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  • richardmitnick 3:40 pm on October 19, 2016 Permalink | Reply
    Tags: , , Cosmic Inflation, , , ,   

    From Ethan Siegel: “Where does our arrow of time come from?” 

    10.19.16
    Ethan Siegel

    1
    The history of the Universe and the arrow of time. Image credit: NASA / GSFC.

    The past is gone, the future not yet here, only the present is now. But why does it always flow the way it does for us?

    “Thus is our treaty written; thus is agreement made. Thought is the arrow of time; memory never fades. What was asked is given; the price is paid.”
    -Robert Jordan

    Every moment that passes finds us traveling from the past to the present and into the future, with time always flowing in the same direction. At no point does it ever appear to either stand still or reverse; the “arrow of time” always points forwards for us. But if we look at the laws of physics — from Newton to Einstein, from Maxwell to Bohr, from Dirac to Feynman — they appear to be time-symmetric. In other words, the equations that govern reality don’t have a preference for which way time flows. The solutions that describe the behavior of any system obeying the laws of physics, as we understand them, are just as valid for time flowing into the past as they are for time flowing into the future. Yet we know from experience that time only flows one way: forwards. So where does the arrow of time come from?

    2
    A ball in mid-bounce has its past and future trajectories determined by the laws of physics, but time will only flow into the future for us. Image credit: Wikimedia commons users MichaelMaggs and (edited by) Richard Bartz, under a c.c.a.-s.a.-3.0 license.

    Many people believe there might be a connection between the arrow of time and a quantity called entropy. While most people normally equate “disorder” with entropy, that’s a pretty lazy description that also isn’t particularly accurate. Instead, think about entropy as a measure of how much thermal (heat) energy could possibly be turned into useful, mechanical work. If you have a lot of this energy capable of potentially doing work, you have a low-entropy system, whereas if you have very little, you have a high-entropy system. The second law of thermodynamics is a very important relation in physics, and it states that the entropy of a closed (self-contained) system can only increase or stay the same over time; it can never go down. In other words, over time, the entropy of the entire Universe must increase. It’s the only law of physics that appears to have a preferred direction for time.

    3
    Still from a lecture on entropy by Clarissa Sorensen-Unruh. Image credit: C. Sorensen-Unruh of YouTube, via https://www.youtube.com/watch?v=Mz8IM7pWkok.

    So, does that mean that we only experience time the way we do because of the second law of thermodynamics? That there’s a fundamentally deep connection between the arrow of time and entropy? Some physicists think so, and it’s certainly a possibility. In an interesting collaboration between the MinutePhysics YouTube channel and physicist Sean Carroll, author of The Big Picture, From Eternity To Here and an entropy/time’s arrow fan, they attempt to answer the question of why time doesn’t flow backwards. Unsurprisingly, they point the finger squarely at entropy.


    Access mp4 video here .

    It’s true that entropy does explain the arrow of time for a number of phenomena, including why coffee and milk mix but don’t unmix, why ice melts into a warm drink but never spontaneously arises along with a warm beverage from a cool drink, and why a cooked scrambled egg never resolves back into an uncooked, separated albumen and yolk. In all of these cases, an initially lower-entropy state (with more available, capable-of-doing-work energy) has moved into a higher-entropy (and lower available energy) state as time has moved forwards. There are plenty of examples of this in nature, including of a room filled with molecules: one side full of cold, slow-moving molecules and the other full of hot, fast-moving ones. Simply give it time, and the room will be fully mixed with intermediate-energy particles, representing a large increase in entropy and an irreversible reaction.

    4
    A system set up in the initial conditions on the left and let to evolve will become the system on the right spontaneously, gaining entropy in the process. Image credit: Wikimedia Commons users Htkym and Dhollm, under a c.c.-by-2.5 license.

    Except, it isn’t irreversible completely. You see, there’s a caveat that most people forget when it comes to the second law of thermodynamics and entropy increase: it only refers to the entropy of a closed system, or a system where no external energy or changes in entropy are added or taken away. A way to reverse this reaction was first thought up by the great physicist James Clerk Maxwell way back in the 1870s: simply have an external entity that opens a divide between the two sides of the room when it allows the “cold” molecules to flow onto one side and the “hot” molecules to flow onto the other. This idea became known as Maxwell’s demon, and it enables you to decrease the energy of the system after all!

    5
    A representation of Maxwell’s demon, which can sort particles according to their energy on either side of a box. Image credit: Wikimedia Commons user Htkym, under a c.c.a.-s.a.-3.0 license.

    You can’t actually violate the second law of thermodynamics by doing this, of course. The catch is that the demon must spend a tremendous amount of energy to segregate the particles like this. The system, under the influence of the demon, is an open system; if you include the entropy of the demon itself in the total system of particles, you’ll find that the total entropy does, in fact, increase overall. But here’s the kicker: even if you lived in the box and failed to detect the existence of the demon — in other words, if all you did was live in a pocket of the Universe that saw its entropy decrease — time would still run forward for you. The thermodynamic arrow of time does not determine the direction in which we perceive time’s passage.

    So where does the arrow of time that correlates with our perception come from? We don’t know. What we do know, however, is that the thermodynamic arrow of time isn’t it. Our measurements of entropy in the Universe know of only one possible tremendous decrease in all of cosmic history: the end of cosmic inflation and its transition to the hot Big Bang. We know our Universe is headed to a cold, empty fate after all the stars burn out, after all the black holes decay, after dark energy drives the unbound galaxies apart from one another and gravitational interactions kick out the last remaining bound planetary and stellar remnants. This thermodynamic state of maximal entropy is known as the “heat death” of the Universe. Oddly enough, the state from which our Universe arose — the state of cosmic inflation — has exactly the same properties, only with a much larger expansion rate during the inflationary epoch than our current, dark energy-dominated epoch will lead to.

    6
    The quantum nature of inflation means that it ends in some “pockets” of the Universe and continues in others, but we do not yet understand either what the amount of entropy was during inflation or how it gave rise to the low-entropy state at the start of the hot Big Bang. Image credit: E. Siegel, from the book Beyond The Galaxy.

    How did inflation come to an end? How did the vacuum energy of the Universe, the energy inherent to empty space itself, get converted into a thermally hot bath of particles, antiparticles and radiation? And did the Universe go from an incredibly high-entropy state during cosmic inflation to a lower-entropy one during the hot Big Bang, or was the entropy during inflation even lower due to the eventual capacity of the Universe to do mechanical work? At this point, we have only theories to guide us; the experimental or observational signatures that would tell us the answers to these questions have not been uncovered.

    7
    From the end of inflation and the start of the hot Big Bang, entropy always increases up through the present day. Image credit: E. Siegel, with images derived from ESA/Planck and the DoE/NASA/ NSF interagency task force on CMB research. From his book, Beyond The Galaxy.

    We do understand the arrow of time from a thermodynamic perspective, and that’s an incredibly valuable and interesting piece of knowledge. But if you want to know why yesterday is in the immutable past, tomorrow will arrive in a day and the present is what you’re living right now, thermodynamics won’t give you the answer. Nobody, in fact, understands what will.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    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 11:36 am on May 16, 2016 Permalink | Reply
    Tags: , , Cosmic Inflation, , ,   

    From NOVA: “Revealing the Universe’s Mysterious Dark Age” 

    PBS NOVA

    NOVA

    06 Apr 2016 [They just put this in social media]
    Marcus Woo

    The universe wasn’t always like this. Today it’s filled with glittering galaxies, scattered across space like city lights seen from above. But there was a time when all was dark. Really dark.

    Dark Ages Universe ESO
    Dark Ages Universe ESO

    1
    A time-lapse visualization of what the cosmic web’s emergence might have looked like. No image credit

    First, a very brief history of time: from the Big Bang, the universe burst onto the scene as a tiny but glowing inferno of energy. Immediately, it expanded and cooled, dimming into darkness as particles condensed out of the hot soup like droplets of morning dew. Electrons and protons coalesced into atoms, which formed stars, galaxies, planets, and eventually us.

    Inflationary Universe. NASA/WMAP
    Inflationary Universe. NASA/WMAP

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

    But a crucial piece still eludes scientists. It’s a gap of several hundred million years that was filled with darkness—a darkness both literal and metaphorical. Astronomers call this period the dark ages, a time that’s not just bereft of illumination, but also devoid of data.

    The Big Bang left a glowing imprint on the entire sky called the cosmic microwave background,,,

    Cosmic Microwave Background per ESA/Planck
    Cosmic Microwave Background per ESA/Planck

    ESA/Planck
    ESA/Planck
    ,,,representing the universe when it was 380,000 years old. Increasingly precise measurements of this radiation have revealed unprecedented details about the earliest cosmic moments. But from then until the emergence of galaxies big and bright enough for today’s telescopes, scientists don’t have any information. Ever mysterious, these dark ages are the final frontier of cosmology.

    And it’s a fundamental frontier. It represents the universe’s most formative years, when it matured from a primordial soup to the cosmos we recognize today.

    Even without much direct data about this era, researchers have made great strides with theory and computer models, simulating the universe through the birth of the first stars. Soon, they may be able to put those theories to the test. In a few years, a suite of new telescopes with new capabilities will start peering into the darkness, and for the first time, astronomers will reach into the unknown.

    The Final Frontier

    Considering that it’s the entire universe they’re trying to understand, cosmologists have done a pretty good job. Increasingly powerful telescopes have allowed them to peer to greater distances, and because the light takes so long to reach the telescopes, astronomers can see farther back in time, capturing snapshots of a universe only a few hundred million years old, just as it emerged from the dark ages. Given that the universe is now 13.7 billion years old, that’s like taking a picture of the cosmos as a toddler.

    That makes the cosmic microwave background, or CMB, clike a detailed ultrasound. This radiation contains the first photons that escaped the yoke of the universe’s primordial plasma. When the universe was a sea of radiation and particles, photons couldn’t travel freely because they kept running into electrons. But about 380,000 years after the Big Bang, the universe had cooled enough that protons were able to lasso electrons into an orbit to form hydrogen atoms. Without electrons in their way, the newly liberated photons could now fly through the cosmos and, more than 13 billion years later, enter the detectors of instruments like the Planck satellite, giving cosmologists the earliest picture of the universe.

    But from this point on, until the universe was a few hundred million years old—the limit of today’s telescopes—astronomers have nothing. It’s as if they have a photo album documenting a person’s entire life, with pictures of young adulthood, adolescence, childhood, and even before birth, but nothing from when the person learned to talk or walk—years of drastic changes.

    That doesn’t mean astronomers have no clue about this period. “People have thought about the first stars since the 1950s,” says Volker Bromm, a professor of astronomy at the University of Texas, Austin. “But they were very speculative because we did not know enough cosmology.” Not until the 1980s did researchers develop more accurate theories that incorporated dark matter, the still-unknown type of particle or particles that comprises about 85% of the matter in the universe. But the first key breakthrough came in 1993, when NASA’s COBE satellite measured the CMB for the first time, collecting basic but crucial data about what the universe was like at the very beginning—the so-called initial conditions of the cosmos. Theorists such as Martin Rees, now the Astronomer Royal of the United Kingdom, and Avi Loeb, a professor of astrophysics at Harvard, realized you could plug these numbers into the equations that govern how the first gas clouds and stars could form. “You could feed them into a computer simulation,” Loeb says. “It’s a well-defined problem.”

    Both Rees and Loeb would influence Bromm, then a graduate student at Yale. Rees and his early work in the 1980s, in particular, inspired Tom Abel, who was a visiting scientist during the 1990s at the University of Illinois, Urbana-Champaign. Independently, Abel and Bromm would make some of the first computer models of their kind to simulate the first stars. “That really opened the field,” Loeb says. “When I started, there were maybe one or a few people even willing to discuss this subject.”

    Theorists like Bromm and Abel, now a professor at Stanford, have since pieced together a blow-by-blow account of the dark ages. Here’s how they think it all went down.

