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  • 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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