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  • richardmitnick 1:08 pm on October 12, 2017 Permalink | Reply
    Tags: Alan Guth, , , , , , ,   

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

    From Ethan Siegel

    Oct 12, 2017

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    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.

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    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

    NASA/WMAP

    CMB per ESA/Planck

    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.

    3
    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.

    4
    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

    5
    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.

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    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.

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    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:

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    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.

    NASA/COBE

    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.

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    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.

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    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

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  • richardmitnick 4:57 pm on May 30, 2017 Permalink | Reply
    Tags: Alan Guth, , , , , , , , ,   

    From Universe Today: “What Was Cosmic Inflation? The Quest to Understand the Earliest Universe” 

    universe-today

    Universe Today

    30 May, 2017
    Fraser Cain

    The Big Bang. The discovery that the Universe has been expanding for billions of years is one of the biggest revelations in the history of science. In a single moment, the entire Universe popped into existence, and has been expanding ever since.

    We know this because of multiple lines of evidence: the cosmic microwave background radiation, the ratio of elements in the Universe, etc. But the most compelling one is just the simple fact that everything is expanding away from everything else. Which means, that if you run the clock backwards, the Universe was once an extremely hot dense region.

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    A billion years after the big bang, hydrogen atoms were mysteriously torn apart into a soup of ions. Credit: NASA/ESA/A. Felid (STScI)).

    Let’s go backwards in time, billions of years. The closer you get to the Big Bang, the closer everything was, and the hotter it was. When you reach about 380,000 years after the Big Bang, the entire Universe was so hot that all matter was ionized, with atomic nuclei and electrons buzzing around each other.

    Keep going backwards, and the entire Universe was the temperature and density of a star, which fused together the primordial helium and other elements that we see to this day.

    Continue to the beginning of time, and there was a point where everything was so hot that atoms themselves couldn’t hold together, breaking into their constituent protons and neutrons. Further back still and even atoms break apart into quarks. And before that, it’s just a big question mark. An infinitely dense Universe cosmologists called the singularity.

    When you look out into the Universe in all directions, you see the cosmic microwave background radiation. That’s that point when the Universe cooled down so that light could travel freely through space.

    And the temperature of this radiation is almost exactly the same in all directions that you look. There are tiny tiny variations, detectable only by the most sensitive instruments.

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    Cosmic microwave background seen by Planck. Credit: ESA

    ESA/Planck

    When two things are the same temperature, like a spoon in your coffee, it means that those two things have had an opportunity to interact. The coffee transferred heat to the spoon, and now their temperatures have equalized.

    When we see this in opposite sides of the Universe, that means that at some point, in the ancient past, those two regions were touching. That spot where the light left 13.8 billion years ago on your left, was once directly touching that spot on your right that also emitted its light 13.8 billion years ago.

    This is a great theory, but there’s a problem: The Universe never had time for those opposite regions to touch. For the Universe to have the uniform temperature we see today, it would have needed to spend enough time mixing together. But it didn’t have enough time, in fact, the Universe didn’t have any time to exchange temperature.

    Imagine you dipped that spoon into the coffee and then pulled it out moments later before the heat could transfer, and yet the coffee and spoon are exactly the same temperature. What’s going on?

    To address this problem, the cosmologist Alan Guth proposed the idea of cosmic inflation in 1980. That moments after the Big Bang, the entire Universe expanded dramatically.

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    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

    5
    Alan Guth’s notes. http://www.bestchinanews.com/Explore/4730.html

    And by “moments”, I mean that the inflationary period started when the Universe was only 10^-36 seconds old, and ended when the Universe was 10^-32 seconds old.

    And by “expanded dramatically”, I mean that it got 10^26 times larger. That’s a 1 followed by 26 zeroes.

    Before inflation, the observable Universe was smaller than an atom. After inflation, it was about 0.88 millimeters. Today, those regions have been stretched 93 billion light-years apart.

    This concept of inflation was further developed by cosmologists Andrei Linde, Paul Steinhardt, Andy Albrecht and others.

    Inflation resolved some of the shortcomings of the Big Bang Theory.

    The first is known as the flatness problem. The most sensitive satellites we have today measure the Universe as flat. Not like a piece-of-paper-flat, but flat in the sense that parallel lines will remain parallel forever as they travel through the Universe. Under the original Big Bang cosmology, you would expect the curvature of the Universe to grow with time.

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    The horizon problem in Big Bang cosmology. How is it that distant parts of the universe possess such similar physical properties? Credit: Addison Wesley.

    The second is the horizon problem. And this is the problem I mentioned above, that two regions of the Universe shouldn’t have been able to see each other and interact long enough to be the same temperature.

    The third is the monopole problem. According to the original Big Bang theory, there should be a vast number of heavy, stable “monopoles”, or a magnetic particle with only a single pole. Inflation diluted the number of monopoles in the Universe so don’t detect them today.

    Although the cosmic microwave background radiation appears mostly even across the sky, there could still be evidence of that inflationary period baked into it.

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    The Big Bang and primordial gravitational waves. Credit: bicepkeck.org

    In order to do this, astronomers have been focusing on searching for primordial gravitational waves. These are different from the gravitational waves generated through the collision of massive objects. Primordial gravitational waves are the echoes from that inflationary period which should be theoretically detectable through the polarization, or orientation, of light in the cosmic microwave background radiation.

