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  • richardmitnick 8:58 am on April 22, 2019 Permalink | Reply
    Tags: "Before the Big Bang", , , , Cosmic Inflation, Cosmic microwave background [CMB] radiation, , , Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey   

    From Harvard Gazette: “Before the Big Bang” 


    Harvard University


    From Harvard Gazette

    April 18, 2019
    Peter Reuell

    Study outlines new proposal for probing the primordial universe.

    1
    NASA WMAP

    Most everybody is familiar with the Big Bang — the notion that an impossibly hot, dense universe exploded into the one we know today. But what do we know about what came before?

    In the quest to resolve several puzzles discovered in the initial condition of the Big Bang, scientists have developed a number of theories to describe the primordial universe, the most successful of which — known as cosmic inflation — describes how the universe dramatically expanded in size in a fleeting fraction of a second right before the Big Bang.

    Inflation

    4
    Alan Guth, from 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

    But as successful as the inflationary theory has been, controversies have led to active debates over the years.

    Some researchers have developed very different theories to explain the same experimental results that have supported the inflationary theory so far. In some of these theories, the primordial universe was contracting instead of expanding, and the Big Bang was thus a part of a Big Bounce.

    Some researchers — including Avi Loeb, the Frank B. Baird, Jr. Professor of Science and chair of the Astronomy Department — have raised concerns about the theory, suggesting that its seemingly endless adaptability makes it all but impossible to test.

    “The current situation for inflation is that it’s such a flexible idea … it cannot be falsified experimentally,” Loeb said. “No matter what result of the observable people set out to measure would turn out to be, there are always some models of inflation that can explain it.” Therefore, experiments can only help to nail down some model details within the framework of the inflationary theory, but cannot test the validity of the framework itself. However, falsifiability should be a hallmark of any scientific theory.

    That’s where Xingang Chen comes in.

    1
    Xingang Chen is one of the authors of a new study that examines what the universe looked like before the Big Bang. Jon Chase/Harvard Staff Photographer.

    A senior lecturer in astronomy, Chen and his collaborators for many years have been developing the idea of using something he called a “primordial standard clock” as a probe of the primordial universe. Together with Loeb and Zhong-Zhi Xianyu, a postdoctoral researcher in the Physics Department, Chen applied this idea to the noninflationary theories after he learned about an intense debate in 2017 that questioned whether inflationary theories make any predictions at all. In a paper published as an Editor’s Suggestion in Physical Review Letters, the team laid out a method that may be used to falsify the inflationary theory experimentally.

    In an effort to find some characteristic that can separate inflation from other theories, the team began by identifying the defining property of the various theories — the evolutionary history of the size of the primordial universe. “For example, during inflation, by definition the size of the universe grows exponentially,” Xianyu said. “In some alternative theories, the size of the universe contracts — in some very slowly and in some very fast.

    “The conventional observables people have proposed so far have trouble distinguishing the different theories because these observables are not directly related to this property,” he continued. “So we wanted to find what the observables are that can be linked to that defining property.”

    The signals generated by the primordial standard clock can serve this purpose.

    That clock, Chen said, is any type of massively heavy elementary particle in the energetic primordial universe. Such particles should exist in any theory, and they oscillate at some regular frequency, much like the swaying of a clock’s pendulum.

    The primordial universe was not entirely uniform. Quantum fluctuations became the seeds of the large-scale structure of today’s universe and one key source of information physicists rely on to learn about what happened before the Big Bang. The theory outlined by Chen suggests that ticks of the standard clock generated signals that were imprinted into the structure of those fluctuations. And because standard clocks in different primordial universes would leave different patterns of signals, Chen said, they may be able to determine which theory of the primordial universe is most accurate.

    “If we imagine all the information we learned so far about what happened before the Big Bang is in a roll of film frames, then the standard clock tells us how these frames should be played,” Chen explained. “Without any clock information, we do not know if the film should be played forward or backward, fast or slow — just like we are not sure if the primordial universe was inflating or contracting, and how fast it did that. This is where the problem lies. The standard clock put time stamps on each of these frames when the film was shot before the Big Bang, and tells us what this film is about.”

    The team calculated how these standard clock signals should look in noninflationary theories, and suggested how to search for them in astrophysical observations. “If a pattern of signals representing a contracting universe were found,” Xianyu said, “it would falsify the entire inflationary theory, regardless of what detailed models one constructs.”

    The success of this idea lies in experimentation. “These signals will be very subtle to detect,” Chen said. “Our proposal is that there should be some kind of massive fields that have generated these imprints and we computed their patterns, but we don’t know how large the overall amplitude of these signals is. It may be that they are very faint and very hard to detect, so that means we will have to search in many different places.

    “The cosmic microwave background [CMB] radiation is one place,” he continued. “The distribution of galaxies is another. We have already started to search for these signals and there are some interesting candidates already, but we still need more data.”

    Cosmic Background Radiation per Planck

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

    See the full article here .

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    Harvard University campus
    Harvard University is the oldest institution of higher education in the United States, established in 1636 by vote of the Great and General Court of the Massachusetts Bay Colony. It was named after the College’s first benefactor, the young minister John Harvard of Charlestown, who upon his death in 1638 left his library and half his estate to the institution. A statue of John Harvard stands today in front of University Hall in Harvard Yard, and is perhaps the University’s best known landmark.

    Harvard University has 12 degree-granting Schools in addition to the Radcliffe Institute for Advanced Study. The University has grown from nine students with a single master to an enrollment of more than 20,000 degree candidates including undergraduate, graduate, and professional students. There are more than 360,000 living alumni in the U.S. and over 190 other countries.

     
  • richardmitnick 11:31 am on January 8, 2019 Permalink | Reply
    Tags: , Antiuniverse, , Cosmic Inflation, CPT symmetry, , Our universe has antimatter partner on the other side of the Big Bang say physicists, , , , The entity that respects the symmetry is a universe–antiuniverse pair   

    From physicsworld.com: “Our universe has antimatter partner on the other side of the Big Bang, say physicists” 

    physicsworld
    From physicsworld.com

    03 Jan 2019

    1
    (Courtesy: shutterstock/tomertu)

    Our universe could be the mirror image of an antimatter universe extending backwards in time before the Big Bang. So claim physicists in Canada, who have devised a new cosmological model positing the existence of an “antiuniverse” [Physical Review Letters] which, paired to our own, preserves a fundamental rule of physics called CPT symmetry. The researchers still need to work out many details of their theory, but they say it naturally explains the existence of dark matter.

    Standard cosmological models tell us that the universe – space, time and mass/energy – exploded into existence some 14 billion years ago and has since expanded and cooled, leading to the progressive formation of subatomic particles, atoms, stars and planets.

    However, Neil Turok of the Perimeter Institute for Theoretical Physics in Ontario reckons that these models’ reliance on ad-hoc parameters means they increasingly resemble Ptolemy’s description of the solar system. One such parameter, he says, is the brief period of rapid expansion known as inflation that can account for the universe’s large-scale uniformity. “There is this frame of mind that you explain a new phenomenon by inventing a new particle or field,” he says. “I think that may turn out to be misguided.”

    Instead, Turok and his Perimeter Institute colleague Latham Boyle set out to develop a model of the universe that can explain all observable phenomena based only on the known particles and fields. They asked themselves whether there is a natural way to extend the universe beyond the Big Bang – a singularity where general relativity breaks down – and then out the other side. “We found that there was,” he says.

    The answer was to assume that the universe as a whole obeys CPT symmetry. This fundamental principle requires that any physical process remains the same if time is reversed, space inverted and particles replaced by antiparticles. Turok says that this is not the case for the universe that we see around us, where time runs forward as space expands, and there’s more matter than antimatter.

    2
    In a CPT-symmetric universe, time would run backwards from the Big Bang and antimatter would dominate (L Boyle/Perimeter Institute of Theoretical Physics)

    Instead, says Turok, the entity that respects the symmetry is a universe–antiuniverse pair. The antiuniverse would stretch back in time from the Big Bang, getting bigger as it does so, and would be dominated by antimatter as well as having its spatial properties inverted compared to those in our universe – a situation analogous to the creation of electron–positron pairs in a vacuum, says Turok.

    Turok, who also collaborated with Kieran Finn of Manchester University in the UK, acknowledges that the model still needs plenty of work and is likely to have many detractors. Indeed, he says that he and his colleagues “had a protracted discussion” with the referees reviewing the paper for Physical Review Letters [link is above] – where it was eventually published – over the temperature fluctuations in the cosmic microwave background. “They said you have to explain the fluctuations and we said that is a work in progress. Eventually they gave in,” he says.

    In very broad terms, Turok says, the fluctuations are due to the quantum-mechanical nature of space–time near the Big Bang singularity. While the far future of our universe and the distant past of the antiuniverse would provide fixed (classical) points, all possible quantum-based permutations would exist in the middle. He and his colleagues counted the instances of each possible configuration of the CPT pair, and from that worked out which is most likely to exist. “It turns out that the most likely universe is one that looks similar to ours,” he says.

    Turok adds that quantum uncertainty means that universe and antiuniverse are not exact mirror images of one another – which sidesteps thorny problems such as free will.

    But problems aside, Turok says that the new model provides a natural candidate for dark matter. This candidate is an ultra-elusive, very massive particle called a “sterile” neutrino hypothesized to account for the finite (very small) mass of more common left-handed neutrinos. According to Turok, CPT symmetry can be used to work out the abundance of right-handed neutrinos in our universe from first principles. By factoring in the observed density of dark matter, he says that quantity yields a mass for the right-handed neutrino of about 5×108 GeV – some 500 million times the mass of the proton.

    Turok describes that mass as “tantalizingly” similar to the one derived from a couple of anomalous radio signals spotted by the Antarctic Impulsive Transient Antenna (ANITA). The balloon-borne experiment, which flies high over Antarctica, generally observes cosmic rays travelling down through the atmosphere. However, on two occasions ANITA appears to have detected particles travelling up through the Earth with masses between 2 and 10×108 GeV. Given that ordinary neutrinos would almost certainly interact before getting that far, Thomas Weiler of Vanderbilt University and colleagues recently proposed that the culprits were instead decaying right-handed neutrinos [Letters in High Energy Physics].