    Then There Was Light

    In the earliest days, during the time that we see in the CMB, the entire universe was bright and as hot as the surface of the sun. But the universe kept expanding and cooling, and after nearly 15 million years, it was as cool as room temperature. “In principle, if there were planets back then, you could’ve had life on them if they had liquid water on their surface,” Loeb says. The temperature continued to fall, and the infrared radiation that suffused the universe lengthened, shifting to radio waves. “Once you cool even further, the universe became a very dark place,” Loeb says. The dark ages had officially begun.

    Meanwhile, the simulations show, things began to stir. The universe was bumpy, with regions of slightly higher and lower densities, which grew from the random quantum fluctuations that emerged in the Big Bang. These denser regions coaxed dark matter to start clumping together, forming a network of sheets and filaments that crisscrossed the universe. At the intersections, denser globs of dark matter formed. Once these roundish halos grew to about 10,000 times the mass of the Sun, Abel says—a few tens of millions of years after the Big Bang—they had enough gravity to corral hydrogen atoms into the first gas clouds.

    Those clouds could then accumulate more gas, heating up to hundreds of degrees. The heat generated enough pressure to prevent further contraction. Soon, the clouds settled into enormous, but rather dull, balls of gas about 100 light years in diameter, Abel says.

    But if the dark matter halos reached masses 100,000 times that of the sun, they could accrue enough gas that the clouds could heat up to about 1000 degrees—and that’s when things got interesting. The surplus energy allowed hydrogen atoms to merge two at a time and form hydrogen molecules—picture two balls attached with a spring. When two hydrogen molecules collide, they vibrate and emit photons that carry away energy.

    When that happens, the molecules are converting the vibrating energy that is heat into radiation that’s lost into space. These interactions cooled the gas, slowing down the molecules and allowing the clouds to collapse. As the clouds grew denser, their temperatures and pressures soared, igniting nuclear fusion. That’s how the first stars were born.

    These first stars, which formed by the time the universe was a couple hundred million years old, were much bigger than those in today’s universe. By the early 2000s, Abel’s simulations, which he says are the most realistic and advanced yet, showed that the first stars weighed about 30 to 300 times the mass of the sun. Using different techniques and algorithms, Bromm says he arrived at a similar answer. For the first time, researchers had a good idea as to what the first objects in the universe were like.

    Massive stars consume fuel like gas-guzzling SUVs. They live fast and die young, collapsing into supernovae after only a few million years.

    Supernova remnant Crab nebula. NASA/ESA Hubble
    Supernova remnant Crab nebula. NASA/ESA Hubble

    NASA/ESA Hubble Telescope
    NASA/ESA Hubble Telescope

    In cosmic timescales, that’s the blink of an eye. “You really want to think of fireworks at these early times,” Abel says. “Just flashing everywhere.”

    In general, the first stars were sparse, separated by thousands of light years. Over the next couple hundred million years, though, guided by the clustering of dark matter, the stars started grouping together to form baby galaxies. During this cosmic dawn, as astronomers call it, galaxies merged with one another and became bigger galaxies. Only after billions and billions of years would they grow into those like our own Milky Way, with hundreds of billions of stars.

    Lifting the Fog

    But there’s more to the story. The first stars shone in many wavelengths, and especially strongly in ultraviolet. The universe’s expansion would’ve stretched this light to visible and infrared wavelengths, which many of our best telescopes are designed to detect. Problem is, during the time of the first stars, a thick fog of neutral hydrogen gas blanketed the whole universe. This gas absorbed shorter-wavelength ultraviolet light, obscuring the view from telescopes. Fortunately, though, this fog would soon lift.

    “This state of affairs can’t last for very long,” says Richard Ellis, an astronomer at the European Southern Observatory in Germany.

    ESO 50 Large
    ESO

    “These ultraviolet photons have sufficient energy to break apart the hydrogen atom back into an electron and a proton.” The hydrogen was ionized, turning into a lone proton that could no longer absorb ultraviolet. The gas was now transparent.

    During this so-called period of reionization, galaxies continued to grow, producing more ultraviolet light that ionized the hydrogen surrounding them, clearing out holes in the fog. “You can imagine the hydrogen like Swiss cheese,” Loeb says. Those bubbles grew, and by the time the universe was around 800 million years old, the ultraviolet radiation ionized the hydrogen between the galaxies, leaving the entire cosmos clear and open to the gaze of telescopes. The dark ages were over, revealing a universe that looked more or less like it does today.

    Seeing into the Dark

    Of course, many details have to be worked out. Astronomers like Ellis are focusing on the latter stages of the dark ages, using the most powerful telescopes to extract clues about this reionization epoch.

    One big question has been whether the ultraviolet light from early galaxies was enough to ionize the whole universe. If it wasn’t, astronomers would have to find another exotic source—like black holes that blast powerful, ionizing jets of radiation—that would have finished the job.

    To find the answer, Ellis and a team of astronomers stretched the Hubble Space Telescope to its limits, extracting as much light as possible from one small patch of sky. These observations reached some of the most distant corners of the universe, discovering some of the earliest galaxies ever seen, during the heart of this reionization era. Their observations suggested that galaxies—large populations of small galaxies, in particular—did seem to have enough ultraviolet light to ionize the universe. Maybe nothing exotic is needed.

    NASA/ESA  Hubble Deep Field
    NASA/ESA Hubble Deep Field

    But to know exactly how it happened, astronomers need new telescopes, like the James Webb Space Telescope set for launch in 2018.

    NASA/ESA/CSA Webb Telescope annotated
    “NASA/ESA/CSA Webb Telescope annotated

    “With the current facilities, it’s just an imponderable,” Ellis says. “We don’t have the power to study these galaxies in any detail.”

    Other astronomers are focusing not on the galaxies, but the hydrogen fog itself. It turns out that the spins of a hydrogen atom’s proton and electron can flip-flop in direction. When the spins go from being aligned to unaligned, the atom releases radiation at a wavelength of 21 centimeters, or 8.27 inches, a telltale signal of neutral hydrogen that astronomers call the 21-cm line. The expanding universe would have stretched this signal to the point where it became a collection of radio waves. The more distant the source of light, the more the radiation gets stretched. By using arrays of radio telescopes to measure the extent of this stretching, astronomers can map the distribution of hydrogen at different points in time. They could then track how those holes in the gas grew and grew until the gas was all ionized.

    “It’s surveying the volume of the universe on a scale that you can’t imagine doing in any way other than through this method—it’s really quite incredible,” says Aaron Parsons, an astronomer at the University of California, Berkeley, who’s leading a project called HERA, which will consist of 352 radio antennae in South Africa.

    HERA NSF
    NSF HERA, South Africa

    Once online, the telescope could give an unprecedented view of reionization. “You can almost imagine making a movie of how the first stars galaxies formed, how they interacted, heated up, ionized, and turned into the galaxies we recognize today.”

    Other telescopes like LOFAR in the Netherlands and the Murchison Widefield Array in Australia will make similar measurements.

    ASTRON LOFAR Map
    ASTRON LOFAR Map

    ASTRON LOFAR Radio Antenna Bank
    ASTRON LOFAR Radio Antenna Bank

    SKA Murchison Widefield Array
    SKA Murchison Widefield Array

    But HERA will be more sensitive, Parsons says. And already with 19 working antennae in place, it might be closest to success, adds Loeb, who isn’t part of the HERA team. “Within a couple years, we should have the first detection of the 21-cm line from this epoch of reionization, which would be fantastic because it would allow us to see the environmental effect of ultraviolet radiation from the first stars and first galaxies on the rest of the universe.”

    This kind of data is crucial for informing computer models like the kind that Abel and Bromm have developed. But despite their successes, theorists are at the point where they need data to test whether their models are accurate.

    Unfortunately, that data won’t be pictures of the first stars. Even the most powerful telescopes won’t be able to see the brightest of them. The first galaxies contain only a few hundred stars and are just too small and faint. “We’ll come ever closer,” Abel says. “It’s very difficult to imagine we’ll actually see those in the near future, but we’ll see their brighter cousins.”

    In fact, the darkest of times, during the couple hundred million years between the CMB and the appearance of the first stars, may always remain beyond astronomers’ grasp. “We currently don’t have any idea of how you could get any direct information about that period,” he says.

    Still, new telescopes over the next few decades promise to reveal much of the dark ages and whether the story theorists are telling is true or even more fantastic than they had thought. “Even though I’m a theorist, I’m modest enough to acknowledge the fact that nature is sometimes more imaginative than we are,” Loeb says. “I’m open to surprises.”

    See the full article here .

    Please help promote STEM in your local schools.

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    NOVA is the highest rated science series on television and the most watched documentary series on public television. It is also one of television’s most acclaimed series, having won every major television award, most of them many times over.

     
  • richardmitnick 6:31 am on April 29, 2016 Permalink | Reply
    Tags: , , Cosmic Inflation,   

    From Ethan Siegel: “The biggest question about the beginning of the Universe” 

    Starts with a bang
    Starts with a Bang

    4.28.16
    Ethan Siegel

    Inflationary Universe. NASA/WMAP
    Inflationary Universe. NASA/WMAP

    “Where did it come from” is pretty high up there!

    “Space is certainly something more complicated than the average person would probably realize. Space is not just an empty background in which things happen.” -Alan Guth

    Our Universe is expanding, getting less dense and cooling today, teaching us that it was hotter and denser in the distant past. If we extrapolate backwards in time, we can reach epochs where:

    gravitation hadn’t yet had time to collapse matter into clusters, galaxies or even stars,
    the temperature of the Universe was too hot to form neutral atoms, ionizing them immediately,
    particles were so energetic that even atomic nuclei were unstable, being immediately split apart into individual protons and neutrons,
    and even to where the energy density was so high that matter/antimatter pairs were spontaneously created from pure energy.

    You might think we could go all the way back even farther, to the very birth of space and time themselves. That was, in fact, the original idea of the Big Bang, but thanks to some spectacular observations, we know that isn’t quite how our Universe began.

    Cosmic Microwave Background per ESA/Planck
    Cosmic Microwave Background per ESA/Planck

    ESA/Planck
    ESA/Planck

    Above is the earliest known “baby picture” of our Universe. When the Universe finally did cool enough to stably form neutral atoms, all the radiation from the earliest times could suddenly travel through space, in a straight line, without being absorbed, re-emitted or scattered off of a free, charged particle. This radiation then had its wavelength stretched by the expansion of the Universe, where it can now be found at microwave frequencies: the Cosmic Microwave Background (CMB), or the leftover glow from the Big Bang. When we look at the fluctuations in it — or the slight imperfections from a perfectly uniform temperature at various locations across the sky — we can use what we know about physics and astrophysics to teach us a number of very important things.

    1
    Image credit: NASA / WMAP science team.

    One of the things we can learn is that our Universe is made up of about 5% normal (atomic) matter, 27% dark matter and 68% dark energy. But no less important is this: we learn that these imperfections were initially the same on all scales, and are of such a small magnitude that the Universe couldn’t have achieved an arbitrarily high temperature in the distant past. Instead, there must have been a phase before the Universe was hot, dense and matter-and-radiation filled that set it all up. Originally conceived by Alan Guth in 1979, this phase — known today as cosmic inflation — solves a number of major problems with the Universe: stretching it flat, giving it the same temperature everywhere, eliminating high-energy relics and defects (like magnetic monopoles) from the Universe, and providing a mechanism to generate those much-needed fluctuations.

    History of the universe, National Science Foundation, E Siegel
    Image credit: National Science Foundation (NASA, JPL, Keck Foundation, Moore Foundation, related) — Funded BICEP2 Program; modifications by E. Siegel.