    A collaboration of scientists used an instrument known as the Background Imaging of Cosmic Extragalactic Polarization (or BICEP2) to search for this polarization, and in 2014, they announced that maybe, just maybe, they had detected it, proving the theory of cosmic inflation was correct.

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

    Unfortunately, another team working with the space-based Planck telescope posted evidence that the fluctuations they saw could be fully explained by intervening dust in the Milky Way.


    Bicep 2 Collaboration Steffen Richter Harvard

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    Planck’s view of its nine frequencies. Credit: ESA and the Planck Collaboration

    The problem is that BICEP2 and Planck are designed to search for different frequencies. In order to really get to the bottom of this question, more searches need to be done, scanning a series of overlapping frequencies. And that’s in the works now.

    BICEP2 and Planck and the newly developed South Pole Telescope as well as some observatories in Chile are all scanning the skies at different frequencies at the same time.

    South Pole Telescope SPTPOL

    Distortion from various types of foreground objects, like dust or radiation should be brighter or dimmer in the different frequencies, while the light from the cosmic microwave background radiation should remain constant throughout.

    There are more telescopes, searching more wavelengths of light, searching more of the sky. We could know the answer to this question with more certainty shortly.

    One of the most interesting implications of cosmic inflation, if proven, is that our Universe is actually just one in a vast multiverse. While the Universe was undergoing that dramatic expansion, it could have created bubbles of spacetime that spawned other universes, with different laws of physics.

    In fact, the father of inflation, Alan Guth, said, “It’s hard to build models of inflation that don’t lead to a multiverse.”

    And so, if inflation does eventually get confirmed, then we’ll have a whole multiverse to search for in the cosmic microwave background radiation.

    The Big Bang was one of the greatest theories in the history of science. Although it did have a few problems, cosmic inflation was developed to address them. Although there have been a few false starts, astronomers are now performing a sensitive enough search that they might find evidence of this amazing inflationary period. And then it’ll be Nobel Prizes all around.

    See the full article here .

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  • richardmitnick 8:25 am on May 25, 2017 Permalink | Reply
    Tags: Alan Guth, , , , , , ,   

    From Nautilus: “The Origin of the Universe” 

    Nautilus

    Nautilus

    April 2017
    John Carlstrom

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    The current South Pole telescope measuring small variations in the cosmic microwave background radiation that permeates the universe. Multiple telescopes with upgraded detectors could unlock additional secrets about the origins of the universe. Jason Gallicchio

    Measuring tiny variations in the cosmic microwave background will enable major discoveries about the origin of the universe.

    CMB per ESA/Planck


    ESA/Planck

    How is it possible to know in detail about things that happened nearly 14 billion years ago? The answer, remarkably, could come from new measurements of the cosmic microwave radiation that today permeates all space, but which was emitted shortly after the universe was formed.

    Previous measurements of the microwave background showed that the early universe was remarkably uniform, but not perfectly so: There are small variations in the intensity (or temperature) and polarization of the background radiation. These faint patterns show close agreement with predictions from what is now the standard theoretical model of how the universe began. That model describes an extremely energetic event—the Big Bang—followed within a tiny fraction of a second by a period of very accelerated expansion of the universe called cosmic inflation.

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    Alan Guth, Highland Park High School, NJ, USA 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

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

    During this expansion, small quantum fluctuations were stretched to astrophysical scales, becoming the seeds that gave rise to the galaxies and other large-scale structures of the universe visible today.

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

    After the cosmic inflation ended, the expansion began to slow and the primordial plasma of radiation and high-energy sub-atomic particles began to cool. Within a few hundred thousand years, the plasma had cooled sufficiently for atoms to form, for the universe to become transparent to light, and for the first light to be released. That first light has since been shifted—its wavelengths stretched 1,000-fold into the microwave spectrum by the continuing expansion of the universe—and is what we now measure as the microwave background [see above].

    Inflationary Universe. NASA/WMAP

    Recently the development of new superconducting detectors and more powerful telescopes are providing the tools to conduct an even more detailed study of the microwave background. And the payoff could be immense, including additional confirmation that cosmic inflation actually occurred, when it occurred, and how energetic it was, in addition to providing new insights into the quantum nature of gravity. Specifically the new research we propose can address a wide range of fundamental questions:

    1. The accelerated expansion of the universe in the first fraction of a second of its existence, as described by the inflation model, would have created a sea of gravitational waves. These distortions in spacetime would in turn would have left a distinct pattern in the polarization of the microwave background. Detecting that pattern would thus provide a key test of the inflation model, because the level of the polarization links directly to the time of inflation and its energy scale.
    2. Investigating the cosmic gravitational wave background would build on the stunning recent discovery of gravity waves, apparently from colliding black holes, helping to further the new field of gravitational wave astronomy.
    3. These investigations would provide a valuable window on physics at unimaginably high energy scales, a trillion times more energetic than the reach of the most powerful Earth-based accelerators.
    4. The cosmic microwave background provides a backlight on all structure in the universe. Its precise measurement will illuminate the evolution of the universe to the present day, allowing unprecedented insights and constraints on its still mysterious contents and the laws that govern them.

    The origin of the universe was a fantastic event. To gain an understanding of that beginning as an inconceivably small speck of spacetime and its subsequent evolution is central to unraveling continuing mysteries such as dark matter and dark energy. It can shed light on how the two great theories of general relativity and quantum mechanics relate to each other. And it can help us gain a clearer perspective on our human place within the universe. That is the opportunity that a new generation of telescopes and detectors can unlock.