    Turok, however, points out a fly in the ointment – which is that the CPT symmetric model requires these neutrinos to be completely stable. But he remains cautiously optimistic. “It is possible to make these particles decay over the age of the universe but that takes a little adjustment of our model,” he says. “So we are still intrigued but I certainly wouldn’t say we are convinced at this stage.”

    See the full article here .


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    Perimeter Institute is the world’s largest research hub devoted to theoretical physics. The independent Institute was founded in 1999 to foster breakthroughs in the fundamental understanding of our universe, from the smallest particles to the entire cosmos. Research at Perimeter is motivated by the understanding that fundamental science advances human knowledge and catalyzes innovation, and that today’s theoretical physics is tomorrow’s technology. Located in the Region of Waterloo, the not-for-profit Institute is a unique public-private endeavour, including the Governments of Ontario and Canada, that enables cutting-edge research, trains the next generation of scientific pioneers, and shares the power of physics through award-winning educational outreach and public engagement.

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  • richardmitnick 10:32 pm on September 10, 2018 Permalink | Reply
    Tags: , Big Bang theory, Cosmic Inflation, , ,   

    From Stanford University: “The String Theory Landscape” 

    Stanford University Name
    From Stanford University

    September 10, 2018
    Ker Than

    1
    The String Theory Landscape combines elements of string theory and cosmic inflation to greatly expand the scope of the Big Bang theory to incorporate the idea of infinite universes in a vast multiverse. (Image credit: Eric Nyquist)

    The most recent update to the Big Bang theory, called the String Theory Landscape, arose out of elements of string theory and cosmic inflation.

    Inflation

    4
    Alan Guth, from 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

    The theory’s inclusion of a multiverse and its denial of immutable physical laws has raised debates that continue to this day. This story is part 1 of a five-part series.

    The Big Bang theory describes the abrupt origins of space and time from a swiftly unfurling singularity – a hot, dense point of pure potential, packed impossibly full with eternity and the rudiments of creation. As with the universe it seeks to explain, the theory is endlessly evolving. Ever since its proposal nearly a century ago, physicists have revised and remade it to reflect new scientific concepts and discoveries.

    The latest draft of the scientific story of genesis is called the String Theory Landscape. Entwined at its heart are two of the strangest and most enduring ideas in modern physics – string theory and cosmic inflation – which Stanford physicists helped bring together nearly two decades ago.

    String theory asserts that the basic building blocks of reality are vibrating, one-dimensional loops of energy that quiver in 10 or more dimensions to strum out the elementary particles and fundamental forces of nature.

    Cosmic inflation holds that the Big Bang began with a period of exponential expansion that swelled our universe from a fragile quantum speck to a vast manor of emptiness a quarter-billion-light-years wide in a flicker of a flicker of time.

    According to the theory, this heavenly sprawl still occurs in distant corners of the cosmos, spinning out a web of related daughter universes that connect to form a much larger “multiverse.”

    For decades, the two theories circled one another, each advancing along a seemingly unique track and independently gaining momentum among physicists, until an unexpected discovery drove them together. The String Theory Landscape was born in the wake of their collision – and physics has never been quite the same since.

    It was an “earthquake that caused enormous consternation and controversy among theoretical physicists,” wrote Leonard Susskind, the Felix Bloch Professor in Physics at Stanford’s School of Humanities and Sciences, in his 2005 book The Cosmic Landscape.

    ____________________________________________________

    “It probably bothered the first human beings who realized that the world was not just their local valley. It probably terrified them a little bit, but by now we’re used to the world getting bigger and bigger. The String Theory Landscape just says it’s way bigger than we thought.”

    —Leonard Susskind

    Professor of Physics

    ____________________________________________________

    An old debate

    The String Theory Landscape rekindled the ashes of an old debate in physics, one that smolders to this day. On one side are those who contend, as Albert Einstein once did, that the laws of nature are elegant, immutable and inevitable, and that they can be discovered and described through mathematics. In contrast, most Landscape proponents believe that while the underlying equations of string theory may be simple and elegant, the solutions to those equations are tremendously complex and infinitely diverse.

    This diversity, they say, is key to explaining certain baffling features of our universe, like the fact that several parameters in physics and cosmology appear to be curiously fine-tuned for life forms like us to exist. Perhaps the most glaring example is the cosmological constant, which relates to a universal repulsive force that is pushing space-time apart. Physicists have struggled to explain why the tiny value of this constant just happens to lie within the narrow band that allows stars and planets to form and biological life to evolve. But if there are innumerable universes, each with differing laws of physics, then it should not be surprising that we inhabit one where the cosmological constant is small – if things were any different, we could not exist to marvel at the coincidence.

    “The String Theory Landscape potentially explains many properties of our world,” said physicist Andrei Linde, the Harald Trap Friis Professor at Stanford. “It may explain not just the cosmological constant, but also why the mass of the proton and neutron are almost exactly the same, why the electron mass is so small, and why we live in a universe with three dimensions of space and not 10. There is no other theory that can do that.”

    The String Theory Landscape also rouses fierce emotions because it touches upon questions that cut to the heart of modern physics and science in general. If gravity’s strength can vary from one universe to the next, what is the point of trying to understand its extraordinary weakness in our universe? And if a theory can’t make testable predictions, is it still science? “One dominant view in the community is that believing in the Landscape might have the negative effect of leading people away from fundamental physics, so we shouldn’t even discuss it,” said Shamit Kachru, who holds the Wells Family Directorship of the Stanford Institute for Theoretical Physics (SITP).

    Landscape supporters say the theory is just the latest helping of humble pie that humanity has had to swallow as its sense of privilege in the universe has been slowly effaced by centuries of scientific progress. “It probably bothered the first human beings who realized that the world was not just their local valley,” Susskind said. “It probably terrified them a little bit, but by now we’re used to the world getting bigger and bigger. The String Theory Landscape just says it’s way bigger than we thought.”

    See the full article here .


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    Stanford University campus. No image credit

    Leland and Jane Stanford founded the University to “promote the public welfare by exercising an influence on behalf of humanity and civilization.” Stanford opened its doors in 1891, and more than a century later, it remains dedicated to finding solutions to the great challenges of the day and to preparing our students for leadership in today’s complex world. Stanford, is an American private research university located in Stanford, California on an 8,180-acre (3,310 ha) campus near Palo Alto. Since 1952, more than 54 Stanford faculty, staff, and alumni have won the Nobel Prize, including 19 current faculty members

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  • richardmitnick 2:42 pm on July 28, 2018 Permalink | Reply
    Tags: , , , , Cosmic Inflation, , , , Hubble Constant not so constant   

    From European Space Agency: “From an almost perfect Universe to the best of both worlds” 

    ESA Space For Europe Banner

    From European Space Agency

    Jan Tauber
    ESA Planck Project Scientist
    European Space Agency
    Email: jan.tauber@esa.int

    Markus Bauer
    ESA Science Communication Officer
    Tel: +31 71 565 6799
    Mob: +31 61 594 3 954
    Email: markus.bauer@esa.int

    17 July 2018

    The Planck consortium has made their final data release, including new processing of the cosmic microwave background temperature and polarisation data. This legacy dataset confirms the model of an ‘almost perfect Universe’, with some remaining oddities giving researchers some intriguing details to puzzle over.

    1
    The Cosmic Microwave Background – as seen by Planck. Credit: ESA and the Planck Collaboration

    ESA/Planck 2009 to 2013

    It was 21 March 2013. The world’s scientific press had either gathered in ESA’s Paris headquarters or logged in online, along with a multitude of scientists around the globe, to witness the moment when ESA’s Planck mission revealed its ‘image’ of the cosmos. This image was taken not with visible light but with microwaves.

    Whereas light that our eyes can see is composed of small wavelengths – less than a thousandth of a millimetre in length – the radiation that Planck was detecting spanned longer wavelengths, from a few tenths of a millimetre to a few millimetres. Most importantly, it had been generated at very beginning of the Universe.

    Collectively, this radiation is known as the cosmic microwave background, or CMB. By measuring its tiny differences across the sky, Planck’s image had the ability to tell us about the age, expansion, history, and contents of the Universe. It was nothing less than the cosmic blueprint.

    Astronomers knew what they were hoping to see. Two NASA missions, COBE in the early 1990s and WMAP in the following decade, had already performed an analogous set of sky surveys that resulted in similar images. But those images did not have the precision and sharpness of Planck.

    The new view would show the imprint of the early Universe in painstaking detail for the first time. And everything was riding on it.

    If our model of the Universe were correct, then Planck would confirm it to unprecedented levels of accuracy. If our model were wrong, Planck would send scientists back to the drawing board.

    When the image was revealed, the data had confirmed the model. The fit to our expectations was too good to draw any other conclusion: Planck had showed us an ‘almost perfect Universe’. Why almost perfect? Because a few anomalies remained, and these would be the focus of future research.

    Now, five years later, the Planck consortium has made their final data release, known as the legacy data release. The message remains the same, and is even stronger.

    2
    Planck’s view of the sky in nine channels at microwave and sub-millimetre wavelenghts.
    Credit: ESA and the Planck Collaboration, animated

    “This is the most important legacy of Planck,” says Jan Tauber, ESA’s Planck Project Scientist. “So far the standard model of cosmology has survived all the tests, and Planck has made the measurements that show it.”

    Standard Model of Cosmology Timeline

    Standard Model of Cosmology Cornell

    All cosmological models are based upon Albert Einstein’s General Theory of Relativity. To reconcile the general relativistic equations with a wide range of observations, including the cosmic microwave background, the standard model of cosmology includes the action of two unknown components.

    Firstly, an attractive matter component, known as cold dark matter, which unlike ordinary matter does not interact with light. Secondly, a repulsive form of energy, known as dark energy, which is driving the currently accelerated expansion of the Universe. They have been found to be essential components to explain our cosmos in addition to the ordinary matter we know about. But as yet we do not know what these exotic components actually are.

    Planck was launched in 2009 and collected data until 2013. Its first release – which gave rise to the almost perfect Universe – was made in the spring of that year. It was based solely on the temperature of the cosmic microwave background radiation, and used only the first two sky surveys from the mission.

