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  • richardmitnick 2:00 pm on April 28, 2018 Permalink | Reply
    Tags: A DIY take on the early universe may reveal cosmic secrets, Alan Guth - Inflation, , , , COSMIC LOOP A rapidly expanding ring of ultracold atoms imitates the physics of the universe just after the Big Bang, ,   

    From ScienceNews: “A DIY take on the early universe may reveal cosmic secrets” 


    ScienceNews

    April 27, 2018
    Emily Conover

    A rapidly expanding ring of ultracold atoms mimics the physics just after the Big Bang.

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    COSMIC LOOP A rapidly expanding ring of ultracold atoms imitates the physics of the universe just after the Big Bang. E. Edwards/JQI.

    A DIY universe mimics the physics of the infant cosmos, a team of physicists reports. The researchers hope to use their homemade cosmic analog to help explain the first instants of the universe’s 13.8-billion-year life.

    For their stand-in, the scientists created a Bose-Einstein condensate — a state of matter in which atoms are chilled until they all take on the same quantum state. Shaped into a tiny, rapidly expanding ring, the condensate grew from about 23 micrometers in diameter to about four times that size in just 15 milliseconds. The behavior of that widening condensate re-created some of the physics of inflation, a brief period just after the Big Bang during which the universe rapidly ballooned in size (SN Online: 12/11/13) before settling into a more moderate expansion rate.

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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

    Alan Guth’s notes:
    5

    In physics, seemingly unrelated systems can have similarities under the hood. Scientists have previously used Bose-Einstein condensates to simulate other mysteries of the cosmos, such as black holes (SN: 11/15/14, p. 14). And the comparison between Bose-Einstein condensates and inflation is particularly apt: A hypothetical substance called the inflaton field is thought to drive the universe’s extreme expansion, and particles associated with that field, known as inflatons, all take on the same quantum state, just as atoms do in the condensate.

    Scientists still don’t fully understand how inflation progressed, “so it’s hard to know how close our system is to what really happened,” says experimental physicist Gretchen Campbell of the Joint Quantum Institute in College Park, Md. “But the hope is that our system can be a good test-bed” for studying various theories. Already, the scientists have spotted several effects in their system similar to those predicted in the baby cosmos, the team reports April 19 in Physical Review X.

    As the scientists expanded the ring, sound waves that were traveling through the condensate increased in wavelength. That change was similar to the way in which light became redshifted — stretched to longer wavelengths and redder colors — as the universe enlarged.

    Nice ring to it
    To mimic the physics of inflation in the early universe, scientists rapidly expanded a ring-shaped Bose-Einstein condensate, which decreased in density as it expanded over 15 milliseconds.
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    S. Eckel et al/Physical Review X 2018

    Likewise, Campbell and colleagues saw a phenomenon akin to what’s known as Hubble friction, which shows up as a decrease in the density of particles in the early universe. In the experiment, this effect appeared in the guise of a weakening in the strength of the sound waves in the condensate.

    And inflation’s finale, an effect known as preheating that occurs at the end of the rapid expansion period, also had a look-alike in the simulated universe. In the cosmic picture, preheating occurs when inflatons transform into other types of particles. In the condensate, this showed up as sound waves converting from one type into another: waves that had been sloshing inward and outward broke up into waves going around the ring.

    However, the condensate wasn’t a perfect analog of the real universe: In particular, while our universe has three spatial dimensions, the expanding ring didn’t. Additionally, in the real universe, inflation proceeds on its own, but in this experiment, the researchers forced the ring to expand. Likewise, there were subtle differences between each of the effects observed and their cosmic counterparts.

    Despite the differences, the analog universe could be useful, says theoretical cosmologist Mustafa Amin of Rice University in Houston. “Who knows?” he says. “New phenomena might happen there that we haven’t thought about in the early universe.”

    Sometimes, when research crosses over between very different systems — such as Bose-Einstein condensates and the early universe — “sparks can fly,” Amin says.

    See the full article here .