    How to Measure Variations in the Microwave Background with Unparalleled Precision

    2
    Figure 1Ultra-sensitive superconducting bolometer detectors manufactured with thin-film techniques. The project proposes to deploy 500,000 such detectors. Chrystian Posada Arbelaez.

    The time for the next generation cosmic microwave background experiment is now. Transformational improvements have been made in both the sensitivity of microwave detectors and the ability to manufacture them in large numbers at low cost. The advance stems from the development of ultra-sensitive superconducting detectors called bolometers. These devices (Figure 1) essentially eliminate thermal noise by operating at a temperature close to absolute zero, but also are designed to make sophisticated use of electrothermal feedback—adjusting the current to the detectors when incoming radiation deposits energy, so as to keep the detector at its critical superconducting transition temperature under all operating conditions. The sensitivity of these detectors is limited only by the noise of the incoming signal—they generate an insignificant amount of noise of their own.

    Equally important are the production advances. These new ultra-sensitive detectors are manufactured with thin film techniques adapted from Silicon Valley—although using exotic superconducting materials—so that they can be rapidly and uniformly produced at greatly reduced cost. That’s important, because the proposed project needs to deploy about 500,000 detectors in all—something that would not be possible with hand-assembled devices as in the past. Moreover, the manufacturing techniques allow these sophisticated detectors to automatically filter the incoming signals for the desired wavelength sensitivity.

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    Figure 2The current focal plane on the South Pole Telescope with seven wafers of detectors plus hand-assembled individual detectors. A single detector wafer of the advanced design proposed here would provide more sensitivity and frequency coverage than this entire focal plane; the project would deploy several hundred such wafers across 10 or more telescopes. Jason Henning.

    To deploy the detectors, new telescopes are needed that have a wide enough focal plane to accommodate a large number of detectors—about 10,000 per telescope to capture enough incoming photons and see a wide enough area of the sky (Figure 2). They need to be placed at high altitude, exceedingly dry locations, so as to minimize the water vapor in the atmosphere that interferes with the incoming photons. The plan is to build on the two sites already established for ongoing background observations, the high Antarctic plateau at the geographic South Pole, and the high Atacama plateau in Chile. Discussions are underway with the Chinese about developing a site in Tibet; Greenland is also under consideration. In all, about 10 specialized telescopes will be needed, and will need to operate for roughly 5 years to accomplish the scientific goals described above. Equally important, the science teams that have come together to do this project will need significant upgrades to their fabrication and testing capabilities.

    The resources needed to accomplish this project are estimated at $100 million over 10 years, in addition to continuation of current federal funding. The technology is already proven and the upgrade path understood. Equally important, a cadre of young, enthusiastic, and well-trained scientists are eager to move forward. Unfortunately, constraints on the federal funding situation are already putting enormous stress on the ability of existing teams just to continue, and the expanded resources to accomplish the objectives described above are not available. This is thus an extraordinary opportunity for private philanthropy—an opportunity to “see” back in time to the very beginning of the universe and to understand the phenomena that shaped our world.

    See the full article here .

    Please help promote STEM in your local schools.

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    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

     
  • richardmitnick 4:42 pm on May 12, 2017 Permalink | Reply
    Tags: Alan Guth, , , , , , ,   

    From Ethan Siegel: “What If Cosmic Inflation Is Wrong?” 

    Ethan Siegel
    May 11, 2017

    1
    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. E. Siegel, with images derived from ESA/Planck and the DoE/NASA/ NSF interagency task force on CMB research.

    All scientific ideas, no matter how accepted or widespread they are, are susceptible to being overturned. For all the successes any idea may have, it only takes one experiment or observation to falsify it, invalidate it, or necessitate that it be revised. Beyond that, every scientific idea or model has a limitation to its range of validity: Newtonian mechanics breaks down close to the speed of light; General Relativity breaks down at singularities; evolution breaks down when you reach the origin of life. Even the Big Bang has its limitations, as there’s only so far back we can extrapolate the hot, dense, expanding state that gave rise to what we see today. Since 1980, the leading idea for describing what came before it has been cosmic inflation, for many compelling reasons. But recently, a spate of public statements has shown a deeper controversy:

    In February, a group of theorists, including one of inflation’s co-founders, claimed that inflation had failed.
    The mainstream group of inflationary cosmologists, including inflation’s inventor, Alan Guth, wrote a rebuttal.
    This prompted the original group to dig in further, denouncing the rebuttal.
    And earlier this week, a major publication and one of the rebuttal’s co-signers highlighted and gave their perspective on the debate.

    2
    The expanding Universe, full of galaxies and complex structure we see today, arose from a smaller, hotter, denser, more uniform state. C. Faucher-Giguère, A. Lidz, and L. Hernquist, Science 319, 5859 (47)

    There are three things going on here: the problems with the Big Bang that led to the development of cosmic inflation, the solution(s) that cosmic inflation provides and generic behavior, and subsequent developments, consequences, and difficulties with the idea. Is that enough to cast doubt on the entire enterprise? Let’s lay it all out for you to see.

