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  • richardmitnick 10:43 am on February 7, 2018 Permalink | Reply
    Tags: Big Bang Science, , ,   

    From The Atlantic Magazine: “The Big Bang May Have Been One of Many” 

    Atlantic Magazine

    The Atlantic Magazine

    Feb 6, 2018
    Natalie Wolchover

    davidope / Quanta Magazine

    Our universe could be expanding and contracting eternally.

    Humans have always entertained two basic theories about the origin of the universe. “In one of them, the universe emerges in a single instant of creation (as in the Jewish-Christian and the Brazilian Carajás cosmogonies),” the cosmologists Mario Novello and Santiago Perez Bergliaffa noted in 2008. In the other, “the universe is eternal, consisting of an infinite series of cycles (as in the cosmogonies of the Babylonians and Egyptians).” The division in modern cosmology “somehow parallels that of the cosmogonic myths,” Novello and Perez Bergliaffa wrote.

    In recent decades, it hasn’t seemed like much of a contest. The Big Bang theory, standard stuff of textbooks and television shows, enjoys strong support among today’s cosmologists. The rival eternal-universe picture had the edge a century ago, but it lost ground as astronomers observed that the cosmos is expanding and that it was small and simple about 14 billion years ago. In the most popular modern version of the theory, the Big Bang began with an episode called “cosmic inflation”—a burst of exponential expansion during which an infinitesimal speck of space-time ballooned into a smooth, flat, macroscopic cosmos, which expanded more gently thereafter.

    With a single initial ingredient (the “inflaton field”), inflationary models reproduce many broad-brush features of the cosmos today. But as an origin story, inflation is lacking; it raises questions about what preceded it and where that initial, inflaton-laden speck came from. Undeterred, many theorists think the inflaton field must fit naturally into a more complete, though still unknown, theory of time’s origin.

    But in the past few years, a growing number of cosmologists have cautiously revisited the alternative. They say the Big Bang might instead have been a Big Bounce. Some cosmologists favor a picture in which the universe expands and contracts cyclically like a lung, bouncing each time it shrinks to a certain size, while others propose that the cosmos only bounced once—that it had been contracting, before the bounce, since the infinite past, and that it will expand forever after. In either model, time continues into the past and future without end.

    With modern science, there’s hope of settling this ancient debate. In the years ahead, telescopes could find definitive evidence for cosmic inflation. During the primordial growth spurt—if it happened—quantum ripples in the fabric of space-time would have become stretched and later imprinted as subtle swirls in the polarization of ancient light called the cosmic microwave background [CMB].

    CMB per ESA/Planck


    Current and future telescope experiments are hunting for these swirls. If they aren’t seen in the next couple of decades, this won’t entirely disprove inflation (the telltale swirls could simply be too faint to make out), but it will strengthen the case for bounce cosmology, which doesn’t predict the swirl pattern.

    Already, several groups are making progress at once. Most significantly, in the last year, physicists have come up with two new ways that bounces could conceivably occur. One of the models, described in a paper that will appear in the Journal of Cosmology and Astroparticle Physics, comes from Anna Ijjas of Columbia University, extending earlier work with her former adviser, the Princeton University professor and high-profile bounce cosmologist Paul Steinhardt. More surprisingly, the other new bounce solution, accepted for publication in Physical Review D, was proposed by Peter Graham, David Kaplan, and Surjeet Rajendran, a well-known trio of collaborators who mainly focus on particle-physics questions and have no previous connection to the bounce-cosmology community. It’s a noteworthy development in a field that’s highly polarized on the bang-vs.-bounce question.

    The question gained renewed significance in 2001, when Steinhardt and three other cosmologists argued that a period of slow contraction in the history of the universe could explain its exceptional smoothness and flatness, as witnessed today, even after a bounce—with no need for a period of inflation.

    The universe’s impeccable plainness, the fact that no region of sky contains significantly more matter than any other and that space is breathtakingly flat as far as telescopes can see, is a mystery. To match its present uniformity, experts infer that the cosmos, when it was one centimeter across, must have had the same density everywhere to within one part in 100,000. But as it grew from an even smaller size, matter and energy ought to have immediately clumped together and contorted space-time. Why don’t our telescopes see a universe wrecked by gravity?

    “Inflation was motivated by the idea that that was crazy to have to assume the universe came out so smooth and not curved,” says the cosmologist Neil Turok, the director of the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, and a coauthor of the 2001 paper [Physical Review D] on cosmic contraction with Steinhardt, Justin Khoury, and Burt Ovrut.

    In the inflation scenario, the centimeter-size region results from the exponential expansion of a much smaller region—an initial speck measuring no more than a trillionth of a trillionth of a centimeter across. As long as that speck was infused with an inflaton field that was smooth and flat, meaning its energy concentration didn’t fluctuate across time or space, the speck would have inflated into a huge, smooth universe like ours. Raman Sundrum, a theoretical physicist at the University of Maryland, says the thing he appreciates about inflation is that “it has a kind of fault tolerance built in.” If, during this explosive growth phase, there was a buildup of energy that bent space-time in a certain place, the concentration would have quickly inflated away. “You make small changes against what you see in the data and you see the return to the behavior that the data suggests,” Sundrum says.

    However, where exactly that infinitesimal speck came from, and why it came out so smooth and flat itself to begin with, no one knows. Theorists have found many possible ways to embed the inflaton field into string theory., a candidate for the underlying quantum theory of gravity. So far, there’s no evidence for or against these ideas.

    Cosmic inflation also has a controversial consequence. The theory—which was pioneered in the 1980s by Alan Guth, Andrei Linde, Aleksei Starobinsky, and (of all people) Steinhardt, almost automatically leads to the hypothesis that our universe is a random bubble in an infinite, frothing multiverse sea. Once inflation starts, calculations suggest that it keeps going forever, only stopping in local pockets that then blossom into bubble universes like ours. The possibility of an eternally inflating multiverse suggests that our particular bubble might never be fully understandable on its own terms, since everything that can possibly happen in a multiverse happens infinitely many times. The subject evokes gut-level disagreement among experts. Many have reconciled themselves to the idea that our universe could be just one of many; Steinhardt calls the multiverse “hogwash.”

    This sentiment partly motivated his and other researchers’ about-face on bounces. “The bouncing models don’t have a period of inflation,” Turok says. Instead, they add a period of contraction before a Big Bounce to explain our uniform universe. “Just as the gas in the room you’re sitting in is completely uniform because the air molecules are banging around and equilibrating,” he says, “if the universe was quite big and contracting slowly, that gives plenty of time for the universe to smooth itself out.”

