Sunspot NM, USA, Altitude2,788 meters (9,147 ft)

    The bright green spots at the center of the Whirlpool and NGC 5195 are created by material surrounding supermassive black holes; additional X-ray sources in the vicinity contribute to the emission. The known ultraluminous neutron star is located on the left side of the Whirlpool. (NASA/JPL-CALTECH, IPAC)

    Excessive emission isn’t present in these cores; the galactic centers are even outshone by outlying neutron stars.

    11
    A composite image of M51, also known as the Whirlpool Galaxy, shows a majestic spiral galaxy. Chandra finds point-like X-ray sources (purple) that are black holes and neutron stars in binary star systems, along with a diffuse glow of hot gas. Data from Hubble (green) and Spitzer (red) both highlight long lanes of stars and gas laced with dust. A view of M51 with GALEX shows hot, young stars that produce lots of ultraviolet energy (blue). (X-RAY: NASA/CXC/WESLEYAN UNIV./R.KILGARD ET AL; UV: NASA/JPL-CALTECH; OPTICAL: NASA/ESA/S. BECKWITH & HUBBLE HERITAGE TEAM (STSCI/AURA); IR: NASA/JPL-CALTECH/ UNIV. OF AZ/R. KENNICUTT)

    This is problematic, according to lead author Murray Brightman:

    Galactic mergers are supposed to generate black hole growth, and the evidence of that would be strong emission of high-energy X-rays. But we’re not seeing that here.

    12
    Earlier observations of the Whirlpool galaxy with observatories like Chandra and XMM-Newton showed fewer soft (i.e., low-energy) X-rays than anticipated. By exploring higher energies with NASA’s NuSTAR mission, scientists were anticipating that the missing energy would appear there, showcasing an active black hole after all. But the black hole’s lack of activity persists. Astronomers have a puzzle to solve. (NASA / JPL-CALTECH / NUSTAR (NUCLEAR SPECTROSCOPIC TELESCOPE ARRAY))

    ESA/XMM Newton

    These results imply black holes flicker on and off more rapidly than anticipated.

    13
    The galaxy Centaurus A is the closest example of an active galaxy to Earth, with its high-energy jets caused by electromagnetic acceleration around the central black hole. Why some galaxies are active and others are inactive is a deeper puzzle than astronomers realized, and observing the Whirlpool galaxy with NuSTAR is what exposed this hole in our understanding in the first place. (NASA/CXC/CFA/R.KRAFT ET AL.)

    Further research is needed; the mystery remains unsolved for now.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 2:54 pm on February 24, 2019 Permalink | Reply
    Tags: "Ask Ethan: How Can We Measure The Curvature Of Spacetime?", A difference in the height of two atomic clocks of even ~1 foot (33 cm) can lead to a measurable difference in the speed at which those clocks run, A team of physicists working in Europe were able to conjugate three atom interferometers simultaneously, At every point you can infer the force of gravity or the amount of spacetime curvature, , Decades before Newton put forth his law of universal gravitation Italian scientists Francesco Grimaldi and Giovanni Riccioli made the first calculations of the gravitational constant G, , Ethan Siegel, , In the future it may be possible to extend this technique to measure the curvature of spacetime not just on Earth but on any worlds we can put a lander on. This includes other planets moons asteroids , It’s been over 100 years since Einstein and over 300 since Newton. We’ve still got a long way to go, Making multiple measurements of the field gradient simultaneously allows you to measure G between multiple locations that eliminates a source of error: the error induced when you move the apparatus. B, Pound-Rebka experiment, , The same law of gravity governs the entire Universe, We can do even better than the Pound-Rebka experiment today by using the technology of atomic clocks, You can even infer G the gravitational constant of the Universe.   

    From Ethan Siegel: “Ask Ethan: How Can We Measure The Curvature Of Spacetime?” 

    From Ethan Siegel
    Feb 23, 2019

    1
    Instead of an empty, blank, 3D grid, putting a mass down causes what would have been ‘straight’ lines to instead become curved by a specific amount. In General Relativity, we treat space and time as continuous, but all forms of energy, including but not limited to mass, contribute to spacetime curvature. For the first time, we can measure the curvature at Earth’s surface, as well as how that curvature changes with altitude. (CHRISTOPHER VITALE OF NETWORKOLOGIES AND THE PRATT INSTITUTE)

    It’s been over 100 years since Einstein, and over 300 since Newton. We’ve still got a long way to go.

    From measuring how objects fall on Earth to observing the motion of the Moon and planets, the same law of gravity governs the entire Universe. From Galileo to Newton to Einstein, our understanding of the most universal force of all still has some major holes in it. It’s the only force without a quantum description. The fundamental constant governing gravitation, G, is so poorly known that many find it embarrassing. And the curvature of the fabric of spacetime itself went unmeasured for a century after Einstein put forth the theory of General Relativity. But much of that has the potential to change dramatically, as our Patreon supporter Nick Delroy realized, asking:

    Can you please explain to us how awesome this is, and what you hope the future holds for gravity measurement. The instrument is obviously localized but my imagination can’t stop coming up with applications for this.

    The big news he’s excited about, of course, is a new experimental technique that measured the curvature of spacetime due to gravity for the first time [Physical Review Letters].

    2
    The identical behavior of a ball falling to the floor in an accelerated rocket (left) and on Earth (right) is a demonstration of Einstein’s equivalence principle. Although you cannot tell whether an acceleration is due to gravity or any other acceleration from a single measurement, measuring differing accelerations at different points can show whether there’s a gravitational gradient along the direction of acceleration. (WIKIMEDIA COMMONS USER MARKUS POESSEL, RETOUCHED BY PBROKS13)

    Think about how you might design an experiment to measure the strength of the gravitational force at any location in space. Your first instinct might be something simple and straightforward: take an object at rest, release it so it’s in free-fall, and observe how it accelerates.

    By measuring the change in position over time, you can reconstruct what the acceleration at this location must be. If you know the rules governing the gravitational force — i.e., you have the correct law of physics, like Newton’s or Einstein’s theories — you can use this information to determine even more information. At every point, you can infer the force of gravity or the amount of spacetime curvature. Beyond that, if you know additional information (like the relevant matter distribution), you can even infer G, the gravitational constant of the Universe.

    3
    Newton’s law of Universal Gravitation relied on the concept of an instantaneous action (force) at a distance, and is incredibly straightforward. The gravitational constant in this equation, G, along with the values of the two masses and the distance between them, are the only factors in determining a gravitational force. Although Newton’s theory has since been superseded by Einstein’s General Relativity, G also appears in Einstein’s theory. (WIKIMEDIA COMMONS USER DENNIS NILSSON)

    This simple approach was the first one taken to investigate the nature of gravity. Building on the work of others, Galileo determined the gravitational acceleration at Earth’s surface. Decades before Newton put forth his law of universal gravitation, Italian scientists Francesco Grimaldi and Giovanni Riccioli made the first calculations of the gravitational constant, G.