    Ever since we first recognized that there are galaxies beyond our own Milky Way, all the indications have shown us that our Universe is expanding. Because the wavelength of light is what determines its energy and temperature, then the fabric of expanding space stretches those wavelengths to be longer, causing the Universe to cool. If the Universe is expanding and cooling as we head into the future, then that means it was closer together, denser, and hotter in the past. As we extrapolate farther and farther back, the hot, dense, uniform Universe tells us a story about its past.

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    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. NASA, ESA, and A. Feild (STScI)

    We arrive at a point where galaxy clusters, individual galaxies or even stars haven’t had time to form due to the influence of gravity. We can go even earlier, where the amount of energy in particles and radiation make it impossible for neutral atoms to form; they’d immediately be blasted apart. Even earlier, and atomic nuclei are blasted apart, preventing anything more complex than a proton or neutron from forming. Even earlier, and we begin creating matter/antimatter pairs spontaneously, due to the high energies present. And if you go all the way back, as far as your equations can take you, you’d arrive at a singularity, where all the matter and energy in the entire Universe were condensed into a single point: a singular event in spacetime. That was the original idea of the Big Bang.

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    If these three different regions of space never had time to thermalize, share information or transmit signals to one another, then why are they all the same temperature? E. Siegel

    If that were the way things worked, there would be a number of puzzles based on the observations we had.

    Why would the Universe be the same temperature everywhere? The different regions of space from different directions wouldn’t have had time to exchange information and thermalize; there’s no reason for them to be the same temperature. Yet the Universe, everywhere we looked, had the same background 2.73 K temperature.
    Why would the Universe be perfectly spatially flat? The expansion rate and the energy density are two completely independent quantities, yet they must be equal to one part in 1024 in order to produce the flat Universe we have today.
    Why are there no leftover high-energy relics, as practically every high-energy theory predicts? There are no magnetic monopoles, no heavy, right-handed neutrinos, no relics from grand unification, etc. Why not?

    In 1979, Alan Guth had the idea that an early phase of exponential expansion preceding the hot Big Bang could solve all of these problems, and would make additional predictions about the Universe that we could go and look for. This was the big idea of cosmic inflation.

    6
    Alan Guth

    7
    In 1979, Alan Guth had a revelation that a period of exponential expansion in the Universe’s past could set up and provide the initial conditions for the Big Bang. Alan Guth’s 1979 notebook, tweeted via @SLAClab

    This type of expansion, exponential expansion, is different from what happened for the majority of the Universe’s history. When your Universe is full of matter and radiation, the energy density drops as the Universe expands. As the volume expands, the density goes down, and so the expansion rate goes down, too. But during inflation, the Universe is filled with energy inherent to space itself, so as the Universe expands, it simply creates more space, and that keeps the density the same, and prevents the expansion rate from dropping. This, all at once, solves the three puzzles as follows:

    The Universe is the same temperature everywhere today because disparate, distant regions were once connected in the distant past, before the exponential expansion drove them apart.
    The Universe is flat because inflation stretched it to be indistinguishable from flat; the part of the Universe that’s observable to us is so small relative to how much inflation stretched it that it’s unlikely to be any other way.
    And the reason there are no high-energy relics is because inflation pushed them away via the exponential expansion, and then when inflation ended and the Universe got hot again, it never achieved the ultra-high temperatures necessary to create them again.

    By the early 1980s, not only did inflation solve those puzzles, but we also began coming up with models that successfully recovered a Universe that was isotropic (the same in all directions) and homogeneous (the same in all location), consistent with all our observations.

    8
    The fluctuations in the Cosmic Microwave Background were first measured accurately by COBE in the 1990s, then more accurately by WMAP in the 2000s and Planck (above) in the 2010s. This image encodes a huge amount of information about the early Universe. ESA and the Planck Collaboration

    NASA WMAP satellite

    ESA/Planck

    These predictions are interesting, but not enough, of course. For a physical theory to go from interesting to compelling to validated, it needs to make new predictions that can then be tested. It’s important not to gloss over the fact that these early models of inflation did exactly that, making six important predictions:

    The Universe should be perfectly flat. Yes, that 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 0%. This prediction has been validated by our ΛCDM model, where 5% is matter, 27% is dark matter and 68% is dark energy; curvature is still 0%.

    9
    Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe)
    Date 2010
    Author User:Coldcreation

    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. For perfect scale invariance, a parameter we call n_s would equal 1 exactly; n_s is observed to be 0.96.

    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 in the early 1980s — further validates inflation.

    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.

    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 (~1019 GeV). What we see, from our observations, is that the Universe achieved temperatures no higher than about 0.1% of that (~1016 GeV) at any point, further confirming inflation.

    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.

    9
    The final prediction of cosmic inflation is the existence of primordial gravitational waves. It is the only prediction to not be verified by observation… yet. National Science Foundation (NASA, JPL, Keck Foundation, Moore Foundation, related) — Funded BICEP2 Program; modifications by E. Siegel

    So inflation has a tremendous number of successes to its name. But since the late 1980s, theorists have spent a lot of time cooking up a variety of inflationary models. They’ve found some incredibly odd, non-generic behavior in some of them, including exceptions that break some of the predictive rules, above. In general, the simplest inflationary models are based on a potential: you draw a line with a trough or well at the bottom, the inflationary field starts off at some point away from that bottom, and it slowly rolls down towards the bottom, resulting in inflation until it settles at its minimum. Quantum effects play a role in the field, but eventually, inflation ends, converting that field energy into matter and radiation, resulting in the Big Bang.