    Although the first contracting-universe models were convoluted and flawed, many researchers became convinced of the basic idea that slow contraction can explain many features of our expanding universe. “Then the bottleneck became literally the bottleneck—the bounce itself,” Steinhardt says. As Ijjas puts it, “The bounce has been the showstopper for these scenarios. People would agree that it’s very interesting if you can do a contraction phase, but not if you can’t get to an expansion phase.”

    Bouncing isn’t easy. In the 1960s, the British physicists Roger Penrose and Stephen Hawking proved a set of so-called “singularity theorems” showing that, under very general conditions, contracting matter and energy will unavoidably crunch into an immeasurably dense point called a singularity. These theorems make it hard to imagine how a contracting universe in which space-time, matter, and energy are all rushing inward could possibly avoid collapsing all the way down to a singularity—a point where Albert Einstein’s classical theory of gravity and space-time breaks down and the unknown quantum-gravity theory rules. Why shouldn’t a contracting universe share the same fate as a massive star, which dies by shrinking to the singular center of a black hole?

    Both of the newly proposed bounce models exploit loopholes in the singularity theorems—ones that, for many years, seemed like dead ends. Bounce cosmologists have long recognized that bounces might be possible if the universe contained a substance with negative energy (or other sources of negative pressure), which would counteract gravity and essentially push everything apart. They’ve been trying to exploit this loophole since the early 2000s, but they always found that adding negative-energy ingredients made their models of the universe unstable, because positive- and negative-energy quantum fluctuations could spontaneously arise together, unchecked, out of the zero-energy vacuum of space. In 2016, the Russian cosmologist Valery Rubakov and colleagues even proved a “no-go” [JCAP] theorem that seemed to rule out a huge class of bounce mechanisms on the grounds that they caused these so-called “ghost” instabilities.

    Then Ijjas found a bounce mechanism that evades the no-go theorem. The key ingredient in her model is a simple entity called a “scalar field,” which, according to the idea, would have kicked into gear as the universe contracted and energy became highly concentrated. The scalar field would have braided itself into the gravitational field in a way that exerted negative pressure on the universe, reversing the contraction and driving space-time apart—without destabilizing everything. Ijjas’ paper “is essentially the best attempt at getting rid of all possible instabilities and making a really stable model with this special type of matter,” says Jean-Luc Lehners, a theoretical cosmologist at the Max Planck Institute for Gravitational Physics in Germany who has also worked on bounce proposals.

    What’s especially interesting about the two new bounce models is that they are “non-singular,” meaning the contracting universe bounces and starts expanding again before ever shrinking to a point. These bounces can therefore be fully described by the classical laws of gravity, requiring no speculations about gravity’s quantum nature.

    Graham, Kaplan, and Rajendran, of Stanford University, Johns Hopkins University and UC Berkeley, respectively, reported their non-singular bounce idea on the scientific preprint site ArXiv.org in September 2017. They found their way to it after wondering whether a previous contraction phase in the history of the universe could be used to explain the value of the cosmological constant—a mystifyingly tiny number that defines the amount of dark energy infused in the space-time fabric, energy that drives the accelerating expansion of the universe.

    In working out the hardest part—the bounce—the trio exploited a second, largely forgotten loophole in the singularity theorems. They took inspiration from a characteristically strange model of the universe proposed by the logician Kurt Gödel in 1949, when he and Einstein were walking companions and colleagues at the Institute for Advanced Study in Princeton, New Jersey. Gödel used the laws of general relativity to construct the theory of a rotating universe, whose spinning keeps it from gravitationally collapsing in much the same way that Earth’s orbit prevents it from falling into the sun. Gödel especially liked the fact that his rotating universe permitted “closed time-like curves,” essentially loops in time, which raised all sorts of Gödelian riddles. To his dying day, he eagerly awaited evidence that the universe really is rotating in the manner of his model. Researchers now know it isn’t; otherwise, the cosmos would exhibit alignments and preferred directions. But Graham and company wondered about small, curled-up spatial dimensions that might exist in space, such as the six extra dimensions postulated by string theory. Could a contracting universe spin in those directions?

    magine there’s just one of these curled-up extra dimensions, a tiny circle found at every point in space. As Graham puts it, “At each point in space there’s an extra direction you can go in, a fourth spatial direction, but you can only go a tiny little distance and then you come back to where you started.” If there are at least three extra compact dimensions, then, as the universe contracts, matter and energy can start spinning inside them, and the dimensions themselves will spin with the matter and energy. The vorticity in the extra dimensions can suddenly initiate a bounce. “All that stuff that would have been crunching into a singularity, because it’s spinning in the extra dimensions, it misses—sort of like a gravitational slingshot,” Graham says. “All the stuff should have been coming to a single point, but instead it misses and flies back out again.”

    he paper has attracted attention beyond the usual circle of bounce cosmologists. Sean Carroll, a theoretical physicist at the California Institute of Technology, is skeptical but called the idea “very clever.” He says it’s important to develop alternatives to the conventional inflation story, if only to see how much better inflation appears by comparison—especially when next-generation telescopes come online in the early 2020s looking for the telltale swirl pattern in the sky caused by inflation. “Even though I think inflation has a good chance of being right, I wish there were more competitors,” Carroll says. Sundrum, the Maryland physicist, feels similarly. “There are some questions I consider so important that even if you have only a 5 percent chance of succeeding, you should throw everything you have at it and work on them,” he says. “And that’s how I feel about this paper.”

    As Graham, Kaplan, and Rajendran explore their bounce and its possible experimental signatures, the next step for Ijjas and Steinhardt, working with Frans Pretorius of Princeton, is to develop computer simulations. (Their collaboration is supported by the Simons Foundation, which also funds Quanta Magazine.) Both bounce mechanisms also need to be integrated into more complete, stable cosmological models that would describe the entire evolutionary history of the universe.

    Beyond these non-singular bounce solutions, other researchers are speculating about what kind of bounce might occur when a universe contracts all the way to a singularity—a bounce orchestrated by the unknown quantum laws of gravity, which replace the usual understanding of space and time at extremely high energies. In forthcoming work, Turok and collaborators plan to propose a model in which the universe expands symmetrically into the past and future away from a central, singular bounce. Turok contends that the existence of this two-lobed universe is equivalent to the spontaneous creation of electron-positron pairs, which constantly pop in and out of the vacuum. “Richard Feynman pointed out that you can look at the positron as an electron going backward in time,” he says. “They’re two particles, but they’re really the same; at a certain moment in time they merge and annihilate.” He added, “The idea is a very, very deep one, and most likely the Big Bang will turn out to be similar, where a universe and its anti-universe were drawn out of nothing, if you like, by the presence of matter.”