    But experiments like this, as valuable as they are, are limited. They can only give you information about gravitation along one dimension: towards the center of the Earth. Acceleration is based on either the sum of all the net forces (Newton) acting on an object, or the net curvature of spacetime (Einstein) at one particular location in the Universe. Since you’re observing an object in free-fall, you’re only getting a simplistic picture.

    4
    According to legend, the first experiment to show that all objects fell at the same rate, irrespective of mass, was performed by Galileo Galilei atop the Leaning Tower of Pisa. Any two objects dropped in a gravitational field, in the absence of (or neglecting) air resistance, will accelerate down to the ground at the same rate. This was later codified as part of Newton’s investigations into the matter. (GETTY IMAGES)

    Thankfully, there’s a way to get a multidimensional picture as well: perform an experiment that’s sensitive to changes in the gravitational field/potential as an object changes its position. This was first accomplished, experimentally, in the 1950s by the Pound-Rebka experiment [ Explanation of the Pound-Rebka experiment http://vixra.org/pdf/1212.0035v1.pdf ].

    What the experiment did was cause a nuclear emission at a low elevation, and note that the corresponding nuclear absorption didn’t occur at a higher elevation, presumably due to gravitational redshift, as predicted by Einstein. Yet if you gave the low-elevation emitter a positive boost to its speed, through attaching it to a speaker cone, that extra energy would balance the loss of energy that traveling upwards in a gravitational field extracted. As a result, the arriving photon has the right energy, and absorption occurs. This was one of the classical tests of General Relativity, confirming Einstein where his theory’s predictions departed from Newton’s.

    5
    Physicist Glen Rebka, at the lower end of the Jefferson Towers, Harvard University, calling Professor Pound on the phone during setup of the famed Pound-Rebka experiment. (CORBIS MEDIA / HARVARD UNIVERSITY)

    We can do even better than the Pound-Rebka experiment today, by using the technology of atomic clocks. These clocks are the best timekeepers in the Universe, having surpassed the best natural clocks — pulsars — decades ago. Now capable of monitoring time differences to some 18 significant features between clocks, Nobel Laureate David Wineland led a team that demonstrated that raising an atomic clock by barely a foot (about 33 cm in the experiment) above another one caused a measurable frequency shift in what the clock registered as a second.

    If we were to take these two clocks to any location on Earth, and adjust the heights as we saw fit, we could understand how the gravitational field changes as a function of elevation. Not only can we measure gravitational acceleration, but the changes in acceleration as we move away from Earth’s surface.

    6
    A difference in the height of two atomic clocks of even ~1 foot (33 cm) can lead to a measurable difference in the speed at which those clocks run. This allows us to measure not only the strength of the gravitational field, but the gradient of the field as a function of altitude/elevation. (DAVID WINELAND AT PERIMETER INSTITUTE, 2015)



    But even these achievements cannot map out the true curvature of space. That next step wouldn’t be achieved until 2015: exactly 100 years after Einstein first put forth his theory of General Relativity. In addition, there was another problem that has cropped up in the interim, which is the fact that various methods of measuring the gravitational constant, G, appear to give different answers.

    Three different experimental techniques have been used to determine G: torsion balances, torsion pendulums, and atom interferometry experiments. Over the past 15 years, measured values of the gravitational constant have ranged from as high as 6.6757 × 10–11 N/kg2⋅m2 to as low as 6.6719 × 10–11 N/kg2⋅m2. This difference of 0.05%, for a fundamental constant, makes it one of the most poorly-determined constants in all of nature.

    6
    In 1997, the team of Bagley and Luther performed a torsion balance experiment that yielded a result of 6.674 x 10^-11 N/kg²/m², which was taken seriously enough to cast doubt on the previously reported significance of the determination of G. Note the relatively large variations in the measured values, even since the year 2000.(DBACHMANN / WIKIMEDIA COMMONS)

    But that’s where the new study, first published in 2015 but refined many times over the past four years, comes in. A team of physicists, working in Europe, were able to conjugate three atom interferometers simultaneously. Instead of using just two locations at different heights, they were able to get the mutual differences between three different heights at a single location on the surface, which enables you to not simply get a single difference, or even the gradient of the gravitational field, but the change in the gradient as a function of distance.

    When you explore how the gravitational field changes as a function of distance, you can understand the shape of the change in spacetime curvature. When you measure the gravitational acceleration in a single location, you’re sensitive to everything around you, including what’s underground and how it’s moving. Measuring the gradient of the field is more informative than just a single value; measuring how that gradient changes gives you even more information.

    7
    The scheme of the experiment that measures the three atomic groupings launched in rapid sequence and then excited by lasers to measure not only the gravitational acceleration, but showing the effects of the changes in curvature that had never been measured before. (G. ROSI ET AL., PHYS. REV. LETT. 114, 013001, 2015)

    That’s what makes this new technique so powerful. We’re not simply going to a single location and finding out what the gravitational force is. Nor are we going to a location and finding out what the force is and how that force is changing with elevation. Instead, we’re determining the gravitational force, how it changes with elevation, and how the change in the force is changing with elevation.

    “Big deal,” you might say, “we already know the laws of physics. We know what those laws predict. Why should I care that we’re measuring something that confirms to slightly better accuracy what we’ve known should be true all along?”

    Well, there are multiple reasons. One is that making multiple measurements of the field gradient simultaneously allows you to measure G between multiple locations that eliminates a source of error: the error induced when you move the apparatus. By making three measurements, rather than two, simultaneously, you get three differences (between 1 and 2, 2 and 3, and 1 and 3) rather than just 1 (between 1 and 2).

    8
    The top of the Makkah royal clock tower runs a few quadrillionths of a second faster than the same clock would at the base, due to differences in the gravitational field. Measuring the changes in the gradient of the gravitational field provides even more information, enabling us to finally measure the curvature of space directly. (AL JAZEERA ENGLISH C/O: FADI EL BENNI)

    But another reason that’s perhaps even more important is to better understand the gravitational pull of the objects we’re measuring. The idea that we know the rules governing gravity is true, but we only know what the gravitational force should be if we know the magnitude and distribution of all the masses that are relevant to our measurement. The Earth, for example, is not a uniform structure at all. There are fluctuations in the gravitational strength we experience everywhere we go, dependent on factors like:

    the density of the crust beneath your feet,
    the location of the crust-mantle boundary,
    the extent of isostatic compensation that takes place at that boundary,
    the presence or absence of oil reservoirs or other density-varying deposits underground,

    and so on. If we can implement this technique of three-atom interferometry wherever we like on Earth, we can better understand our planet’s interior simply by making measurements at the surface.

    9
    Various geologic zones in the Earth’s mantle create and move magma chambers, leading to a variety of geological phenomena. It’s possible that external intervention could trigger a catastrophic event. Improvements in geodesy could improve our understanding of what’s happening, existing, and changing beneath Earth’s surface. (KDS4444 / WIKIMEDIA COMMONS)

    In the future, it may be possible to extend this technique to measure the curvature of spacetime not just on Earth, but on any worlds we can put a lander on. This includes other planets, moons, asteroids and more. If we want to do asteroid mining, this could be the ultimate prospecting tool. We could improve our geodesy experiments significantly, and improve our ability to monitor the planet. We could better track internal changes in magma chambers, as just one example. If we applied this technology to upcoming spacecrafts, it could even help correct for Newtonian noise in next-generation gravitational wave observatories like LISA or beyond.