    10
    The Universe we see today is based on the initial conditions it began with, which are dictated, predictively, by which model of cosmic inflation you choose. Sloan Digital Sky Survey (SDSS)

    SDSS Telescope at Apache Point Observatory, NM, USA

    But you can make multi-field models, fast-roll models instead of slow-roll models, contrived models that have large departures from flatness, and so on. In other words, if you can make the models as complex as you want, you can find one that gives departures from the generic behavior described above, sometimes even resulting in departures from one or more of these six predictions.

    11
    The fluctuations in the CMB are based on primordial fluctuations produced by inflation. In particular, the ‘flat part’ on large scales (at left) have no explanation without inflation. NASA / WMAP Science Team.

    This is what the current controversy is all about! One side goes so far as to claim that because you can contrive models that can give you almost arbitrary behavior, inflation fails to rise to the standard of a scientific theory. The other side claims that inflation makes these generic, successful predictions, and that the better we measure these parameters of the Universe, the more we constrain which models are viable, and the closer we come to understanding which one(s) best describe our physical reality.

    12
    The shape of gravitational wave fluctuations is indisputable from inflation, but the magnitude of the spectrum is entirely model-dependent. Measuring this will put the debate over inflation to rest, but if the magnitude is too low to be detected over the next 25 years or so, the argument may never be settled. Planck science team.

    The facts that no one disputes are that without inflation, or something else that’s very much like inflation (stretching the Universe flat, preventing it from reaching high energies, creating the density fluctuations we see today, causing the Universe to begin at the same temperatures everywhere, etc.), there’s no explanation for the initial conditions the Universe starts off with. Alternatives to inflation have that hurdle to overcome, and right now there is no alternative that has displayed the same predictive power that the inflationary paradigm brings. That doesn’t mean that inflation is necessarily right, but there sure is a lot of good evidence for it, and many of the “possible” models that can be concocted have already been ruled out. Until an alternative model can achieve all of inflation’s successes, cosmic inflation will remain the leading idea for where our hot Big Bang came from.

    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 4:42 pm on January 12, 2016 Permalink | Reply
    Tags: Alan Guth, , , ,   

    From Science Friday: “10 Questions for Alan Guth, Pioneer of the Inflationary Model of the Universe” 

    Science Friday

    Science Friday

    January 7, 2016
    Christina Couch

    The theoretical physicist discusses the expanding universe and the infinite possibilities it brings.

    Buried under a mountain of papers and empty Coke Zero bottles, Alan Guth ponders the origins of the cosmos. A world-renowned theoretical physicist and professor at the Massachusetts Institute of Technology, Guth is best known for pioneering the theory of cosmic inflation, a model that explains the exponential growth of the universe mere fractions of a second after the Big Bang, and its continued expansion today.

    Cosmic inflation not only describes the underlying physics of the Big Bang, however. Guth believes it also supports the idea that our universe is one of many, with even more universes yet to form.

    Science Friday headed to MIT (where this writer also works, but in a different department) to chat with Guth in his office about the infinite possibilities in an unending cosmos, and the fortune cookie that changed his life.

    1
    Alan Guth in 2007. Photo by Betsy Devine/Wikipedia/CC BY-SA 3.0

    Science Friday: What made you realize that you wanted to be a scientist?
    Alan Guth: I remember an event in high school, which maybe is indicative of my desires to be a theoretical physicist in particular. I was taking high school physics, and a friend of mine was doing an experiment which consisted of taking a yard stick and punching holes in it in different places and pivoting it on these different holes and seeing how the period depended on where the hole was. At this point, I had just learned enough basic physics and calculus to be able to calculate what the answer to that question is supposed to be. I remember one afternoon, we got together and compared my formula with his data using a slide rule to do the calculations. It actually worked. I was very excited about the idea that we can really calculate things, and they actually do reflect the way the real world works.

    You did your dissertation on particle physics and have said that it didn’t turn out exactly how you wanted. Could you tell me about that?
    My dissertation was about the quark model and about how quarks and anti-quarks could bind to form mesons. But it was really just before the theory of quarks underwent a major revolution [when physicists went from believing that quarks are heavy particles that have a large binding energy when they combine, to the quantum chromodynamics theory that quarks are actually very light and their binding energy [gluons] increases as they’re pulled farther apart]. I was on the wrong side of that revolution. My thesis, more or less, became totally obsolete about the time I wrote it. I certainly learned a lot by doing it.

    What got you into cosmology?
    It wasn’t really until the eighth year of my being a [particle physics] postdoc that I got into cosmology. A fellow postdoc at Cornell named Henry Tye got interested in what was then a newfangled class of particle theories called grand unified theories [particle physics models that describe how three of the four fundamental forces in the universe—electromagnetism, weak nuclear interactions, and strong nuclear interactions—act as one force at extremely high energies]. He came to me one day and asked me whether these grand unified theories would predict that there should be magnetic monopoles [particles that have a net magnetic north charge or a net magnetic south charge.]

    I didn’t know about grand unified theories at the time, so he had to teach me, which he did, very successfully. Then I knew enough to put two and two together and conclude—as I’m sure many people did around the world—that yes, grand unified theories do predict that magnetic monopoles should exist, but that they would be outrageously heavy. They would weigh something like 10 to the 16th power times as much as a proton [which means that scientists should theoretically be able to observe them in the universe, although no one has yet].