    The fluctuations are remarkable in particular, because two distinct types of them — density (scalar) fluctuations and gravitational wave (tensor) fluctuations — were both predicted by inflation before the evidence for either one existed. As of today, we’ve not only directly observed the scalar ones and have strict limits on the tensor ones, but we’ve measured what the spectrum of these initial fluctuations were, which tells us something about the various types of inflation that could have occurred. In general, you can visualize inflation as a ball rolling down any type of hill you can imagine, into a valley.

    3
    Image credit: E. Siegel, of three “hills-and-valleys” potentials that could describe cosmic inflation. Created with Google’s graph tool.

    In order to have enough inflation to reproduce the Universe that we see, we need for the ball to roll slowly enough down that hill so that the Universe can be stretched flat, made the same temperature everywhere and to have those quantum fluctuations (that create the density fluctuations) get stretched across the Universe. In order to determine which model of inflation is the one our Universe has — in other words, what the shape of that “hill” actually looks like — there are two things that help us out:

    1. The fluctuations can be more important on small scales or on large ones, and by measuring the full spectrum of them, we can know what the slope of that hill was when inflation came to an end.
    2. If we can measure the gravitational wave fluctuations and compare them to the density fluctuations, we can reconstruct how the slope was changing when inflation ended.

    In other words, we can “cook up” any model for inflation that we like, but only some of them will give us the right values — that match our Universe — for these two different types of fluctuations.

    4
    Various models of inflation and what they predict for the scalar (x-axis) and tensor (y-axis) fluctuations from inflation. Image credit: Planck Collaboration: P. A. R. Ade et al., 2013, A&A preprint, with additional annotations by E. Siegel.

    Thanks to the Planck spacecraft, we now have very tight restrictions on the density fluctuations, disfavoring many of the simplest models. As superior (polarization) data from projects like Planck, BICEP, POLARBEAR and others continues to come in, hope that we’ll either detect the gravitational wave signatures or set stronger limits than ever before rises even higher.

    BICEP 2
    BICEP 2

    POLARBEAR McGill Telescope located in the Atacama Desert of northern Chile in the Antofagasta Region. The POLARBEAR experiment is mounted on the Huan Tran Telescope (HTT) at the James Ax Observatory in the Chajnantor Science Reserve.
    POLARBEAR McGill Telescope located in the Atacama Desert of northern Chile in the Antofagasta Region. The POLARBEAR experiment is mounted on the Huan Tran Telescope (HTT) at the James Ax Observatory in the Chajnantor Science Reserve.

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

    Caltech/MIT Advanced aLIGO Hanford Washington USA installation
    Caltech/MIT Advanced aLIGO Hanford Washington USA installation

    ESA/LISA Pathfinder
    ESA/LISA Pathfinder

    People have argued for a long time that cosmic inflation has too many solutions, but the better we get at making these measurements, the more hope we have that the number of solutions will eventually be reduced to one unique one.

    Inflation to gravitational waves derived from ESAPlanck and the DoENASA NSF interagency task force on CMB research
    Inflation to gravitational waves derived from ESAPlanck and the DOE NASA NSF interagency task force on CMB research

    The Universe has a great story to tell us about its origin, to the limits of what we can conceivably measure. The better we get at actually making those measurements, the better we can understand how it all got its start. Cosmic inflation is almost definitely the answer to what happened before the Big Bang. But what was cosmic inflation like? We’re closer than ever to actually coming up with the answer.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    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 5:02 pm on April 19, 2016 Permalink | Reply
    Tags: , , , Cosmic Inflation,   

    From Quanta: “Physicists Hunt for the Big Bang’s Triangles” 

    Quanta Magazine
    Quanta Magazine

    The story of the universe’s birth — and evidence for string theory — could be found in triangles and myriad other shapes in the sky.

    1
    Hannes Hummel and Olena Shmahalo/Quanta Magazine

    April 19, 2016
    Natalie Wolchover

    Once upon a time, about 13.8 billion years ago, our universe sprang from a quantum speck, ballooning to one million trillion trillion trillion trillion trillion trillion times its initial volume (by some estimates) in less than a billionth of a trillionth of a trillionth of a second. It then continued to expand at a mellower rate, in accordance with the known laws of physics.

    So goes the story of cosmic inflation, the modern version of the Big Bang theory.

    Inflationary Universe. NASA/WMAP
    Inflationary Universe. NASA/WMAP

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

    SDSS Telescope at Apache Point, NM, USA
    SDSS Telescope at Apache Point, NM, USA

    That single short, outrageous growth spurt fits all existing cosmological data well and accounts for the universe’s largeness, smoothness, flatness and lack of preferred direction.

    Cosmic Microwave Background per ESA/Planck
    Cosmic Microwave Background per ESA/Planck

    ESA/Planck
    ESA/Planck

    But as an explanation of how and why the universe began, inflation falls short. The questions it raises — why the growth spurt happened, how it happened, what (if anything) occurred beforehand — have confounded cosmologists since the theory emerged in the 1980s. “We have very strong evidence that there was this period of inflation,” said Matthew Kleban, a cosmologist at New York University. “But we have no idea — or we have many, many ideas — too many ideas — what inflation was, fundamentally.”

    To understand the origin of the universe, today’s cosmologists seek to identify the unknown driver of inflation, dubbed the “inflaton.” Often envisioned as a field of energy permeating space and driving it apart, the inflaton worked, experts say, like a clock. With each tick, it doubled the size of the universe, keeping nearly perfect time — until it stopped. Theorists like Kleban, then, are the clocksmiths, devising altogether hundreds of different models that might replicate the clockwork of the Big Bang.

    Like many cosmological clocksmiths, Kleban is an expert in string theory — the dominant candidate for a “theory of everything” that attempts to describe nature across all distances, times and energies. The known equations of physics falter when applied to the tiny, fleeting and frenzied environment of the Big Bang, in which they struggle to cram an enormous amount of energy into infinitesimal space and time. But string theory flourishes in this milieu, positing extra spatial dimensions that diffuse the energy. Familiar point particles become, at this highest energy and zoom level, one-dimensional “strings” and higher-dimensional, membranous “branes,” all of which traverse a 10-dimensional landscape. These vibrating, undulating gears may have powered the Big Bang’s clock.

    At his office on a recent afternoon, Kleban sketched his latest inflaton design on the blackboard. First, he drew a skinny cylinder to depict the string landscape. Its length represented the three spatial dimensions of macroscopic reality, and its circumference signified the six other spatial dimensions that string theory says exist, but which are too small to see. On the side of the cylinder, he drew a circle. This is Kleban’s timepiece: a membrane that bubbles into being and naturally expands. As its inflating interior forms a new universe, its energy incrementally ticks down in clocklike fashion each time the expanding circle winds around the cylinder’s circumference and overlaps itself. When the energy of the “brane” dilutes, the clock stops ticking, and inflation ends. It’s a scheme that some string cosmologists have hailed for its economy. “I think it’s pretty plausible that some version of this happens,” he said.

    2
    A sketch by the string theorist and cosmologist Matthew Kleban of his Big Bang model known as unwinding inflation. Olena Shmahalo/Quanta Magazine

    Though Kleban acknowledges that it’s too soon to tell whether he or anyone else is on to something, plans are under way to find out.

    The record of the inflaton’s breakneck ticking can be read in the distribution of galaxies, galaxy clusters and superclusters that span the cosmos. These structures (and everything in them, including you) are artifacts of “mistakes in the clock,” as Matias Zaldarriaga, a cosmologist at the Institute for Advanced Study (IAS) in Princeton, N.J., put it. That is, time is intrinsically uncertain, and so the universe inflated at slightly different rates in different places and moments, producing density variations throughout. The jitter in time can also be thought of as a jitter in energy that occurred as pairs of particles spontaneously surfaced all over an “inflaton field” and stretched apart like two points on an inflating balloon. These particles were the seeds that gravity grew into galactic structures over the course of eons. The pairs of structures spanning the largest distances in the sky today came from the earliest quantum fluctuations during inflation, while structures that are closer together were produced later. This nested distribution across all cosmic distance scales “is telling you in detail that the clock was ticking,” said Nima Arkani-Hamed, a theoretical physicist at IAS. “But it doesn’t tell you anything about what it was made of.”

    To reverse-engineer the clockwork, cosmologists are seeking a new kind of data. Their calculations indicate that galaxies and other structures are not merely randomly spread out in pairs across the sky; instead, they have a slight tendency to be arranged in more complex configurations: triangles, rectangles, pentagons and all manner of other shapes, which trace back not just to quantum jitter in the Big Bang’s clock, but to a much more meaningful turning of the gears.

    Teasing out the cosmological triangles and other shapes — which have been named “non-Gaussianities” to contrast them with the Gaussian bell curve of randomly distributed pairs of structures — will require more precise observations of the cosmos than have been made to date. And so plans are being laid for a timeline of increasingly sensitive experiments. “We’re going to have far more information than we have now, and sensitivity to far subtler effects than we can probe now,” said Marc Kamionkowski, a cosmologist at Johns Hopkins University. In the meantime, theorists are making significant progress in determining what shapes to look for and how to look for them. “There’s been a great renaissance of understanding,” said Eva Silverstein, a string cosmologist at Stanford University who devised the dimensional-winding mechanism used by Kleban, as well as many clock designs of her own.

    The rigorous study of non-Gaussianities took off in 2002, when Juan Maldacena, a revered, monklike theorist at IAS, calculated what’s known as the “gravitational floor”: the minimum number of triangles and other shapes that are guaranteed to exist in the sky, due to the unavoidable effect of gravity during cosmic inflation. Cosmologists had been struggling to calculate the gravitational floor for more than a decade, since it would provide a concrete goal for experimenters. If the floor is reached, and still no triangles are detected, Maldacena explained, “then inflation is wrong.”

    When Maldacena first calculated the gravitational floor, actually detecting it seemed a distant goal indeed. At the time, all precise knowledge of the universe’s birth came from observations of the “cosmic microwave background” — the oldest light in the sky, which illuminates a two-dimensional slice of the infant universe as it appeared 380,000 years after the Big Bang. Based on the limited number of nascent structures that appear in this 2-D snapshot, it seemed impossible that their slight propensity to be configured in triangles and other shapes could ever be detected with statistical certainty. But Maldacena’s work gave theorists the tools to calculate other, more pronounced forms of non-Gaussianity that might exist in the sky, due to stronger effects than gravity. And it motivated researchers to devise better ways to search for the signals.

    A year after Maldacena made his calculation, Zaldarriaga and collaborators showed that measuring the distribution of galaxies and groupings of galaxies that make up the universe’s “large-scale structure” would yield many more shapes than observing the cosmic microwave background. “It’s a 3-D versus 2-D argument,” said Olivier Doré, a cosmologist at NASA’s Jet Propulsion Laboratory who is working on a proposed search for non-Gaussianities in the large-scale structure. “If you start counting triangles in 3-D like you can do with galaxy surveys, there are really many more you can count.”

    The notion that counting more shapes in the sky will reveal more details of the Big Bang is implied in a central principle of quantum physics known as “unitarity.” Unitarity dictates that the probabilities of all possible quantum states of the universe must add up to one, now and forever; thus, information, which is stored in quantum states, can never be lost — only scrambled. This means that all information about the birth of the cosmos remains encoded in its present state, and the more precisely cosmologists know the latter, the more they can learn about the former.

    But how did details of the Big Bang get encoded in triangles and other shapes? According to Zaldarriaga, Maldacena’s calculation “opened up the understanding of how it comes about.” In a universe governed by quantum mechanics, all of nature’s constituents are cross-wired, morphing into and interacting with one another with varying degrees of probability. This includes the inflaton field, the gravitational field, and whatever else existed in the primordial universe: Particles arising in these fields would have morphed into and scattered with each other to produce triangles and other geometric configurations, like billiard balls scattering on a table.