    ESA/NASA eLISA space based, the future of gravitational wave research

    10
    The gold-platinum alloy cubes, of central importance to the upcoming LISA mission, have already been built and tested in the proof-of-concept LISA Pathfinder mission.

    ESA/LISA Pathfinder


    This image shows the assembly of one of the Inertial Sensor Heads for the LISA Technology Package (LTP). Improved techniques for accounting for Newtonian noise in the experiment might improve LISA’s sensitivity significantly. (CGS SPA)

    The Universe is not simply made of point masses, but of complex, intricate objects. If we ever hope to tease out the most sensitive signals of all and learn the details that elude us today, we need to become more precise than ever. Thanks to three-atom interferometry, we can, for the first time, directly measure the curvature of space.

    Understanding the Earth’s interior better than ever is the first thing we’re going to gain, but that’s just the beginning. Scientific discovery isn’t the end of the game; it’s the starting point for new applications and novel technologies. Come back in a few years; you might be surprised at what becomes possible based on what we’re learning for the first time today.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 3:02 pm on February 16, 2019 Permalink | Reply
    Tags: Ask Ethan: What Will Our First Direct Image Of An Earth-Like Exoplanet Look Like?, , , , , Ethan Siegel, You’d be amazed at what you can learn from even one single pixel   

    From Ethan Siegel: “Ask Ethan: What Will Our First Direct Image Of An Earth-Like Exoplanet Look Like?” 

    From Ethan Siegel
    Feb 16, 2019

    You’d be amazed at what you can learn from even one single pixel.

    1
    Left, an image of Earth from the DSCOVR-EPIC camera. Right, the same image degraded to a resolution of 3 x 3 pixels, similar to what researchers will see in future exoplanet observations.(NOAA/NASA/STEPHEN KANE)

    NOAA DISCOVR Deep Space Climate Observatory

    NOAA Deep Space Climate Observatory

    NASA EPIC (Earth Polychromatic Imaging Camera) on NOAA DSCOVR (Deep Space Climate Observatory)

    Over the past decade, owing largely to NASA’s Kepler mission, our knowledge of planets around star systems beyond our own has increased tremendously.

    NASA/Kepler Telescope

    From just a few worlds — mostly massive, with quick, inner orbits, and around lower-mass stars — to literally thousands of widely-varying sizes, we now know that Earth-sized and slightly larger worlds are extremely common. With the next generation of coming observatories from both space (like the James Webb Space Telescope) and the ground (with observatories like GMTand ELT), the closest such worlds will be able to be directly imaged. What will that look like? That’s what Patreon supporter Tim Graham wants to know, asking:

    “[W]hat kind of resolution can we expect? [A] few pixels only or some features visible?”

    The picture itself won’t be impressive. But what it will teach us is everything we could reasonably dream of.

    NASA/ESA/CSA Webb Telescope annotated

    Giant Magellan Telescope, to be at the Carnegie Institution for Science’s Las Campanas Observatory, to be built some 115 km (71 mi) north-northeast of La Serena, Chile, over 2,500 m (8,200 ft) high

    ESO/E-ELT,to be on top of Cerro Armazones in the Atacama Desert of northern Chile. located at the summit of the mountain at an altitude of 3,060 metres (10,040 ft).

    2
    An artist’s rendition of Proxima b orbiting Proxima Centauri. With 30-meter class telescopes like GMT and ELT, we’ll be able to directly image it, as well as any outer, yet-undetected worlds. However, it won’t look anything like this through our telescopes. (ESO/M. KORNMESSER)

    Let’s get the bad news out of the way first. The closest star system to us is the Alpha Centauri system, itself located just over 4 light years away. It consists of three stars:

    Alpha Centauri A, which is a Sun-like (G-class) star,
    Alpha Centauri B, which is a little cooler and less massive (K-class), but orbits Alpha Centauri A at a distance of the gas giants in our Solar System, and
    Proxima Centauri, which is much cooler and less massive (M-class), and is known to have at least one Earth-sized planet.

    Centauris Alpha Beta Proxima 27, February 2012. Skatebiker

    While there might be many more planets around this trinary star system, the fact is that planets are small and the distances to them, particularly beyond our own Solar System, are tremendous.

    3
    This diagram shows the novel 5-mirror optical system of ESO’s Extremely Large Telescope (ELT). Before reaching the science instruments the light is first reflected from the telescope’s giant concave 39-metre segmented primary mirror (M1), it then bounces off two further 4-metre-class mirrors, one convex (M2) and one concave (M3). The final two mirrors (M4 and M5) form a built-in adaptive optics system to allow extremely sharp images to be formed at the final focal plane. This telescope will have more light-gathering power and better angular resolution, down to 0.005″, than any telescope in history. (ESO)

    The largest telescope being built of all, the ELT, will be 39 meters in diameter, meaning it has a maximum angular resolution of 0.005 arc seconds, where 60 arc seconds make up 1 arc minute, and 60 arc minutes make up 1 degree. If you put an Earth-sized planet at the distance of Proxima Centauri, the nearest star beyond our Sun at 4.24 light years, it would have an angular diameter of 67 micro-arc seconds (μas), meaning that even our most powerful upcoming telescope would be about a factor of 74 too small to fully resolve an Earth-sized planet.

    The best we could hope for was a single, saturated pixel, where the light bled into the surrounding, adjacent pixels on our most advanced, highest-resolution cameras. Visually, it’s a tremendous disappointment for anyone hoping to get a spectacular view like the illustrations NASA has been putting out.

    5
    Artist’s conception of the exoplanet Kepler-186f, which may exhibit Earth-like (or early, life-free Earth-like) properties. As imagination-sparking as illustrations like this are, they’re mere speculations, and the incoming data won’t provide any views akin to this at all. (NASA AMES/SETI INSTITUTE/JPL-CALTECH)


    But that’s where the letdown ends. By using coronagraph technology, we’ll be able to block out the light from the parent star, viewing the light from the planet directly. Sure, we’ll only get a pixel’s worth of light, but it won’t be one continuous, steady pixel at all. Instead, we’ll get to monitor that light in three different ways:

    In a variety of colors, photometrically, teaching us what the overall optical properties of any imaged planet are.

    Spectroscopically, which means we can break that light up into its individual wavelengths, and look for signatures of particular molecules and atoms on its surface and in its atmosphere.

    Over time, meaning we can measure how both of the above change as the planet both rotates on its axis and revolves, seasonally, around its parent star.

    From just a single pixel’s worth of light, we can determine a whole slew of properties about any world in question. Here are some of the highlights.

    6
    Illustration of an exoplanetary system, potentially with an exomoon orbiting it. (NASA/DAVID HARDY, VIA ASTROART.ORG)

    By measuring the light reflecting off of a planet over the course of its orbit, we’ll be sensitive to a variety of phenomena, some of which we already see on Earth. If the world has a difference in albedo (reflectivity) from one hemisphere to another, and rotates in any fashion other than one that’s tidally locked to its star in a 1-to-1 resonance, we’ll be able to see a periodic signal emerging as the star-facing side changes with time.