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  • richardmitnick 4:00 pm on December 28, 2017 Permalink | Reply
    Tags: Alan Guth - Inflation, , , Can Bose-Einstein condensates simulate cosmic inflation?, ,   

    From physicsworld.com: “Can Bose-Einstein condensates simulate cosmic inflation?” 

    physicsworld
    physicsworld.com

    Dec 28, 2017
    Tim Wogan

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    Rolling downhill: illustration of a coherent quantum phase transition

    Cosmological inflation, first proposed by Alan Guth in 1979, describes a hypothetical period when the early Universe expanded faster than the speed of light.

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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

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

    The model, which answers fundamental questions about the formation of the Universe we know today, has become central to modern cosmology, but many details remain uncertain. Now atomic physicists in the US have developed a laboratory analogue by shaking a Bose-Einstein condensate (BEC). The team’s initial results suggest that the Universe may have remained quantum coherent throughout inflation and beyond. The researchers hope their condensate model may provide further insights into inflation in a more accessible system, however not everyone agrees on its usefulness.

    Dynamical instability occurs in all sorts of physical systems that are out of equilibrium. A ball perched at the top of a hill, for example, may stay put for short time. But the tiniest perturbation will send the ball falling towards a lower-energy state at the bottom of the hill. Guth realized that a very short, very rapid period of expansion could occur if the Universe got stuck out of equilibrium around 10-35 s after the Big Bang, causing it to expand by a factor of around 1026 in a tiny fraction of a second. The details of the inflationary model have been revised many times, and numerous questions remain. “This is where I can contribute, even though I’m not a cosmologist,” says Cheng Chin of the University of Chicago in Illinois: “We have only one Universe, so it becomes very hard to say whether our theories really capture the whole physics as we can’t repeat the experiment.”

    Shake it up

    Chin and colleagues created their model system by cooling 30,000 atoms in an optical trap into a BEC, in which all the atoms occupy a single quantum state. Initially, this BEC was sitting still in the centre of the trap. The researchers then began to shake the condensate by moving the trapping potential from side to side with increasing amplitude. This raised the energy of the state in which the condensate was stationary relative to the trapping potential. When the shaking amplitude was increased past a critical value, the energy of this “stationary” state became higher than the energy of two other states with the condensate oscillating in opposite directions inside the trap. The condensate therefore underwent a dynamical phase transition, splitting into two parts that each entered one of these two momentum states.

    Between 20-30 ms after the phase transition, the researchers saw a clear interference pattern in the density of the condensate. This shows, says Chin, that the condensate had undergone a quantum coherent separation, with each atom entering a superposition of both momentum states. After this, the clear interference pattern died out. This later period corresponds, says Chin, to the period of cosmological relaxation in which, after inflation had finished, different parts of the Universe relaxed to their new ground states. More detailed analysis of the condensate in this phase showed that, although its quantum dynamics were more complicated – with higher harmonics of the oscillation frequencies becoming more prominent – the researchers’ observations could not be described classically.

    Chin says that cosmologists may find this observation interesting. Although “in principle, everything is quantum mechanical,” he explains, the practical impossibility of performing a full quantum simulation of the Universe as its complexity grows leads cosmologists to fall back on classical models. “The value of our research is to try and point out that we shouldn’t give up [on quantum simulation] that early,” he says. “Even in inflation and the subsequent relaxation process, we have one concrete example to show that quantum mechanics and coherence still play a very essential role.”

    Inflated claims?

    James Anglin of the University of Kaiserslautern in Germany is impressed by the research. “Understanding what happens to small initial quantum fluctuations after a big instability has saturated is an important and basic question in physics, and it really is an especially relevant question for cosmology,” he explains. “The big difference, of course, is that the cosmic inflation scenario includes gravity as curved spacetime in general relativity, such that space expands enormously while the inflaton field [the field thought to drive inflation] finds its true ground state. A malicious critic might say that this experiment is a perfect analogue for cosmological inflation, except for the inflation part.”

    “This is indeed nice work,” he concludes: “The language is simply a little bit inflated!” The research is described in Nature Physics.

    See the full article here .

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  • richardmitnick 12:56 pm on November 25, 2017 Permalink | Reply
    Tags: Alan Guth - Inflation, , , , , , , Scientific Theories Never Die Not Unless Scientists Choose To Let Them   

    From Ethan Siegel: “Scientific Theories Never Die, Not Unless Scientists Choose To Let Them” 

    From Ethan Siegel

    Nov 23, 2017

    As wonderful as the evidence that supports or invalidates a theory is, it can never truly kill the ones that don’t work out.