    It remains to be seen whether this universe/anti-universe bounce model can accommodate all observations of the cosmos, but Turok likes how simple it is. Most cosmological models are far too complicated in his view. The universe “looks extremely ordered and symmetrical and simple,” he says. “That’s very exciting for theorists, because it tells us there may be a simple—even if hard-to-discover—theory waiting to be discovered, which might explain the most paradoxical features of the universe.”

    See the full article here .

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  • richardmitnick 4:29 pm on October 15, 2017 Permalink | Reply
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    From Goddard: “NASA’s James Webb Space Telescope and the Big Bang: A Short Q&A with Nobel Laureate Dr. John Mather” 

    NASA Goddard Banner
    NASA Goddard Space Flight Center

    Oct. 11, 2017
    Maggie Masetti
    NASA’s Goddard Space Flight Center

    Dr. John Mather, a Nobel laureate and the senior project scientist for NASA’s James Webb Space Telescope. Credits: NASA/Chris Gunn

    Q: What is the Big Bang?

    A: The Big Bang is a really misleading name for the expanding universe that we see. We see an infinite universe with distant galaxies all rushing away from each other.

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

    The name Big Bang conveys the idea of a firecracker exploding at a time and a place — with a center. The universe doesn’t have a center, at least not one we can find. The Big Bang happened everywhere at once and was a process happening in time, not a point in time. We know this because 1) we see galaxies rushing away from each other, not from a central point; 2) we see the heat that was left over from early times, and that heat uniformly fills the universe; and 3) we can calculate and imagine what the universe was like when the parts were much closer together, and the calculations match everything we can see.

    Q: Can we see the Big Bang?

    A: No, the Big Bang itself is not something we can see.

    Q: What can we see?

    A: We can see the heat radiation that was there when the universe was young. We see this heat as it was about 380,000 years after the expansion of the universe began 13.8 billion years ago (which is what we refer to as the Big Bang). This heat covers the entire sky and fills the universe. (In fact it still does.) We were able to map it with satellites we (NASA and ESA) built called the Cosmic Background Explorer (COBE), the Wilkinson Microwave Anisotropy Probe (WMAP), and Planck. The universe at this point was extremely smooth, with only tiny ripples in temperature.

    Cosmic Infrared Background, Credit: Michael Hauser (Space Telescope Science Institute), the COBE/DIRBE Science Team, and NASA


    All-sky image of the infant universe, created from nine years of data from the Wilkinson Microwave Anisotropy Probe (WMAP).
    Credits: NASA/WMAP Science Team


    CMB per ESA/Planck


    Q: I heard the James Webb Space Telescope will see back further than ever before. What will Webb see?

    NASA/ESA/CSA Webb Telescope annotated

    A: COBE, WMAP, and Planck all saw further back than Webb, though it’s true that Webb will see farther back than Hubble.

    NASA/ESA Hubble Telescope

    Webb was designed not to see the beginnings of the universe, but to see a period of the universe’s history that we have not seen yet.

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

    Specifically, we want to see the first objects that formed as the universe cooled down after the Big Bang. That time period is perhaps hundreds of millions of years later than the one COBE, WMAP, and Planck were built to see. We think that the tiny ripples of temperature they observed were the seeds that eventually grew into galaxies. We don’t know exactly when the universe made the first stars and galaxies — or how for that matter. That is what we are building Webb to help answer.

    Q: Why can’t Hubble see the first stars and galaxies forming?

    A: The only way we can see back to the time when these objects were forming is to look very far away. Hubble isn’t big enough or cold enough to see the faint heat signals of these objects that are so far away.

    Q: Why do we want to see the first stars and galaxies forming?

    A: The chemical elements of life were first produced in the first generation of stars after the Big Bang. We are here today because of them — and we want to better understand how that came to be! We have ideas, we have predictions, but we don’t know. One way or another the first stars must have influenced our own history, beginning with stirring up everything and producing the other chemical elements besides hydrogen and helium. So if we really want to know where our atoms came from, and how the little planet Earth came to be capable of supporting life, we need to measure what happened at the beginning.

    Dr. John Mather is the senior project scientist for the James Webb Space Telescope. Dr. Mather shares the 2006 Nobel Prize for Physics with George F. Smoot of the University of California for their work using the COBE satellite to measure the heat radiation from the Big Bang.

    The James Webb Space Telescope, the scientific complement to NASA’s Hubble Space Telescope, will be the premier space observatory of the next decade. Webb is an international project led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).

    For more information about the Webb telescope, visit: http://www.webb.nasa.gov or http://www.nasa.gov/webb

    See the full article here.

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    NASA’s Goddard Space Flight Center is home to the nation’s largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.

    Named for American rocketry pioneer Dr. Robert H. Goddard, the center was established in 1959 as NASA’s first space flight complex. Goddard and its several facilities are critical in carrying out NASA’s missions of space exploration and scientific discovery.

    NASA/Goddard Campus

  • richardmitnick 1:08 pm on October 12, 2017 Permalink | Reply
    Tags: , , , , Big Bang Science, , ,   

    From Ethan Siegel: “Inflation Isn’t Just Science, It’s The Origin Of Our Universe” 

    From Ethan Siegel

    Oct 12, 2017

    The stars and galaxies we see today didn’t always exist, and the farther back we go, the closer to an apparent singularity the Universe gets, but there is a limit to that extrapolation. To go all the way back, we need a modification to the Big Bang: cosmological inflation. Image credit: NASA, ESA, and A. Feild (STScI).

    “There’s no obvious reason to assume that the very same rare properties that allow for our existence would also provide the best overall setting to make discoveries about the world around us. We don’t think this is merely coincidental.” -Guillermo Gonzalez

    In order to be considered a scientific theory, there are three things your idea needs to do. First off, you have to reproduce all of the successes of the prior, leading theory. Second, you need to explain a new phenomenon that isn’t presently explained by the theory you’re seeking to replace. And third, you need to make a new prediction that you can then go out and test: where your new idea predicts something entirely different or novel from the pre-existing theory. Do that, and you’re science. Do it successfully, and you’re bound to become the new, leading scientific theory in your area. Many prominent physicists have recently come out against inflation, with some claiming that it isn’t even science. But the facts say otherwise. Not only is inflation science, it’s now the leading scientific theory about where our Universe comes from.

    The expanding Universe, full of galaxies and the complex structure we observe today, arose from a smaller, hotter, denser, more uniform state. But even that initial state had its origins, with cosmic inflation as the leading candidate for where that all came from. Image credit: C. Faucher-Giguère, A. Lidz, and L. Hernquist, Science 319, 5859 (47).

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

    The Big Bang was first confirmed in the 1960s, with the observation of the Cosmic Microwave Background [CMB].