    About six months later, there was a visit to Cornell by [Nobel laureate] Steve Weinberg, who’s a fabulous physicist and someone I had known from my graduate student days at MIT. He was working on how grand unified theories might explain the excess of matter over anti-matter [in the universe], but it involved the same basic physics that determining how many monopoles existed in the early universe would involve. I decided that if it was sensible enough for Steve Weinberg to work on, why not me, too?

    After a little while, Henry Tye and I came to the conclusion that far too many magnetic monopoles would be produced if one combined conventional cosmology with conventional grand unified theories. We were scooped in publishing that, but Henry and I decided that we would continue to try to figure out if there was anything that could be changed that maybe would make it possible for grand unified theories to be consistent with cosmology as we know it.

    How did you come up with the idea of cosmic inflation?
    A little bit before I started talking to Henry Tye about monopoles, there was a lecture at Cornell by Bob Dicke, a Princeton physicist and cosmologist, in which he presented something that was called the flatness problem, a problem about the expansion rate of the early universe and how precisely fine-tuned it had to be for the universe to work to produce a universe like the one we live in [that is, one that has little or no space-time curvature and is therefore almost perfectly “flat”]. In this talk, Bob Dicke told us that if you thought about the universe at one second after the beginning, the expansion rate really had to be just right to 15 decimal places, or else the universe would either fly apart too fast for any structure to form or re-collapse too fast for any structure to form.

    At the time, I thought that was kind of amazing but didn’t even understand it. But after working on this magnetic monopole question for six months, I came to the realization one night that the kind of mechanism that we were thinking about that would suppress the amount of magnetic monopoles produced after the Big Bang [the “mechanism” being a phase transition that occurs after a large amount of super-cooling] would have the surprising effect of driving the universe into a period of exponential expansion—which is what we now call inflation—and that exponential expansion would solve this flatness problem. It would also draw the universe to exactly the right expansion rate that the Big Bang required [to create a universe like ours].

    You’ve said in previous talks that a fortune cookie played a legitimately important part in your career. How so?
    During the spring of 1980, after having come up with this idea of inflation, I decided that the best way to publicize it would be to give a lot of talks about it. I visited MIT, but MIT had not advertised any positions that year. During the very last day of this six-week trip, I was at the University of Maryland, and they took me out for a Chinese dinner, and the fortune I got in my Chinese fortune cookie said, “An exciting opportunity awaits you if you’re not too timid.” I thought about that and decided that it might be trying to tell me something. When I got back to California, I called one of the faculty members at MIT and said in some stammering way that I hadn’t applied for any jobs because there weren’t any jobs at MIT, but I wanted to tell them that if they might be interested in me, I’d be interested in coming. Then they got back to me in one day and made me an offer. It was great. I came to MIT as a faculty member, and I’ve been here ever since.

    When and where do you do your best work?
    I firmly believe that I do my best thinking in the middle of the night. I very much like to be able to have reasonably long periods of time, a few hours, when I can concentrate on something and not be interrupted, and that only happens at night. What often happens is I fall asleep at like 9:30 and wake up at 1 or 2 and start working and then fall asleep again at 5.

    Who is a dream collaborator you’d love to work with?
    I bet it would have been a lot of fun to work with [Albert] Einstein. What I really respect about Einstein is his desire to throw aside all conventional modes and just concentrate on what seems to be the closest we can get to an accurate theory of nature.

    What are you currently working on?
    The most concrete project I’m working on is a project in collaboration with a fairly large group here at MIT in which we’re trying to calculate the production of primordial black holes that might have happened with a certain version of inflation. If this works out, these primordial black holes could perhaps be the seeds for the super massive black holes in the centers of galaxies, which are very hard to explain. It would be incredibly exciting if that turns out to be the case.

    What else are you mulling over?
    A bigger question, which has been in the back of my mind for a decade, is the problem of understanding probabilities in eternally inflating universes. In an eternally inflating universe, these pocket universes [like the one we live in] go on being formed literally forever. An infinite number of pocket universes are formed, and that means that anything that’s physically allowed will ultimately happen an infinite number of times.

    Normally we interpret probabilities as relative occurrences. We think one-headed cows are more probable than two-headed cows because we think there are a lot more one-headed cows than two-headed cows. I don’t know if there are any two-headed cows on earth, but let’s pretend there are. In an eternally inflating universe, assuming that a two-headed cow is at least possible, there will be an infinite number of two-headed cows and an infinite number of one-headed cows. It’s hard to know what you mean if you try to say that one is more common than the other.

    If anything can happen in an eternally inflating universe, is there a situation in which I am the cosmologist and you are the journalist?
    [Laughs] Probably, yes. I think what we would know for sure is that anything that’s physically possible—and I don’t see why this is not physically possible—will happen an infinite number of times.

    See the full article here .

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  • richardmitnick 2:02 pm on September 22, 2014 Permalink | Reply
    Tags: Alan Guth, , , , , , ,   

    From Symmetry: “Cosmic dust proves prevalent” 

    Symmetry

    September 22, 2014
    Kathryn Jepsen

    Space dust accounts for at least some of the possible signal of cosmic inflation the BICEP2 experiment announced in March. How much remains to be seen.