    A world with continents and oceans, for example, would display a signal that rose-and-fell in a variety of wavelengths, corresponding to the portion that was in direct sunlight reflecting that light back to our telescopes here in the Solar System.

    7
    Hundreds of candidate planets have been discovered so far in the data collected and released by NASA’s Transiting Exoplanet Survey Satellite (TESS), with eight of them having been confirmed thus far by follow-up measurements.

    NASA/MIT TESS

    Three of the most unique, interesting exoplanets are illustrated here, with many more to come. Some of the closest worlds to be discovered by TESS will be candidates for being Earth-like and within the reach of direct imaging. (NASA/MIT/TESS)

    Owing to the power of direct imaging, we could directly measure changes in the weather on a planet beyond our own Solar System.

    8
    The 2001–2002 composite images of the Blue Marble, constructed with NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) data.

    NASA Terra MODIS schematic

    NASA Terra satellite

    As an exoplanet rotates and its weather changes, we can tease out or reconstruct variations in the planetary continent/ocean/icecap ratios, as well as the signal of cloud cover.(NASA)

    Life may be a more difficult signal to tease out, but if there were an exoplanet with life on it, similar to Earth, we would see some very specific seasonal changes. On Earth, the fact that our planet rotates on its axis means that in winter, where our hemisphere faces away from the Sun, the icecaps grow larger, the continents grow more reflective with snow extending down to lower latitudes, and the world becomes less green in its overall color.

    Conversely, in the summer, our hemisphere faces towards the Sun. The icecaps shrink while the continents turn green: the dominant color of plant life on our planet. Similar seasonal changes will affect the light coming from any exoplanet we image, allowing us to tease out not only seasonal variations, but the specific percent changes in color distribution and reflectivity.

    8
    In this image of Titan, the methane haze and atmosphere is shown in a near-transparent blue, with surface features beneath the clouds displayed. A composite of ultraviolet, optical, and infrared light was used to construct this view. By combining similar data sets over time for a directly imaged exoplanet, even with just a single pixel, we could reconstruct a huge slew of its atmospheric, surface, and seasonal properties. (NASA/JPL/SPACE SCIENCE INSTITUTE)

    Overall planetary and orbital characteristics should emerge as well. Unless we’ve observed a planetary transit from our point of view — where the planet in question passes between us and the star it orbits — we cannot know the orientation of its orbit.

    Planet transit. NASA/Ames

    This means we can’t know what the planet’s mass is; we can only know some combination of its mass and the angle of its orbit’s tilt.

    But if we can measure how the light from it changes over time, we can infer what its phases must look like, and how those change over time. We can use that information to break that degeneracy, and determine its mass and orbital tilt, as well as the presence or absence of any large moons around that planet. From even just a single pixel, the way the brightness changes once color, cloud cover, rotation, and seasonal changes are subtracted out should allow us to learn all of this.

    9
    The phases of Venus, as viewed from Earth, are analogous to an exoplanet’s phases as it orbits its star. If the ‘night’ side exhibits certain temperature/infrared properties, exactly the ones that James Webb [above] will be sensitive to, we can determine whether they have atmospheres, as well as spectroscopically determining what the atmospheric contents are. This remains true even without measuring them directly via a transit. (WIKIMEDIA COMMONS USERS NICHALP AND SAGREDO)

    This will be important for a huge number of reasons. Yes, the big, obvious hope is that we’ll find an oxygen-rich atmosphere, perhaps even coupled with an inert but common molecule like nitrogen gas, creating a truly Earth-like atmosphere. But we can go beyond that and look for the presence of water. Other signatures of potential life, like methane and carbon dioxide, can be sought out as well. And another fun advance that’s greatly underappreciated today will come in the direct imaging of super-Earth worlds. Which ones have giant hydrogen and helium gas envelopes and which ones don’t? In a direct fashion, we’ll finally be able to draw a conclusive line.

    10
    The classification scheme of planets as either rocky, Neptune-like, Jupiter-like or stellar-like. The border between Earth-like and Neptune-like is murky, but direct imaging of candidate super-Earth worlds should enable us to determine whether there’s a gas envelope around each planet in question or not. (CHEN AND KIPPING, 2016, VIA ARXIV.ORG/PDF/1603.08614V2.PDF)

    If we truly wanted to image features on a planet beyond our Solar System, we’d need a telescope hundreds of times as large as the largest ones currently being planned: multiple kilometers in diameter. Until that day comes, however, we can look forward to learning so many important things about the nearest Earth-like worlds in our galaxy. TESS is out there, finding those planets right now. James Webb is complete, waiting for its 2021 launch date. Three 30-meter class telescopes are in the works, with the first one (GMT) slated to come online in 2024 and the largest one (ELT) to see first light in 2025. By this time a decade from now, we’ll have direct image (optical and infrared) data on dozens of Earth-sized and slightly larger worlds, all beyond our Solar System.

    A single pixel may not seem like much, but when you think about how much we can learn — about seasons, weather, continents, oceans, icecaps, and even life — it’s enough to take your breath away.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 11:24 am on February 13, 2019 Permalink | Reply
    Tags: , , , , , Ethan Siegel, ,   

    From Ethan Siegel: “We Must Not Give Up On Answering The Biggest Scientific Questions Of All” 

    From Ethan Siegel
    Feb 12, 2019

    1
    The doubly charmed baryon, Ξcc++, contains two charm quarks and one up quark, and was first experimentally discovered at CERN. Now, researchers have simulated how to synthesize it from other charmed baryons that ‘melt’ together, and the energy yields are tremendous. To uncover yet-unrevealed truths about the Universe requires investing in experiments that have never yet been performed. (DANIEL DOMINGUEZ, CERN)

    Theoretical work tells you where to look, but only experiments can reveal what you’ll find.

    There are fundamental mysteries out there about the nature of the Universe itself, and it’s our inherent curiosity about those unanswered questions that drives science forward. There’s an incredible amount we’ve learned already, and the successes of our two leading theories — the quantum field theory describing the Standard Model and General Relativity for gravity — is a testament to how far we’ve come in understanding reality itself.

    Many people are pessimistic about our current attempts and future plans to try and solve the great cosmic mysteries that stymie us today. Our best hypotheses for new physics, including supersymmetry, extra dimensions, technicolor, string theory and more, have all failed to yield any experimental confirmation at all. But that doesn’t mean physics is in crisis. It means it’s working exactly as we’d expect: by telling the truth about the Universe. Our next steps will show us how well we’ve been listening.

