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  • richardmitnick 8:57 pm on May 5, 2017 Permalink | Reply
    Tags: , , , Is this the only universe?, Multiverse theory,   

    From Symmetry: “Is this the only universe?” 

    Symmetry Mag

    Symmetry

    07/28/15 [Never saw this before in social media.]
    Laura Dattaro

    1
    No image credit

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

    Human history has been a journey toward insignificance.

    As we’ve gained more knowledge, we’ve had our planet downgraded from the center of the universe to a chunk of rock orbiting an average star in a galaxy that is one among billions.

    Milky Way NASA/JPL-Caltech /ESO R. Hurt

    So it only makes sense that many physicists now believe that even our universe might be just a small piece of a greater whole. In fact, there may be infinitely many universes, bubbling into existence and growing exponentially. It’s a theory known as the multiverse.

    Multiverse. Image credit: public domain, retrieved from https://pixabay.com/

    One of the best pieces of evidence for the multiverse was first discovered in 1998, when physicists realized that the universe was expanding at ever increasing speed. They dubbed the force behind this acceleration dark energy.

    3
    The universe has been expanding since the Big Bang kickstarted the growth about 13.8 billion years.

    The value of its energy density, also known as the cosmological constant [Λ], is bizarrely tiny: 120 orders of magnitude smaller than theory says it should be.

    For decades, physicists have sought an explanation for this disparity. The best one they’ve come up with so far, says Yasunori Nomura, a theoretical physicist at the University of California, Berkeley, is that it’s only small in our universe. There may be other universes where the number takes a different value, and it is only here that the rate of expansion is just right to form galaxies and stars and planets where people like us can observe it. “Only if this vacuum energy stayed to a very special value will we exist,” Nomura says. “There are no good other theories to understand why we observe this specific value.”

    For further evidence of a multiverse, just look to string theory, which posits that the fundamental laws of physics have their own phases, just like matter can exist as a solid, liquid or gas. If that’s correct, there should be other universes where the laws are in different phases from our own—which would affect seemingly fundamental values that we observe here in our universe, like the cosmological constant. “In that situation you’ll have a patchwork of regions, some in this phase, some in others,” says Matthew Kleban, a theoretical physicist at New York University.

    These regions could take the form of bubbles, with new universes popping into existence all the time. One of these bubbles could collide with our own, leaving traces that, if discovered, would prove other universes are out there. We haven’t seen one of these collisions yet, but physicists are hopeful that we might in the not so distant future.

    If we can’t find evidence of a collision, Kleban says, it may be possible to experimentally induce a phase change—an ultra-high-energy version of coaxing water into vapor by boiling it on the stove. You could effectively prove our universe is not the only one if you could produce phase-transitioned energy, though you would run the risk of it expanding out of control and destroying the Earth. “If those phases do exist—if they can be brought into being by some kind of experiment—then they certainly exist somewhere in the universe,” Kleban says.

    No one is yet trying to do this.

    There might be a (relatively) simpler way. Einstein’s general theory of relativity implies that our universe may have a “shape.” It could be either positively curved, like a sphere, or negatively curved, like a saddle. A negatively curved universe would be strong evidence of a multiverse, Nomura says. And a positively curved universe would show that there’s something wrong with our current theory of the multiverse, while not necessarily proving there’s only one. (Proving that is a next-to-impossible task. If there are other universes out there that don’t interact with ours in any sense, we can’t prove whether they exist.)

    In recent years, physicists have discovered that the universe appears almost entirely flat. But there’s still a possibility that it’s slightly curved in one direction or the other, and Nomura predicts that within the next few decades, measurements of the universe’s shape could be precise enough to detect a slight curvature. That would give physicists new evidence about the nature of the multiverse. “In fact, this evidence will be reasonably strong since we do not know any other theory which may naturally lead to a nonzero curvature at a level observable in the universe,” Nomura says.

    If the curvature turned out to be positive, theorists would face some very difficult questions. They would still be left without an explanation for why the expansion rate of the universe is what it is. The phases within string theory would also need re-examining. “We will face difficult problems,” Nomura says. “Our theory of dark energy is gone if it’s the wrong curvature.”

    But with the right curvature, a curved universe could reframe how physicists look at values that, at present, appear to be fundamental. If there were different universes with different phases of laws, we might not need to seek fundamental explanations for some of the properties our universe exhibits.

    And it would, of course, mean we are tinier still than we ever imagined. “It’s like another step in this kind of existential crisis,” Kleban says. “It would have a huge impact on people’s imaginations.”

