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  • richardmitnick 12:12 pm on March 23, 2019 Permalink | Reply
    Tags: "This Is Why The Multiverse Must Exist", Alan Guth-Inflation theory, , , , ,   

    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.

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    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.

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    Binary pulsars via Universe Today

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    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.

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    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.

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    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.

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    (Illustration: Getty Images)

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    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.

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    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 .

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    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 10:15 am on September 12, 2018 Permalink | Reply
    Tags: "The fractal universe" Part 3, Alan Guth-Inflation theory, Andrei Linde-Professor of Physics, , , , , , ,   

    From Stanford University: “The fractal universe” Part 3 

    Stanford University Name
    From Stanford University

    1
    The concept of a multiverse, created in a fiery bloom of matter and radiation, is a central part of the String Theory Landscape. (Image credit: Eric Nyquist)

    September 12, 2018
    Ker Than

    Late one summer night nearly 40 years ago, Andrei Linde was seized by a sudden conviction that he knew how the universe was born. His nocturnal eureka moment would lead to the concept of a multiverse, a central part of the String Theory Landscape. This story is part 3 of a five-part series.

    Late one summer night in 1981, while still a junior research fellow at Lebedev Physical Institute in Moscow, Andrei Linde was struck by a revelation. Unable to contain his excitement, he shook awake his wife, Renata Kallosh, and whispered to her in their native Russian, “I think I know how the universe was born.”

    Kallosh, a theoretical physicist herself, muttered some encouraging words and fell back asleep. “It wasn’t until the next morning that I realized the full impact of what Andrei had told me,” recalled Kallosh, now a professor of physics at the Stanford Institute for Theoretical Physics.

    Linde’s nocturnal eureka moment had to do with a problem in cosmology that he and other theorists, including Stephen Hawking, had struggled with for months.

    A year earlier, a 32-year-old postdoc at SLAC National Accelerator Laboratory named Alan Guth shocked the physics community by proposing a bold modification to the Big Bang theory. According to Guth’s idea, which he called “inflation,” our universe erupted from a vacuum-like state and underwent a brief period of faster-than-light expansion.

    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 Mittelmann Coldcreation

    Alan Guth’s notes:
    5

    In less than a billionth of a trillionth of a trillionth of a second, space-time doubled more than 60 times from a subatomic speck to a volume many times larger than the observable universe.

    Guth envisioned the powerful repulsive force fueling the universe’s exponential growth as a field of energy flooding space. As the universe unfurled, this “inflaton field” decayed, and its shed energy was transfigured into a fiery bloom of matter and radiation. This pivot, from nothing to something and timelessness to time, marked the beginning of the Big Bang. It also prompted Guth to famously quip that the inflationary universe was the “ultimate free lunch.”

    As theories go, inflation was a beauty. It explained in one fell swoop why the universe is so large, why it was born hot, and why its structure appears to be so flat and uniform over vast distances. There was just one problem – it didn’t work.

    Tunneling

    To conclude the unpacking of space-time, Guth borrowed a trick from quantum mechanics called “tunneling” to allow his inflaton field to randomly and instantly skip from a higher, less stable energy state to a lower one, thus bypassing a barrier that could not be scaled by classical physics.

    3
    Andrei Linde and Renata Kallosh, both professors of physics. (Image credit: L.A. Cicero)

    But closer inspection revealed that quantum tunneling caused the inflaton field to decay quickly and unevenly, resulting in a universe that was neither flat nor uniform. Aware of the fatal flaw in his theory, Guth wrote at the end of his paper on inflation: “I am publishing this paper in the hope that it will … encourage others to find some way to avoid the undesirable features of the inflationary scenario.”

    Guth’s plea was answered by Linde, who on that fateful summer night realized that inflation didn’t require quantum tunneling to work. Instead, the inflaton field could be modeled as a ball rolling down a hill of potential energy that had a very shallow, nearly flat slope. While the ball rolls lazily downhill, the universe is inflating, and as it nears the bottom, inflation slows further and eventually ends. This provided a “graceful exit” to the inflationary state that was lacking in Guth’s model and produced a cosmos like the one we observe. To distinguish it from Guth’s original model while still paying homage to it, Linde dubbed his model “new inflation.”