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    Lucy Reading-Ikkanda for Quanta Magazine

    These dynamical events would be mixed in with the more mundane quantum jitter from those particle pairs that popped up in the inflaton field and engendered so-called “two-point correlations” throughout the sky. A pair of particles might, for instance, have surfaced in some other primordial field, and one member of this pair might then have decayed into two inflaton particles while the other decayed into just a single inflaton particle, yielding a three-point correlation, or triangle, in the sky. Or, two mystery particles might have collided and split into four inflaton particles, producing a four-point correlation. Rarer events would have yielded five-point, six-point and even higher-point correlations, with their numbers, sizes and interior angles encoding the types and relationships of the particles that produced them. The unitarity principle promises that by tallying the shapes ever more precisely, cosmologists will achieve an increasingly detailed account of the primordial universe, just as physicists at the Large Hadron Collider in Europe hone their theory of the known particles and look for evidence of new ones by collecting statistics on how particles morph and scatter during collisions.

    Following Maldacena’s calculation of the gravitational floor, other researchers demonstrated that even many simple inflationary models generate much more pronounced non-Gaussianity than the bare minimum. Clocksmiths like Silverstein and Kleban have since been busy working out the distinct set of triangles that their models would produce — predictions that will become increasingly testable in the coming years. Progress accelerated in 2014, when a small experiment based at the South Pole appeared to make a momentous discovery about the universe’s birth. The announcement drummed up interest in cosmological triangles, even though the supposed discovery ultimately proved a grave disappointment.

    As news began to spread on March 17, 2014, that the “smoking gun” of cosmic inflation had been detected, Stanford University’s press office posted a celebratory video on YouTube. In the footage, the cosmologist Andrei Linde, one of the decorated pioneers of inflationary cosmology, and his wife, the string and supergravity theorist and cosmologist Renata Kallosh, answer their door to find their Stanford colleague Chao-Lin Kuo on the doorstep, accompanied by a camera crew.

    “It’s five sigma, at point two,” Kuo says in the video.

    “Discovery?” Kallosh asks, after a beat. She hugs Kuo, almost melting, as Linde exclaims, “What?”

    Viewers learn that BICEP2, an experiment co-led by Kuo, has detected a swirl pattern in the cosmic microwave background that would have been imprinted by ripples in space-time known as “primordial gravitational waves.”

    BICEP 2
    BICEP 2

    And these could only have arisen during cosmic inflation, as corkscrew-like particles popped up in the gravitational field and then became stretched and permanently frozen into the shape of the universe.

    In the next scene, Linde sips champagne with his wife and their guest. In the early 1980s, Linde, Alexei Starobinsky, Alan Guth and other young cosmologists devised the theory of cosmic inflation as a patch for the broken 1930s-era Big Bang theory, which described the universe as expanding outward from a “singularity” — a nonsensical point of infinite density — and couldn’t explain why the universe hadn’t become mottled and contorted as it grew. Cosmic inflation provided a clever fix for these problems, and BICEP2’s finding suggested that the theory was conclusively proved.

    Gravitational Wave Background
    Gravitational Wave Background [?] from BICEP2

    “If this is true,” Linde says to the camera, “this is a moment of understanding of nature of such a magnitude that it just overwhelms. Let’s see. Let’s just hope that this is not a trick.”

    To many researchers, the most exciting thing about the alleged discovery was the strength of the swirl signal, measured as r = 0.2. The measurement indicated that inflation occurred at an extremely high energy scale and at the earliest moments in time, near the time-energy domain where gravity, as well as the effects of strings, branes or other exotica, would have been strong. The higher the energy scale of inflation, the more cross-wiring there would be between the inflaton and these other primordial ingredients. The result would be pronounced triangles and other non-Gaussianities in the sky.

    “After BICEP, we all stopped what we were doing and started thinking about inflation,” Arkani-Hamed said. “Inflation is like having a gigantic particle accelerator at much higher energy scales than you can get to on Earth.” The question became how such an accelerator would operate, he said, “and if there really was exotic stuff up there [near the inflation scale], how you could go about looking for it.”

    As these investigations took off, more details of BICEP2’s analysis emerged. It became clear that the discovery was indeed a trick of nature: The team’s telescope at the South Pole had picked up the swirly glow of galactic dust rather than the effect of primordial gravitational waves. A mix of anguish and anger swept through the field. Two years on, primordial gravitational waves still haven’t been detected. In January, BICEP2’s predecessor, the BICEP/Keck Array, reported that the value of r can be no more than 0.07, which lowers the ceiling on the energy scale of inflation and moves it further below the scale of strings or other exotic physics.

    Keck Array
    Keck Array

    Nonetheless, many researchers were now aware of the potential gold mine of information contained in triangles and other non-Gaussianities. It had become apparent that these fossils from inflation were worth digging for, even if they were buried deeper than BICEP2 had briefly promised. “Yeah, r went down a little bit,” Maldacena said. But it’s not so bad, in his opinion: A relatively high scale is still possible.

    In a paper last spring that drew on previous work by other researchers, Maldacena and Arkani-Hamed used symmetry arguments to show that a key feature of string theory could manifest itself in triangles. String theory predicts an infinite tower of “higher-spin states” — essentially, strings vibrating at an infinitely rising sequence of pitches. So far, no fundamental particles with a “spin” value greater than two have been discovered. Maldacena and Arkani-Hamed showed that the existence of such a higher-spin state would result in alternating peaks and troughs in the strength of the signal produced by triangles in the sky as they grow more elongated. For string theorists, this is exciting. “You can’t build a consistent interacting theory of such a particle except if you have an infinite tower of them” like the tower in string theory, explained Daniel Baumann, a theoretical cosmologist at the University of Amsterdam. Finding the oscillatory pattern in the triangles in the sky would confirm that this tower exists. “Just seeing one particle of spin greater than two would be indicative of string theory being present.”

    Other researchers are pursuing similarly general predictions. In February, Kamionkowski and collaborators reported detailed information about primordial particles that is encoded in the geometry of four-point correlations, which “get interesting,” he said, because four points can lie flat or sweep into the third dimension. Observing the signals predicted by Arkani-Hamed, Maldacena and Kamionkowski would be like striking gold, but the gold is buried deep: Their strength is probably near the gravitational floor and will require at least 1,000 times the sensitivity of current equipment to detect. Other researchers prefer to tinker with bespoke string models that predict more pronounced triangles and other shapes. “So far we’ve explored only, I think, a very small fraction of the possibilities for non-Gaussianity,” Kamionkowski said.

    Meanwhile, Linde and Kallosh are pushing in a totally different direction. Over the past three years, they’ve become enamored with a class of models called “cosmological alpha-attractors” that do not predict any non-Gaussianities above the gravitational floor at all. According to these models, cosmic inflation was completely pure, driven by a solitary inflaton field. The field is described by a Kähler manifold, which maps onto the geometric disk seen in Escher’s drawing of angels and devils. The Escherian geometry provides a continuum of possible values for the energy scale of inflation, including values so low that the inflaton’s cross-wiring to the gravitational field and other primordial fields would be extremely weak. If such a model does describe the universe, then swirls, triangles and other shapes might never be detected.

    Linde isn’t bothered by this. In supporting the alpha-attractor models, he and Kallosh are staking a position in favor of simplicity and theoretical beauty, at the expense of ever knowing for sure whether their cosmological origin story is correct. An alpha-attractor universe, Linde said, is like one of the happy families in the famous opening line of Anna Karenina. As he paraphrased Tolstoy: “Any happy family, well, they look in a sense alike. But all unhappy families — they’re unhappy for different reasons.”

    Will our universe turn out to be “happy” and completely free of distinguishing features? Baumann, who co-authored a book last year on string cosmology, argues that models like Linde’s and Kallosh’s are too simple to be plausible. “They are building these models from the bottom up,” he said. “Introducing a single field, trying to be very minimal — it would have been a beautiful model of the world.” But, he said, when you try to embed inflation into a fundamental theory of nature, it’s very hard to engineer a single field acting by itself, immune to the effects of everything else. “String theory has many of these effects; you can’t ignore them.”

    And so the search for triangles and other non-Gaussianities is under way. Between 2009 and 2013, the Planck space telescope mapped the cosmic microwave background at the highest resolution yet, and scientists have since been scouring the map for statistical excesses of triangles and other shapes. As of their most recent analysis, they haven’t found any; given the sensitivity of their instruments and their 2-D searching ground, they only ever had an outside chance of doing so. But the scientists are continuing to parse the data in new ways, with another non-Gaussianity analysis expected this year.

    Hiranya Peiris, an astrophysicist at University College London who searches for non-Gaussianities in the Planck data, said that she and her collaborators are taking cues from string cosmologists in determining which signals to look for. Peiris is keen to test a string-inflationary mechanism called axion monodromy, including variants recently developed by Silverstein and collaborators Raphael Flauger, Mehrdad Mibabayi, and Leonardo Senatore that generate an oscillatory pattern in triangles as a function of their size that can be much more pronounced than the pattern studied by Arkani-Hamed and Maldacena. To find such a signal, Peiris and her team must construct templates of the pattern and match them with the data “in a very numerically intensive and demanding analysis,” she said. “Then we have to do careful statistical tests to make sure we are not being fooled by random fluctuations in the data.”

    Some string models have already been ruled out by this data analysis. Regarding the public debate about whether string theory is too divorced from empirical testing to count as science, Silverstein said, “I find it surreal, because we are currently doing some traditional science with string theory.”

    LSST/Camera, built at SLAC
    LSST Interior
    LSST telescope, currently under construction in Chile
    LSST camera, built at SLAC, LSST telescope, currently under construction in Chile.

    Moving forward, cosmologists plan to scour ever larger volumes of the universe’s large-scale structure. Starting in 2020, the proposed SPHEREx mission could measure non-Gaussianity sensitively enough in the distribution of 300 million galaxies to determine whether inflation was driven by one clock or two cross-wired clocks (according to models of the theory known as single- and multi-field inflation, respectively).

    4

    “Just to reach this level would dramatically reduce the number of possible inflation theories,” said Doré, who is working on the SPHEREx project. A few years further out, the Large Synoptic Survey Telescope will map 20 billion cosmological structures. If the statistical presence of triangles is not detected in the universe’s large-scale structure, there is yet another, perhaps final, approach. By mapping an ultra-faint radio signal called the 21-centimeter line, which is emitted by hydrogen atoms and traces back to the creation of the first stars, cosmologists would be able to measure even more “modes,” or arrangements of structures. “It’s going to have information about the whole volume of the universe,” Maldacena said.

    If or when triangles show up, they will, one by one, reveal the nature of the inflaton clock and why it ticked. But will enough clues be gathered before we run out of sky in which to gather them?

    The promise of unitarity — that information can be scrambled but never lost — comes with a caveat.

    “If we assume we can make perfect measurements and we have an infinite sky and so on,” Maldacena said, “then in principle all the interactions and information about particles during inflation is contained in these correlators” — that is, three-point correlations, four-point correlations and so on. But perfect measurements are impossible. And worse, the sky is finite. There is a cosmic horizon: the farthest distance from which light has had time to reach us, and thus, beyond which we cannot see. During inflation, and over the entire history of the accelerating expansion of the universe since then, swirls, triangles, quadrilaterals and other shapes have been flying past this horizon and out of sight. And with them, the subtlest of signals, associated with the rarest, highest-energy processes during inflation, are lost: Cosmologists will never be able to gather enough statistics in our finite patch of sky to tease them out, precluding a complete accounting of nature’s fundamental constituents.

    In his paper with Maldacena, Arkani-Hamed initially included a discussion of this issue, but he removed most of it. He finds the possibility of a limit to knowledge “tremendously disturbing” and sees it as evidence that quantum mechanics must be extended. One possible way to do this is suggested by his work on the amplituhedron, which casts quantum mechanical probabilities (and with them, unitarity) as emergent consequences of an underlying geometry. He plans to discuss this possibility in a forthcoming paper that will relate an analogue of the amplituhedron to non-Gaussianities in the sky.