    Cosmic Microwave Background NASA/WMAP


    CMB per ESA/Planck


    Since that first detection of the leftover glow, predicted from an early, hot, dense state, we’ve been able to validate and confirm the Big Bang’s predictions in a number of important ways. The large-scale structure of the Universe is consistent with having formed from a nearly-uniform past state, under the influence of gravity over billions of years. The Hubble expansion and the temperature in the distant past is consistent with an expanding, cooling Universe filled with matter and energy of various types. The abundances of hydrogen, helium, lithium, and their various isotopes matches the predictions from an early, hot, dense state. And the blackbody spectrum of the Big Bang’s leftover glow matches our observations precisely.

    The light from the cosmic microwave background and the pattern of fluctuations from it gives us one way to measure the Universe’s curvature. To the best of our measurements, to within 1 part in about 400, the Universe is perfectly spatially flat. Image credit: Smoot Cosmology Group / Lawrence Berkeley Labs.

    But there are a number of things that we observe that the Big Bang doesn’t explain. The fact that the Universe is the same exact temperature in all directions, to better than 99.99%, is an observational fact without a theoretical cause. The fact that the Universe, in all directions, appears to be spatially flat (rather than positively or negatively curved), is another true fact without an explanation. And the fact that there are no leftover high-energy relics, like magnetic monopoles, is a curiosity that we wouldn’t expect if the Universe began from an arbitrarily hot, dense state.

    In other words, the implication is that despite all of the Big Bang’s successes, it doesn’t explain everything about the origin of the Universe. Either we can look at these unexplained phenomena and conjecture, “maybe the Universe was simply born this way,” or we can look for an explanation that meets our requirements for a scientific theory. That’s exactly what Alan Guth did in 1979, when he first stumbled upon the idea of cosmological inflation.

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

    HPHS Owls

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

    Alan Guth’s notes. http://www.bestchinanews.com/Explore/4730.html

    The big idea of cosmic inflation was that the matter-and-radiation-filled Universe, the one that has been expanding and cooling for billions of years, arose from a very different state that existed prior to what we know as our observable Universe. Instead of being filled with matter-and-radiation, space was full of vacuum energy, which caused it to expand not just rapidly, but exponentially, meaning the expansion rate doesn’t fall with time as long as inflation goes on. It’s only when inflation comes to an end that this vacuum energy gets converted into matter, antimatter, and radiation, and the hot Big Bang results.

    This illustration shows regions where inflation continues into the future (blue), and where it ends, giving rise to a Big Bang and a Universe like ours (red X). Note that this could go back indefinitely, and we’d never know. Image credit: E. Siegel / Beyond The Galaxy.

    It was generally recognized that inflation, if true, would solve those three puzzles that the Big Bang could only posit as initial conditions: the horizon (temperature), flatness (curvature), and monopole (lack-of-relics) problems. In the early-to-mid 1980s, lots of work went into meeting that first criteria: reproducing the successes of the Big Bang. The key was to arrive at an isotropic, homogeneous Universe with conditions that matched what we observed.

    he two simplest classes of inflationary potentials, with chaotic inflation (L) and new inflation (R) shown. Image credit: E. Siegel / Google Graph.

    After a few years, we had two generic classes of models that worked:

    “New inflation” models, where vacuum energy starts off at the top of a hill and rolls down it, with inflation ending when the ball rolls into the valley, and
    “Chaotic inflation” models, where vacuum energy starts out high on a parabola-like potential, rolling into the valley to end inflation.

    Both of these classes of models reproduced the successes of the Big Bang, but also made a number of similar, quite generic predictions for the observable Universe. They were as follows:

    The earliest stages of the Universe, before the Big Bang, are what set up the initial conditions that everything we see today has evolved from. Image credit: E. Siegel, with images derived from ESA/Planck and the DoE/NASA/ NSF interagency task force on CMB research.

    1. The Universe should be nearly perfectly flat. Yes, the flatness problem was one of the original motivations for it, but at the time, we had very weak constraints. 100% of the Universe could be in matter and 0% in curvature; 5% could be matter and 95% could be curvature, or anywhere in between. Inflation, quite generically, predicted that 100% needed to be “matter plus whatever else,” but curvature should be between 0.01% and 0.0001%. This prediction has been validated by our ΛCDM model, where 5% is matter, 27% is dark matter and 68% is dark energy; curvature is constrained to be 0.25% or less. As observations continue to improve, we may, in fact, someday be able to measure the non-zero curvature predicted by inflation.

    2. There should be an almost scale-invariant spectrum of fluctuations. If quantum physics is real, then the Universe should have experienced quantum fluctuations even during inflation. These fluctuations should be stretched, exponentially, across the Universe. When inflation ends, these fluctuations should get turned into matter and radiation, giving rise to overdense and underdense regions that grow into stars and galaxies, or great cosmic voids. Because of how inflation proceeds in the final stages, the fluctuations should be slightly greater on either small scales or large scales, depending on the model of inflation, which means there should be a slight departure from perfect scale invariance. If scale invariance were exact, a parameter we call n_s would equal 1; n_s is observed to be 0.96, and wasn’t measured until WMAP in the 2000s.

    3. There should be fluctuations on scales larger than light could have traveled since the Big Bang. This is another consequence of inflation, but there’s no way to get a coherent set of fluctuations on large scales like this without something stretching them across cosmic distances. The fact that we see these fluctuations in the cosmic microwave background and in the large-scale structure of the Universe — and didn’t know about them until the COBE and WMAP satellites in the 1990s and 2000s — further validates inflation.


    Cosmic Infrared Background, Credit: Michael Hauser (Space Telescope Science Institute), the COBE/DIRBE Science Team, and NASA

    4. These quantum fluctuations, which translate into density fluctuations, should be adiabatic. Fluctuations could have come in different types: adiabatic, isocurvature, or a mixture of the two. Inflation predicted that these fluctuations should have been 100% adiabatic, which should leave unique signatures in both the cosmic microwave background and the Universe’s large-scale structure. Observations bear out that yes, in fact, the fluctuations were adiabatic: of constant entropy everywhere.

    5. There should be an upper limit, smaller than the Planck scale, to the temperature of the Universe in the distant past. This is also a signature that shows up in the cosmic microwave background: how high a temperature the Universe reached at its hottest. Remember, if there were no inflation, the Universe should have gone up to arbitrarily high temperatures at early times, approaching a singularity. But with inflation, there’s a maximum temperature that must be at energies lower than the Planck scale (~10^19 GeV). What we see, from our observations, is that the Universe achieved temperatures no higher than about 0.1% of that (~10^16 GeV) at any point, further confirming inflation. This is an even better solution to the monopole problem than the one initially envisioned by Guth.