    2
    From macroscopic scales down to subatomic ones, the sizes of the fundamental particles play only a small role in determining the sizes of composite structures. Whether the building blocks are truly fundamental and/or point-like particles is still not known.(MAGDALENA KOWALSKA / CERN / ISOLDE TEAM)

    CERN ISOLDE

    3
    The ALPHA-g detector, built at Canada’s particle accelerator facility, TRIUMF, is the first of its kind designed to measure the effect of gravity on antimatter. When oriented vertically, it should be able to measure in which direction antimatter falls, and at what magnitude. Experiments such as this were unfathomable a century ago, as antimatter’s existence was not even known. (STU SHEPHERD/TRIUMF)

    4
    In nuclear fusion, two lighter nuclei fuse together to create a heavier one, but where the final products have less mass than the initial reactants, and where energy is therefore released via E = mc². In the ‘melting quark’ scenario, two baryons with heavy quarks produce a doubly-heavy baryon, releasing energy via the same mechanism.(GERALD A. MILLER / NATURE)

    With everything we know about the fundamental particles, we know there should be more to the Universe than just the ones we know of. We cannot explain dark matter’s apparent existence, nor do we understand dark energy or why the Universe expands with the properties it does.

    We do not know why the particles have the masses that they do, why matter dominates the Universe and not antimatter, or why neutrinos have mass at all. We do not know if the proton is stable or will someday decay, or whether gravity is an inherently quantum force in nature. And even though we know the Big Bang was preceded by inflation, we do not know whether inflation itself had a beginning, or was eternal to the past.

    5
    There is certainly new physics beyond the Standard Model, but it might not show up until energies far, far greater than what a terrestrial collider could ever reach. Still, whether this scenario is true or not, the only way we’ll know is to look. In the meantime, properties of the known particles can be better explored with a future collider than any other tool. (UNIVERSE-REVIEW.CA)

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    Most of the ideas one can concoct in physics have already been either ruled out or highly constrained by the data we already have in our coffers. If you want to discover a new particle, field, interaction, or phenomenon, it doesn’t do you any good to postulate something that’s inconsistent with what we already know to be true today. Sure, there might be assumptions we’ve made that later turn out to be incorrect, but the data itself must be in agreement with any new theory.

    6
    The vertices shown in the above Feynman diagrams all contain three Higgs bosons meeting at a single point, which would enable us to measure the Higgs self-coupling, a key parameter in understanding fundamental physics. (ALAIN BLONDEL AND PATRICK JANOT / ARXIV:1809.10041)

    That’s why the greatest amount of effort in physics goes not into new theories or new ideas, but into experiments that push past the regimes we’ve already explored. Sure, finding the Higgs boson may make tremendous headlines, but how strongly does the Higgs couple to the Z-boson? What are all the couplings between those two particles and the others in the Standard Model? How easy are they to create? And once you create them, are there any mutual decays that are different from a standard Higgs decay plus a standard Z-boson decay?

    There’s a technique you can use to probe this: create an electron-positron collision at exactly the mass of the Higgs plus the Z-boson. Instead of a few dozen to perhaps 100 events that create both a Higgs and a Z-boson, which is what the LHC has yielded, you can create thousands, hundreds of thousands, or even millions.

    7
    When you collide electrons at high energies with hadrons (such as protons) moving in the opposite direction at high energies, you can gain the ability to probe the internal structure of the hadrons as never before. This was a trememdous advance of the DESY (German Electron Synchrotron) experiment. (JOACHIM MEYER; DESY / HERA)

    H1 detector at DESY HERA ring

    Not every experiment is designed to make new particles, nor should they be. Some are designed to probe matter that we already know exists, and to study its properties in detail as never before. LEP, the Large Electron-Positron collider and the predecessor to the LHC, never found a single new fundamental particle. Neither did the DESY experiment, which collided electrons with protons. Neither did RHIC, the Relativistic Heavy Ion Collider.

    CERN LEP Collider

    BNL/RHIC


    And that’s to be expected; that wasn’t the point of those colliders. Their purpose was to study the matter that we know exists to never-before-studied precisions.

    6
    With six quarks and six antiquarks to choose from, where their spins can sum to 1/2, 3/2 or 5/2, there are expected to be more pentaquark possibilities than all baryon and meson possibilities combined.(CERN / LHC / LHCB COLLABORATION)

    CERN/LHCb detector

    The purpose of the next great science experiment isn’t to simply look for one new thing or test one new theory. It’s to gather a huge suite of otherwise unattainable data, and to let that data guide the development of the field.

    8
    A hypothetical new accelerator, either a long linear one or one inhabiting a large tunnel beneath the Earth, could dwarf the LHC’s energies. Even at that, there’s no guarantee we’ll find anything new, but we’re certain to find nothing new if we fail to try. (ILC COLLABORATION)

    Linear Collider Collaboration

    CERN FCC Future Circular Collider details of proposed 100km-diameter successor to LHC

    Proposed Future Colliders

    Sure, we can design and build experiments or observatories with an eye towards what we anticipate might be there. But the best bet for the future of science is a multi-purpose machine that can gather large and varied amounts of data that could never be collected without such a tremendous investment. It’s why Hubble was so successful, why Fermilab and the LHC have pushed boundaries as never before, and why future missions such as the James Webb Space Telescope, future 30-meter class observatories like the GMT or the ELT, or future colliders beyond the LHC such as the FCC, CLIC, or the ILC are required if we ever hope to answer the most fundamental questions of all.

    NASA/ESA Hubble Telescope


    LHC

    CERN map


    CERN LHC Tunnel

    CERN LHC particles

    NASA/ESA/CSA Webb Telescope annotated

    Giant Magellan Telescope, to be at the Carnegie Institution for Science’s Las Campanas Observatory, to be built some 115 km (71 mi) north-northeast of La Serena, Chile, over 2,500 m (8,200 ft) high

    ESO/E-ELT,to be on top of Cerro Armazones in the Atacama Desert of northern Chile. located at the summit of the mountain at an altitude of 3,060 metres (10,040 ft).

    CLIC collider

    ILC schematic, being planned for the Kitakami highland, in the Iwate prefecture of northern Japan

    There’s an old saying in business that applies to science just as well: “Faster. Better. Cheaper. Pick two.” The world is moving faster than ever before. If we start pinching pennies and don’t invest in “better,” it’s tantamount to already having given up.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 1:32 pm on February 2, 2019 Permalink | Reply
    Tags: , , , Big Bang Observer, , , , Ethan Siegel, , Gravity is talking. Lisa will listen,   

    From Ethan Siegel: “Ask Ethan: How Can LISA, Without Fixed-Length Arms, Ever Detect Gravitational Waves?” 

    From Ethan Siegel
    2.2.19

    LIGO, here on Earth, has exquisitely-precise distances its lasers travel. With three spacecrafts in motion, how could LISA work?

    Since it began operating in 2015, advanced LIGO has ushered in an era of a new type of astronomy: using gravitational wave signals. The way we do it, however, is through a very special technique known as laser interferometry. By splitting a laser and sending each half of the beam down a perpendicular path, reflecting them back, and recombining them, we can create an interference pattern. If the lengths of those paths change, the interference pattern changes, enabling us to detect those waves. And that leads to the best question I got about science during my recent Astrotour in Iceland, courtesy of Ben Turner, who asked:

    LIGO works by having these exquisitely precise lasers, reflected down perfectly length-calibrated paths, to detect these tiny changes in distance (less than the width of a proton) induced by a passing gravitational wave. With LISA, we plan on having three independent, untethered spacecrafts freely-floating in space. They’ll be affected by all sorts of phenomena, from gravity to radiation to the solar wind. How can we possibly get a gravitational wave signal out of this?