    The data also provided further evidence for a very early phase of accelerated expansion, called inflation, in the first tiny fraction of a second in the Universe’s history, during which the seeds of all cosmic structures were sown. Inflation

    4
    Alan Guth, from 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

    Yielding a quantitative measure of the relative distribution of these primordial fluctuations, Planck provided the best confirmation ever obtained of the inflationary scenario.

    Besides mapping the temperature of the cosmic microwave background across the sky with unprecedented accuracy, Planck also measured its polarisation, which indicates if light is vibrating in a preferred direction. The polarisation of the cosmic microwave background carries an imprint of the last interaction between the radiation and matter particles in the early Universe, and as such contains additional, all-important information about the history of the cosmos. But it could also contain information about the very first instants of our Universe, and give us clues to understand its birth.

    In 2015, a second data release folded together all data collected by the mission, which amounted to eight sky surveys. It gave temperature and polarisation but came with a caution.

    “We felt the quality of some of the polarisation data was not good enough to be used for cosmology,” says Jan. He adds that – of course – it didn’t prevent them from doing cosmology with it but that some conclusions drawn at that time needed further confirmation and should therefore be treated with caution.

    And that’s the big change for this 2018 Legacy data release. The Planck consortium has completed a new processing of the data. Most of the early signs that called for caution have disappeared. The scientists are now certain that both temperature and polarisation are accurately determined.

    “Now we really are confident that we can retrieve a cosmological model based on solely on temperature, solely on polarisation, and based on both temperature and polarisation. And they all match,” says Reno Mandolesi, principal investigator of the LFI instrument on Planck at the University of Ferrara, Italy.

    “Since 2015, more astrophysical data has been gathered by other experiments, and new cosmological analyses have also been performed, combining observations of the CMB at small scales with those of galaxies, clusters of galaxies, and supernovae, which most of the time improved the consistency with Planck data and the cosmological model supported by Planck,” says Jean-Loup Puget, principal investigator of the HFI instrument on Planck at the Institut d’Astrophysique Spatiale in Orsay, France.

    This is an impressive feat and means that cosmologists can be assured that their description of the Universe as a place containing ordinary matter, cold dark matter and dark energy, populated by structures that had been seeded during an early phase of inflationary expansion, is largely correct.

    But there are some oddities that need explaining – or tensions as cosmologists call them. One in particular is related to the expansion of the Universe. The rate of this expansion is given by the so-called Hubble Constant.

    To measure the Hubble constant astronomers have traditionally relied on gauging distances across the cosmos. They can only do this for the relatively local Universe by measuring the apparent brightness of certain types of nearby variable stars and exploding stars, whose actual brightness can be estimated independently. It is a well-honed technique that has been developed over the course of the last century, pioneered by Henrietta Leavitt and later applied, in the late 1920s, by Edwin Hubble and collaborators, who used variable stars in distant galaxies and other observations to reveal that the Universe was expanding.

    The figure astronomers derive for the Hubble Constant using a wide variety of cutting-edge observations, including some from Hubble’s namesake observatory, the NASA/ESA Hubble Space Telescope, and most recently from ESA’s Gaia mission, is 73.5 km/s/Mpc, with an uncertainty of only two percent. The slightly esoteric units give the velocity of the expansion in km/s for every million parsecs (Mpc) of separation in space, where a parsec is equivalent to 3.26 light-years.

    A second way to estimate the Hubble Constant is to use the cosmological model that fits the cosmic microwave background image, which represents the very young Universe, and calculate a prediction for what the Hubble Constant should be today. When applied to Planck data, this method gives a lower value of 67.4 km/s/Mpc, with a tiny uncertainty of less than a percent.

    1
    Measurements of the Hubble constant over the past two decades.
    Credit: ESA and the Planck Collaboration

    On the one hand, it is extraordinary that two such radically different ways of deriving the Hubble constant – one using the local, mature Universe, and one based on the distant, infant Universe – are so close to each other. On the other hand, in principle these two figures should agree to within their respective uncertainties. This is the tension, and the question is how can they be reconciled?

    Both sides are convinced that any remaining errors in their measurement methodologies are now too small to cause the discrepancy. So could it be that there is something slightly peculiar about our local cosmic environment that makes the nearby measurement somewhat anomalous? We know for example that our Galaxy sits in a slightly under-dense region of the Universe, which could affect the local value of the Hubble constant. Unfortunately, most astronomers think that such deviations are not large enough to resolve this problem.

    “There is no single, satisfactory astrophysical solution that can explain the discrepancy. So, perhaps there is some new physics to be found,” says Marco Bersanelli, deputy principal investigator of the LFI instrument at the University of Milan, Italy.

    ‘New physics’ means that exotic particles or forces could be influencing the results. Yet, as exciting as this prospect feels, the Planck results place severe constraints on this train of thought because it fits so well with the majority of observations.

    “It is very hard to add new physics alleviating the tension and still keep the standard model’s precise description of everything else that already fits,” says François Bouchet, deputy principal investigator of the HFI instrument at the Institut d’Astrophysique de Paris, France.

    As a result, no one has been able to come up with a satisfactory explanation for the differences between the two measurements, and the question remains to be resolved.

    “For the moment, we shouldn’t get too excited about finding new physics: it could well be that the relatively small discrepancy can be explained by a combination of small errors and local effects. But we need to keep improving our measurements and thinking about better ways to explain it,” says Jan.

    This is the legacy of Planck: with its almost perfect Universe, the mission has given researchers confirmation of their models but with a few details to puzzle over. In other words: the best of both worlds.

    See the full article here .

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    The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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  • richardmitnick 8:47 am on July 18, 2018 Permalink | Reply
    Tags: , , , , Cosmic Inflation, , , ,   

    From European Space Agency: “From an almost perfect Universe to the best of both worlds” 

    ESA Space For Europe Banner

    From European Space Agency

    17 July 2018

    Jan Tauber
    ESA Planck Project Scientist
    European Space Agency
    Email: jan.tauber@esa.int

    Markus Bauer
    ESA Science Communication Officer
    Tel: +31 71 565 6799
    Mob: +31 61 594 3 954
    Email: markus.bauer@esa.int

    1
    CMB per Planck

    ESA/Planck 2009 to 2013

    It was 21 March 2013. The world’s scientific press had either gathered in ESA’s Paris headquarters or logged in online, along with a multitude of scientists around the globe, to witness the moment when ESA’s Planck mission revealed its ‘image’ of the cosmos. This image was taken not with visible light but with microwaves.

    Whereas light that our eyes can see is composed of small wavelengths – less than a thousandth of a millimetre in length – the radiation that Planck was detecting spanned longer wavelengths, from a few tenths of a millimetre to a few millimetres. Most importantly, it had been generated at very beginning of the Universe.

    Collectively, this radiation is known as the cosmic microwave background, or CMB. By measuring its tiny differences across the sky, Planck’s image had the ability to tell us about the age, expansion, history, and contents of the Universe. It was nothing less than the cosmic blueprint.

    Astronomers knew what they were hoping to see. Two NASA missions, COBE in the early 1990s and WMAP in the following decade, had already performed an analogous set of sky surveys that resulted in similar images. But those images did not have the precision and sharpness of Planck.

    COBE/CMB

    NASA/COBE 1989 to 1993.

    CMB per NASA/WMAP

    NASA/WMAP 2001 to 2010

    The new view would show the imprint of the early Universe in painstaking detail for the first time. And everything was riding on it.

    If our model of the Universe were correct, then Planck would confirm it to unprecedented levels of accuracy. If our model were wrong, Planck would send scientists back to the drawing board.

    When the image was revealed, the data had confirmed the model. The fit to our expectations was too good to draw any other conclusion: Planck had showed us an ‘almost perfect Universe’. Why almost perfect? Because a few anomalies remained, and these would be the focus of future research.

    Now, five years later, the Planck consortium has made their final data release, known as the legacy data release. The message remains the same, and is even stronger.

    All cosmological models are based upon Albert Einstein’s General Theory of Relativity. To reconcile the general relativistic equations with a wide range of observations, including the cosmic microwave background, the standard model of cosmology includes the action of two unknown components.

    Firstly, an attractive matter component, known as cold dark matter, which unlike ordinary matter does not interact with light. Secondly, a repulsive form of energy, known as dark energy, which is driving the currently accelerated expansion of the Universe. They have been found to be essential components to explain our cosmos in addition to the ordinary matter we know about. But as yet we do not know what these exotic components actually are.

    3
    CMB temperature and polarisation

    Planck was launched in 2009 and collected data until 2013. Its first release – which gave rise to the almost perfect Universe – was made in the spring of that year. It was based solely on the temperature of the cosmic microwave background radiation, and used only the first two sky surveys from the mission.

    The data also provided further evidence for a very early phase of accelerated expansion, called inflation, in the first tiny fraction of a second in the Universe’s history, during which the seeds of all cosmic structures were sown.

    Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe) Date 2010 Credit: Alex Mittelmann Cold creation

    Yielding a quantitative measure of the relative distribution of these primordial fluctuations, Planck provided the best confirmation ever obtained of the inflationary scenario.

    Inflation

    4
    Alan Guth, from 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

    Besides mapping the temperature of the cosmic microwave background across the sky with unprecedented accuracy, Planck also measured its polarisation, which indicates if light is vibrating in a preferred direction. The polarisation of the cosmic microwave background carries an imprint of the last interaction between the radiation and matter particles in the early Universe, and as such contains additional, all-important information about the history of the cosmos. But it could also contain information about the very first instants of our Universe, and give us clues to understand its birth.

    In 2015, a second data release folded together all data collected by the mission, which amounted to eight sky surveys. It gave temperature and polarisation but came with a caution.

    5
    5 February 2015 New maps from ESA’s Planck satellite uncover the ‘polarised’ light from the early Universe across the entire sky, revealing that the first stars formed much later than previously thought.

    “We felt the quality of some of the polarisation data was not good enough to be used for cosmology,” says Jan. He adds that – of course – it didn’t prevent them from doing cosmology with it but that some conclusions drawn at that time needed further confirmation and should therefore be treated with caution.