    People vary in the extent to which they are bothered by a limit to knowledge. “I’m more practical,” Zaldarriaga said. “There are, like, tens or many tens or orders of magnitude more modes that in principle we could see, that we have not been able to measure just because of technological or theoretical inability. So, these ‘in principle’ questions are interesting, but we are way before this point.”

    Kleban also feels hopeful. “Yeah, it’s a finite amount of information,” he said. “But you could say the same thing about evolution, right? There’s a limited number of fossils, and yet we have a pretty good idea of what happened, and it’s getting better and better.”

    If all goes well, enough fossils will turn up in the sky to tell a more complete story. A vast searching ground awaits.

    See the full article here .

    Please help promote STEM in your local schools.

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    Formerly known as Simons Science News, Quanta Magazine is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

     
  • richardmitnick 8:31 pm on January 14, 2016 Permalink | Reply
    Tags: , , Cosmic Inflation, ,   

    From BNL: “New Theory of Secondary Inflation Expands Options for Avoiding an Excess of Dark Matter” 

    Brookhaven Lab

    January 14, 2016
    Chelsea Whyte, (631) 344-8671
    Peter Genzer, (631) 344-3174

    Physicists suggest a smaller secondary inflationary period in the moments after the Big Bang could account for the abundance of the mysterious matter.

    Temp 1
    No image credit found

    Standard cosmology—that is, the Big Bang theory with its early period of exponential growth known as inflation—is the prevailing scientific model for our universe, in which the entirety of space and time ballooned out from a very hot, very dense point into a homogeneous and ever-expanding vastness. This theory accounts for many of the physical phenomena we observe. But what if that’s not all there was to it?

    A new theory from physicists at the U.S. Department of Energy’s Brookhaven National Laboratory, Fermi National Accelerator Laboratory, and Stony Brook University, which will publish online on January 18 in Physical Review Letters, suggests a shorter secondary inflationary period that could account for the amount of dark matter estimated to exist throughout the cosmos.

    Temp 2
    Brookhaven Lab physicist Hooman Davoudiasl published a theory that suggests a shorter secondary inflationary period that could account for the amount of dark matter estimated to exist throughout the cosmos.

    “In general, a fundamental theory of nature can explain certain phenomena, but it may not always end up giving you the right amount of dark matter,” said Hooman Davoudiasl, group leader in the High-Energy Theory Group at Brookhaven National Laboratory and an author on the paper. “If you come up with too little dark matter, you can suggest another source, but having too much is a problem.”

    Measuring the amount of dark matter in the universe is no easy task. It is dark after all, so it doesn’t interact in any significant way with ordinary matter. Nonetheless, gravitational effects of dark matter give scientists a good idea of how much of it is out there. The best estimates indicate that it makes up about a quarter of the mass-energy budget of the universe, while ordinary matter—which makes up the stars, our planet, and us—comprises just 5 percent. Dark matter is the dominant form of substance in the universe, which leads physicists to devise theories and experiments to explore its properties and understand how it originated.

    Some theories that elegantly explain perplexing oddities in physics—for example, the inordinate weakness of gravity compared to other fundamental interactions such as the electromagnetic, strong nuclear, and weak nuclear forces—cannot be fully accepted because they predict more dark matter than empirical observations can support.

    This new theory solves that problem. Davoudiasl and his colleagues add a step to the commonly accepted events at the inception of space and time.

    In standard cosmology, the exponential expansion of the universe called cosmic inflation began perhaps as early as 10-35 seconds after the beginning of time—that’s a decimal point followed by 34 zeros before a 1. This explosive expansion of the entirety of space lasted mere fractions of a fraction of a second, eventually leading to a hot universe, followed by a cooling period that has continued until the present day. Then, when the universe was just seconds to minutes old – that is, cool enough – the formation of the lighter elements began. Between those milestones, there may have been other inflationary interludes, said Davoudiasl.

    “They wouldn’t have been as grand or as violent as the initial one, but they could account for a dilution of dark matter,” he said.

    In the beginning, when temperatures soared past billions of degrees in a relatively small volume of space, dark matter particles could run into each other and annihilate upon contact, transferring their energy into standard constituents of matter—particles like electrons and quarks. But as the universe continued to expand and cool, dark matter particles encountered one another far less often, and the annihilation rate couldn’t keep up with the expansion rate.

    “At this point, the abundance of dark matter is now baked in the cake,” said Davoudiasl. “Remember, dark matter interacts very weakly. So, a significant annihilation rate cannot persist at lower temperatures. Self-annihilation of dark matter becomes inefficient quite early, and the amount of dark matter particles is frozen.”

    However, the weaker the dark matter interactions, that is, the less efficient the annihilation, the higher the final abundance of dark matter particles would be. As experiments place ever more stringent constraints on the strength of dark matter interactions, there are some current theories that end up overestimating the quantity of dark matter in the universe. To bring theory into alignment with observations, Davoudiasl and his colleagues suggest that another inflationary period took place, powered by interactions in a “hidden sector” of physics. This second, milder, period of inflation, characterized by a rapid increase in volume, would dilute primordial particle abundances, potentially leaving the universe with the density of dark matter we observe today.

    “It’s definitely not the standard cosmology, but you have to accept that the universe may not be governed by things in the standard way that we thought,” he said. “But we didn’t need to construct something complicated. We show how a simple model can achieve this short amount of inflation in the early universe and account for the amount of dark matter we believe is out there.”

    Proving the theory is another thing entirely. Davoudiasl said there may be a way to look for at least the very feeblest of interactions between the hidden sector and ordinary matter.

    “If this secondary inflationary period happened, it could be characterized by energies within the reach of experiments at accelerators such as the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider [LHC],” he said.

    BNL RHIC Campus
    BNL RHIC
    RHIC with map

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN with map.

    Only time will tell if signs of a hidden sector show up in collisions within these colliders, or in other experimental facilities.

    Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

    See the full article here .

    Please help promote STEM in your local schools.

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    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
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  • richardmitnick 5:28 pm on December 23, 2015 Permalink | Reply
    Tags: , , Cosmic Inflation, , Why the universe did not immediately collapse   

    From phys.org: “Physicists continue to investigate why the universe did not collapse” 

    physdotorg
    phys.org

    December 23, 2015
    Lisa Zyga

    1
    This is the “South Pillar” region of the star-forming region called the Carina Nebula. Like cracking open a watermelon and finding its seeds, the infrared telescope “busted open” this murky cloud to reveal star embryos tucked inside finger-like pillars of thick dust. Credit: NASA/Spitzer

    According to the best current physics models, the universe should have collapsed shortly after inflation—the period that lasted for a fraction of a second immediately after the Big Bang.

    The problem lies in part with Higgs bosons, which were produced during inflation and which explain why other particles have the masses that they do. Previous research has shown that, in the early universe, the Higgs field may have acquired large enough fluctuations to overcome an energy barrier that caused the universe to transition from its standard vacuum state to a negative energy vacuum state, which would have caused the universe to quickly collapse in on itself.

    In a new paper published in Physical Review Letters, Matti Herranen at the University of Copenhagen and coauthors may have come a step closer to solving the problem by constraining the strength of the coupling between the Higgs field and gravity, which is the last unknown parameter of the standard model.

    2
    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.

    As the physicists explain, the stronger the Higgs field is coupled to gravity, the larger are the fluctuations that may eventually trigger a fatal transition to the negative energy vacuum state.

    In the new paper, the scientists calculated that a collapse after inflation would have happened only if the coupling strength had been above a value of 1.

    Combining this result with the lower bound of 0.1, which the same physicists derived last year by analyzing the requirements for stability during (rather than after) inflation, and the range of 0.1-1 constrains the coupling to near its historically estimated value of 1/6. This value of 1/6 is traditionally used as an estimate because it corresponds to zero Higgs-gravity coupling, though it is likely incorrect.

    Narrowing down the Higgs-gravity coupling strength will guide physicists when analyzing experimental data to help pinpoint the coupling value with greater precision. Data on the cosmic microwave background [CMB] radiation and gravitational waves, for example, are expected to help further constrain the value. When combined with other parameters, the Higgs-gravity coupling strength should produce a picture of a universe that did not transition to a state of collapse.

    CMB Planck ESA
    CMB per ESA/Planck

    ESA Planck
    ESA/Planck

    “It’s a combination of parameters that actually determines the occurrence of such a transition, including the Higgs coupling to gravity, but also the energy scale of the inflation, which are not tightly constrained by current measurements,” Herranen told Phys.org. “So, presently it is not possible to draw a conclusion on whether the standard model is in trouble due to instability-related issues, but it would be very interesting if the Higgs-gravity coupling and the scale of inflation could be constrained more tightly in the future by independent measurements, for example by observing primordial gravity waves resulting from inflation.”

    Taken together, the results should help scientists modify inflation models in order to describe a universe more like the one we live in.

    More information: M. Herranen, et al. “Spacetime Curvature and Higgs Stability after Inflation.” Physical Review Letters. DOI: 10.1103/PhysRevLett.115.241301

    See the full article here .

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  • richardmitnick 5:23 pm on October 28, 2015 Permalink | Reply
    Tags: , , Cosmic Inflation, ,   

    From New Scientist: “Mystery bright spots could be first glimpse of another universe” 

    NewScientist

    New Scientist

    28 October 2015
    Joshua Sokol

    Light given off by hydrogen shortly after the big bang has left some unexplained bright patches in space. Are they evidence of bumping into another universe?

    1

    THE curtain at the edge of the universe may be rippling, hinting that there’s more backstage. Data from the European Space Agency’s Planck telescope could be giving us our first glimpse of another universe, with different physics, bumping up against our own.

    ESA Planck
    ESA/Planck

    That’s the tentative conclusion of an analysis by Ranga-Ram Chary, a researcher at Planck’s US data centre in California. Armed with Planck’s painstaking map of the cosmic microwave background (CMB) – light lingering from the hot, soupy state of the early universe – Chary revealed an eerie glow that could be due to matter from a neighbouring universe leaking into ours.

    Cosmic Background Radiation Planck
    CMB per Planck

    This sort of collision should be possible, according to modern cosmological theories that suggest the universe we see is just one bubble among many. Such a multiverse may be a consequence of cosmic inflation, the widely accepted idea that the early universe expanded exponentially in the slimmest fraction of a second after the big bang.

    Once it starts, inflation never quite stops, so a multitude of universes becomes nearly inevitable. “I would say most versions of inflation in fact lead to eternal inflation, producing a number of pocket universes,” says Alan Guth of the Massachusetts Institute of Technology, an architect of the theory.

    Energy hidden in empty space drives inflation, and the amount that’s around could vary from place to place, so some regions would eventually settle down and stop expanding at such a manic pace. But the spots where inflation is going gangbusters would spawn inflating universes. And even areas within these new bubbles could balloon into pocket universes themselves.

    Like compositions on the same theme, each universe produced this way would be likely to have its own spin on physics. The matter in some bubbles – the boring ones – would fly apart within 10-40 seconds of their creation. Others would be full of particles and rules similar to ours, or even exactly like ours. In the multiverse of eternal inflation, everything that can happen has happened – and will probably happen again.

    That notion could explain why the physical constants of our universe seem to be so exquisitely tuned to allow for galaxies, stars, planets and life (see Just right for life? below).

    Sadly, if they do exist, other bubbles are nigh on impossible to learn about. With the space between them and us always expanding, light is too slow to carry any information between different regions. “They could never even know about each other’s existence,” says Matthew Johnson of York University in Toronto, Canada. “It sounds like a fun idea but it seems like there’s no way to test it.”

    Bubble trouble

    However, if two bubbles started out close enough that they touched before expanding space pushed them apart forever, they could leave an imprint on each other. “You need to get lucky,” Johnson says.