    Space is full of dust, according to a new analysis from the European Space Agency’s Planck experiment.

    planck

    That includes the area of space studied by the BICEP2 experiment, which in March announced seeing a faint pattern left over from the big bang that could tell us about the first moments after the birth of the universe.

    gwb
    Gravitational Wave Background from BICEP2

    The Planck analysis, which started before March, was not meant as a direct check of the BICEP2 result. It does, however, reveal that the level of dust in the area BICEP2 scientists studied is both significant and higher than they thought.

    “There is still a wide range of possibilities left open,” writes astronomer Jan Tauber, ESA project scientist for Planck, in an email. “It could be that all of the signal is due to dust; but part of the signal could certainly be due to primordial gravitational waves.”

    BICEP2 scientists study the cosmic microwave background, a uniform bath of radiation permeating the universe that formed when the universe first cooled enough after the big bang to be transparent to light. BICEP2 scientists found a pattern within the cosmic microwave background, one that would indicate that not long after the big bang, the universe went through a period of exponential expansion called cosmic inflation. The BICEP2 result was announced as the first direct evidence of this process.

    The problem is that the same pattern, called B-mode polarization, also appears in space dust. The BICEP2 team subtracted the then known influence of the dust from their result. But based on today’s Planck result, they didn’t manage to scrub all of it.

    How much the dust influenced the BICEP2 result remains to be seen.

    In November, Planck scientists will release their own analysis of B-mode polarization in the cosmic microwave background, in addition to a joint analysis with BICEP2 specifically intended to check the BICEP2 result. These results could answer the question of whether BICEP2 really saw evidence of cosmic inflation.

    “While we can say the dust level is significant,” writes BICEP2 co-leader Jamie Bock of Caltech and NASA’s Jet Propulsion Laboratory, “we really need to wait for the joint BICEP2-Planck paper that is coming out in the fall to get the full answer.”

    [Me? I am rooting for my homey, Alan Guth, from Highland Park, NJ, USA]

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.


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  • richardmitnick 3:32 pm on April 6, 2014 Permalink | Reply
    Tags: Alan Guth, , , , , ,   

    From Symmetry: “Inflation” 

    January 01, 2005
    Logbook

    In 1978 Alan Guth heard about the “flatness problem” of the universe while attending a talk on cosmology—a field he was only marginally curious about. A year later, Guth found a solution.

    Alan Guth

    At the beginning of the big bang, for an incredibly small fraction of a second, the universe could have expanded exponentially fast, rapidly transforming curved space into flat one. Quickly running out of energy, the expansion would slow down, eventually reaching today’s sluggish pace. Such an initial explosive rush, which Guth later called inflation, could solve a number of cosmic paradoxes (see Growth of Inflation).

    Although scientists still debate the driving force behind inflation—Guth soon realized his original idea of “supercooling” wouldn’t work—the concept of inflation has become the leading theme and the crux of modern cosmology.

    inflation
    Courtesy of Alan Guth and the Adler Planetarium and Astronomy Museum in Chicago

    Guth’s notebook is now part of a permanent exhibit at the Adler Planetarium and Astronomy Museum in Chicago.

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.



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  • richardmitnick 9:24 am on March 20, 2014 Permalink | Reply
    Tags: Alan Guth, , , , , ,   

    From M.I.T.: “3 Questions: Alan Guth on new insights into the ‘Big Bang’” 

    March 19, 2014
    Steve Bradt, MIT News Office

    Earlier this week, scientists announced that a telescope observing faint echoes of the so-called “Big Bang” had found evidence of the universe’s nearly instantaneous expansion from a mere dot into a dense ball containing more than 1090 particles. This discovery, using the BICEP2 telescope at the South Pole, provides the first strong evidence of “cosmic inflation” at the birth of our universe, when it expanded billions of times over.

    BICEP Telescope
    BICEP2 Telescope at South Pole

    The theory of cosmic inflation was first proposed in 1980 by Alan Guth, now the Victor F. Weisskopf Professor of Physics at MIT. Inflation has become a cornerstone of Big Bang cosmology, but until now it had remained a theory without experimental support. Guth discussed the significance of the new BICEP2 results with MIT News.

    ag
    Dr. Alan Guth

    Q: Can you explain the theory of cosmic inflation that you first put forth in 1980?

    A: I usually describe inflation as a theory of the “bang” of the Big Bang: It describes the propulsion mechanism that drove the universe into the period of tremendous expansion that we call the Big Bang. In its original form, the Big Bang theory never was a theory of the bang. It said nothing about what banged, why it banged, or what happened before it banged.

    The original Big Bang theory was really a theory of the aftermath of the bang. The universe was already hot and dense, and already expanding at a fantastic rate. The theory described how the universe was cooled by the expansion, and how the expansion was slowed by the attractive force of gravity.

    Inflation proposes that the expansion of the universe was driven by a repulsive form of gravity. According to [Isaac] Newton, gravity is a purely attractive force, but this changed with [Albert] Einstein and the discovery of general relativity. General relativity describes gravity as a distortion of spacetime, and allows for the possibility of repulsive gravity.

    Modern particle theories strongly suggest that at very high energies, there should exist forms of matter that create repulsive gravity. Inflation, in turn, proposes that at least a very small patch of the early universe was filled with this repulsive-gravity material. The initial patch could have been incredibly small, perhaps as small as 10-24 centimeter, about 100 billion times smaller than a single proton. The small patch would then start to exponentially expand under the influence of the repulsive gravity, doubling in size approximately every 10-37 second. To successfully describe our visible universe, the region would need to undergo at least 80 doublings, increasing its size to about 1 centimeter. It could have undergone significantly more doublings, but at least this number is needed.