    And that’s the big change for this 2018 Legacy data release. The Planck consortium has completed a new processing of the data. Most of the early signs that called for caution have disappeared. The scientists are now certain that both temperature and polarisation are accurately determined.

    “Now we really are confident that we can retrieve a cosmological model based on solely on temperature, solely on polarisation, and based on both temperature and polarisation. And they all match,” says Reno Mandolesi, principal investigator of the LFI instrument on Planck at the University of Ferrara, Italy.

    6

    The history of the Universe

    “Since 2015, more astrophysical data has been gathered by other experiments, and new cosmological analyses have also been performed, combining observations of the CMB at small scales with those of galaxies, clusters of galaxies, and supernovae, which most of the time improved the consistency with Planck data and the cosmological model supported by Planck,” says Jean-Loup Puget, principal investigator of the HFI instrument on Planck at the Institut d’Astrophysique Spatiale in Orsay, France.

    This is an impressive feat and means that cosmologists can be assured that their description of the Universe as a place containing ordinary matter, cold dark matter and dark energy, populated by structures that had been seeded during an early phase of inflationary expansion, is largely correct.

    But there are some oddities that need explaining – or tensions as cosmologists call them. One in particular is related to the expansion of the Universe. The rate of this expansion is given by the so-called Hubble Constant.

    To measure the Hubble constant astronomers have traditionally relied on gauging distances across the cosmos. They can only do this for the relatively local Universe by measuring the apparent brightness of certain types of nearby variable stars and exploding stars, whose actual brightness can be estimated independently. It is a well-honed technique that has been developed over the course of the last century, pioneered by Henrietta Leavitt and later applied, in the late 1920s, by Edwin Hubble and collaborators, who used variable stars in distant galaxies and other observations to reveal that the Universe was expanding.

    7
    Measurements of the Hubble constant
    Released 17/07/2018 3:00 pm
    Copyright ESA/Planck Collaboration

    The evolution of measurements of the rate of the Universe’s expansion, given by the so-called Hubble Constant, over the past two decades. The slightly esoteric units give the velocity of the expansion in km/s for every million parsecs (Mpc) of separation in space, where a parsec is equivalent to 3.26 light-years.
    In recent years, the figure astronomers derive for the Hubble Constant using a wide variety of cutting-edge observations to gauge distances across the cosmos is 73.5 km/s/Mpc, with an uncertainty of only two percent. These measurements are shown in blue.
    Alternatively, the Hubble Constant can also be estimated from the cosmological model that fits observations of the cosmic microwave background, which represents the very young Universe, and calculate a prediction for what the Hubble Constant should be today. Measurements based on this method using data from NASA’s WMAP satellite are shown in green, and those obtained using data from ESA’s Planck mission are shown in red.
    When applied to Planck data, this method gives a lower value of 67.4 km/s/Mpc, with a tiny uncertainty of less than a percent.

    On the one hand, it is extraordinary that two such radically different ways of deriving the Hubble constant – one using the local, mature Universe, and one based on the distant, infant Universe – are so close to each other. On the other hand, in principle these two figures should agree to within their respective uncertainties, causing what cosmologists call a ‘tension’ – an oddity that still needs explaining.

    The single purple point is a measurement obtained through yet another method, using data from the first simultaneous observation of light and gravitational waves emitted by the same source – a pair of coalescing neutron stars.

    The figure astronomers derive for the Hubble Constant using a wide variety of cutting-edge observations, including some from Hubble’s namesake observatory, the NASA/ESA Hubble Space Telescope, and most recently from ESA’s Gaia mission, is 73.5 km/s/Mpc, with an uncertainty of only two percent. The slightly esoteric units give the velocity of the expansion in km/s for every million parsecs (Mpc) of separation in space, where a parsec is equivalent to 3.26 light-years.

    NASA/ESA Hubble Telescope

    ESA/GAIA satellite

    A second way to estimate the Hubble Constant is to use the cosmological model that fits the cosmic microwave background image, which represents the very young Universe, and calculate a prediction for what the Hubble Constant should be today. When applied to Planck data, this method gives a lower value of 67.4 km/s/Mpc, with a tiny uncertainty of less than a percent.

    On the one hand, it is extraordinary that two such radically different ways of deriving the Hubble constant – one using the local, mature Universe, and one based on the distant, infant Universe – are so close to each other. On the other hand, in principle these two figures should agree to within their respective uncertainties. This is the tension, and the question is how can they be reconciled?

    Both sides are convinced that any remaining errors in their measurement methodologies are now too small to cause the discrepancy. So could it be that there is something slightly peculiar about our local cosmic environment that makes the nearby measurement somewhat anomalous? We know for example that our Galaxy sits in a slightly under-dense region of the Universe, which could affect the local value of the Hubble constant. Unfortunately, most astronomers think that such deviations are not large enough to resolve this problem.

    “There is no single, satisfactory astrophysical solution that can explain the discrepancy. So, perhaps there is some new physics to be found,” says Marco Bersanelli, deputy principal investigator of the LFI instrument at the University of Milan, Italy.

    ‘New physics’ means that exotic particles or forces could be influencing the results. Yet, as exciting as this prospect feels, the Planck results place severe constraints on this train of thought because it fits so well with the majority of observations.

    “It is very hard to add new physics alleviating the tension and still keep the standard model’s precise description of everything else that already fits,” says François Bouchet, deputy principal investigator of the HFI instrument at the Institut d’Astrophysique de Paris, France.

    As a result, no one has been able to come up with a satisfactory explanation for the differences between the two measurements, and the question remains to be resolved.

    “For the moment, we shouldn’t get too excited about finding new physics: it could well be that the relatively small discrepancy can be explained by a combination of small errors and local effects. But we need to keep improving our measurements and thinking about better ways to explain it,” says Jan.

    This is the legacy of Planck: with its almost perfect Universe, the mission has given researchers confirmation of their models but with a few details to puzzle over. In other words: the best of both worlds.

    Notes for Editors
    A series of scientific papers describing the new results was published on 17 July and can be downloaded here.

    The Planck Legacy Archive
    More about Planck

    See the full article here .


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    The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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  • richardmitnick 2:17 pm on February 24, 2018 Permalink | Reply
    Tags: , , , , Cosmic Inflation, , , , Why Haven't We Bumped Into Another Universe Yet?   

    From Ethan Siegel: “Why Haven’t We Bumped Into Another Universe Yet?” 

    From Ethan Siegel
    Feb 24, 2018

    1
    The multiverse idea states that there are an arbitrarily large number of Universes like our own, but that doesn’t necessarily mean there’s another version of us out there, and it certainly doesn’t mean there’s any chance of running into an alternate version of yourself… or anything from another Universe at all. Lee Davy / flickr.

    The Universe we inhabit is vast, full of matter and energy, and expanding at a tremendous clip. Looking billions of light years away, we can see billions of years into our ancient past, finding evidence of newly-forming planets, stars, and galaxies. We’ve seen so far back that we’ve identified clouds of gas that have never yet formed a single star, and found galaxies from when the Universe was only 3% of its current age. Most spectacularly, we can actually see the leftover glow from the Big Bang, from a time when the Universe was a mere 380,000 years old. Yet in all of this cosmic enormity, we’ve never found evidence that our Universe has bumped into another one in this vast Multiverse. Why not? That’s what Rod Russo wants to know:

    “If the Multiverse Theory is true, shouldn’t our expanding universe have bumped into another universe by now? After all, our universe is now so large that some describe it as “infinite” in size.”

    This is not only what logic dictates, it’s what no less an authority than Roger Penrose has claimed. But Penrose — and conventional wisdom — are both wrong here. Our Universe is, and should be, isolated and alone in the Multiverse.

    2
    Artist’s logarithmic scale conception of the observable universe. Note that we’re limited in how far we can see back by the amount of time that’s occurred since the hot Big Bang: 13.8 billion years, or (including the expansion of the Universe) 46 billion light years. Anyone living in our Universe, at any location, would see almost exactly the same thing from their vantage point. Wikipedia user Pablo Carlos Budassi.

    Although there’s a lot of hype and controversy surrounding it, there’s an extremely strong physical motivation for the existence of the Multiverse. If you combine two of our leading ideas about how the Universe works, cosmic inflation and quantum physics, it’s all but inescapable that we’ll conclude that our Universe resides in a Multiverse. Coming along for the ride is another conclusion: that every single Universe that gets created — that every hot Big Bang that ensues — is immediately and forever causally disconnected from all the others, eternally into the future. Here’s how that happens, and here’s how we know.

    3
    The expanding Universe, full of galaxies and the complex structure we observe today, arose from a smaller, hotter, denser, more uniform state. But what lies outside the observable Universe, by definition, cannot be observed. C. Faucher-Giguère, A. Lidz, and L. Hernquist, Science 319, 5859 (47).

    Cosmic inflation came about as an add-on to the Big Bang, successfully providing a mechanism for explaining why it began with certain conditions.

    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:

    In particular, inflation provided answer to the questions of:

    why the Universe was the same temperature everywhere,
    why it was so spatially flat,
    and why there were no leftover high-energy relics like magnetic monopoles,

    while simultaneously making new predictions that could be tested. These predictions included a specific spectrum for the density fluctuations the Universe was born with, a maximum temperature that the Universe achieved in the early stages of the hot Big Bang, the existence of fluctuations on scales larger than the cosmic horizon, and a particular spectrum of gravitational wave fluctuations. All of these, except the very last, have since been observationally confirmed.

    6
    Inflation set up the hot Big Bang and gave rise to the observable Universe we have access to, but we can only measure the last tiny fraction of a second of inflation’s impact on our Universe. This is enough, however, to give us a large slew of predictions to go out an look for, many of which have already been observationally confirmed. E. Siegel, with images derived from ESA/Planck and the DoE/NASA/ NSF interagency task force on CMB research

    What cosmic inflation is, exactly, is a period prior [?*] to the Big Bang where the Universe is dominated by the energy inherent to space itself. Unlike today, where the value of dark energy is extremely small, inflation posits that it was extremely large: larger by far than even the energy density when the Universe was full of matter and radiation in the extremely hot, early stages after the Big Bang. Since the expansion was dominated by the energy inherent to space, the rate of expansion was exponential, meaning that new space was continuously and rapidly created. If the Universe doubled in size after a certain amount of time, then after ten times that amount of time passed, it’d be 210, or over 1000, times as large in all dimensions. In extremely short order, any non-flat, matter-containing region of space would become indistinguishable from flat, and would have all the matter particles inflated away so that no two would ever meet.

