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  • richardmitnick 9:39 am on June 12, 2018 Permalink | Reply
    Tags: , , , , Cosmic inflation theory,   

    From astrobites: “Testing micro with macro – from quantum to the cosmos” 

    Astrobites bloc

    From astrobites

    June 12, 2018
    Philippa Cole

    Title: Precision test of quantum mechanics – our Universe
    Authors: Julian Georg and Carl Rosenzweig

    First Author’s Institution: Department of Physics, Syracuse University, Syracuse, NY 13244, USA
    Status: Open access on arXiv

    Quantum mechanics governs what goes on at mind-bogglingly small scales. So far it’s provided a really good description of microscopic systems that we’ve been able to test on earth, but today’s authors muse that it’s not really had any competition – “all theories benefit from having an alternative to serve as a foil”.

    Since quantum laws should work on all scales, why not zoom all the way out and use the increasingly precise measurements we have on cosmological scales to test our quantum framework? In order to do this we need something to describe the relationship between the unfathomably large and the unimaginably small, and luckily, the leading theory of the early universe connects the two – that theory is 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

    Alan Guth’s notes:
    5

    See the full article here .


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    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 1:08 pm on October 12, 2017 Permalink | Reply
    Tags: , , , , , Cosmic inflation theory, ,   

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

    From Ethan Siegel

    Oct 12, 2017

    1
    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.

    2
    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.

    5
    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.

    6
    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:

    7
    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.

    7
    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.

    8
    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 .

    Please help promote STEM in your local schools.

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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 7:28 am on October 7, 2017 Permalink | Reply
    Tags: , , , Cosmic inflation theory, , , Is the inflationary Universe a scientific theory? Not anymore   

    From Ethan Siegel: “Is the inflationary Universe a scientific theory? Not anymore” 

    Ethan Siegel

    Oct 6, 2017

    1
    The expanding Universe, full of galaxies and complex structure we see today, arose from a smaller, hotter, denser, more uniform state. Image credit: C. Faucher-Giguère, A. Lidz, and L. Hernquist, Science 319, 5859 (47).

    This article was written by Sabine Hossenfelder. Sabine is a theoretical physicist specialized in quantum gravity and high energy physics. She also freelance writes about science.

    One of inflation’s cofounders has turned his back on the idea. But practically no one else is following him. Is he right?

    “I know of no other scientist, no other theoretical physicist alive who has a clearer focus on whether our theories and ideas are relevant to the real world. And that’s always what he’s after.” -Neil Turok, on Paul Steinhardt

    We are made from stretched quantum fluctuations. At least that’s cosmologists’ currently most popular explanation. According to their theory, the history of our existence began billions of years ago with a — now absent — field that propelled the universe into a phase of rapid expansion called “inflation.” When inflation ended, the field decayed and its energy was converted into radiation and particles which are still around today.

    Inflation was proposed more than 35 years ago, among others, by Paul Steinhardt. But Steinhardt has become one of the theory’s most fervent critics. In a recent article in Scientific American, Steinhardt together with Anna Ijjas and Avi Loeb, don’t hold back. Most cosmologists, they claim, are uncritical believers:

    “[T]he cosmology community has not taken a cold, honest look at the big bang inflationary theory or paid significant attention to critics who question whether inflation happened. Rather cosmologists appear to accept at face value the proponents’ assertion that we must believe the inflationary theory because it offers the only simple explanation of the observed features of the universe.”

    2
    The quantum fluctuations inherent to space, stretched across the Universe during cosmic inflation, gave rise to the density fluctuations imprinted in the cosmic microwave background, which in turn gave rise to the stars, galaxies, and other large-scale structure in the Universe today. Image credit: E. Siegel, with images derived from ESA/Planck and the DoE/NASA/ NSF interagency task force on CMB research.

    And it’s even worse, they argue, inflation is not even a scientific theory:

    “[I]nflationary cosmology, as we currently understand it, cannot be evaluated using the scientific method.”

    As alternative to inflation, Steinhardt et al. promote a “big bounce.” In this scenario, the universe’s current expansion was preceded by a phase of contraction, yielding similar benefits to inflation.

    The group’s fight against inflation isn’t news. They laid out their arguments in a series of papers during the last years (on which I previously commented here). But the recent SciAm piece called The Defenders Of Inflation onto the stage. Led by David Kaiser, they signed a letter to Scientific American in which they complained that the magazine gave space to the inflationary criticism.

    The letter’s list of undersigned is an odd selection of researchers who themselves work on inflation and of physics luminaries who have little if anything to do with inflation. Interestingly, Slava Mukhanov — one of the first to derive predictions from inflation — did not sign. And it’s not because he wasn’t asked. In an energetic talk delivered at Stephen Hawking’s birthday conference two months ago, Mukhanov made it pretty clear that he thinks most of inflationary model-building is but a waste of time.