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 12:39 pm on March 2, 2017 Permalink | Reply
    Tags: , Hugh Everett III, Max Tegmark, Multiverse theory   

    From Nautilus: “Evil Triumphs in These Multiverses, and God Is Powerless” 

    Nautilus

    Nautilus

    March 2, 2017
    Dean Zimmerman

    The challenge that the multiverse poses for the idea of an all-good, all-powerful God is often focused on fine-tuning. If there are infinite universes, then we don’t need a fine tuner to explain why the conditions of our universe are perfect for life, so the argument goes. But some kinds of multiverse pose a more direct threat. The many-worlds interpretation of quantum physicist Hugh Everett III and the modal realism of cosmologist Max Tegmark include worlds that no sane, good God would ever tolerate. The theories are very different, but each predicts the existence of worlds filled with horror and misery.

    Of course, plenty of thoughtful people argue that the Earth alone contains too much pain and suffering to be the work of a good God. But many others have disagreed, finding fairly nuanced things to say about what might justify God’s creation of a world that includes a planet like ours. For example, there is no forgiveness, courage, or fortitude without at least the perception of wrongs, danger, and difficulty. The most impressive human moral achievements seem to require such obstacles.

    Still, many horrifying things happen with nothing seemingly gained from them. And, Everett’s many-worlds and Tegmark’s modal realism both seem to imply that there are huge numbers of horrific universes inhabited solely by such unfortunates. Someone like myself, who remains attracted to the traditional picture of God as loving creator, is bound to find such consequences shocking, and will wonder just how strong the evidence is for these theories.

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    Mathematical Multiverse: According to Tegmark, for every possible way in which mathematical models dictate that matter can be consistently arranged to fill a spacetime universe, there exists such a universe. platonicsolids.info

    The many-worlds interpretation arises from a problem in quantum mechanics. The Schrödinger equation, the fundamental law of quantum theory, is a description of the evolving states of particles. But some of the states it predicts are combinations—“superpositions”—of seemingly incompatible states, such as a coin landing both on heads and tails. We can wonder: What explains the fact that we don’t ever observe the combined incompatible states, but only observe coins that land on heads or tails? One answer many theorists provide is that there is more going on than the Schrödinger equation describes. They add a process called “the collapse of the wave function,” which results in a definite outcome of heads or tails.

    But in the 1950s, Everett proposed a bold alternative. His theory has no collapses, but instead holds that all the parts of these combined—or “superposed”—states occur as parts of equally real but relatively isolated worlds. There are some complete copies of the universe in which the coin lands heads, and in others tails. And this applies to all other physical states—not just flipping coins. There are some universes where you make the train and get to work on time, and others where you don’t, and so on. These slight differences create multiple overlapping universes, all branching off from some initial state in a great world-tree.

    Old-fashioned quantum theory assigns a tiny likelihood to things going really badly in the future. It also implies that, from any point in our actual past, things could have gone much worse than they actually did. Since the many worlds interpretation takes these possibilities as actual occurrences, it predicts that there are branching universes in which things do go as awfully as possible.

    For example, whenever there is a minute chance of a catastrophe that leaves all human beings utterly miserable but just barely healthy enough to reproduce, there is a branch in the world-tree in which this sorry state of affairs actually happens, generation after generation. So there are worlds in which the emergence of the human race proves to be an unmitigated tragedy—or so it seems.

    A religious Everettian might hope that God would just prune the tree, and leave only those branches where good triumphs over evil. But as the philosopher Jason Turner of the University of Arizona has pointed out, such pruning undermines the Schrödinger equation. If God prevents the worst universes from emerging on the world-tree, then the deterministic law would not truly describe the evolution of the multiverse. Not all the superposed states that it predicts would actually occur, but only those that God judges to be “good enough.”

    Even if the pruning argument doesn’t work, there is another reason to think that the many-worlds interpretation doesn’t pose a serious threat to belief in God. Everett’s multiverse is just a much expanded physical world like this one, and finding we were in it would be like finding we were in a world with many more inhabited planets, some the amplified versions of the worst parts of our planet and others the amplified versions of the best parts. And so, even the worst parts of an Everettian multiverse are just particularly ugly versions of planet Earth. If an afterlife helps to explain our seemingly pointless suffering, then it would help explain the seemingly pointless suffering in even the worst of these Everett worlds, if we suppose that everyone in every branch, shows up in an afterlife.