    When it comes to science, we like to think that we formulate hypotheses, test them, throw away the ones that fail to match, and continue testing the successful one until only the best ideas are left. But the truth is a lot muddier than that. The actual process of science involves tweaking your initial hypothesis over and over, trying to pull it in line with what we already know. It involves a leap-of-faith that when you formulate your theory correctly, the predictions it makes will be even more successful, across-the-board, than any other alternatives. And when things don’t work out, it doesn’t always necessitate abandoning your original hypothesis. In fact, most scientists don’t. In a very real way, scientific theories can never truly be killed. The only way they ever go away is if people stop working on them.

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    Without dark energy, the Universe wouldn’t be accelerating. But to explain the distant supernovae we see, among other features, dark energy (or something that mimics it exactly) appears to be necessary. Image credit: NASA & ESA, of possible models of the expanding Universe.

    When distant supernovae were first discovered to be fainter than they otherwise should have been based on their redshift, it brought about a revolution in cosmology. The way the Universe expands is inextricably linked to the matter and energy present within it, and so the goal of cosmology, for a long time, was to measure the expansion rate and how it changes over time.

    The expectation was that it would either recollapse or expand forever, or remain in an in-between state right on the border between those two. Instead, these supernovae showed that a fourth option was most likely: the most distant galaxies of all were speeding up as they moved away from us. There must be some new form of energy in the Universe — dark energy — different from all other forms of energy, permeating all of space.

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    The Bubble Nebula is on the outskirts of a supernova remnant occurring thousands of years ago. If distant supernovae are in dustier environments than their modern-day counterparts, perhaps they’re not indicative of dark energy after all. Image credit: T.A. Rector/University of Alaska Anchorage, H. Schweiker/WIYN and NOAO/AURA/NSF.


    NOAO WIYN 3.5 meter telescope at Kitt Peak, AZ, USA, Altitude 2,096 m (6,877 ft)

    But for many years, most physicists and astronomers approached this idea with skepticism, wondering if there weren’t another explanation. Perhaps, one alternative theory posited, space wasn’t expanding with an extra value due to some form of dark energy, but rather there was something occurring at large distances to block the light. So that became a proposition: there was some additional dust in the distant Universe, and the reason the supernovae appeared fainter wasn’t because they were farther away due to an extra expansion of space, but because dust was blocking the light.

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    Infrared light penetrates more dust and gas than visible light, allowing details to become visible in this nebula. Similarly, blue light is blocked preferentially compared to red light, indicating that if dust were responsible for dimming supernovae, they’d appear different in color from their nearby counterparts. Image credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA), and J. Hester.

    NASA/ESA Hubble Telescope

    Dust grains, however, come in particular sizes, and the size of the dust grains determines which wavelengths of light are preferentially blocked, with most dust better at blocking blue than red light. Measurements of different wavelengths of light, however, showed that both red and blue light were reduced by equal amounts.

    Was that sufficient to rule out the “dust” theory? In that incarnation, yes. But what if the dust in the distant Universe was of a new type, that blocked all the wavelengths of light equally? This undiscovered type of dust, dubbed “grey dust,” could block all wavelengths equally. So we needed some way to put that to the test, and that involved looking at supernovae at a variety of distances, to see whether dust would continue to block more and more light at greater distances, as more and more “grey dust” would tend to do.

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    The observation of even more distant supernovae allowed us to discern the difference between ‘grey dust’ and dark energy, ruling the former out. But the modification of ‘replenishing grey dust’ is still indistinguishable from dark energy. Image credit: A.G. Riess et al. (2004), The Astrophysical Journal, Volume 607, Number 2.

    It didn’t. So does that mean dark energy must be real? Not necessarily, because you can modify your “grey dust” explanation to include dust that changes in density and location over time: “replenishing grey dust.” By the addition of enough extra free parameters, caveats, behaviors, or modifications to your theory, you can literally salvage any idea. As long as you’re willing to tweak what you’ve come up with sufficiently, you can never rule anything out.