    6. And finally, there should be a set of primordial gravitational waves, with a particular spectrum. Just as we had an almost perfectly scale-invariant spectrum of density fluctuations, inflation predicts a spectrum of tensor fluctuations in General Relativity, which translate into gravitational waves. The magnitude of these fluctuations are model-dependent on inflation, but the spectrum has a set of unique predictions. This sixth prediction is the only one that has not been verified observationally in any way.

    The contribution of gravitational waves left over from inflation to the B-mode polarization of the Cosmic Microwave background has a known shape, but its amplitude is dependent on the specific model of inflation. These B-modes from gravitational waves from inflation have not yet been observed. Image credit: Planck science team.

    On all three counts — of reproducing the successes of the non-inflationary Big Bang, of explaining observations that the Big Bang cannot, and of making new predictions that can be (and, in large number, have been) verified — inflation undoubtedly succeeds as science. It does so in a way that other theories which only give rise to non-observable predictions, such as string theory, does not. Yes, when critics talk about inflation and mention a huge amount of model-building, that is a problem; inflation is a theory in search of a single, unique, definitive model. It’s true that you can contrive as complex a model as you want, and it’s virtually impossible to rule them out.

    A variety of inflationary models and the scalar and tensor fluctuations predicted by cosmic inflation. Note that the observational constraints leave a huge variety of inflationary models as still valid. Image credit: Kamionkowski and Kovetz, ARAA, 2016, via http://lanl.arxiv.org/abs/1510.06042.

    But that is not a flaw inherent to the theory of inflation; it is an indicator that we don’t yet know enough about the mechanics of inflation to discern which models have the features our Universe requires. It is an indicator that the inflationary paradigm itself has limits to its predictive power, and that a further advance will be necessary to move the needle forward. But simply because inflation isn’t the ultimate answer to everything doesn’t mean it isn’t science. Rather, it’s exactly in line with what science has always shown itself to be: humanity’s best toolkit for understanding the Universe, one incremental improvement at a time.

    See the full article here .

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

  • richardmitnick 1:00 pm on June 17, 2017 Permalink | Reply
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    From phys.org: “No Universe without Big Bang” 


    June 15, 2017

    Credit: J.-L. Lehners (Max Planck Institute for Gravitational Physics)

    According to Einstein’s theory of relativity, the curvature of spacetime was infinite at the big bang. In fact, at this point all mathematical tools fail, and the theory breaks down. However, there remained the notion that perhaps the beginning of the universe could be treated in a simpler manner, and that the infinities of the big bang might be avoided. This has indeed been the hope expressed since the 1980s by the well-known cosmologists James Hartle and Stephen Hawking with their “no-boundary proposal”, and by Alexander Vilenkin with his “tunnelling proposal”. Now scientists at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute/AEI) in Potsdam and at the Perimeter Institute in Canada have been able to use better mathematical methods to show that these ideas cannot work.

    One of the principal goals of cosmology is to understand the beginning of our universe. Data from the Planck satellite mission shows that 13.8 billion years ago the universe consisted of a hot and dense soup of particles. Since then the universe has been expanding. This is the main tenet of the hot big bang theory, but the theory fails to describe the very first stages themselves, as the conditions were too extreme. Indeed, as we approach the big bang, the energy density and the curvature grow until we reach the point where they become infinite.

    As an alternative, the “no-boundary” and “tunneling” proposals assume that the tiny early universe arose by quantum tunnelling from nothing, and subsequently grew into the large universe that we see. The curvature of spacetime would have been large, but finite in this beginning stage, and the geometry would have been smooth – without boundary (see Fig. 1, left panel). This initial configuration would replace the standard big bang. However, for a long time the true consequences of this hypothesis remained unclear. Now, with the help of better mathematical methods, Jean-Luc Lehners, group leader at the AEI, and his colleagues Job Feldbrugge and Neil Turok at Perimeter Institute, managed to define the 35 year old theories in a precise manner for the first time, and to calculate their implications [Physical Review D]. The result of these investigations is that these alternatives to the big bang are no true alternatives. As a result of Heisenberg’s uncertainty relation, these models do not only imply that smooth universes can tunnel out of nothing, but also irregular universes. In fact, the more irregular and crumpled they are, the more likely (see Fig. 1, right panel). “Hence the “no-boundary proposal” does not imply a large universe like the one we live in, but rather tiny curved universes that would collapse immediately”, says Jean-Luc Lehners, who leads the “theoretical cosmology” group at the AEI.

    Hence one cannot circumvent the big bang so easily. Lehners and his colleagues are now trying to figure out what mechanism could have kept those large quantum fluctuations in check under the most extreme circumstances, allowing our large universe to unfold.

    The big bang, in its complicated glory, retains all its mystery.

    See the full article here .

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    About Phys.org in 100 Words

    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

  • richardmitnick 12:44 pm on February 20, 2017 Permalink | Reply
    Tags: , Big Bang Science, ,   

    From ALMA via ESO: “ALMA’s Hole in the Universe” 

    ALMA Array


    20 February 2017
    No writer credit

    Credit: ALMA (ESO/NAOJ/NRAO)/T. Kitayama (Toho University, Japan)/ESA/Hubble & NASA

    The events surrounding the Big Bang were so cataclysmic that they left an indelible imprint on the fabric of the cosmos. We can detect these scars today by observing the oldest light in the Universe. As it was created nearly 14 billion years ago, this light — which exists now as weak microwave radiation and is thus named the cosmic microwave background (CMB) — has now expanded to permeate the entire cosmos, filling it with detectable photons.

    CMB per ESA/Planck
    CMB per ESA/Planck

    The CMB can be used to probe the cosmos via something known as the Sunyaev-Zel’dovich (SZ) effect, which was first observed over 30 years ago. We detect the CMB here on Earth when its constituent microwave photons travel to us through space. On their journey to us, they can pass through galaxy clusters that contain high-energy electrons. These electrons give the photons a tiny boost of energy. Detecting these boosted photons through our telescopes is challenging but important — they can help astronomers to understand some of the fundamental properties of the Universe, such as the location and distribution of dense galaxy clusters.

    This image shows the first measurements of the thermal Sunyaev-Zel’dovich effect from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile (in blue). Astronomers combined data from ALMA’s 7- and 12-metre antennas to produce the sharpest possible image. The target was one of the most massive known galaxy clusters, RX J1347.5–1145, the centre of which shows up here in the dark “hole” in the ALMA observations. The energy distribution of the CMB photons shifts and appears as a temperature decrease at the wavelength observed by ALMA, hence a dark patch is observed in this image at the location of the cluster.