    I agree with Muhkanov’s assessment. The Steinhardt et al. article isn’t exactly a masterwork of science writing. It’s also unfortunate they’re using SciAm to promote some other theory of how the universe began rather than sticking to their criticism of inflation. But some criticism is overdue.

    3
    Various models of inflation and what they predict for the scalar (x-axis) and tensor (y-axis) fluctuations from inflation. Note how just a small subset of viable inflationary models gives rise to a huge variety of possible predictions for these parameters.

    The problem with inflation isn’t the idea per se, but the overproduction of useless inflationary models. There are literally hundreds of these models, and they are — as the philosophers say — severely underdetermined. This means if one extrapolates the models that fit current data to regimes which are still untested, the result is ambiguous. Different models lead to very different predictions for not-yet made observations. Presently, it is therefore utterly pointless to twiddle with the details of inflation because there are literally infinitely many models that one can think up, giving rise to infinitely many different “predictions.”

    Rather than taking on this overproduction problem, however, Steinhardt et al. in their SciAm piece focus on inflation’s failure to solve the problems it was meant to solve. However, this criticism is off-target because the problems that inflation was meant to solve aren’t problems to begin with.

    I’m serious. Let’s look at those one by one:

    4
    If the symmetry restoring grand unification were broken, a large number of magnetic monopoles would be produced. But our Universe doesn’t exhibit them; if cosmic inflation took place after this symmetry were broken, at most one monopole would still be present within the observable Universe. Image credit: E. Siegel / Beyond The Galaxy.

    1. The Monopole Problem:

    Guth invented inflation to solve the “monopole problem.”

    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

    If the early universe underwent a phase-transition, for example because the symmetry of grand unification was broken — then topological defects, like monopoles, should have been produced abundantly. We do not, however, see any of them. Inflation dilutes the density of monopoles (and other worries) so that it’s unlikely we’ll ever encounter one.

    But a plausible explanation for why we don’t see any monopoles is that there aren’t any. We don’t know there is any grand symmetry that was broken in the early universe, or if there is, we don’t know when it was broken, or if the breaking produced any defects. Indeed, all searchers for evidence of grand symmetry — mostly via proton decay — turned out negative. This motivation is interesting today merely for historical reasons.

    6
    The quantum fluctuations that occur during inflation do indeed get stretched across the Universe, but the larger feature of inflation is that the Universe gets stretched flat, removing any pre-existing curvature. Image credit: E. Siegel / Beyond the Galaxy.

    2. The Flatness Problem

    The flatness problem is a finetuning problem. The universe currently seems to be almost flat, or if it has any spatial curvature, that curvature must be very small. The curvature contribution to the dynamics of the universe however increases in relevance relative to that of matter. This means if the curvature is small today, it must have been even smaller in the past. Inflation serves to make any initial curvature contribution smaller by something like 100 orders of magnitude or so.

    This is supposed to be an explanation, but it doesn’t explain anything, for now you can ask, well, why wasn’t the original curvature larger than some other number? The reason that some physicists believe something is being explained here is that numbers close to 1 are pretty according to current beauty-standards, while numbers much smaller than 1 numbers aren’t. The flatness problem, therefore, is an aesthetics problem, and I don’t think it’s an argument any scientist should take seriously.

    6
    The Universe appears to be the same temperature everywhere, even in causally disconnected regions of the sky. This is colloquially known as the horizon problem. No image credit.

    3. The Horizon Problem

    The Cosmic Microwave Background (CMB) has almost the exact same temperature in all directions.

    CMB per ESA/Planck

    ESA/Planck

    The problem is, if you trace back the origin of the background radiation without inflation, then you find that the radiation that reached us from different directions was never in causal contact with each other. Why then does it have the same temperature in all directions?

    To see why this problem isn’t a problem, you have to know how the theories that we currently use in physics work. We have an equation — a “differential equation” — that tells us how a system (eg, the universe) changes from one place to another and one moment to another. To make any use of this equation, however, we also need starting values or “initial conditions.”*

    The horizon problem asks “why this initial condition” for the universe. This question is justified if an initial condition is complicated in the sense of requiring a lot of information. But a homogeneous temperature isn’t complicated. It’s dramatically easy. And not only isn’t there much to explain, inflation doesn’t even answer the question “why this initial condition” because it still needs an initial condition. It’s just a different initial condition. It’s not any simpler and it doesn’t explain anything.

