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

    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: , , , , , , Inflation, ,   

    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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  • richardmitnick 12:17 pm on March 19, 2014 Permalink | Reply
    Tags: , , , , , , Inflation   

    From Fermilab: “From quantum to cosmos” 


    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    Wednesday, March 19, 2014

    ch
    Craig Hogan, head of the Center for Particle Astrophysics, wrote this column.

    On Monday morning, cosmologists around the world felt a wave of ecstasy as they learned of a breathtaking discovery: a particular pattern of light coming from the early universe, imprinted on the cosmic expansion during its first moments. It feels like a love letter from Mother Nature has invited us to share her deepest secrets.

    CMB Planck ESA
    Cosmic Background from ESA/Planck

    All forms of matter and energy come in quanta — the “particles” of particle physics. For the first time, we have now detected a quantum behavior of space and time. The new result invokes an interplay among all the scales of physical universe, from the smallest to largest, from the beginning to the present day. It spectacularly confirms many of the “inner space/outer space” connections pioneered over several decades by Fermilab’s astrophysics theory group. This includes the amazing idea that quantum fluctuations can be amplified to enormous size by cosmic expansion and lead not only to gravitational waves, but ultimately to the formation of all cosmic structures, including galaxies, stars, planets and life.

    The now discovered polarization of cosmic background light displays a faint but distinctive pattern of swirls that can be created only by an extraordinarily exotic process known as inflation, a stretching of space-time (gravitational waves), caused by its own subatomic, quantum fluctuations. This unique signature reaches us intact across all the vast stretches of space since the beginning of time and can now be studied in precise detail.

    The discovery, published in this paper, came sooner than anyone expected. Theorists, including Fermilab’s Albert Stebbins, proposed long ago the possibility of isolating the distinctive swirling signature used to make the discovery, but everyone was surprised this week that the signal in the real universe is so strong. The implications for cosmology are immediate and profound. We now know far more reliably what conditions were during the cosmic inflation that created our expansion; for example, the new data directly measures how fast things were expanding back then. We can now delve much more concretely into the new physics that governs cosmic origins and how it connects to the unification of the Standard Model particles and forces studied at the Tevatron and the LHC. Cosmic polarization experiments may even provide real data addressing the quantum system underlying unification of the Standard Model with gravity — the “theory of everything.”

    sm
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    Fermilab Tevatron
    Tevatron

    CERN LHC
    Inside the LHC

    The discovery was inspired by theory but propelled in recent years by new transformational technology, in particular, a new generation of sensors being developed at Argonne, Berkeley, Jet Propulsion Laboratory and NIST. Large focal plane arrays of antennas are fabricated on silicon wafers, together with superconducting detectors that achieve quantum-noise-limited performance. In experiments, they are deployed in advanced telescopes at the world’s best site for peering deep into space, the South Pole.

    The newly discovered effect is strong enough to confirm soon with other experiments, perhaps even using data already obtained. The next step will be to improve the quality of the measurements with a larger area of sky, more frequency bands and higher angular resolution. That will require larger focal planes with more detection elements and a larger telescope.

    We are already developing this next-generation experiment. It will use the world’s leading facility for cosmic background studies, the South Pole Telescope (SPT). As part of a new joint effort with Argonne, the University of Chicago and other partners, Fermilab is playing a central role in developing and building the new SPT-3G cryogenic camera system, an order of magnitude more capable than that currently deployed. Over the next two years, the system will be assembled, integrated and tested at Fermilab by a team led by Brad Benson, using many of the facilities previously developed for the Dark Energy Camera and the QUIET polarization experiment, before being shipped to the South Pole.

    South Pole Telescope
    South Pole Telescope

    Fermilab DECam
    DECam

    Plans are also under way for an even more ambitious fourth-generation cosmic microwave background polarization experiment, by a larger consortium of national labs and universities. A recent APS Community Summer Study (“Snowmass“) report, co-led by Fermilab’s Scott Dodelson, identified such an experiment, in synergy with other surveys, as a unique opportunity to study many aspects of new physics, including neutrino masses, new relativistic species (so-called dark radiation) and dark energy. A study group proposes to expand CMB polarization capabilities by another order of magnitude beyond SPT-3G, including the addition of more telescopes to access more of the sky not visible from the South Pole. The new discovery extends and enriches the science reach of this enterprise to a new and deeper level — one we had hardly dared to dream about until this week.

    See the full article here.

    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics.


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