    7
    Inflation causes space to expand exponentially, which can very quickly result in any pre-existing curved space appearing flat. E. Siegel (L); Ned Wright’s cosmology tutorial (R).

    On the other hand, inflation must come to an end at some point. The energy inherent to space cannot remain there forever, otherwise the Big Bang never would have occurred [?*], and the Universe as we know it would never have come to be. Somehow, that energy needs to get transferred from the fabric of space itself and dumped into matter and radiation. A nice way to visualize this is to view inflation as a field that occurs when a ball is at the top of a hill. As long as the ball remains up high, inflation, and this exponential expansion, continues. But in order for inflation to end, whatever quantum field is responsible for it has to roll from the high-energy, unstable state that drives inflation down into a low-energy, equilibrium state. That transition, and “rolling” down into the valley, is what causes inflation to come to an end, and create the hot Big Bang.

    8
    When cosmic inflation occurs, the energy inherent in space is large, as it is at the top of this hill. As the ball rolls down into the valley, that energy converts into particles. E. Siegel.

    But here’s the kicker: what I just described is how a classical field works, but we just said that inflation has to be, like all physical fields, an inherently quantum one. Like all quantum fields, it’s described by a wavefunction, with the probability of that wave spreading out over time. If the value of the field is rolling slowly-enough down the hill, then the quantum spreading of the wavefunction will be faster than the roll, meaning that it’s possible — even probable — for inflation to wind up farther away from ending and giving rise to a Big Bang as time goes on.

    9
    If inflation is a quantum field, then the field value spreads out over time, with different regions of space taking different realizations of the field value. In many regions, the field value will wind up in the bottom of the valley, ending inflation, but in many more, inflation will continue, arbitrarily far into the future. E. Siegel / Beyond The Galaxy.

    Because space is expanding at an exponential rate during inflation, this means that exponentially more regions of space are being created as time goes on. The thing is, inflation isn’t compelled to end everywhere at once; different regions will see the value of their quantum fields spread out by different amounts and in different directions over time! In a few regions, inflation will come to an end, as long as the field rolls down into the valley. But in others, inflation will continue on, giving rise to more and more space, where it continues to expand exponentially.

    10
    Wherever inflation occurs (blue cubes), it gives rise to exponentially more regions of space with each step forward in time. Even if there are many cubes where inflation ends (red Xs), there are far more regions where inflation will continue on into the future. The fact that this never comes to an end is what makes inflation ‘eternal’ once it begins. E. Siegel / Beyond The Galaxy.

    This is where the phenomenon known as eternal inflation, and the idea of a multiverse, comes from. Where inflation ends, we get a hot Big Bang and a Universe — of which we can observe part of the one we’re in — very much like our own. (Denoted by the red “X” above.) But surrounding each of those regions where a hot Big Bang occurs is one where inflation doesn’t end, and the exponential expansion continues. In those regions, more inflating space is produced, driving apart the regions where inflation ended at a faster rate than they’re capable of expanding at. This gives rise to other regions that will have hot Big Bangs, but each and every one of them will be causally disconnected from our own, at the moment of the hot Big Bang and forever into the future.

    If you picture the Multiverse as an enormous ocean, you can picture the individual Universes where a hot Big Bang occurs as little bubbles appearing in it. The bubbles, like real air bubbles that rise from the bottom of the ocean, will expand as time goes on, just as our own Universe is expanding. But unlike the liquid water of the ocean, the “ocean” of inflating spacetime keeps on expanding at a faster rate than the bubbles themselves can ever expand. As long as the space between them continues to inflate, and inflation predicts they will for an eternity, no two bubbles should ever collide. Unlike the boiling water on your stove, the bubbles don’t percolate.

    It would be an enormous surprise that runs counter to inflation and quantum theory’s predictions if any two Universes ever did collide. While bubble-wall collisions might leave a telltale sign on our Universe, we’ve examined the leftover glow from the Big Bang in gory detail, and no evidence for such a collision exists. Thankfully for our most robust theories of the early Universe, this is exactly in line with what’s been predicted. The reason we don’t see evidence for our Universe colliding with another is because our Universe has never collided with another one, just as our leading theories predict. Anyone who tells you otherwise has got some serious explaining to do.

    *I question Siegel’s assertion that inflation occurred prior to the Big Bang. I have never seen that and Alan Guth did not see that. From Wikipedia:

    “In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the early universe. The inflationary epoch lasted from 10−36 seconds after the conjectured Big Bang singularity to sometime between 10^−33 and 10^−32 seconds after the singularity. Following the inflationary period, the Universe continues to expand, but at a less rapid rate…As a junior particle physicist, [Alan] Guth developed the idea of cosmic inflation in 1979 at Cornell and gave his first seminar on the subject in January 1980.Moving on to Stanford University Guth formally proposed the idea of cosmic inflation in 1981, the idea that the nascent universe passed through a phase of exponential expansion that was driven by a positive vacuum energy density (negative vacuum pressure). The results of the WMAP mission in 2006 made the case for cosmic inflation very compelling.”

    I mean really, Ethan, how can you post inflation prior to the Big Bang? I have seen no one posit this before.

    See the full article here .

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

     
  • richardmitnick 1:47 pm on July 19, 2017 Permalink | Reply
    Tags: , , , , Cosmic Inflation, , Scientists Are Using the Universe as a "Cosmological Collider",   

    From CfA: “Scientists Are Using the Universe as a “Cosmological Collider” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    July 19, 2017
    Megan Watzke
    Harvard-Smithsonian Center for Astrophysics
    +1 617-496-7998
    mwatzke@cfa.harvard.edu

    Peter Edmonds
    Harvard-Smithsonian Center for Astrophysics
    +1 617-571-7279
    pedmonds@cfa.harvard.edu

    1

    Physicists are capitalizing on a direct connection between the largest cosmic structures and the smallest known objects to use the universe as a “cosmological collider” and investigate new physics.

    The three-dimensional map of galaxies throughout the cosmos and the leftover radiation from the Big Bang – called the cosmic microwave background (CMB) – are the largest structures in the universe that astrophysicists observe using telescopes.

    CMB per ESA/Planck

    ESA/Planck

    Subatomic elementary particles, on the other hand, are the smallest known objects in the universe that particle physicists study using particle colliders.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    A team including Xingang Chen of the Harvard-Smithsonian Center for Astrophysics (CfA), Yi Wang from the Hong Kong University of Science and Technology (HKUST) and Zhong-Zhi Xianyu from the Center for Mathematical Sciences and Applications at Harvard University has used these extremes of size to probe fundamental physics in an innovative way. They have shown how the properties of the elementary particles in the Standard Model of particle physics may be inferred by studying the largest cosmic structures. This connection is made through a process called cosmic inflation.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    Inflationary Universe. NASA/WMAP

    Cosmic inflation is the most widely accepted theoretical scenario to explain what preceded the Big Bang. This theory predicts that the size of the universe expanded at an extraordinary and accelerating rate in the first fleeting fraction of a second after the universe was created.

    Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe) Date 2010 Credit: Alex MittelmannColdcreation

    It was a highly energetic event, during which all particles in the universe were created and interacted with each other. This is similar to the environment physicists try to create in ground-based colliders, with the exception that its energy can be 10 billion times larger than any colliders that humans can build.

    Inflation was followed by the Big Bang, where the cosmos continued to expand for more than 13 billion years, but the expansion rate slowed down with time. Microscopic structures created in these energetic events got stretched across the universe, resulting in regions that were slightly denser or less dense than surrounding areas in the otherwise very homogeneous early universe. As the universe evolved, the denser regions attracted more and more matter due to gravity. Eventually, the initial microscopic structures seeded the large-scale structure of our universe, and determined the locations of galaxies throughout the cosmos.

    In ground-based colliders, physicists and engineers build instruments to read the results of the colliding events. The question is then how we should read the results of the cosmological collider.

    “Several years ago, Yi Wang and I, Nima Arkani-Hamed and Juan Maldacena from the Institute of Advanced Study, and several other groups, discovered that the results of this cosmological collider are encoded in the statistics of the initial microscopic structures. As time passes, they become imprinted in the statistics of the spatial distribution of the universe’s contents, such as galaxies and the cosmic microwave background, that we observe today,” said Xingang Chen. “By studying the properties of these statistics we can learn more about the properties of elementary particles.”

    As in ground-based colliders, before scientists explore new physics, it is crucial to understand the behavior of known fundamental particles in this cosmological collider, as described by the Standard Model of particle physics.

    “The relative number of fundamental particles that have different masses – what we call the mass spectrum – in the Standard Model has a special pattern, which can be viewed as the fingerprint of the Standard Model,” explained Zhong-Zhi Xiangyu. “However, this fingerprint changes as the environment changes, and would have looked very different at the time of inflation from how it looks now.”

    The team showed what the mass spectrum of the Standard Model would look like for different inflation models. They also showed how this mass spectrum is imprinted in the appearance of the large-scale structure of our universe. This study paves the way for the future discovery of new physics.

    “The ongoing observations of the CMB and large-scale structure have achieved impressive precision from which valuable information about the initial microscopic structures can be extracted,” said Yi Wang. “In this cosmological collider, any observational signal that deviates from that expected for particles in the Standard Model would then be a sign of new physics.”

    The current research is only a small step towards an exciting era when precision cosmology will show its full power.

    “If we are lucky enough to observe these imprints, we would not only be able to study particle physics and fundamental principles in the early universe, but also better understand cosmic inflation itself. In this regard, there are still a whole universe of mysteries to be explored,” said Xianyu.

    This research is detailed in a paper published in the journal Physical Review Letters on June 29, 2017, and the preprint is available online.

    See the full article here .

    Please help promote STEM in your local schools.

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    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

     
  • richardmitnick 3:05 pm on June 3, 2017 Permalink | Reply
    Tags: , , , Cosmic Inflation, , , What does the edge of the Universe look like?   