    In 2007, Johnson and his PhD adviser proposed that these clashing bubbles might show up as circular bruises on the CMB. They were looking for cosmic dance partners that resembled our own universe, but with more of everything. That would make a collision appear as a bright, hot ring of photons.

    By 2011, they were able to search for them in data from NASA’s WMAP probe, the precursor to Planck.

    NASA WMAP
    NASA/WMAP

    Cosmic Microwave Background WMAP
    CMB per WMAP

    But they came up empty-handed.

    Now Chary thinks he may have spotted a different signature of a clash with a foreign universe.

    “There are two approaches, looking for different classes of pocket universes,” Johnson says. “They’re hunting for lions, and we’re hunting for polar bears.”

    Instead of looking at the CMB itself, Chary subtracted a model of the CMB from Planck’s picture of the entire sky. Then he took away everything else, too: the stars, gas and dust.

    With our universe scrubbed away, nothing should be left except noise. But in a certain frequency range, scattered patches on the sky look far brighter than they should. If they check out, these anomalous clumps could be caused by cosmic fist-bumps: our universe colliding with another part of the multiverse (arxiv.org/abs/1510.00126).

    These patches look like they come from the era a few hundred thousand years after the big bang when electrons and protons first joined forces to create hydrogen, which emits light in a limited range of colours. We can see signs of that era, called recombination, in the light from that early hydrogen. Studying the light from recombination could be a unique signature of the matter in our universe – and potentially distinguish signs from beyond.

    “This signal is one of the fingerprints of our own universe,” says Jens Chluba of the University of Cambridge. “Other universes should leave a different mark.”

    Since this light is normally drowned out by the glow of the cosmic microwave background, recombination should have been tough for even Planck to spot. But Chary’s analysis revealed spots that were 4500 times as bright as theory predicts.

    One exciting explanation for this is if a surplus of protons and electrons – or something a lot like them – got dumped in at the point of contact with another universe, making the light from recombination a lot brighter. Chary’s patches require the universe at the other end of the collision to have roughly 1000 times as many such particles as ours.

    “To explain the signals that Dr Chary found with the cosmological recombination radiation, one needs a large enhancement in the number of [other particles] relative to photons,” Chluba says. “In the realm of alternative universes, this is entirely possible.”

    Of course there are caveats, and recent history provides an important reality check. In 2014, a team using the BICEP2 telescope at the South Pole announced another faint signal with earth-shaking cosmological implications.

    BICEP 2
    BICEP2 on the right, South Pole telescope on the left

    The spirals of polarised light, spotted in the cosmic background, would have provided more observational evidence for the idea of inflation and helped us understand how inflation occurred. But it turned out that signal came from dust grains within our galaxy.

    Gravitational Wave Background
    Theorized gravitational waves

    2

    Princeton University’s David Spergel, who played a major role in debunking the BICEP2 finding, thinks dust may again be clouding our cosmological insights. “I suspect that it would be worth looking into alternative possibilities,” he says. “The dust properties are more complicated than we have been assuming, and I think that this is a more plausible explanation.”

    Joseph Silk of Johns Hopkins University in Baltimore, Maryland, is even more pessimistic, calling claims of an alternate universe “completely implausible”. While he thinks the paper is a good analysis of anomalies in Planck data, Silk also believes something is getting in the way. “My view is that they are almost certainly due to foregrounds,” he says.

    Chary acknowledges that his idea is as tentative as it is exciting. “Unusual claims like evidence for alternate universes require a very high burden of proof,” he writes.

    He makes an effort to rule out more prosaic explanations. If it is dust, Chary argues, it would be the coldest dust we’ve ever seen. It’s probably not noise masquerading as a signal. It could be carbon monoxide moving toward us, but we don’t usually see that. It could be faraway carbon, but that emission is too weak.

    “I am certain he made every effort to ensure that the analysis is solid,” says Chluba. Even so, foregrounds and poorly understood patterns could still be the source of the signals. “It will be important to carry out an independent analysis and confirm his finding,” Chluba says.

    Sensitive solutions

    One obstacle to checking is that we’re limited by the data itself. Planck was hyper-sensitive to the cosmic microwave background, but it wasn’t intended to measure the spectral distortions Chary is looking for. Johnson’s team also plans to use Planck to look for their own alternate universes, once the data they need is released to the public – but they estimate that Planck will only make them twice as sensitive to the bubble collisions they’re looking for as they were with WMAP.

    An experiment that could help might be on its way. Scientists at NASA’s Goddard Space Flight Center plan to submit PIXIE, the Primordial Inflation Explorer, to be considered for funding at the end of 2016.

    NASA PIXIE
    NASA Goddard PIXIE

    PIXIE’s spectral resolution could help characterise Chary’s signals if they really are there, Chluba says. But even if they aren’t, reconstructing how inflation happened could still lead us once again back to the multiverse – and tell us what kind of bubble collisions we should look for next.

    __________________________________________________________________________

    Just right for life?

    If our universe is just one of many, that could explain why it seems so exquisitely tuned for our existence.

    If dark energy, the repulsive influence hiding in empty space that speeds up the expansion of the universe, were just a little stronger, matter would be flung apart before galaxies could ever form. If it were attractive instead, the universe would collapse. But it is shockingly puny, and that’s weird, unless our universe is one of many in the multiverse.

    Compared with what we might expect from quantum theory, dark energy is 120 orders of magnitude too small. So far, no compelling explanation for that discrepancy has emerged. But if the multiverse exists, and dark energy varies from bubble to bubble (see main story), that might not seem so strange.

    That’s because our own universe might be an oddball compared to most bubbles. In many, dark energy would be too strong for galaxies, stars and planets to form, but not in all. “Plenty of them would have energies as small as what we observe,” says physicist Alan Guth of MIT.

    That still leaves us struggling to explain why our universe is one of the special ones. Our best answer so far, Guth says, is a philosophical headache: our universe has to be special because we are alive in it. In a more average region, where dark energy is stronger, stars, planets, and life would never have evolved.

    That could mean life only exists in a sliver of the multiverse, with any conscious beings convinced their own slice of space is special, too.

    __________________________________________________________________________

    See the full article here .

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  • richardmitnick 8:05 am on September 14, 2015 Permalink | Reply
    Tags: , , Cosmic Inflation,   

    From COSMOS- “New model of the cosmos: a Universe that begins again” 

    Cosmos Magazine bloc

    COSMOS

    14 Sep 2015
    Michael D. Lemonick

    The failure so far to find gravitational waves has some cosmologists wondering if the ‘inflationary’ theory of the Big Bang is right. Michael D. Lemonick explains.

    On 17 March, 2014, the Harvard-Smithsonian Centre for Astrophysics held a press conference to announce “a major discovery”. It was not an exaggeration. A team of astrophysicists had detected evidence of gravitational waves from a time when the Universe was almost indescribably young.

    Gravitational Wave Background
    Representation of possible gravitational waves from BICEP2

    BICEP 2
    BICEP2

    It was the most powerful confirmation yet of the 30-year-old theory of inflation which explains why the cosmos looks the way it does. The distribution of galaxies, the relative proportions of ordinary matter and dark matter3, the curvature of space-time, the fact that the cosmos looks essentially the same no matter where you look – all of this can be understood if you assume that the entire visible Universe expanded for the briefest interval from something about the size of a proton to something about the size of a grapefruit at faster than the speed of light when it was less than a billionth of a trillionth of a trillionth of a second old. In the words of University of California, Santa Cruz, cosmologist Joel Primack: “No theory this beautiful has ever been wrong.”

    Evidently, it had been proven right. Using an exquisitely sensitive microwave telescope known as BICEP2 located at the South Pole, Harvard’s John Kovac and a team of observers had detected a twist in the orientation of microwaves generated about 300,000 years after the Big Bang. Known as B-mode polarisation, it had been predicted by inflation theory. The fantastic energy released by an inflating Universe would have rippled space-time itself.

    Alternative theories about how the Universe got its structure – such as the one developed by Princeton University’s Paul Steinhardt – did not predict these ripples. “If this is correct, we’re finished,” Steinhardt commented. He had been one of the pioneers of inflation theory but had since abandoned it in favour of his own competing theory.

    1
    The swirls detected in this picture of the Milky Way were initially believed to be caused by gravitational waves, but later measurements showed cosmic dust could create the same effect.Credit: ESA / Planck Collaboration

    ESA Planck
    ESA PLanck

    The announcement at the Harvard press conference reverberated in headlines around the world. “Space Ripples Reveal Big Bang’s Smoking Gun,” trumpeted the New York Times. “Primordial gravitational wave discovery heralds ‘whole new era’ in physics,” declared the Guardian. Like virtually every other story that appeared on that day, there were dutiful caveats along the lines of “The results will require confirmation …” They barely dented the feverish tone.

    Within days of the announcement the reporters were wishing they’d been more than merely dutiful. Kovac’s scientific report (revealed online on arXiv – a forum for work to be published soon) wasn’t released until the press conference. Once other astrophysicists got a look at it, they became suspicious. Primordial gravitational waves aren’t the only thing that could polarise microwaves. The Milky Way’s swirling dust clouds could do it too – “schmutz”, Princeton’s David Spergel called it, using a Yiddish word meaning “dirt.”

    As independent physicists scrutinised the report more closely, they became increasingly sceptical as to whether the Harvard team had seen gravitational waves at all. Finally in February 2015, a combined analysis of the data from Kovac’s BICEP2 team; the Keck Array (located next to BICEP2 at the South Pole); and Planck, the European Space Agency’s orbiting space observatory, left the researchers in no doubt. “What we see”, Kovac conceded “is compatible with no inflationary gravitational waves”.

    Keck Array
    Keck Array

    That hardly means that inflation is dead. What these three very sensitive instruments saw is also compatible with inflationary gravitational waves hiding within the dust. Inflation, moreover, isn’t a single theory: it’s a class of theories, and many predict gravitational waves 10 orders of magnitude lower than any existing instrument is capable of detecting. “Am I worried?” asks Stanford University theorist Andrei Linde, one of the founders of inflation theory. “Why should I be?”

    But for a small number of theoretical astrophysicists, the failure to detect gravitational waves raises the stock for an alternative theory of the birth of the Universe. Known as the cyclic model, it was first proposed in 2003 by Princeton’s Steinhardt and Neil Turok, then at the University of Cambridge (now director of Canada’s Perimeter Institute for Theoretical Physics). These days it is championed by a handful of theorists mostly in the US and the UK. It posits that the observable Universe has gone through alternating phases of expansion and contraction – perhaps forever.

    This model of cosmology explains everything we know about the Universe just as well as inflation does, they say. A major point of departure though, is that primordial gravitational waves are not part of the cyclical model.

    While most physicists are not even close to abandoning inflation, they don’t rule out that this beautiful theory may also be wrong. “Paul has a bunch of concerns about the inflation theory, which I think are valid,” says Charles Bennett, an experimental physicist at Johns Hopkins University.

    Joanna Dunkley, a cosmologist at the University of Cambridge, agrees the failure to detect gravitational waves “should make us think more seriously about whether inflation is the only option”.

    “I think most of the community is focused on inflationary models, and I think some of that is fashion,” adds David Spergel, Steinhardt’s Princeton colleague.

    3
    Neil Turok argues the case for a cyclic view of the Universe.Credit: Peter Power

    Fashion explains some of their focus, perhaps, but hardly all of it. When inflation theory first emerged in the 1980s, it was nothing short of breathtaking in the way it explained a series of problems that had bedevilled cosmologists since the 1964 discovery of the cosmic microwave background (CMB) radiation.

    Cosmic Background Radiation Planck
    CMB per Planck

    At the time, there were two competing theories about how the Universe began. One was the Steady State, which posited that the Universe has always been expanding, and that new matter is created to fill in the gaps as existing matter spreads apart.