    See the full article here .

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    The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA is funded in Europe by the European Organization for Astronomical Research in the Southern Hemisphere (ESO), in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and in East Asia by the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Academia Sinica (AS) in Taiwan.

    ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

    NRAO Small

    ESO 50 Large


  • richardmitnick 4:49 pm on February 12, 2017 Permalink | Reply
    Tags: Big Bang Science, , oscillon,   

    From U Basel: “Ancient Signals From the Early Universe” 


    U Basel

    February 12, 2017
    No writer credit

    The animation shows a computer simulation of an oscillon, a strong localized fluctuation of the inflaton field of the early universe. According to the calculations of Prof. Stefan Antusch and his team, oscillons produced a characteristic peak in the otherwise broad spectrum of gravitational waves. © Department of Physics, University of Basel

    For the first time, theoretical physicists from the University of Basel in Switzerland have calculated the signal of specific gravitational wave sources that emerged fractions of a second after the Big Bang. The source of the signal is a long-lost cosmological phenomenon called “oscillon”. The journal Physical Review Letters has published the results.

    Although Albert Einstein had already predicted the existence of gravitational waves, their existence was not actually proven until fall 2015, when highly sensitive detectors received the waves formed during the merging of two black holes. Gravitational waves are different from all other known waves. As they travel through the universe, they shrink and stretch the space-time continuum; in other words, they distort the geometry of space itself. Although all accelerating masses emit gravitational waves, these can only be measured when the mass is extremely large, as is the case with black holes or supernovas.

    Gravitational waves transport information from the Big Bang

    However, gravitational waves not only provide information on major astrophysical events of this kind but also offer an insight into the formation of the universe itself. In order to learn more about this stage of the universe, Prof. Stefan Antusch and his team from the Department of Physics at the University of Basel are conducting research into what is known as the stochastic background of gravitational waves. This background consists of gravitational waves from a large number of sources that overlap with one another, together yielding a broad spectrum of frequencies. The Basel-based physicists calculate predicted frequency ranges and intensities for the waves, which can then be tested in experiments.

    A highly compressed universe

    Shortly after the Big Bang, the universe we see today was still very small, dense, and hot. “Picture something about the size of a football,” Antusch explains. The whole universe was compressed into this very small space, and it was extremely turbulent. Modern cosmology assumes that at that time the universe was dominated by a particle known as the inflaton and its associated field.

    Oscillons generate a powerful signal

    The inflaton underwent intensive fluctuations, which had special properties. They formed clumps, for example, causing them to oscillate in localized regions of space. These regions are referred to as oscillons and can be imagined as standing waves. “Although the oscillons have long since ceased to exist, the gravitational waves they emitted are omnipresent – and we can use them to look further into the past than ever before,” says Antusch.

    Using numerical simulations, the theoretical physicist and his team were able to calculate the shape of the oscillon’s signal, which was emitted just fractions of a second after the Big Bang. It appears as a pronounced peak in the otherwise rather broad spectrum of gravitational waves. “We would not have thought before our calculations that oscillons could produce such a strong signal at a specific frequency,” Antusch explains. Now, in a second step, experimental physicists must actually prove the signal’s existence using detectors.

    Original article

    Stefan Antusch, Francesco Cefalà, and Stefano Orani
    Gravitational Waves from Oscillons after Inflation
    Physical Review Letters (2017), doi: 10.1103/PhysRevLett.118.011303

    See the full article here .

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    The University of Basel fosters the development of critically thinking and tolerant individuals who are capable of taking initiative and taking on responsibility. It is the aim of the University to enable these individuals to deepen their knowledge and field-specific academic training and further education.

    Through research and teaching, the University imparts the insights past down over the ages in addition to producing new knowledge. It is guided by the principle of meaningfulness and purpose rather than feasibility.

    The University is aware of the duties arising from knowledge, fulfilling these duties through critical reflection and the services it provides. It takes its own position concerning problems facing society.

    The University realizes its aims by taking responsibility with respect to future generations, the society that supports them, the international academic community and the culture that is passed down from generation to generation.

  • richardmitnick 4:51 pm on August 23, 2016 Permalink | Reply
    Tags: , , Big Bang Science, ,   

    From Symmetry: “Five facts about the Big Bang” 

    Symmetry Mag


    Matthew R. Francis

    Illustration by Sandbox Studio, Chicago with Corinne Mucha

    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

    It’s the cornerstone of cosmology, but what is it all about?

    Astronomers Edwin Hubble and Milton Humason in the early 20th century discovered that galaxies are moving away from the Milky Way. More to the point: Every galaxy is moving away from every other galaxy on average, which means the whole universe is expanding. In the past, then, the whole cosmos must have been much smaller, hotter and denser.

    That description, known as the Big Bang model, has stood up against new discoveries and competing theories for the better part of a century. So what is this “Big Bang” thing all about?

    The Big Bang happened everywhere at once.

    The universe has no center or edge, and every part of the cosmos is expanding. That means if we run the clock backward, we can figure out exactly when everything was packed together—13.8 billion years ago. Because every place we can map in the universe today occupied the same place 13.8 billion years ago, there wasn’t a location for the Big Bang: Instead, it happened everywhere simultaneously.

    The Big Bang may not describe the actual beginning of everything.

    “Big Bang” broadly refers to the theory of cosmic expansion and the hot early universe. However, sometimes even scientists will use the term to describe a moment in time—when everything was packed into a single point. The problem is that we don’t have either observations or theory that describes that moment, which is properly (if clumsily) called the “initial singularity.”

    The initial singularity is the starting point for the universe we observe, but there might have been something that came before.

    The difficulty is that the very hot early cosmos and the rapid expansion called “inflation” that likely happened right after the singularity wiped out most—if not all—of the information about any history that preceded the Big Bang. Physicists keep thinking of new ways to check for signs of an earlier universe, and though we haven’t seen any of them so far, we can’t rule it out yet.

    The Big Bang theory explains where all the hydrogen and helium in the universe came from.

    In the 1940s, Ralph Alpher and George Gamow calculated that the early universe was hot and dense enough to make virtually all the helium, lithium and deuterium (hydrogen with a neutron attached) present in the cosmos today; later research showed where the primordial hydrogen came from. This is known as “Big Bang nucleosynthesis,” and it stands as one of the most successful predictions of the theory. The heavier elements (such as oxygen, iron and uranium) were formed in stars and supernova explosions.

    The best evidence for the Big Bang is in the form of microwaves. Early on, the whole universe was dense enough to be completely opaque. But at a time roughly 380,000 years after the Big Bang, expansion spread everything out enough to make the universe transparent.