    From Ethan Siegel: “What does the edge of the Universe look like?” 

    From Ethan Siegel
    June 3, 2017

    1
    The simulated large-scale structure of the Universe shows intricate patterns of clustering that never repeat. But from our perspective, we can only see a finite volume of the Universe. What lies beyond this edge? Image credit: V. Springel et al., MPA Garching, and the Millenium Simulation.

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

    “The Edge… there is no honest way to explain it because the only people who really know where it is are the ones who have gone over.”
    -Hunter S. Thompson

    13.8 billion years ago, the Universe as we know it began with the hot Big Bang. Over that time, space itself has expanded, the matter has undergone gravitational attraction, and the result is the Universe we see today. But as vast as it all is, there’s a limit to what we can see. Beyond a certain distance, the galaxies disappear, the stars twinkle out, and no signals from the distant Universe can be seen. What lies beyond that? That’s this week’s question from Dan Newman, who asks:

    If the universe is finite in volume, then is there a boundary? Is it approachable? And what might the view in that direction be?

    Let’s start by starting at our present location, and looking out as far into the distance as we can.

    2
    Nearby, the stars and galaxies we see look very much like our own. But as we look farther away, we see the Universe as it was in the distant past: less structured, hotter, younger, and less evolved. Image credit: NASA, ESA, and A. Feild (STScI).

    NASA/ESA Hubble Telescope

    In our own backyard, the Universe is full of stars. But go more than about 100,000 light years away, and you’ve left the Milky Way behind. Beyond that, there’s a sea of galaxies: perhaps two trillion in total contained in our observable Universe. They come in a great diversity of types, shapes, sizes and masses. But as you look back to the more distant ones, you start to find something unusual: the farther away a galaxy is, the more likely it is to be smaller, lower in mass, and to have its stars be intrinsically bluer in color than the nearby ones.

    3
    How galaxies appear different at different points in the Universe’s history: smaller, bluer, younger, and less evolved at earlier times. Image credit: NASA, ESA, P. van Dokkum (Yale University), S. Patel (Leiden University), and the 3D-HST Team.

    This makes sense in the context of a Universe that had a beginning: a birthday. That’s what the Big Bang was, the day that the Universe as we know it was born. For a galaxy that’s relatively close by, it’s just about the same age that we are. But when we look at a galaxy that’s billions of light years away, that light has needed to travel for billions of years to reach our eyes. A galaxy whose light takes 13 billion years to reach us must be less than one billion years old, and so the farther away we look, we’re basically looking back in time.

    4
    The full UV-visible-IR composite of the Hubble eXtreme Deep Field; the greatest image ever released of the distant Universe. Image credit: NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI).

    The above image is the Hubble eXtreme Deep Field (XDF), the deepest image of the distant Universe ever taken. There are thousands of galaxies in this image, at a huge variety of distances from us and from one another. What you can’t see in simple color, though, is that each galaxy has a spectrum associated with it, where clouds of gas absorb light at very particular wavelengths, based on the simple physics of the atom. As the Universe expands, that wavelength stretches, so the more distant galaxies appear redder than they otherwise would. That physics allows us to infer their distance, and lo and behold, when we assign distances to them, the farthest galaxies are the youngest and smallest ones of all.

    Beyond the galaxies, we expect there to be the first stars, and then nothing but neutral gas, when the Universe hadn’t had enough time to pull matter into dense enough states to form a star yet. Going back additional millions of years, the radiation in the Universe was so hot that neutral atoms couldn’t form, meaning that photons bounced off of charged particles continuously. When neutral atoms did form, that light should simply stream in a straight line forever, unaffected by anything other than the expansion of the Universe. The discovery of this leftover glow — the Cosmic Microwave Background — more than 50 years ago was the ultimate confirmation of the Big Bang.

    Cosmic Microwave Background WMAP

    NASA WMAP

    CMB per ESA/Planck

    ESA/Planck

    4
    Schematic diagram of the Universe’s history, highlighting reionization. Before stars or galaxies formed, the Universe was full of light-blocking, neutral atoms. While most of the Universe doesn’t become reionized until 550 million years afterwards, a few fortunate regions are mostly reionized at earlier times. Image credit: S. G. Djorgovski et al., Caltech Digital Media Center.

    So from where we are today, we can look out in any direction we like and see the same cosmic story unfolding. Today, 13.8 billion years after the Big Bang, we have the stars and galaxies we know today. Earlier, galaxies were smaller, bluer, younger and less evolved. Before that, there were the first stars, and prior to that, just neutral atoms. Before neutral atoms, there was an ionized plasma, then even earlier there were free protons and neutrons, spontaneous creation of matter-and-antimatter, free quarks and gluons, all the unstable particles in the Standard Model, and finally the moment of the Big Bang itself. Looking to greater and greater distances is equivalent to looking all the way back in time.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    5
    Artist’s logarithmic scale conception of the observable universe. Galaxies give way to large-scale structure and the hot, dense plasma of the Big Bang at the outskirts. This ‘edge’ is a boundary only in time. Image credit: Wikipedia user Pablo Carlos Budassi.

    Although this defines our observable Universe — with the theoretical boundary of the Big Bang located 46.1 billion light years from our current position — this is not a real boundary in space. Instead, it’s simply a boundary in time; there’s a limit to what we can see because the speed of light allows information to only travel so far over the 13.8 billion years since the hot Big Bang. That distance is farther than 13.8 billion light years because the fabric of the Universe has expanded (and continues to expand), but it’s still limited. But what about prior to the Big Bang? What would you see if you somehow went to the time just a tiny fraction of a second earlier than when the Universe was at its highest energies, hot and dense, and full of matter, antimatter and radiation?

    6
    Inflation set up the hot Big Bang and gave rise to the observable Universe we have access to. The fluctuations from inflation planted the seeds that grew into the structure we have today. Image credit: Bock et al. (2006, astro-ph/0604101); modifications by E. Siegel.

    You’d find that there was a state called cosmic inflation: where the Universe was expanding ultra fast, and dominated by energy inherent to space itself. Space expanded exponentially during this time, where it was stretched flat, where it was given the same properties everywhere, where pre-existing particles were all pushed away, and where fluctuations in the quantum fields inherent to space were stretched across the Universe. When inflation ended where we are, the hot Big Bang filled the Universe with matter and radiation, giving rise to the part of the Universe — the observable Universe — that we see today. 13.8 billion years later, here we are.

    Inflation theorist Alan Guth:

    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

    6
    The observable Universe might be 46 billion light years in all directions from our point of view, but there’s certainly more, unobservable Universe, perhaps even an infinite amount, just like ours beyond that. Image credit: Frédéric MICHEL and Andrew Z. Colvin, annotated by E. Siegel.

    The thing is, there’s nothing special about our location, neither in space nor in time. The fact that we can see 46 billion light years away doesn’t make that boundary or that location anything special; it simply marks the limit of what we can see. If we could somehow take a “snapshot” of the entire Universe, going way beyond the observable part, as it exists 13.8 billion years after the Big Bang everywhere, it would all look like our nearby Universe does today. There would be a great cosmic web of galaxies, clusters, filaments, and cosmic voids, extending far beyond the comparatively small region we can see. Any observer, at any location, would see a Universe that was very much like the one we see from our own perspective.

    7
    One of the most distant views of the Universe showcases nearby stars and galaxies seen along the way, but the galaxies closer to the outer regions are simply seen at a younger, earlier stage of evolution. From their perspective, they are 13.8 billion years old (and more evolved), and we appear as we did billions of years ago. Image credit: NASA, ESA, the GOODS Team and M. Giavalisco (STScI/University of Massachusetts).

    The individual details would be different, just as the details of our own solar system, galaxy, local group, and so on, are different from any other observer’s viewpoint. But the Universe itself isn’t finite in volume; it’s only the observable part that’s finite. The reason for that is that there’s a boundary in time — the Big Bang — that separates us from the rest. We can approach that boundary only through telescopes (which look to earlier times in the Universe) and through theory. Until we figure out how to circumvent the forward flow of time, that will be our only approach to better understand the “edge” of the Universe. But in space? There’s no edge at all. To the best that we can tell, someone at the edge of what we see would simply see us as the edge instead!

    See the full article here .

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  • richardmitnick 2:09 pm on June 1, 2017 Permalink | Reply
    Tags: , , , Cosmic Inflation, , The Inflated Debate Over Cosmic Inflation   

    From Nautilus: “The Inflated Debate Over Cosmic Inflation” 

    Nautilus

    Nautilus

    June 1, 2017
    Amanda Gefter

    Why the majority of physicists are on one side of a recent exchange of letters.

    On the morning of Dec. 7, 1979, a 32-year-old Alan Guth woke up with an idea. It had come into his head the previous night, but now, in the light of a California day, he could see the shape of the thing, and was itching to work through the math. He hopped on his bike and rode to his office at the Stanford Linear Accelerator Center. His excitement got him there in record time: 9 minutes, 32 seconds. At his desk, Guth neatly carried out the calculations in his notebook, forming the numbers and symbols in tight, careful lines. Then, at the top of a fresh page, he wrote in all caps: SPECTACULAR REALIZATION.

    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

    A year later and some 6,000 miles away, in Moscow, in the middle of the night, Andrei Linde, having read Guth’s paper, had his own spectacular realization. He had been working on his own idea and now he saw how to bring it to life by fixing the difficulties that plagued Guth’s theory. He woke his sleeping wife. “I think I know how the universe was created.”

    Guth and Linde had worked out the beginnings of the theory of cosmic inflation. The theory would go through several incarnations over the next few decades, as kinks were worked out and details honed. But the core idea was spectacularly simple: In the earliest fraction of a second of time, a small patch of universe expanded faster than the speed of light, doubling its size again and again, growing a million trillion trillion times bigger in the blink of an eye. A little patch of world, about the size of a dime, grew into our entire observable universe.