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger

    Gravity is talking. Lisa will listen. Dialogos of Eide

    ESA/eLISA the future of gravitational wave research

    Localizations of gravitational-wave signals detected by LIGO in 2015 (GW150914, LVT151012, GW151226, GW170104), more recently, by the LIGO-Virgo network (GW170814, GW170817). After Virgo came online in August 2018


    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    It’s a great question, and the toughest one posed to me all year thus far. Let’s explore the answer.

    2
    3D rendering of the gravitational waves emitted from a binary neutron star system at merger. The central region (in density) is stretched by a factor of ~5 for better visibility. The orientation of the merger itself determines how the signal will be polarized. (AEI POTSDAM-GOLM)

    Since the dawn of time, humanity has been practicing astronomy with light, which has progressed from naked-eye viewing to the use of telescopes, cameras, and wavelengths that go far beyond the limits of human vision. We’ve detected cosmic particles from space in a wide variety of flavors: electrons, protons, atomic nuclei, antimatter, and even neutrinos.

    But gravitational waves are an entirely new way for humanity to view the Universe. Instead of some detectable, discrete quantum particle that interacts with another, leading to a detectable signal in some sort of electronic device, gravitational waves act as ripples in the fabric of space itself. With a certain set of properties, including:

    propagation speed,
    orientation,
    polarization,
    frequency, and
    amplitude,

    they affect everything occupying the space that they pass through.

    3
    Gravitational waves propagate in one direction, alternately expanding and compressing space in mutually perpendicular directions, defined by the gravitational wave’s polarization. Gravitational waves themselves, in a quantum theory of gravity, should be made of individual quanta of the gravitational field: gravitons. (M. PÖSSEL/EINSTEIN ONLINE)

    When one of these gravitational waves passes through a LIGO-like detector, it does exactly what you might suspect. The gravitational wave, along the direction it propagates at the speed of gravity (which equals the speed of light), doesn’t affect space at all. Along the plane perpendicular to its propagation, however, it alternately causes space to expand and contract in mutually perpendicular directions. There are multiple types of polarization that are possible:

    “plus” (+) polarization, where the up-down and left-right directions expand and contract,
    “cross” (×) polarization, where the left-diagonal and right-diagonal directions expand and contract,
    or “circularly” polarized waves, similar to way light can be circularly polarized; this is a different parameterization of plus and cross polarizations.

    Whatever the physical case, the polarization is determined by the nature of the source.

    When a wave enters a detector, any two perpendicular directions will be compelled to contract and expand, alternately and in-phase, relative to one another. The amount that they contract or expand is related to the amplitude of the wave. The period of the expansion and contraction is determined by the frequency of the wave, which a detector of a specific arm length (or effective arm length, where there are multiple reflections down the arms, as in the case of LIGO) will be sensitive to.

    With multiple such detectors in a variety of orientations to one another in three-dimensional space, the location, orientation, and even polarization of the original source can be reconstructed. By using the predictive power of Einstein’s General Relativity and the effects of gravitational waves on the matter-and-energy occupying the space they pass through, we can learn about events happening all across the Universe.

    4
    LIGO and Virgo have discovered a new population of black holes with masses that are larger than what had been seen before with X-ray studies alone (purple). This plot shows the masses of all ten confident binary black hole mergers detected by LIGO/Virgo (blue), along with the one neutron star-neutron star merger seen (orange). LIGO/Virgo, with the upgrade in sensitivity, should detect multiple mergers every week. (LIGO/VIRGO/NORTHWESTERN UNIV./FRANK ELAVSKY)

    But it’s only due to the extraordinary technical achievement of these interferometers that we can actually make these measurements. In a terrestrial, LIGO-like detector, the distances of the two perpendicular arms are fixed. Laser light, even if reflected back-and-forth along the arms thousands of times, will eventually see the two beams come back together and construct a very specific interference pattern.

    If the noise can be minimized below a certain level, the pattern will hold absolutely steady, so long as no gravitational waves are present.

    If, then, a gravitational wave passes through, and one arm contracts while the other expands, the pattern will shift.

    5
    When the two arms are of exactly equal length and there is no gravitational wave passing through, the signal is null and the interference pattern is constant. As the arm lengths change, the signal is real and oscillatory, and the interference pattern changes with time in a predictable fashion. (NASA’S SPACE PLACE)

    By measuring the amplitude and frequency at which the pattern shifts, the properties of a gravitational wave can be reconstructed. By measuring a coincident signal in multiple such gravitational wave detectors, the source properties and location can be reconstructed as well. The more detectors with differing orientations and locations are present, the better-constrained the properties of the gravitational wave source will be.

    This is why adding the Virgo detector to the twin LIGO detectors in Livingston and Hanford enabled a far superior reconstruction of the location of gravitational wave sources. In the future, additional LIGO-like detectors in Japan and India will allow scientists to pinpoint gravitational waves in an even superior fashion.

    But there’s a limit to what we can do with detectors like this. Seismic noise from being located on the Earth itself limits how sensitive a ground-based detector can be. Signals below a certain amplitude can never be detected. Additionally, when light signals are reflected between mirrors, the noise generated by the Earth accumulates cumulatively.

    The fact that the Earth itself exists in the Solar System, even if there were no plate tectonics, ensures that the most common type of gravitational wave events — binary stars, supermassive black holes, and other low-frequency sources (taking 100 seconds or more to oscillate) — cannot be seen from the ground. Earth’s gravitational field, human activity, and natural geological processes means that these low-frequency signals cannot be practically seen from Earth. For that, we need to go to space.

    And that’s where LISA comes in.

    5
    The sensitivities of a variety of gravitational wave detectors, old, new, and proposed. Note, in particular, Advanced LIGO (in orange), LISA (in dark blue), and BBO (in light blue). LIGO can only detect low-mass and short-period events; longer-baseline, lower-noise observatories are needed for more massive black holes. (MINGLEI TONG, CLASS.QUANT.GRAV. 29 (2012) 155006)

    LISA is the Laser Interferometer Space Antenna. In its current design, it consists of three dual-purpose spacecrafts, separated in an equilateral triangle configuration by roughly 5,000,000 kilometers along each laser arm.

    Inside each spacecraft, there are two free-floating cubes that are shielded by the spacecraft itself from the effects of interplanetary space. They will remain at a constant temperature, pressure, and will be unaffected by the solar wind, radiation pressure, or the bombardment of micrometeorites.

    By carefully measuring the distances between pairs of cubes on different spacecrafts, using the same laser interferometry technique, scientists can do everything that multiple LIGO detectors do, except for these long-period gravitational waves that only LISA is sensitive to. Without the Earth to create noise, it seems like an ideal setup.