    Another way to see that this is a non-problem: if you’d go back in time far enough without inflation, you’d eventually get to a period when matter was so dense and curvature so high that quantum gravity was important. And what do we know about the likelihood of initial conditions in a theory of quantum gravity? Nothing. Absolutely nothing.

    That we’d need quantum gravity to explain the initial condition for the universe, however, is an exceedingly unpopular point of view because nothing can be calculated and no predictions can be made.

    Inflation, on the other hand, is a wonderfully productive model that allows cosmologists to churn out papers.

    7
    The power spectrum of the fluctuations in the CMB are best fit by a single, unique curve. This curve can be uniquely derived, in both shape and magnitude, from the contents of the Universe and the initial conditions provided by the predictions of inflation. No image credit.

    You will find the above three problems religiously repeated as a motivation for inflation, in lectures and textbooks and popular science pages all over the place. But these problems aren’t problems, never were problems, and never required a solution.

    Even though inflation was ill-motivated when conceived, however, it later turned out to actually solve some real problems. Yes, sometimes physicists work on the wrong things for the right reasons, and sometimes they work on the right things for the wrong reasons. Inflation is an example for the latter.

    The reasons why many physicists today think something like inflation must have happened are not that it supposedly solves the three above problems. It’s that some features of the CMB have correlations (the “TE power spectrum”) which depend on the size of the fluctuations, and implies a dependence on the size of the universe. This correlation, therefore, cannot be easily explained by just choosing an initial condition, since it is data that goes back to different times. It really tells us something about how the universe changed with time, not just where it started from.**

    Two other, convincing features of inflation are that, under fairly general circumstances, the model also explains the absence of certain correlations in the CMB (the “non-Gaussianities”) and how many CMB fluctuations there are of any size, quantified by what is known as the “scale factor.”

    But here is the rub. To make predictions with inflation one cannot just say “there once was exponential expansion and it ended somehow.” No, to be able to calculate something, one needs a mathematical model. The current models for inflation work by introducing a new field — the “inflaton” — and give this field a potential energy. The potential energy depends on various parameters. And these parameters can then be related to observations.

    7
    Three possible ‘hills-and-valleys’ potentials that could describe cosmic inflation. Though they give somewhat different results for the various parameters of the Universe, there is no motivation for choosing one model over another. Created with Google’s graph tool.

    The scientific approach to the situation would be to choose a model, determine the parameters that best fit observations, and then revise the model as necessary — i.e., as new data comes in. But that’s not what cosmologists presently do. Instead, they have produced so many variants of models that they can now “predict” pretty much anything that might be measured in the foreseeable future.

    It is this abundance of useless models that gives rise to the criticism that inflation is not a scientific theory. And on that account, the criticism is justified. It’s not good scientific practice. It is a practice that, to say it bluntly, has become commonplace because it results in papers, not because it advances science.

    I was therefore dismayed to see that the criticism by Steinhardt, Ijas, and Loeb was dismissed so quickly by a community which has become too comfortable with itself. Inflation is useful because it relates existing observations to an underlying mathematical model, yes. But we don’t yet have enough data to make reliable predictions from it. We don’t even have enough data to convincingly rule out alternatives.

    There hasn’t been a Nobel Prize for inflation, and I think the Nobel committee did well in that decision.

    There’s no warning sign you when you cross the border between science and blabla-land. But inflationary model building left behind reasonable scientific speculation long ago. I, for one, am glad that at least some people are speaking out about it. And that’s why I approve of the Steinhardt et al. criticism.

    • Contrary to what the name suggest, the initial conditions could be at any moment, not necessarily the initial one. We would still call them initial conditions.

    ** This argument is somewhat circular because extracting the time-dependence for the modes already presumes something like inflation. But at least it’s a strong indicator.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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

     
  • richardmitnick 4:57 pm on May 30, 2017 Permalink | Reply
    Tags: , , , , , , Cosmic inflation theory, , ,   

    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.

    2
    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.

    3
    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.

    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

    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.

    4
    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.

    5
    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

    6
    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 .

    Please help promote STEM in your local schools.

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  • richardmitnick 8:48 am on May 13, 2017 Permalink | Reply
    Tags: , , , Cosmic inflation theory, ,   

    From Science Alert: “Stephen Hawking And 32 Top Physicists Just Signed a Heated Letter on The Universe’s Origin” 

    ScienceAlert

    Science Alert

    12 MAY 2017
    FIONA MACDONALD

    Inflationary Universe. NASA/WMAP

    For centuries, people have puzzled over how our Universe began. But the heat just got turned way up on a debate that’s quietly been raging between cosmologists, with 33 of the world’s most famous physicists publishing a letter angrily defending one of the leading hypotheses we have for the origin of the Universe.