    The other was the Big Bang, ironically coined by English astronomer Sir Fred Hoyle as a term of ridicule – he was the leading proponent of the Steady State. The original idea here was that the Universe was born out of the violent expansion of an extremely dense, hot gas cloud (a modern version holds that it began from a singularity – a pinpoint of sub-atomic proportions) which has been expanding ever since. If that were true, then the brilliant light generated by that bang should still be echoing through the Universe – except the expansion of the Universe would have stretched the light into the microwave region of the electromagnetic spectrum.

    4
    Paul Steinhardt is another insurgent challenging the theory of inflation.Credit: Beverly Schaefer

    In 1964, radio astronomers Arno Penzias and Robert Wilson at the Bell Telephone Laboratories in New Jersey, stumbled across that stretched ancient light. They were experimenting with Bell Lab’s giant radio antenna – originally built to track satellites – to see if they could repurpose it to peer at the Universe.

    5
    Robert Woodrow Wilson (left) with Arno Allan Penzias at the Bell Labs giant radio antenna

    Annoyingly, their efforts were thwarted by a mysterious microwave frequency hiss in the antenna. When the meticulous pair had ruled out all other explanations (including pigeon poop) they suggested the hiss was cosmic in origin. Around the same time, just an hour’s drive to the west, Robert Dicke and several other physicists at Princeton University were setting out to look for relic microwaves from the Big Bang. Penzias and Wilson heard about Dicke’s project and called during one of his group meetings. As those who were present recall, Dicke listened patiently, hung up and said “boys, we’ve been scooped”.

    Both groups published simultaneously in The Astrophysical Journal in 1965 (only Penzias and Wilson got the Nobel, however). The discovery tipped the scales firmly in favour of the Big Bang.

    Cosmologists leapt at the opportunity to study the CMB in detail – it was the first glimpse of our youthful, 400,000-year-old Universe. It turned out to be a mysterious place. For one thing, they were struck by its uncannily uniform temperature – it hovers at 2.725° above absolute zero, varying by no more than one part in 100,000 in either direction, no matter where in the sky you look. The turbulent super-heated gas cloud from which the Universe erupted would have had spots that varied significantly in temperature and density and some of that messiness should have been on show in the structure of the early expanded Universe.

    Another problem was that while the strapping 400,000-year-old Universe was as smooth and even as a baby’s bottom, the mature universe is wrinkled with features such as galaxies. But how did these age-related wrinkles arise?

    Physicists were also worried by the apparent topology of the early Universe. Over large scales, their measurements showed that it appeared to be geometrically “flat”. And it was unclear why monopoles – particles with either a north or south magnetic charge but not both – had never been found.

    Cosmologists scratched their heads for more than a decade. Then in 1980 a young physicist named Alan Guth figured out these conundrums would vanish if a proton-sized Universe experienced an ultra-fast expansion in its very earliest moments.

    6
    Alan Guth

    A proton-sized beginning that suddenly inflated would explain the evenness of the Universe. It would have ballooned out so fast there was no time for any fluctuations to wrinkle the expanding fabric of space-time.

    On the other hand, the fact that the entire Universe was once sub-atomic in size made it subject to quantum effects such as “uncertainty” – a state in which physical variables can fluctuate unpredictably. These random quantum fluctuations seeded the wrinkles that gave rise to features such as galaxies.

    Finally, inflation explained why the visible cosmos appears so flat. Perhaps it started off with significant curvature like the surface of a balloon. Imagine that you’re a fly balancing on the ball. Suddenly, it expands to the size of the Sun. You’re still standing on a curved surface, but to you it now looks utterly flat as far as the eye can see. Without the rapid expansion, the balloon wouldn’t have expanded sufficiently to create the flatness we observe.

    Guth’s original version of inflation left some gaps but they were filled by Linde, turning the theory into a robust set of predictions that cosmologists have been testing ever since.

    There was a problem, however.

    “We discovered early on that we completely misunderstood something at the beginning,” says Steinhardt, who was one of the pioneers of inflation theory. “We thought that inflation was essentially a story about stretching the Universe. And then we thought if you add a little bit of quantum mechanics to explain why the Universe isn’t perfectly uniform” – why it has galaxies and clusters of galaxies – “we seem to have a consistent story”.

    However, there’s no such thing as a little bit of quantum mechanics, says Steinhardt. “Quantum physics is constantly producing fluctuations in all forms of energy, including the energy that’s driving inflation, so that it ends in some places a little bit later than others,” he says.

    He and others soon realised that quantum uncertainty complicated matters.

    In our patch of the Universe, for instance, inflation stopped billions of years ago, but in some other patches it’s still going on. Given inflation’s breakneck expansion rate, these regions would now be unimaginably large – as though bits of the original balloon had bulged outward to form gigantic protuberances, much larger than the original. “This will occur over and over and over again,” Steinhardt explains. Linde, who is mostly responsible for this idea, calls it “chaotic inflation” or “eternal inflation”. It means that our own visible Universe is just one patch in a far larger multiverse – a patch within a patch within a patch, ad infinitum – and each patch could have its own unique laws of physics. “The multiverse will explore every conceivable physical property and possibility and produce every conceivable outcome,” says Steinhardt.

    And that’s the problem. “What can you predict from such a theory?” Steinhardt asks. “Nothing. Literally nothing, since anything that’s physically possible will occur.” But it’s worse than that: since an infinite number of patches exist with an infinite variety of physical laws and constants, the fundamental question that physicists have been trying to answer since the time of Aristotle – why is the Universe the way it is? – becomes meaningless. It’s the way it is because the Universe is every possible way all at once. Ours happens to look the way it does because that’s the part we happen to be living in. This is what’s known as the anthropic principle, and since it says in essence that there’s no explanation for anything, it pulls the rug out from under science. That doesn’t make it wrong, but physicists tend to abhor it.

    There’s a second problem as well. “It’s remarkable that we have a theory that can describe what’s going on and match the observations so beautifully,” says Spergel. “But it doesn’t explain how it got into that phase.” In other words inflation might have happened but nobody knows why it started. Inflationary theorists say that’s a problem to be solved later, says Steinhardt. “But it’s a big problem to be solved later,” he says, “because we’ve been trying to solve that problem and we think the conditions under which inflation could begin are very, very rare.” Unless you believe in a Creator, that’s not a good place to be.

    There was a third problem: dark energy. In 1999 cosmologists confirmed that this mysterious force is ballooning out the Universe at an ever-accelerating rate. Inflation theory, conceived in the 1980s, was blissfully unaware of dark energy.

    “It was a total surprise,” says the Perimeter Institute’s Turok. “Inflation was already something of an artificial add-on to the Big Bang, and now you’ve got this new add-on, which has nothing to do with inflation.” Turok says you also have to account for the fact that inflation dominated the earliest moments of our part of the Universe, then went away – and that dark energy (tiny compared with the energy of inflation) would emerge billions of years later to dominate the Universe.

    Inflationists consider dark energy to be something entirely different from inflation – a second expansionary force that only became significant many billions of years after inflation ran out of steam. The fact that you need to explain not one, but two different forces makes Steinhardt and Turok uncomfortable with the inflation model. “It’s horribly fine-tuned,” says Turok.

    For this pair of physicists, dark energy had finally robbed inflationary theory of its beautiful shine. There had to be a simpler, better theory. After several years of intensive work, they came up with the cyclic model.

    In the cyclic model, dark energy doesn’t suddenly turn off after the creation of the Universe and then return. Instead, it is dark energy – which we can observe as opposed to inflation which is theoretical – that drives the initial expansion of the Universe and continues the process, strengthening as the Universe ages.

    Ultimately it also reverses direction, a possibility that other theorists had considered even before the cyclic Universe scenario was proposed. The reversal takes a long time – perhaps as much as 10500 years. But eventually the Universe collapses to a tiny size (the model doesn’t specify precisely how small, but it’s far larger than inflation calls for). Then the dark energy reverses direction again, the Universe begins to expand, and a new cycle bounces into being. “In this model,” Turok says, “there is no inflation, and dark energy isn’t a bizarre add-on: it’s essential.”

    By positing a Universe that expands for many billions of years, then contracts then expands again, perhaps infinitely many times, Steinhardt’s and Turok’s theory addresses many of the same mysteries inflation appeared to solve.

    For example, because the cosmos has gone through many, many cycles, it has had ample time for different regions to have come into temperature equilibrium, so there’s no problem with the fact that opposite sides of the visible Universe look essentially the same. And the topological “flatness” of the visible Universe might emerge not from ultra-fast expansion but from the effect of dark energy during the contraction. Precisely how the reversal happens is something Turok and Steinhardt haven’t worked out yet. “There’s a lot of effort in the field right now,” says Steinhardt, “different approaches for thinking about these bounces, but they all have the feature that they are continuous processes, meaning there can’t be anything too crazy that happens as you’re going through them”– for example, nothing as crazy as the singularity where density becomes infinite and physics breaks down – a state that appears inevitable if the Universe expands only once.

    While both physicists are convinced that the cyclic theory is more straightforward and plausible than the inflationary model, they realise their arguments won’t be enough to wean their colleagues away from inflation. Both theories match existing observations very well, and neither Steinhardt nor Turok is prepared to say the cyclic model is clearly better at this point. But there’s one observation that could decide between them. Gravitational waves are predicted by inflation; cyclic models say they shouldn’t exist.

    If the BICEP2 telescope had actually found the signal its scientists claimed last spring, that would have been the end of the road for Steinhardt’s ideas. The fact that it didn’t, he says, should inspire other physicists and astrophysicists to take another look at cyclic models.

    For Steinhardt, cosmology is experiencing a challenge akin to that faced by planetary astronomers of the mid-1500s. Ptolemy’s Earth-centred Solar System was the reigning view but contested by Copernicus’ Sun-centered theory. “Copernicus could explain some things conceptually that Ptolemy couldn’t”, says Steinhardt, “and vice versa”. It was only when Kepler realised the planets follow elliptical rather than circular paths that Copernicus’ model pulled ahead. In Steinhardt’s view this is a Kepler moment.

    Most physicists aren’t quite ready for that. “It’s still possible with the BICEP2 and Planck data that there could be a whopping great gravitational wave signature,” says Cambridge’s Joanna Dunkley. “It’s not that BICEP2 has got no signal at all, it’s just the signal is much more likely to be dust than the Big Bang.” As observers continue to refine their observations of the dust, however, it will become easier for them to subtract the dust signal electronically and see if there are any truly primordial polarised microwaves hiding behind it – much as they do now when observing vanishingly dim galaxies through the Earth’s atmosphere.

    And even if no inflation signal emerges out of the dust, the waves could well be out there but beyond the limits of current detectors to find them. “There’s a very large spectrum of possibilities for the intensity of those gravity waves,” says Guth.

    That could change over the next few years, however, as Planck satellite data continues to be analysed and as other ground-based CMB detectors continue their watch for signals from the ancient Universe. They include the balloon-borne SPIDER detector, which just completed a loop around Antarctica; the Atacama Cosmology Telescope, the POLARBEAR experiment and the Cosmology Large Angular Scale Surveyor in Chile; the South Pole Telescope; the Harvard group’s Keck Array, and more. All of them are looking for polarised light – some scanning larger patches of sky in less detail, others looking at small patches more intensively. “A lot of people are thinking up new ways to measure this very, very tiny signal,” says Lyman Page, Steinhardt’s Princeton colleague “and we’ve been thinking about it for years”.

    Princeton Atacama Technology Telescope
    Princeton Atacama Cosmology Telescope

    POLARBEAR McGill Telescope
    POLARBEAR Telescope

    Cosmology Large Angular Scale Surveyor
    Cosmology Large Angular Scale Surveyor

    South Pole Telescope
    South Pole Telescope

    Each instrument will make valuable observations in its own right, says Bill Jones, a Princeton physicist who works with the SPIDER experiment. “It’s sort of like a force multiplier in the sense that we can take advantage of the different strengths that they have in order to really nail the signal,” he says.