    2
    The objectors: From left to right, Anna Ijjas, Paul Steinhardt, and Avi Loeb.

    What began as a radical notion has now become standard wisdom among physicists—except, notably, Paul Steinhardt, Anna Ijjas, and Avi Loeb. The three physicists recently wrote a scathing article in Scientific American arguing that it’s time to abandon inflation and look for a competing idea. (What idea, you ask? Steinhardt, conveniently, has one that he’s been pushing for decades.) Inflation is too unlikely to occur, too flexible to be confirmed or rejected experimentally, and too messy in its implications, the threesome argued. It “cannot be evaluated using the scientific method.”

    It’s not surprising, then, that Guth and Linde—along with physicists David Kaiser and Yasunori Nomura—published a terse response in Scientific American earlier this month defending their theory. What is more surprising, perhaps, is that 29 more of the world’s leading physicists signed it—including four Nobel laureates and a Field’s medalist.

    In the media flurry that followed, the disagreement between these groups of physicists was presented as a straight debate, of the kind that often occurs in science when there are multiple interpretations of data. But describing an equivalence between the opinions of Steinhardt, Ijjas, and Loeb on the one hand, and nearly the entirely cosmology community on the other, is a mistake.

    The long list of signatories to the recent rebuttal letter in Scientific American puts the lie to the claim that the community is divided. When Ed Witten, Steven Weinberg, Leonard Susskind, Frank Wilczek, Juan Maldacena, Eva Silverstein, Sir Martin Rees, and Stephen Hawking (to name a few) write a letter saying you’ve gotten something wrong … well it’s probably worth considering.

    The rebuttal letter also challenges us to understand more clearly why so many scientists are passionate about inflation. What is it about this theory that has the greatest minds in the known universe leaping to its defense?

    From its inception, inflation has offered a remarkable synthesis of seemingly unrelated aspects of physics. It draws on a concept from particle physics called scalar fields—fields that look the same no matter how you view them, but can contain energy or pressure. Their high level of symmetry suggests that one would be most likely to find them in the earliest moments of the universe’s history, which makes them relevant to cosmology. And scalar fields have the special property that they can have negative pressure—a curiosity that takes on deeper meaning in the context of general relativity, where pressure contributes to the curvature of spacetime. Normal pressure produces gravity. Negative pressure produces inflation.

    Inflation shows us that we can take a scalar field from particle physics, apply Einstein’s theory of general relativity, sprinkle in some quantum fluctuations, and get the entire universe replete with all the features we observe when we look around us—features that otherwise would remain inexplicable—from the homogenous distribution of stars and galaxies in all directions and the large-scale geometry of spacetime to the precise bumps and wiggles in the remnant heat from the Big Bang to the very existence of matter itself. When the incredible burst of inflation begins, the uncertainty that rules nature’s tiniest scales is stretched to astronomical proportions, linking the quantum world with the cosmic. When it ends, the expansion energy is transformed into matter and radiation, which sinks into the ripples and divots of spacetime forged by those quantum fluctuations, laying a blueprint for the formation of stars and galaxies.

    As Kaiser, the letter’s co-author and a physicist at the Massachusetts Institute of Technology, explains, “Inflation is a conservative, minimalist outcome of two of the most important conceptual principles in physics: the equivalence principle of general relativity and the uncertainty principle of quantum mechanics.” If a theory’s explanatory power, as co-author Nomura of the University of California, Berkeley says, lies in the ratio of the number of things it can explain to the number of assumptions it takes to explain them, inflation packs a serious punch.

    To be fair, when Guth and Linde first put forth the idea, there were aspects that seemed a little, well, odd—as if inflation arose by exploiting loopholes in physics. Yes, it’s true nothing can travel through space faster than light [in a vacuum], but space itself can expand faster than light; no one had ever seen a scalar field, but physics didn’t expressly forbid it; Einstein himself had conceived of an antigravitational force that would stretch space, but no one had ever observed the stuff. But in the decades since, all of those weird ingredients have shown up. In 1998, astrophysicists discovered an antigravitational force—“dark energy”—that’s driving the accelerated expansion of space right now, with the galaxies farthest from us crossing out of our cosmic horizon faster than the speed of light. In 2012, physicists at the Large Hadron Collider in CERN found clear evidence of a scalar field—the Higgs field. As Murray Gell-Mann once quipped, in physics, “Everything not forbidden is compulsory.” Including, it seems, the universe itself.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    CERN CMS Higgs Event

    CERN ATLAS Higgs Event

    In its early days, too, testing inflation seemed nearly impossible. It predicted that the background heat from the early universe that pervades the sky today—stretched into microwave wavelengths now by 13 billion years of cosmic expansion—would be uniform in temperature to 1 part in 100,000, but beyond that, tiny temperature fluctuations would take on a specific statistical distribution across the sky. No one in 1980 could have imagined the minute level of detail with which spacecraft like NASA’s WMAP, launched in 2001, and the ESA’s Planck Satellite, launched in 2009, would map those tiny differences, bearing out the expectations of inflationary models.

    Cosmic Microwave Background WMAP

    NASA WMAP satellite

    CMB per ESA/Planck

    ESA/Planck

    “The most astonishing thing for me is that it has proved so susceptible to experimental-observational confirmation,” says Susskind, the Stanford physicist and founder of string theory who co-signed the letter. “The outlook for further confirmation is excellent and to say otherwise indicates a lack of appreciation for the accomplishments to date.” Ongoing experiments—including telescopes that are now searching the skies for primordial gravitational waves—could further confirm the predictions of inflation.

    (Susskind, incidentally, was one of the first people with whom Guth shared his spectacular realization on that fateful December day back in 1979. Susskind listened to his colleague’s jubilant news, then said, “You know, the most amazing thing is that they pay us for this.”)

    One of inflation’s early predictions seemed, at the time, flat out wrong. A universe that underwent inflation ought to appear extremely flat (its spacetime metric Euclidean to any measurable degree), because any curvature it had will have been stretched to such huge proportions that you’d never notice it—just like you don’t notice the Earth’s curvature when you’re standing on a flat sidewalk. But the metric of spacetime, according to general relativity, is determined by how much stuff is in it, and a flat metric requires a critical amount of mass and energy. Adding up the weight of all the galaxies in the observable universe, physicists came up about 96 percent short.

    That’s not a little wrong—that’s absurdly wrong. And yet, in the days since, astrophysicists have discovered that the universe is full of invisible dark matter, detectable by its gravitational effects, which brought the total up to 27 percent of the critical mass. Then came the discovery of dark energy, which could be weighed by its effect on the expansion of space, bringing the total to a perfect 100 percent—the critical number for a flat universe, far too conspiratorial to be a fluke.

    Given all of inflation’s successes, why are Steinhardt, Ijjas and Loeb claiming that it isn’t science?

    First, they argue that inflation is too unlikely to occur. The initial conditions required for that scalar field to start inflating, they say, requires an improbable amount of fine-tuning. Within the chaotic conditions at the beginning of time, they argue, you’d need a large, smooth, flat patch of spacetime within which inflation could occur. But large, smooth, flat patches of spacetime are hard to come by—in fact, they are the very features of our universe that inflation was invented to explain. Getting the right initial conditions to trigger inflation, then, would render inflation totally unnecessary.

    That might have been true in the past, but it was never clear that it really mattered. If you start with chaos, there’s bound to be a smooth patch in it somewhere, just randomly, and it doesn’t matter how rare it is because once it inflates it grows so big it completely dominates the universe. That’s the thing about cosmology—you don’t have to show that the universe began easily or quickly. You just have to show that it could begin at all.

    In any case, the story has since changed dramatically in the last few years. Major developments [1] in what’s known as “full numerical general relativity”—powerful computer simulations of the actual dynamics of spacetime—have shown, surprisingly, that inflation can begin much more easily than anyone ever thought. In fact, you don’t need a smooth, flat patch—even lumpy, messy regions will start inflating. “This has been one of the biggest leaps forward,” Kaiser says.

    “The problem of the initial smooth patch has disappeared, in our opinion,” says Leonardo Senatore, a Stanford physicist who worked on the simulations and signed the letter to Scientific American. According to the work, only very few barriers to inflation remain. This “reversed the problem of the probability to start inflation,” says Senatore. “Right now, it seems unlikely for it not to start.” “The problem of initial conditions was solved in 2015,” Linde agrees. “This criticism shows a total ignorance of what is going on.”

    So what about the second criticism, that inflation is too flexible to be tested? It’s true that while the idea behind inflation is simple, its parameters can be tweaked in seemingly endless ways: You can change the energy scale at which inflation begins, the features of the scalar field that drives its expansion, or the number of times spacetime doubles in size before inflation rolls to an end. Turning the dial on any of those parameters leads to different patterns in the microwave background radiation, different arrangements of stars and galaxies and different amplitudes of gravitational waves. In other words, the critics say, go out and measure almost anything and someone will say, “hey, that’s evidence for inflation.” Theories that can predict anything predict nothing. Inflation, they say, isn’t science.

    But supporters argue that this shows a fundamental misunderstanding of what inflation is. It’s not a single model, they insist—it’s a class of models, a sweeping principle, a paradigm from which individual models can be derived and then tested. The key is to figure out which model of inflation is right—if any—and not to prove or falsify all of them all in one fell swoop. “Each model makes specific predictions, and can be tested with precision by the traditional methods of empirical science,” says Guth, now at MIT. Darwin’s concept of evolution by natural selection does not predict exactly which species of animal you’ll see outside your window; Einstein’s concept that gravity is the curvature of spacetime does not predict the actual spacetime geometry of our universe; and inflation doesn’t predict every last bump and wiggle in the microwave background radiation.

    It’s fashionable to refer to the philosopher Karl Popper’s falsification criterion as a kind of litmus test to determine what is and is not science—Susskind has called those who are quick to cry Popper “the Popperazzi.” But in the case of inflation, invoking Popper doesn’t quite add up. “I don’t think that Popper, or any other responsible thinker, has ever advocated that to decide if a theory is scientific, one should ask what class of theories does that theory belong to, and then ask if there is an experimental finding that would rule out that entire class at once,” Guth says. “That would make no sense.”