    The letter is in response to a Scientific American feature published back in February, in which three physicists heavily criticised inflation theory – the idea that the Universe expanded just like a balloon shortly after the Big Bang. The article went as far as claiming that the model “cannot be evaluated using the scientific method” – the academic equivalent of saying it isn’t even real science.

    In response, 33 of the world’s top physicists, including Stephen Hawking, Lisa Randall, and Leonard Susskind, have fired back by publishing their own open letter in Scientific American. The Cliff’s note version is this: they’re really angry.

    2
    Alan Guth

    Inflation theory was first proposed by cosmologist Alan Guth, now at MIT, back in 1980.

    It’s based on the idea that a fraction of a second after the Big Bang, the Universe expanded rapidly, spinning entire galaxies out of quantum fluctuations.

    “By the time it slowed down, what had been a tiny, quivering quantum realm was stretched out until it looked smooth and flat, save for speckles of denser matter that later became galaxies, stars, and planets,” writes Joshua Sokol for The Atlantic.

    In the following years, Guth’s original idea was improved and updated by Stanford physicists Andrei Linde, and they’ve since spent their careers refining the inflation model – which has become the leading theory for how the Universe was born.

    In fact, most of us were taught inflation theory at high school and university when discussing the Universe’s origins.

    Guth and Linde, along with cosmologists David Kaiser and Yasunori Nomura, were the ones who recruited the other 29 signees behind this week’s letter.

    Interestingly, one of Guth and Linde’s former colleagues, physicist Paul Steinhardt, is part of the trio they’re rallying against. Guth, Linde, and Steinhardt all shared the prestigious Dirac prize “for development of the concept of inflation in cosmology” back in 2002.

    But in the years since, Steinhardt has gone rogue, and has become an active critic of inflationary theory. He was one of the authors of Scientific American’s February feature, originally titled “Pop goes the Universe”, along with Princeton physicist Anna Ijjas, and Harvard astronomer Abraham Loeb.

    That article highlighted recent research into the cosmic microwave background, which doesn’t match up with the predictions of inflationary theory.

    It also criticised the fact that inflation would have generated primordial gravitational waves, which have never been found.

    “The data suggest cosmologists should reassess this favoured paradigm and consider new ideas about how the universe began,” summarises an ‘In Brief’ wrap up of the article.

    That criticism in itself wasn’t a huge deal – these kinds of arguments are healthy in the science world.

    But what really pissed off Guth, Linde, and the 31 other signees, was the suggestion that inflationary theory couldn’t actually be tested in the first place, and therefore wasn’t really science.

    “They [made] the extraordinary claim that inflationary cosmology ‘cannot be evaluated using the scientific method’ and go on to assert that some scientists who accept inflation have proposed ‘discarding one of [science’s] defining properties: empirical testability,’ thereby ‘promoting the idea of some kind of nonempirical science’,” the physicists write in their open letter.

    “We have no idea what scientists they are referring to. We disagree with a number of statements in their article, but in this letter, we will focus on our categorical disagreement with these statements about the testability of inflation.”

    Their argument is that inflation theory is based on many models, and there’s no illusion that all of these models are correct. Over the past 37 years, some of the models have made correct, testable predictions – including the average mass density of the Universe, and its flat shape. Many are still unresolved.

    But either way, these models are all testable, which means they’re proper science, and they can be proven or disproven depending on the evidence we find in the coming years.

    Ryan F. Mandelbaum has done incredible coverage of this feud over at Gizmodo, and points to a blog entry by Sean Carroll, one of the physicists who signed the letter, on the controversy:

    “We judge theories by what predictions they make that we can test, not the ones they make that can’t be tested. It’s absolutely true that there are important unanswered questions facing the inflationary paradigm. But the right response in that situation is to either work on trying to answer them, or switch to working on something else (which is a perfectly respectable option). It’s not to claim that the questions are in principle unanswerable, and therefore the field has dropped out of the realm of science.”

    The authors of the original article have since responded to the letter with their own extended FAQ on the debate. And they maintain their position – that inflation was once testable, but “what began in the 1980s as a theory that seemed to make definite predictions has become a theory that makes no definite predictions”.

    Which takes us right back to where we started… some cosmologists have publicly slammed inflation theory, and others have angrily responded.

    Unfortunately there’s no neat resolution to this debate on the horizon, with both sides standing pretty firm. The one thing they both agree on is the fact that inflation theory isn’t perfect, and we should all keep an open mind about what really happened at the birth of our Universe as new data comes in.

    Or as Guth told Mandelbaum in the ultimate mic drop when asked what would happen next: “I think we’ll all continue on with our research.”

    You can read the original article here, the responding open letter here, and the original authors’ response here.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
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