    The light released from this transition, known as the cosmic microwave background (CMB), still exists.

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

    It was first observed in the 1960s by Arno Penzias and Robert Wilson.

    Big Ear, Arno Penzias and Robert Wilson, AT&T, Holmdel, NJ USA
    Big Ear, Arno Penzias and Robert Wilson, AT&T, Holmdel, NJ USA

    That discovery cemented the Big Bang theory as the best description of the universe; since then, observatories such WMAP and Planck have used the CMB to tell us a lot about the total structure and content of the cosmos.

    One of the first people to think scientifically about the origin of the universe was a Catholic priest.

    In addition to his religious training and work, Georges Lemaître was a physicist who studied the general theory of relativity and worked out some of the conditions of the early cosmos in the 1920s and ’30s.


    His preferred metaphors for the origin of the universe were “cosmic egg” and “primeval atom,” but they never caught on, which is too bad, because …

    It seems nobody likes the name “Big Bang.”

    Until the 1960s, the idea of a universe with a beginning was controversial among physicists. The name “Big Bang” was actually coined by astronomer Fred Hoyle, who was the leading proponent of an alternative theory, where universe continues forever without a beginning.

    His shorthand for the theory caught on, and now we’re kind of stuck with it. Calvin and Hobbes’ attempt to get us to adopt “horrendous space kablooie” has failed so far.

    The Big Bang is the cornerstone of cosmology, but it’s not the whole story. Scientists keep refining the theory of the universe, motivated by our observation of all the weird stuff out there. Dark matter (which holds galaxies together) and dark energy (which makes the expansion of the universe accelerate) are the biggest mysteries that aren’t described by the Big Bang theory by itself.

    Our view of the universe, like the cosmos itself, keeps evolving as we discover more and more new things. But rather than fading away, our best explanation for why things are the way they are has remained—the fire at the beginning of the universe.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 8:05 am on September 14, 2015 Permalink | Reply
    Tags: , Big Bang Science, ,   

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

    Cosmos Magazine bloc


    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

    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.

    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.

    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.

    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.

    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.

    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.

    See the full article here .

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  • richardmitnick 2:41 pm on February 26, 2015 Permalink | Reply
    Tags: , Big Bang Science,   

    From livescience: “Big Bang, Deflated? Universe May Have Had No Beginning” 


    February 26, 2015
    Tia Ghose


    If a new theory turns out to be true, the universe may not have started with a bang. In the new formulation, the universe was never a singularity, or an infinitely small and infinitely dense point of matter. In fact, the universe may have no beginning at all. “Our theory suggests that the age of the universe could be infinite,” said study co-author Saurya Das, a theoretical physicist at the University of Lethbridge in Alberta, Canada. The new concept could also explain what dark matter — the mysterious, invisible substance that makes up most of the universe — is actually made of, Das added.

    Big Bang under fire

    According to the Big Bang theory, the universe was born about 13.8 billion years ago. All the matter that exists today was once squished into an infinitely dense, infinitely tiny, ultra-hot point called a singularity. This tiny fireball then exploded and gave rise to the early universe. The singularity comes out of the math of Einstein’s theory of general relativity, which describes how mass warps space-time, and another equation (called Raychaudhuri’s equation) that predicts whether the trajectory of something will converge or diverge over time. Going backward in time, according to these equations, all matter in the universe was once in a single point — the Big Bang singularity.

    But that’s not quite true. In Einstein’s formulation, the laws of physics actually break before the singularity is reached. But scientists extrapolate backward as if the physics equations still hold, said Robert Brandenberger, a theoretical cosmologist at McGill University in Montreal, who was not involved in the study. “So when we say that the universe begins with a big bang, we really have no right to say that,” Brandenberger told Live Science. There are other problems brewing in physics — namely, that the two most dominant theories, quantum mechanics and general relativity, can’t be reconciled. Quantum mechanics says that the behavior of tiny subatomic particles is fundamentally uncertain. This is at odds with Einstein’s general relativity, which is deterministic, meaning that once all the natural laws are known, the future is completely predetermined by the past, Das said.

    And neither theory explains what dark matter, an invisible form of matter that exerts a gravitational pull on ordinary matter but cannot be detected by most telescopes, is made of.

    Quantum correction

    Das and his colleagues wanted a way to resolve at least some of these problems. To do so, they looked at an older way of visualizing quantum mechanics, called Bohmian mechanics. In it, a hidden variable governs the bizarre behavior of subatomic particles. Unlike other formulations of quantum mechanics, it provides a way to calculate the trajectory of a particle. Using this old-fashioned form of quantum theory, the researchers calculated a small correction term that could be included in Einstein’s theory of general relativity. Then, they figured out what would happen in deep time.

    The upshot? In the new formulation, there is no singularity, and the universe is infinitely old.

    A way to test the theory

    One way of interpreting the quantum correction term in their equation is that it is related to the density of dark matter, Das said. If so, the universe could be filled with a superfluid made of hypothetical particles, such as the gravity-carrying particles known as gravitons, or ultra-cold, ghostlike particles known as axions, Das said. One way to test the theory is to look at how dark matter is distributed in the universe and see if it matches the properties of the proposed superfluid, Das said. “If our results match with those, even approximately, that’s great,” Das told Live Science.

    However, the new equations are just one way to reconcile quantum mechanics and general relativity. For instance, a part of string theory known as string gas cosmology predicts that the universe once had a long-lasting static phase, while other theories predict there was once a cosmic “bounce,” where the universe first contracted until it reached a very small size, then began expanding, Brandenberg said.

    Either way, the universe was once very, very small and hot.

    “The fact that there’s a hot fireball at very early times: that is confirmed,” Brandenberg told Live Science. “When you try to go back all the way to the singularity, that’s when the problems arise.”

    The new theory was explained in a paper published Feb. 4 in the journal Physical Letters B, and another paper that is currently under peer review, which was published in the preprint journal arXiv.

    See the full article here.

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  • richardmitnick 11:53 am on February 14, 2015 Permalink | Reply
    Tags: , , Big Bang Science, ,   

    From Ethan Siegel: “How can we still see the Big Bang?” 

    Starts with a bang
    Starts with a Bang

    Feb 14, 2015
    Ethan Siegel

    If it happened billions of years ago, what’s it still doing here?

    “We like to admit to only that which already glows, although it is nobler to support brightness before it glows, not afterwards.” –Dejan Stojanovic

    Sometimes, the simplest questions make for the most profound answers, and give us the opportunity to really dig deep into how we view the fabric of the Universe itself. This week, after sifting through your questions and suggestions for our Ask Ethan column, I couldn’t pass up the spectacular but straightforward question of Joseph McFarland, who wants to know:

    Why do we continue to detect the cosmic background radiation?
    Is the fact that we continue to eternally see the cosmic background radiation billions of years after it was generated proof of either inflation, or that the universe must be curved back upon itself (i.e. that it is finite but unbounded)?
    Or if neither of these are requirements, then what are other explanations?