    Quantum birth of galaxies

    By the time Linde and Kallosh moved to Stanford in 1990, experiments had begun to catch up with the theory. Space missions were finding temperature variations in the energetic afterglow of the Big Bang – called the cosmic microwave background radiation – that confirmed a startling prediction made by the latest inflationary models. These updated models went by various names – “chaotic inflation,” “eternal inflation,” “eternal chaotic inflation” and many more – but they all shared in common the graceful exit that Linde pioneered.

    According to these models, galaxies like the Milky Way grew from faint wrinkles in the fabric of space-time. The density of matter in these wrinkles was slightly greater compared to surrounding areas and this difference was magnified during inflation, allowing them to attract even more matter. From these dense primordial seeds grew the cosmic structures we see today. “Galaxies are children of random quantum fluctuations produced during the first 10-35 seconds after the birth of the universe,” Linde said.

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

    Inflation predicted that these quantum fluctuations would leave imprints on the universe’s background radiation in the form of hotter and colder regions, and this is precisely what two experiments – dubbed COBE and WMAP – found. “After the COBE and WMAP experiments, inflation started to become part of the standard model of cosmology,” Shamit Kachru said.

    COBE/CMB


    NASA/COBE 1989 to 1993.

    CMB per NASA/WMAP


    NASA/WMAP 2001 to 2010

    CMB per ESA/Planck


    ESA/Planck 2009 to 2013

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    Shamit Kachru, Professor of Physics and Director, Stanford Institute for Theoretical Physics (Image credit: L.A. Cicero)

    The multiverse

    Linde and others later realized that the same quantum fluctuations that produced galaxies can give rise to new inflating regions in the universe. Even though inflation ended in our local cosmic neighborhood 14 billion years ago, it can still continue at the outermost fringes of the universe. The consequence is an ever-expanding sea of inflating space-time dotted with “island universes” or “pocket universes” like our own where inflation has ceased.

    Multiverse. Image credit: public domain, retrieved from https://pixabay.com/

    “As a result, the universe becomes a multiverse, an eternally growing fractal consisting of exponentially many exponentially large parts,” Linde wrote. “These parts are so large that for all practical purposes they look like separate universes.”

    Linde took the multiverse idea even further by proposing that each pocket universe could have differing properties, a conclusion that some string theorists were also reaching independently. “It’s not that the laws of physics are different in each universe, but their realizations,” Linde said. “An analogy is the relationship between liquid water and ice. They’re both H2O but realized differently.”

    Linde’s multiverse is like a cosmic funhouse filled with reality-distorting mirrors. Some pocket universes are resplendent with life, while others were stillborn because they were cursed with too few (or too many) dimensions, or with physics incompatible with the formation of stars and galaxies. An infinite number are exact replicas of ours, but infinitely more are only near-replicas. Right now, there could be countless versions of you inhabiting worlds with histories divergent from ours in ways large and small. In an infinitely expanding multiverse, anything that can happen will happen.

    “The inflationary universe is not just the ultimate free lunch, it’s the only lunch where all possible dishes are served,” Linde said.

    While disturbing to some, this eternal aspect of inflation was just what a small group of string theorists were looking for to help explain a surprise discovery that was upending the physics world – dark energy.

    Dark Energy Survey


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Stanford University campus. No image credit

    Leland and Jane Stanford founded the University to “promote the public welfare by exercising an influence on behalf of humanity and civilization.” Stanford opened its doors in 1891, and more than a century later, it remains dedicated to finding solutions to the great challenges of the day and to preparing our students for leadership in today’s complex world. Stanford, is an American private research university located in Stanford, California on an 8,180-acre (3,310 ha) campus near Palo Alto. Since 1952, more than 54 Stanford faculty, staff, and alumni have won the Nobel Prize, including 19 current faculty members

    Stanford University Seal

     
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