    6
    The primary scientific goal of the Laser Interferometer Space Antenna (LISA) mission is to detect and observe gravitational waves from massive black holes and galactic binaries with periods in the range of a tens of seconds to a few hours. This low-frequency range is inaccessible to ground-based interferometers because of the unshieldable background of local gravitational noise arising from atmospheric effects and seismic activity. (ESA-C. VIJOUX)

    But even without the terrestrial effects of human activity, seismic noise, and being deep within Earth’s gravitational field, there are still sources of noise that LISA must contend with. The solar wind will strike the detectors, and the LISA spacecrafts must be able to compensate for that. The gravitational influence of other planets and solar radiation pressure will induce tiny orbital changes relative to one another. Quite simply, there is no way to hold the spacecract at a fixed, constant distance of exactly 5 million km, relative to one another, in space. No amount of rocket fuel or electric thrusters will be able to maintain that exactly.

    Remember: the goal is to detect gravitational waves — themselves a tiny, minuscule signal — over and above the background of all this noise.

    7
    The three LISA spacecraft will be placed in orbits that form a triangular formation with center 20° behind the Earth and side length 5 million km. This figure is not to scale. (NASA)

    So how does LISA plan to do it?

    The secret is in these gold-platinum alloy cubes. In the center of each optical system, a solid cube that’s 4 centimeters (about 1.6″) on each side floats freely in the weightless conditions of space. While external sensors monitor the solar wind and solar radiation pressure, with electronic sensors compensating for those extraneous forces, the gravitational forces from all the known bodies in the Solar System can be calculated and anticipated.

    As the spacecrafts, and the cubes, move relative to one another, the lasers adjust in a predictable, well-known fashion. So long as they continue to reflect off of the cubes, the distances between them can be measured.

    The gold-platinum alloy cubes, of central importance to the upcoming LISA mission, have already been built and tested in the proof-of-concept LISA Pathfinder mission

    ESA/LISA Pathfinder

    It’s not a matter of keeping the distances fixed and measuring a tiny change due to a passing wave; it’s a matter of understanding exactly how the distances will behave over time, accounting for them, and then looking for the periodic departures from those measurements to a high-enough precision. LISA won’t hold the three spacecrafts in a fixed position, but will allow them to adjust freely as Einstein’s laws dictate. It’s only because gravity is so well-understood that the additional signal of the gravitational waves, assuming the wind and radiation from the Sun is sufficiently compensated for, can be teased out.

    8
    The proposed ‘Big Bang Observer’ would take the design of LISA, the Laser Interferometer Space Antenna, and create a large equilateral triangle around Earth’s orbit to get the longest-baseline gravitational wave observatory ever. (GREGORY HARRY, MIT, FROM THE LIGO WORKSHOP OF 2009, LIGO-G0900426)

    If we want to go even farther, we have dreams of putting three LISA-like detectors in an equilateral triangle around different points in Earth’s orbit: a proposed mission called Big Bang Observer (BBO). While LISA can detect binary systems with periods ranging from minutes to hours, BBO will be able to detect the grandest behemonths of all: supermassive binary black holes anywhere in the Universe, with periods of years.

    If we’re willing to invest in it, space-based gravitational wave observatories could allow us to map out all of the most massive, densest objects located throughout the entire Universe. The key isn’t holding your laser arms fixed, but simply in knowing exactly how, in the absence of gravitational waves, they’d move relative to one another. The rest is simply a matter of extracting the signal of each gravitational wave out. Without the Earth’s noise to slow us down, the entire cosmos is within our reach.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 11:42 am on January 5, 2019 Permalink | Reply
    Tags: Ask Ethan: How Close Could Two Alien Civilizations Get To One Another?, , , , , Ethan Siegel, There are lots of steps that have to happen to make life but the ingredients for it are literally everywhere.   

    From Ethan Siegel: “Ask Ethan: How Close Could Two Alien Civilizations Get To One Another?” 

    From Ethan Siegel
    May 12, 2018

    9
    Here on Earth, the closest world to us is our barren, uninhabited moon. But in many imaginable cases, there could be another inhabited world close by our own, maybe even within our Solar System. How close could one be? (flickr user Kevin Gill)

    Here on Earth, all the right conditions occurred for intelligent life to come about, but the nearest aliens, if they’re on another world, are light years away. But it doesn’t have to be that way at all!

    Here on planet Earth, in orbit around the Sun, we’re the only intelligent-life game in town. There might be possibilities for either past life or microbial life elsewhere in the Solar System, but as far as intelligent, complex, differentiated and multicellular life goes, what’s on our world is far more advanced than anything else we could hope to find. Intelligent aliens, if they’re out there inhabiting another world, are at least four light years away. But must that be the case for aliens anywhere in the galaxy? That’s what our Patreon supporter Jason McCampbell wants to know:

    What’s [the] closest two, independent intelligent civilizations could be, ignoring interstellar travel and assuming they develop in different star systems and follow roughly what we know as ‘life’? Globular clusters can have a high density of stars, but does too high a density rule out habitability? An astrophysicist in a dense cluster would have a much different view of the universe and the search for exoplanets.

    There are lots of steps that have to happen to make life, but the ingredients for it are literally everywhere. Even if you’re restricting yourself to looking for life that looks (chemically) like us, the Universe is full of possibilities.

    1
    Atoms can link up to form molecules, including organic molecules and biological processes, in interstellar space as well as on planets. Is it possible that life began not only prior to Earth, but not on a planet at all? (Jenny Mottar)

    You need to form enough heavy elements so that you can have rocky planets, organic molecules, and the building blocks of life. The Universe isn’t born with these! In the aftermath of the Big Bang, the Universe is 99.999999% hydrogen and helium, with no carbon, no oxygen, no nitrogen, phosphorous, calcium, iron, or any of the other complex elements necessary for life. In order to get there, we have to have multiple generations of stars live, burn through their fuel, die in a supernova explosion, and recycle those newly-created heavy elements into the next generation of stars. We need neutron star-neutron star mergers to build up the heaviest elements, many of which are necessary for life processes here on Earth and in our bodies, in copious amounts. This requires a lot of astrophysics to make it so.

    2
    The Omega nebula, known also as Messier 17, is an intense and active region of star formation, viewed edge-on, which explains its dusty and beam-like appearance. Stars that form at different times in the Universe’s history have different abundances of heavy elements. (ESO / VST survey)

    ESO VST interior


    ESO VST telescope, at ESO’s Cerro Paranal Observatory, with an elevation of 2,635 metres (8,645 ft) above sea level

    Even though Earth formed over 9 billion years after the Big Bang, the Universe didn’t have to wait so long. We classify stars into three populations:

    Population I: stars like the Sun, with 1–2% of the elements making them up being heavier than hydrogen and helium. This material is very processed and leads to solar systems with a mix of gas giants and rocky planets capable of housing life.
    Population II: these are mostly older, more pristine stars. They may only have 0.001–0.1% of the heavy elements the Sun has, and most of their worlds are diffuse, gassy worlds. These may be too primitive and too low in heavy elements for life.
    Population III: the first stars in the Universe, that must be entirely unpolluted by heavy elements. These haven’t yet been discovered, but are theoretically the first stars of all.

    When we look at the earliest galaxies, they’re full of pretty much all Population II stars. But nearby, we have a mix of young-and-old, metal-rich and metal-poor stars.