    I want you to think about the history of the Universe.

    Image credit: NASA / CXC / M.Weiss.

    In particular, I want you to think of why it’s such a remarkable thing that we do detect the Cosmic Microwave Background at all. The story starts at the moment of the Big Bang, or more specifically, at the hot Big Bang.

    Image credit: RHIC collaboration, Brookhaven, via http://www.bnl.gov/newsroom/news.php?a=11403.

    The hot Big Bang refers to a time some 13.8 billion years ago, when the Universe first emerged from an inflationary state — one where all the energy in it was inherent to space itself — and got converted into matter, antimatter and radiation. We can think of this as inflation being a field that’s in an unstable state, like a ball at the top of a hill, that then rolls down that hill and into a valley.

    While the ball is at the top of the hill, space itself expands at an exponential rate. When the ball rolls into the valley, and starts oscillating back-and-forth, that energy-of-space gets converted into matter, antimatter and radiation: a process known as reheating.

    Image credit: E. Siegel. Inflation ends when the ball rolls into the valley.

    The Universe still continues to expand, but because it’s filled with matter, antimatter and radiation, it no longer maintains a very large expansion rate for long. The expansion rate is tied — in General Relativity — to the energy density of the Universe, or how much energy there is per-unit-volume.

    When all you had was energy inherent to space itself, as the Universe expanded, you simply made more empty space, and the energy density stayed the same. But now that you’ve got stuff in the Universe instead, it dilutes (and gets less dense) as the Universe expands. In the case of radiation, the wavelength of light also stretches, which is why the Universe not only gets less dense, it also cools as time goes on.

    Images credit: TAKE 27 LTD / Science Photo Library, via Nature {above], Chris Palma of Penn State / Chaisson and McMillan, Astronomy [below].

    As the Universe expands and cools, from an incredibly hot, dense, uniform, rapidly expanding state down to a cool, sparse, clumpy, slowly expanding state, a huge number of important events happen:

    The fundamental symmetries of nature that are restored at the highest energies become broken, giving rise to things like particle rest masses.
    The Universe gets cool enough so that photons stop spontaneously forming matter/antimatter pairs. The excess antimatter annihilates away, leaving only 1 matter particle per ~1,400,000,000 photons.
    The interaction strength and rate drops significantly enough that neutrinos stop interacting with everything else in the Universe.
    The photon temperature drops enough so that the first stable, atomic nuclei can form without immediately being blasted apart.
    The temperature drops even further — by about another factor of a million — so that neutral atoms can stably form.

    And after that, the overdense regions grow into stars, galaxies and clusters of galaxies, giving rise to the Universe we see today, all while the photon energy continues to drop thanks to the ongoing expansion.

    Image credit: NASA / GSFC, via http://cosmictimes.gsfc.nasa.gov/universemashup/archive/pages/expanding_universe.html

    That next-to-last step — the one about the atoms becoming neutral — is where the Cosmic Microwave Background (CMB) originates. Prior to that time, the atoms were all ionized, meaning that they were simply positively charged nuclei and free electrons, bathed in a sea of photons. But photons have an extremely large scattering cross-section with electrons, meaning that they bounced around a tremendous amount.

    It’s only when the Universe cooled enough to become neutral that photons stopped seeing free electrons and started seeing only neutral, stable atoms. Because neutral atoms only absorb photons at very particular frequencies, and most of the photons that exist are not at those frequencies, these atoms are effectively transparent to all the photons that exist in the Universe!

    Images credit: Amanda Yoho, of the ionized plasma [upper] before the CMB is emitted, followed by the transition to a neutral Universe [lower] that’s transparent to photons.

    But because the Universe has been expanding and cooling for so long, you can take our location in space and fix it, and recognize one disconcerting fact: all the light from the Big Bang in the regions surrounding our own has been passing us by, continuously, for 13.8 billion years.

    All the stars, galaxies, large-scale structure, gas clouds and cosmic voids located thousands, millions, billions or even tens of billions of light-years away saw their CMB light pass us by ages and ages ago.

    Image credit: Wikimedia Commons user Unmismoobjetivo; of a logarithmic view of the Universe as centered on the Earth.

    Yet — to the point of Joseph’s original question — we still see the CMB, which corresponds (today) to a surface that’s some 45.3 billion light-years away.

    The fact that we still see the CMB at all tells us something very important: the Big Bang happened everywhere at once in a region of space that’s at least 45.3 billion light-years in radius, as seen from our perspective.

    Image credit: NASA/WMAP SCIENCE TEAM.

    And the fact that the CMB is not only visible in all directions, but is of a uniform temperature in all directions tells us — in the context of an inflationary Universe — that the amount that the (observable) Universe inflated must have taken it from an initial size that was, at maximum, 10^-29 meters (or less than a trillionth of 1% the size of a proton) and grew it by at least a factor of 10,000,000,000,000,000,000,000.

    The part of the Universe that we see, today, as our observable Universe could have been even smaller than that scale of 10^-29 meters, initially, and the amount that inflation grew that initial patch of space could have been arbitrarily larger than the factor of 10^22; there is no upper limit on that.

    Image credit: ESA and the Planck collaboration.

    So when we look at the Cosmic Microwave Background, at its uniformity and its small-scale, low-magnitude fluctuations, and the fact that there are no regions of it that are identifiable with one another (i.e., that the Universe does not exhibit a closed topology), we can conclude from this alone that the Big Bang must have occurred everywhere at once in a large region as viewed from our perspective.

    In the context of inflation — something we know an awful lot about — this gives us a lower bound as to the duration and scope of inflation, and ties it in to our observable Universe. The reason the CMB is still around is because the Big Bang, which itself came about at the end of inflation, happened over an incredibly large region of space, a region that’s at least as large as where we observe the CMB to still be. In all probability, that true region is much larger, and that not only will observers anywhere in the Universe see roughly the same CMB, but that we’ll continue to see it (albeit, redshifted a little farther) arbitrarily far into the future.

    Images credit: Wikimedia Commons users Theresa Knott and chris 論, modified by me (L); NASA / COBE science team (R), DMR (top) and FIRAS (bottom).

    Thanks for a great question, Joseph, and thanks to all of you for sending in a great selection of questions and suggestions for Ask Ethan! The truths of the Universe are written on the face of the Universe itself, and we’re doing everything we can to uncover them!

    See the full article here.

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    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.

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