    Philosophers of science have long known that falsification is not as black and white as it sounds. For every theoretical prediction we put to the test, there are scores of auxiliary assumptions implicit in the entire experimental set-up—observations are “theory-laden,” as the philosophers say. If a prediction doesn’t pan out, is it the theory we’re testing that’s wrong, or one of the auxiliary assumptions? They’re impossible to disentangle. Historians of science, meanwhile, know that science has never proceeded by falsification anyway. If a theory has real explanatory power, scientists don’t abandon it just because it seems too flexible or even if it’s disproven by an anomalous observation. They abandon it if a better theory comes along.

    Take Newtonian gravity. It was a remarkably elegant idea—connecting the motions of falling apples with the motions of orbiting planets—but it had its problems. One of them was that Mercury’s orbit did not conform to its equations. Mercury, by Popperazzi standards, had rendered Newtonian gravity falsified. Wash your hands of it, take it out with the trash falsified. But no one tossed the theory aside, nor should they have. It was only when general relativity came along—which could accurately predict Mercury’s orbit, yes, but also had more elegance, more explanatory power—that Newtonian gravity was declared wrong. “Wrong” is too strong a term, really—when velocities are small and gravity is weak, Einstein’s equations reduce to Newton’s. Newtonian gravity was right—it just wasn’t the whole picture.

    Inflation produces a remarkably accurate account of the geometry of the observable universe and explains why distant patches of sky that would never otherwise have come into contact are in near perfect thermal equilibrium. Like Newtonian gravity, inflation isn’t the whole picture. It can’t be—because it isn’t formulated using quantum gravity, the complete “theory of everything” that will unify quantum mechanics with general relativity. “In my opinion, the problems with inflation are probably going to be solved by a deeper theory of quantum gravity, or by some other process that occurred before slow roll (non-eternal) inflation started in our patch of the universe,” says co-signer Juan Maldacena of the Institute for Advanced Study. “The problems with the hot Big Bang theory were not removed by discarding the Big Bang theory. They were solved by another type of evolution prior to the big bang phase (namely, inflation). Similarly, I think that the problems with inflation will not be solved by ditching inflation but by some other theory of what happened before.”

    And here’s the kicker: Inflationary cosmology itself provides the best hope we have for getting an empirical look at quantum gravity in action. After all, the whole point of inflation is that it takes the quantum-scale dynamics of spacetime itself and magnifies them to cosmic proportions. In doing so, it allows us to study physics at energies 10 billion times greater than the energy scales reached by the Large Hadron Collider at CERN. We will never find a better magnifying glass to peer at the most intricate details of reality. The horizon of a ginormous black hole would make a decent one, but it would still be nothing compared to inflation. “This may be the closest we will ever get to seeing the combined effects of quantum mechanics and general relativity,” Susskind says. One can begin to understand, then, why physicists from fields ranging from the most concrete experimental astrophysics to the most abstract M-theory signed the letter supporting inflation.

    Now for the third and final criticism leveraged by Steinhardt, Ijjas, and Loeb. Back in the early days of inflation, Linde realized that thanks to quantum uncertainty, inflation won’t stop at precisely the same time everywhere. So as our universe exits the inflationary phase and begins its ordinary subluminal expansion, a little patch of scalar field remains. That little patch inflates into a whole new universe, which in turn leaves behind yet another patch, creating yet another universe, ad infinitum. Each universe can contain different fields with different particles with different masses with different behavior. Linde called it the eternal self-reproducing universe. Today, physicists call it the multiverse.

    The multiverse was yet another aspect of inflation that seemed kind of crazy at first, but then the rest of physics caught up. String theory, for instance, turned out to describe a near-infinite number of universes, all of which cried out for a physical mechanism that might produce them. Meanwhile, observations like the value of dark energy were turning up that seemed improbably fine-tuned for the existence of biological life, crying out for an explanation. In each case, eternal inflation came to the rescue.

    Still, not everyone likes the idea of a multiverse. Steinhardt, Ijjas, and Loeb refer to it as “the multimess.” They dislike the fact that various features of physics can differ from one universe to the next, because that reduces the features of our little universe to mere happenstance. “I believe it is a great advantage of the theory,” Linde says, “but they believe it’s a crime.” But not liking the implications of a theory doesn’t make it wrong. “It does seem to make some people uncomfortable—but the comfort zone is not necessarily where we want to be,” Susskind says.

    It does seem like universes forever beyond our reach might also lie beyond the reach of experiment. But there’s an interesting way that eternal inflation can be put to the test. Energy is always conserved in physics—you can’t create more stuff than what you started with. And eternal inflation seems, on glance, to violate this with abandon. There’s another loophole, though: Gravity is a form of negative energy. As inflation creates more universes, it simultaneously creates more gravity, and the two work to perfectly cancel out. Energy—which adds up to zero—is conserved. What about other conservation laws? Angular momentum is conserved—but if you tally up the angular momentum of all the galaxies in the universe, it sums to zero. Electric charge is conserved, but the universe is electrically neutral; it adds up to zero, too. Eternal inflation can make universes like ours precisely because it doesn’t have to violate any conservation laws to do it. It’s making more and more of nothing.

    Again, inflation has taken what seems like a loophole in physics and exposes it to be a profound glimpse into the nature of reality: You can create a universe from nothing—you can create infinite universes from nothing—as long as they all add up to nothing. Not only is that a deep insight, it also creates a testable prediction. “Eternal inflation certainly predicts that the average density of all conserved quantities should be zero,” Guth says. “So if we ever became convinced that the universe has a nonzero density of electric charge or angular momentum, eternal inflation would no longer be an option.”

    Still, infinity makes Steinhardt, Ijjas, and Loeb uneasy because it makes it extremely difficult to define probabilities for the outcomes of measurements. In an infinite multiverse, anything that can happen will happen—an infinite number of times. Such a situation requires what’s called a probability measure to assign different likelihoods to different events, even when there an infinite number of them. But different measures yield different probabilities, and it hasn’t been clear which measure is the right one. That leaves us in a situation where we can’t predict anything, the critics say.

    That might be true—but all it means is that physicists have to figure out which measure to use, not that the multiverse is a free-for-all. “Even the rarest of events will occur an infinite number of times,” Guth explains. “But such events will remain extremely rare. The claim that no outcome will be preferred over any other has absolutely no basis in logic. Mathematicians have known for nearly a century that probabilities can be rigorously defined on infinite spaces, and it is certainly not the case that all events must be equally likely. So, unfortunately, even if there is a multiverse, the chances of my winning the Massachusetts lottery tomorrow will remain incredibly small.”

    “The problem of the measure is very complicated,” Linde says. “It’s very similar to what happened with the interpretation of quantum mechanics. Everyone knows that quantum mechanics works, but people have been debating its interpretation for 100 years. The multiverse is somewhat similar. It is a deep problem, putting a quantum mechanical description of gravity and cosmology all together.”

    A deep problem, indeed—and far subtler than critics of the multiverse imply. (Steinhardt, Ijjas, and Loeb, it should be noted, are far from the only multiverse critics.)The infinite universes that comprise the multiverse are separated from one another by event horizons which, because they are described by both general relativity and quantum mechanics, are strange objects, and not always what they seem. In the last few decades, physicists have discovered that fundamental assumptions about the nature of reality come into question whenever an event horizon lurks. Thought experiments and paradoxes concerning the fate of information that falls behind the horizon of a black hole led Susskind to introduce the notion of “horizon complementarity”: The two sides of a horizon should not be thought of as distinct regions of spacetime, but more like two different descriptions of the very same reality. If horizon complementarity holds in the multiverse, it’s possible that the multiverse is a kind of vast redundancy, and the fundamental theory of the universe may well be written in terms of a single observable universe, rendering the measure problem moot. All the metaphysical baggage of the multiverse, and the distaste some people have for it, might be nothing more than an artifact of all-too-classical thinking. “You have to interpret the multiverse carefully,” says Nomura. “Our world is quantum mechanical.”

    Hawking—who signed the letter—has been working on a model he calls top-down cosmology. In his view, in light of quantum mechanics, it doesn’t make sense to talk about the origin and evolution of the universe as if it followed a single unique trajectory. Instead, he argues, we ought to use the universe as we observe it right now—coupled with the assumption that it arose from nothing—and take a quantum superposition of every possible history that could have led from nothing to now. It’s not that we don’t know which history really occurred—it’s that they all occurred. Rather than a multiverse with a single history, you have a single universe with multiple histories. When Hawking takes the sum of these histories to determine the most probable path, it is—voila!—a history in which the early universe went through inflation. Inflation pops out on its own, from a theory that doesn’t involve a multiverse.

    Many roads, it seems, lead back to inflation and inflation in turn leads to unexpected places. Steinhardt, Ijjas and Loeb are standing by their criticisms of the theory, and have made a website to reiterate them. But the 33 leading physicists who signed the letter—and countless others—are more confident in inflation than ever, exploring its strange territory, optimistic that it will eventually lead them to its own replacement: a more complete theory of the universe’s origin. That, certainly, is science. And it is pretty spectacular.

    See the full article here .

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  • richardmitnick 8:25 am on May 25, 2017 Permalink | Reply
    Tags: , , , , Cosmic Inflation, , ,   

    From Nautilus: “The Origin of the Universe” 

    Nautilus

    Nautilus

    April 2017
    John Carlstrom

    1
    The current South Pole telescope measuring small variations in the cosmic microwave background radiation that permeates the universe. Multiple telescopes with upgraded detectors could unlock additional secrets about the origins of the universe. Jason Gallicchio

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

    CMB per ESA/Planck


    ESA/Planck

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

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

    4
    Alan Guth, Highland Park High School, NJ, USA and M.I.T., who first proposed cosmic inflation

    HPHS Owls

    Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe) Date 2010 Credit: Alex MittelmannColdcreation

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

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

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

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

    Inflationary Universe. NASA/WMAP

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

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

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

    How to Measure Variations in the Microwave Background with Unparalleled Precision

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

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

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

    3
    Figure 2The current focal plane on the South Pole Telescope with seven wafers of detectors plus hand-assembled individual detectors. A single detector wafer of the advanced design proposed here would provide more sensitivity and frequency coverage than this entire focal plane; the project would deploy several hundred such wafers across 10 or more telescopes. Jason Henning.

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

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

    See the full article here .

    Please help promote STEM in your local schools.

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    Stem Education Coalition

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

     
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