    Like most of his colleagues, Jones acknowledges that the cyclic models are interesting –even intriguing. But he adds: “I think that when the average cosmologist wakes up in the morning, he or she probably still thinks something like inflation happened.”

    Steinhardt, Turok and the other crusaders for the cyclic model are fine with that. For now.

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  • richardmitnick 5:42 pm on December 6, 2014 Permalink | Reply
    Tags: , , , Cosmic Inflation, , , Princeton SPIDER   

    From Princeton- ” SPIDER: Searching for the Echoes of Inflation” 

    Princeton University
    Princeton University

    Princeton SPIDER Inflation

    December 5, 2014
    Zigmund Kermish
    Zigmund Kermish is an associate research scholar at Princeton University.

    Wait, why am I in Antarctica?

    I realized I’ve not yet written a blog post explaining why my experiment is in Antarctica. Things are temporarily quiet on the Ice while we’ve been waiting for the SPIDER cryostat to cool down, so now’s a good time to make the attempt.

    To get the best results from SPIDER, we have to go to very high and dry locations. This is because water vapor in the atmosphere limits SPIDER’s sensitivity. There are currently two terrestrial locations that are commonly used: the Atacama Desert POLARBEAR and ACTPol
    sit at about 5,200 meters above sea level) and the South Pole (where the South Pole Telescope, the KECK array, and this year BICEP3 operate at 2,800 meters).

    POLARBEAR McGill Telescope
    POLARBEAR

    ACT Telescope
    Princeton Atacama Cosmology Telescope

    South Pole Telescope
    South Pole Telescope (SPT)

    Keck Array
    Keck Array

    BICEP 2
    BICEP 2 interior
    BICEP

    Of course, one can always go beyond terrestrial limits. With a big enough budget and enough time to develop the project, you can launch a dedicated satellite mission to eliminate the atmosphere all together, achieving dramatically improved individual detector sensitivities. Historically, satellite-based instruments have provided the definitive measurements of various aspects of the cosmic microwave background (the faint signal left over from the Big Bang), but they usually build upon the groundbreaking discoveries made closer to Earth. These discoveries have been made from the ground and from one other platform: balloons.

    Balloon-borne instruments have one big advantage: they allow us to get above nearly all of the atmosphere, approaching the detector sensitivity of satellite-based instruments at a fraction of the cost of a satellite mission.

    Princeton SPIDER instrument

    This increased detector sensitivity has two advantages: you can observe a larger fraction of the sky for a significantly shorter amount of time and still get a higher fidelity map than what you can do from the ground (observing for days rather than years) and you can observe in frequency channels that are difficult (if not impossible) to use from the ground. Both of these features, multiple frequencies and larger sky coverage, are necessary to ultimately demonstrate the ‘cosmological nature’ of the signals we’re looking for – to show that it’s not just a signal from some foreground in our local galaxy and that it has the required statistical properties across the sky we expect from proposed theories.

    As shown in the below gif, SPIDER can observe a large fraction of the ‘clean’ sky (the white outline) for 20 days and get nearly the same sensitivity over that region as a ground based experiment like the BICEP2 project had on their smaller region (green outline) after several years of observation.
    dust_regions

    g

    A map of the dust intensity seen in the sky, the bright center band the emission from our own Milky Way galaxy. The overlay that is fading in shows several things: The colored diamonds show the most recent data about the *polarization* strength of the dust signal, blue being less polarized dust, the outlines on the overlay show the regions observed (or to be observed shortly!) by BICEP2 (green), POLARBEAR (red), and SPIDER (white).

    Ok, so that’s why we want to dangle our instrument from a balloon. But why Antarctica? Why don’t we just launch our balloon from New Jersey?

    Well, for one, at some point, we need to bring the instrument back down to Earth, and that involves literally letting it fall to the ground so that we can recover it. That’s why scientific payload balloon flights only happen in places with low population density. In the US, payloads are flown out of Fort Sumner, New Mexico. They used to fly out of Palestine, Texas as well. Payloads flown out of these locations are limited to flights anywhere from a few hours to a few days because they eventually start getting too close to population centers.

    Antarctica doesn’t have any population centers, so rather than being limited by distance, flights are limited by how long the balloons can stay afloat. Currently, that’s about 40 days. Beyond that, weather patterns setup circumpolar winds during the austral summer here.

    So if you launch a balloon at the right time, it’ll come back close to where it started, making recovery of the instrument easier (it takes about a week to ‘boomerang’ back around). This is especially important for an experiment like ours since we need to physically recover our data off the drives that fly with the instrument. The bandwidth of in-flight communications limits us to only getting a small fraction of the data from the instrument during flight. One of the many ballooning challenges is to make the system as autonomous as possible so minimal human intervention based on the limited information we decide to ‘downlink’ to the ground is needed.

    The other fundamental challenges of ballooning that make this a very different game from ground-based experiments I’ve worked on: weight and power constraints. Having to fly the batteries you need to power the experiment, the solar panels to keep them charged, the cryogenic system to keep the everything cool and all the readout and control electronics systems while still staying below the maximum mass limits current balloons can float makes a project like this a fun problem to solve. The absence of day-night cycles during the austral summer in Antarctica helps address the power and weight constraints by giving us a continual source of solar power. This means we only need to fly a few heavy batteries to provide a non-variable power source and we can dedicate more of our mass budget to the scientific instruments. More compromises have to be made when designing payloads to fly at mid-latitudes, where enough batteries need to fly to power the payload throughout the night. There are many advantages to these mid-latitude flights though: larger available sky and longer (100 day!) flights with NASA’s new, soon-to-launch-with-science-payloads super pressure balloon platform (SPB).

    The CMB Cosmology group at Case is led by Prof. John Ruhl. The current members of our group are (GS = Graduate Student, UGS = Undergraduate Student):

    Tom Montroy (Senior Research Assoc.)
    Rick Bihary (Technician of Everything)
    Sean Bryan (GS, Spider)
    J.T. Sayre (GS, SPT)
    Ben Saliwanchik (GS, SPT)
    Adam Stohs (UGS)
    Dane Pittock (UGS)

    Phone numbers (all have 216 area code):

    Rock 117 lab: 368-1153
    Rock 117a lab: 368-3608
    Rock 117a fax: 368-0952
    Rock 114 lab and GS office: 368-2489
    Physics Student Shop: 368-3053
    Prof. Ruhl’s office: 368-4049

    We are located in Rockefeller Hall, on the main quad campus of Case Western Reserve University. Our shipping address is:

    Physics Dept, Rockefeller Hall
    Case Western Reserve University
    10900 Euclid Ave.
    Cleveland, OH 44106-7079

    Spider is a balloon-borne instrument designed to search for the signature of primordial gravity waves that is (hopefully) encoded in the polarization of the CMB. The design consists of six independent telescopes operating at three frequencies (100, 150, and 220GHz), with the optics cooled to 4 Kelvin and the bolometric detectors cooled to 0.25K.

    Gravitational Wave Background

    Spider’s first test flight will be in the fall of 2009, from Alice Springs, Australia. The test flight will be 2-4 nights duration, limited by the requirement that the balloon be brought down before it leaves the continent. The full “around the world” flight will be a year later, if all goes well.
    There are two publications describing Spider:

    “Spider Optimization: Probing the Systematics of a Large Scale B-Mode Experiment”, C. J. MacTavish etal, arXiv:0710.0375, submitted to ApJ. (This discusses Spider’s potential systematics and scan strategies).
    “SPIDER: a new balloon-borne experiment to measure CMB polarization on large angular scales”, T. E. Montroy etal, Proceedings of the SPIE, ed L. M. Step, v 6267, p62670R, (2006). (This describes the Spider instrument as originally conceived.)

    In addition to the effort at Case, the Spider collaboration includes groups at Caltech, JPL, U. Toronto, UBC, NIST, Cardiff, and the Imperial College of London. The main SPT website is maintained at Caltech, at http://www.astro.caltech.edu/~lgg/spider_front.htm.
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    See the full article here.

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    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

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  • richardmitnick 12:25 pm on December 5, 2014 Permalink | Reply
    Tags: , , , , , Cosmic Inflation, , ,   

    From physicsworld: “Planck offers another glimpse of the early universe” 

    physicsworld
    physicsworld.com

    Dec 4, 2014
    Tushna Commissariat

    Results of four years of observations made by the Planck space telescope provide the most precise confirmation so far of the Standard Model of cosmology, and also place new constraints on the properties of potential dark-matter candidates. That is the conclusion of astronomers working on the €700m mission of the European Space Agency (ESA). Planck studies the intensity and the polarization of the cosmic microwave background (CMB), which is the thermal remnant of the Big Bang. These latest results will no doubt frustrate cosmologists, because Planck has so far failed to shed much light on some of the biggest mysteries of physics, including what constitutes the dark matter and dark energy that appears to dominate the universe.

    e
    Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe)

    ESA Planck
    ESA Planck schematic
    ESA/Planck

    Cosmic Background Radiation Planck
    Cosmic Background Radiation per Planck

    WMAP
    NASA/WMAP spacecraft

    Cosmic Background Radiation per WMAP
    Cosmic Background Radiation per WMAP

    Planck ran from 2009–2013, and the first data were released in March last year, comprising temperature data taken during the first 15 months of observations. A more complete data set from Planck will be published later this month, and is being previewed this week at a conference in Ferrara, Italy (Planck 2014 – The microwave sky in temperature and polarization). So far, Planck scientists have revealed that a previous disagreement of 1–1.5% between Planck and its predecessor – NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) – regarding the mission’s “absolute-temperature” measurements has been reduced to 0.3%.

    Winnowing dark matter

    Planck’s latest measurement of the CMB polarization rules out a class of dark-matter models involving particle annihilation in the early universe. These models were developed to explain excesses of cosmic-ray positrons that have been measured by three independent experiments – the PAMELA mission, the Alpha Magnetic Spectrometer and the Fermi Gamma-Ray Space Telescope.

    INFN PAMELA spacecraft
    PAMELA

    AMS-02
    AMS-02

    NASA Fermi Telescope
    NASA/Fermi

    The Planck collaboration also revealed that it has, for the first time, “detected unambiguously” traces left behind by primordial neutrinos on the CMB. Such neutrinos are thought to have been released one second after the Big Bang, when the universe was still opaque to light but already transparent to these elusive particles. Planck has set an upper limit (0.23 eV/c2) on the sum of the masses of the three types of neutrinos known to exist. Furthermore, the new data exclude the existence of a fourth type of neutrino that is favoured by some models.

    Planck versus BICEP2

    Despite the new data, the collaboration did not give any insights into the recent controversy surrounding the possible detection of primordial “B-mode” polarization of the CMB by astronomers working on the BICEP2 telescope.

    BICEP 2
    BICEP 2 interior
    BICEP 2 with South Pole Telescope

    If verified, the BICEP2 observation would be “smoking-gun” evidence for the rapid “inflation” of the early universe – the extremely rapid expansion that cosmologists believe the universe underwent a mere 10–35 s after the Big Bang. A new analysis of polarized dust emission in our galaxy, carried out by Planck earlier in September, showed that the part of the sky observed by BICEP2 has much more dust than originally anticipated, and while this did not completely rule out BICEP2’s original claim, it established that the dust emission is nearly as big as the entire BICEP2 signal. Both Planck and BICEP2 have since been working together on joint analysis of their data, but a result is still forthcoming.

    [THIS IS THE BEST WE CAN DO UNTIL ESA RELEASES THEIR LATEST FINDINGS FROM PLANCK]

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    PhysicsWorld is a publication of the Institute of Physics. The Institute of Physics is a leading scientific society. We are a charitable organisation with a worldwide membership of more than 50,000, working together to advance physics education, research and application.

    We engage with policymakers and the general public to develop awareness and understanding of the value of physics and, through IOP Publishing, we are world leaders in professional scientific communications.
    IOP Institute of Physics

     
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