    During the period of exponential expansion, any ordinary material would thin out, with the density diminishing to almost nothing. The behavior in this case, however, is very different: The repulsive-gravity material actually maintains a constant density as it expands, no matter how much it expands! While this appears to be a blatant violation of the principle of the conservation of energy, it is actually perfectly consistent.

    This loophole hinges on a peculiar feature of gravity: The energy of a gravitational field is negative. As the patch expands at constant density, more and more energy, in the form of matter, is created. But at the same time, more and more negative energy appears in the form of the gravitational field that is filling the region. The total energy remains constant, as it must, and therefore remains very small.

    It is possible that the total energy of the entire universe is exactly zero, with the positive energy of matter completely canceled by the negative energy of gravity. I often say that the universe is the ultimate free lunch, since it actually requires no energy to produce a universe.

    At some point the inflation ends because the repulsive-gravity material becomes metastable. The repulsive-gravity material decays into ordinary particles, producing a very hot soup of particles that form the starting point of the conventional Big Bang. At this point the repulsive gravity turns off, but the region continues to expand in a coasting pattern for billions of years to come. Thus, inflation is a prequel to the era that cosmologists call the Big Bang, although it of course occurred after the origin of the universe, which is often also called the Big Bang.

    Q: What is the new result announced this week, and how does it provide critical support for your theory?

    A: The stretching effect caused by the fantastic expansion of inflation tends to smooth things out — which is great for cosmology, because an ordinary explosion would presumably have left the universe very splotchy and irregular. The early universe, as we can see from the afterglow of the cosmic microwave background (CMB) radiation, was incredibly uniform, with a mass density that was constant to about one part in 100,000.

    CMB Planck ESA
    Cosmic Microwave Background

    ESA Planck
    ESA/Planck

    The tiny nonuniformities that did exist were then amplified by gravity: In places where the mass density was slightly higher than average, a stronger-than-average gravitational field was created, which pulled in still more matter, creating a yet stronger gravitational field. But to have structure form at all, there needed to be small nonuniformities at the end of inflation.

    In inflationary models, these nonuniformities — which later produce stars, galaxies, and all the structure of the universe — are attributed to quantum theory. Quantum field theory implies that, on very short distance scales, everything is in a state of constant agitation. If we observed empty space with a hypothetical, and powerful, magnifying glass, we would see the electric and magnetic fields undergoing wild oscillations, with even electrons and positrons popping out of the vacuum and then rapidly disappearing. The effect of inflation, with its fantastic expansion, is to stretch these quantum fluctuations to macroscopic proportions.

    The temperature nonuniformities in the cosmic microwave background were first measured in 1992 by the COBE satellite, and have since been measured with greater and greater precision by a long and spectacular series of ground-based, balloon-based, and satellite experiments. They have agreed very well with the predictions of inflation. These results, however, have not generally been seen as proof of inflation, in part because it is not clear that inflation is the only possible way that these fluctuations could have been produced.

    NASA COBE satellite
    NASA/COBE

    The stretching effect of inflation, however, also acts on the geometry of space itself, which according to general relativity is flexible. Space can be compressed, stretched, or even twisted. The geometry of space also fluctuates on small scales, due to the physics of quantum theory, and inflation also stretches these fluctuations, producing gravity waves in the early universe.

    The new result, by John Kovac and the BICEP2 collaboration, is a measurement of these gravity waves, at a very high level of confidence. They do not see the gravity waves directly, but instead they have constructed a very detailed map of the polarization of the CMB in a patch of the sky. They have observed a swirling pattern in the polarization (called “B modes”) that can be created only by gravity waves in the early universe, or by the gravitational lensing effect of matter in the late universe.

    But the primordial gravity waves can be separated, because they tend to be on larger angular scales, so the BICEP2 team has decisively isolated their contribution. This is the first time that even a hint of these primordial gravity waves has been detected, and it is also the first time that any quantum properties of gravity have been directly observed.

    Q: How would you describe the significance of these new findings, and your reaction to them?

    A: The significance of these new findings is enormous. First of all, they help tremendously in confirming the picture of inflation. As far as we know, there is nothing other than inflation that can produce these gravity waves. Second, it tells us a lot about the details of inflation that we did not already know. In particular, it determines the energy density of the universe at the time of inflation, which is something that previously had a wide range of possibilities.

    By determining the energy density of the universe at the time of inflation, the new result also tells us a lot about which detailed versions of inflation are still viable, and which are no longer viable. The current result is not by itself conclusive, but it points in the direction of the very simplest inflationary models that can be constructed.

    Finally, and perhaps most importantly, the new result is not the final story, but is more like the opening of a new window. Now that these B modes have been found, the BICEP2 collaboration and many other groups will continue to study them. They provide a new tool to study the behavior of the early universe, including the process of inflation.

    When I (and others) started working on the effect of quantum fluctuations in the early 1980s, I never thought that anybody would ever be able to measure these effects. To me it was really just a game, to see if my colleagues and I could agree on what the fluctuations would theoretically look like. So I am just astounded by the progress that astronomers have made in measuring these minute effects, and particularly by the new result of the BICEP2 team. Like all experimental results, we should wait for it to be confirmed by other groups before taking it as truth, but the group seems to have been very careful, and the result is very clean, so I think it is very likely that it will hold up.

    See the full article here.


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