    There have been many ideas in this vein that have the same problem (or feature) inherent to them: so long as you’re willing to make the theory more complicated, you can fit any data that comes back. The discovery of the CMB ruled out the Steady-State theory, but they added reflected starlight to explain that leftover glow. When the spectrum of the CMB was measured, ruling out reflected starlight, they added a series of bursts and “mini-bangs” in the past, creating a Quasi-Steady-State theory. When the fluctuations in the CMB’s temperature were discovered, ruling that out, its proponents tweaked it still further.

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    Three different types of measurements, distant stars and galaxies, the large scale structure of the Universe, and the fluctuations in the CMB, tell us the expansion history of the Universe, and rule out alternatives to the Big Bang. Image credit: NASA/ESA Hubble (top L), SDSS (top R), ESA and the Planck Collaboration (bottom).

    SDSS Telescope at Apache Point Observatory, NM, USA, Altitude 2,788 meters (9,147 ft)

    ESA/Planck

    This behavior isn’t unique to scientists, but has been a feature (or bug) of science for centuries. It led Max Planck, more than 100 years ago, to make the following now-famous statement:

    “A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it.”

    This is often paraphrased as “physics advances one funeral at a time,” owing to the fact that ideas cannot be proven wrong as we commonly think. Rather, they need to be tweaked so thoroughly and so frequently that they lose their predictive power, instead always playing catch-up as new observations come in.

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    Combining quantum field theory and the standard model of particle physics with General Relativity enables us to calculate practically everything we can conceive of in the Universe at a fundamental level. Image credit: SLAC National Accelerator Laboratory.

    SLAC Campus

    It’s why theories like quantum field theory and general relativity are so powerful: even after all these decades, they’re still making new predictions that are being successfully borne out by experiment. It’s why dark matter is here to stay, as its successful predictions include the speeds of galaxy pairs, the large-scale cosmic web, the fluctuations in the CMB, baryon acoustic oscillations, gravitational lensing and more. It’s why cosmic inflation — with its successful predictions including superhorizon fluctuations, the acoustic peaks in the Big Bang’s leftover glow, the departure from scale invariance, etc. — is the leading theory for the origin of the Big Bang. And it’s why their alternatives are so thoroughly fringe.

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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

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

    5
    As ripples through space arising from distant gravitational waves pass through our Solar System, including Earth, they ever-so-slightly compress and expand the space around them. Alternatives can be constrained incredibly tightly thanks to our measurements in this regime. Image credit: European Gravitational Observatory, Lionel BRET/EUROLIOS.

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    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    You can always add another loophole, parameter, or epicycle to your own pet theory to make it be “not ruled out.” I, along with most physicists, feel this way about a great many non-standard alternatives, including MOND, f(R) gravity, the Quasi-Steady-State model, tired-light cosmology, the plasma Universe, and so on. At some point, you just have to say “enough.” You have to recognize that the level of contortions you need to perform are absurd, and that these theories don’t have any useful predictive power. They’re simply an example of special pleading.

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    The warm-hot intergalactic medium (WHIM) has been seen before, along incredibly overdense regions, like the Sculptor wall, illustrated above. But it’s conceivable that there are still surprises out there in the Universe, and our current understanding will once again be subject to a revolution. Image credit: Spectrum: NASA/CXC/Univ. of California Irvine/T. Fang. Illustration: CXC/M. Weiss.

    Of course, their adherents don’t think so. They think they’re being marginalized, oppressed, ignored, or not taken seriously. On very rare occasion, they’re actually correct, and that’s when a scientific revolution occurs. It’s important to keep your mind open to those possibilities, to explore them, and to consider what it would look like if these alternatives were correct after all. But for the overwhelming majority of scientists working on these alternative ideas, their life’s work will turn out to be a blind alley, and their ideas will die out when they (and possibly their students) die. It’s both sad and tragic to look back at history and realize that the last decades of the scientific careers of Einstein, Hoyle, Burbidge, Schrodinger, and many more were a total waste. But whether even the most brilliant scientist accepts a new scientific truth or not is irrelevant. Our knowledge and understanding march forward.

    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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