    3
    The distances between the Sun and many of the nearest stars shown here are accurate, but each star — even the largest ones here — would be less than one-one millionth of a pixel in diameter if this were to scale. Image credit: Andrew Z. Colvin, under a c.c.a.-s.a.-3.0.(Andrew Z. Colvin / Wikimedia Commons)

    One of the most important lessons came from the Kepler mission, and specifically the system Kepler-444. This is a Population I star (with planets around it), but it’s much, much older than Earth. While our world is about 4.5 billion years old, Kepler-444 is 11.2 billion years old, meaning that the Universe could’ve formed a world like Earth very early on, at least ~7 billion years earlier than Earth formed. Given that possibility, and the fact that areas like the center of our galaxy got even more metal-rich than our region did very, very quickly, it’s possible that there are locations in the Universe (and perhaps even in the Milky Way) that are even more conducive to bringing about intelligent life than the Sun-Earth system is.

    4
    Sugar molecules in the gas surrounding a young, Sun-like star. The raw ingredients for life may exist everywhere, but not every planet that contains them will develop life. (ALMA (ESO/NAOJ/NRAO)/L. Calçada (ESO) & NASA/JPL-Caltech/WISE Team)

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    NASA Wise Telescope

    So given all that we know about where the stars that are good candidates for life can be, what’s the closest two alien civilizations could be to one another? Where would be the places to look? And what would the answers be under different circumstances? Let’s look at five major possibilities.

    5
    This artist’s impression displays TRAPPIST-1 and its planets reflected in a surface. The potential for water on each of the worlds is also represented by the frost, water pools, and steam surrounding the scene. However, it is unknown whether any of these worlds actually still possess atmospheres, or if they’ve been blown away by their parent star. One thing is certain, however: the potentially habitable worlds are close to each other: separated by only ~1 million km each. (NASA/R. Hurt/T. Pyle)

    1.) The same solar system. This is the real dream. In the early days of our Solar System, it’s plausible that Venus, Earth, and Mars (and potentially even Theia, the hypothetical planet that collided with Earth to create the Moon) all had the same life-friendly conditions. They likely had a crust and atmosphere full of the ingredients for life, along with a past history of liquid water on their surface. Venus and Mars each, at closest approach to Earth, come within a few tens of millions of kilometers: 38 million for Venus and 54 million for Mars. But around an M-class (red dwarf) star, planetary separation distances are much smaller: separation distances are approximately only 1 million km between potentially habitable worlds in the TRAPPIST-1 system. Twin moons around a giant world, or a binary planet, could be even closer. If life succeeds once given certain conditions, why not twice in almost exactly the same place?

    6
    The globular cluster Terzan 5 as seen by the ESO’s Very Large Telescope, with other data as well. The densities in the center of a globular cluster are higher, while still being stable, than anyplace else. (ESO-VLT, F.R. Ferraro et al., HST-NICMOS, ESA/Hubble & NASA)

    ESO VLT at Cerro Paranal in the Atacama Desert, •ANTU (UT1; The Sun ),
    •KUEYEN (UT2; The Moon ),
    •MELIPAL (UT3; The Southern Cross ), and
    •YEPUN (UT4; Venus – as evening star).
    elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo

    NASA/ESA Hubble Telescope

    2.) Within a globular cluster. Globular clusters are massive collections of somewhere around hundreds of thousands of star contained within a sphere of perhaps a few dozen light years in radius. In the outer regions, stars are typically separated by a light year, but in the innermost regions of the densest clusters, star separations may be as small as the distance from the Sun to the Kuiper belt. The orbits of planets within those star systems should be stable even in these dense environments, and given that we know of globular clusters far younger than the 11.2 billion years that Kepler-444 is, there should be good candidates for life and habitability among them. A few hundred astronomical units, although this distance will change over time as stars move, could be a fascinatingly close encounter between two civilizations.

    6
    High resolution near-infrared imaging has led to the discovery of three stellar superclusters at the Galactic Center. Since near-infrared wavelengths cut through the dense dust between Earth and the Galactic Center, we are able to see these superclusters. They include the Central Parsec, Quintuplet, and Arches clusters. But all the stars found there, and in the galactic center in general, are quite young. (Gemini Observatory)

    3.) Near the galactic center. The closer you get to the center of the galaxy, the denser the stars get. Within the central few light years, we have extremely high densities of stars, rivaling what we see in the cores of globular clusters. In some ways, the galactic center is an even denser environment, with large black holes, extremely massive stars, and new star-forming clusters, all things that globular clusters don’t have. But the problem with the stars that we see in the Milky Way’s core is that they’re all relatively young. Perhaps due to the volatility of the environment there, stars rarely make it to even a billion years of age. Despite the increased density, these stars are unlikely to have advanced civilizations. They just don’t live long enough.

    7
    Stars form in a wide variety of sizes, colors and masses, including many bright, blue ones that are tens or even hundreds of times as massive as the Sun. This is demonstrated here in the open star cluster NGC 3766, in the constellation of Centaurus. (ESO)

    4.) In a dense star cluster or spiral arm. Okay, so what about the star clusters that form in the galactic plane? Spiral arms are denser than typical regions of a galaxy, and that’s where new stars are likely to form. The star clusters that remain from those epochs often contain thousands of stars located in a region just a few light years wide. But again, stars don’t remain in these environments for very long. The typical open star cluster dissociates after a few hundred million years, with only a small fraction lasting billions of years. Stars move in-and-out of spiral arms all the time, including the Sun. Overall, even though stars inside may have typical distances between them of between 0.1 and 1 light year, they’re unlikely to be good candidates for life.

    8
    A logarithmic chart of distances, showing the Voyager spacecraft, our Solar System and our nearest star, for comparison. (NASA / JPL-Caltech)

    5.) Distributed throughout interstellar space. Otherwise, we come back to what we see in our own neighborhood: distances that are typically a few light years. As you get closer to the center of a galaxy, you can decrease that to the same distance you see in an open cluster: between 0.1–1 light years. But if you try to get closer than that, you run into the problem we’ve seen too close to the galactic center: mergers, interactions, and other catastrophes are likely to ruin your stable environment. You can get closer, but typical interstellar space isn’t the way to go. If you insist on it, your best bet is to wait for another star to pass close by, something that happens about once every million years for a typical star.

    9
    A plot of how frequently stars within the Milky Way is likely to pass within a certain distance of our Sun. This is a log-log plot, with distance on the y-axis and how long you typically need to wait for such an event to happen on the x-axis. (E. Siegel)

    While we don’t expect intelligent alien life to be ubiquitous and plentiful throughout the Universe in the same way that planets and stars are, every such world that meets the right conditions is a chance. And every time you get a chance, that’s an opportunity, with finite odds, for success. Each one of these possibilities could be real! They may not be likely, but until we go out and find what is (and isn’t) out there, it’s vital to keep an open mind about what the Universe could bring to us as far as alien intelligence is concerned. The truth is no doubt out there, but it’s important to recognize that if we had gotten a lot luckier, it could be closer than we dare to imagine today.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
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