    A theist may also take comfort in the fact that the many-worlds interpretation is still far from scientific orthodoxy. Although beloved by Oxford philosophers and accepted by a growing number of theoretical physicists, the theory remains highly controversial, and there are fundamental problems still being hashed out by the experts.

    The Everettian multiverse contains worlds that are hard to reconcile with a good God, but Tegmark’s multiverse might contain the worst. His theory, from his 2014 book Our Mathematical Universe, isn’t anchored in quantum mechanics but in modal realism, the doctrine proposed by philosopher David Lewis that every possible way that things could have gone—every consistent, total history of a universe—is as real as our own universe.

    Most philosophers talk about possible worlds as abstract things, like numbers, located outside of space and time, and as if they are very different from the actual world, which is substantial and made out of good old-fashioned matter. Tegmark agrees that other merely possible universes are abstract like numbers. But he denies that this makes them less real than the physical world. He thinks our universe is itself fundamentally a mathematical structure. Every physicist agrees that there is a set of mathematical entities standing in relations that perfectly models the distribution of fields and particles which a perfect physics would ascribe to our world. But Tegmark argues that our universe is identical to those mathematical things.

    If the world we inhabit is a purely mathematical structure, then all the other possible worlds we can imagine are equally real, their existence a necessary result of slightly different mathematical structures. For every possible way in which mathematical models dictate that matter can be consistently arranged to fill a spacetime universe, there exists such a universe.

    These possible arrangements of matter are bound to include ones corresponding to miserable universes full of pointless suffering—universes like all of the worst branches in the Everettian world-tree, and infinitely many more just as bad. But there would also be worlds that are worse. Unlike Everett’s worlds that are generated by a physical theory, Tegmark’s worlds are generated by mere possibility, which he identifies with mathematical consistency.

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    Budding Universes: Everett’s many worlds interpretation holds that there are multiple overlapping universes, all branching off from some initial state in a great world-tree. Jacopo Werther

    According to Tegmark, every possible story about living creatures that can be told by means of a mathematical model of the underlying physical facts is a true story. This means that even if some of Tegmark’s universes last long enough to include episodes in which their inhabitants have an afterlife, the existence of mathematical structures with every possible shape and size requires shorter worlds, too. And, infinitely many of these worlds will not last long enough for their inhabitants to enjoy an afterlife.

    There is one way, then, in which Everett’s multiverse poses less of a challenge to the theist than Tegmark’s. Everett’s theory doesn’t predict that God won’t do anything for people with short, miserable lives, and it doesn’t predict that God won’t somehow compensate them in an afterlife. Rather, it only predicts that there will be many more short, miserable lives than just the ones in our universe; whereas Tegmark’s theory implies that there have to be worlds in which there are short miserable lives and no afterlife.

    Adding insult to injury, since the horrifying worlds are consequences of pure mathematics, they exist as a matter of absolute necessity—so there is nothing God can do about it! The resulting picture will remain offensive to pious ears: A God who loved all creatures, but was forced to watch infinitely many of them endure lives of inconsolable suffering, would be a God embroiled in a tragedy.

    But there is still hope for the theist.

    Unlike the Everettian many worlds, which issue from experimental theories in physics and so are harder to dismiss, Tegmark’s theory is based on frail philosophical arguments. Take, for example, his claim that the physical universe is a purely mathematical structure: Why should we accept this? Ordinarily, physicists use mathematical structures as models for how the physical world might work, but they do not identify the mathematical model with the world itself. Tegmark’s reason for taking the latter approach is his conviction that physics must be purged of anything but mathematical terms. Non-mathematical concepts, he says, are “anthropocentric baggage,” and must be eliminated for objectivity’s sake. But why think that the only objective descriptions that can truly apply to things as they are in themselves are mathematical descriptions? So far as I can see, he never justifies this assumption. And such a counterintuitive starting point isn’t enough to threaten one’s belief in a benevolent God.

    Apart from the threats posed by the awful worlds within the multiverses of Everett and Tegmark, the idea that we inhabit a multiverse doesn’t have to undermine a belief in God. Every theist should take seriously the possibility that there might exist more universes, simply on the grounds that God would have reason to create more good stuff. Indeed, an infinitely ingenious, resourceful, and creative Being might be expected to work on canvases the size of worlds—some filled with frenetic activity, others more like vast minimalist paintings, many maybe even featuring intelligent beings like ourselves. And the theories of physicists such as Alan Guth and Andrei Linde—whose multiverse is an eternally inflating field that spins off baby universes—or Paul Steinhardt and Neil Turok—whose multiverse amounts to an endless cyclical universe punctuated by big bangs and big crunches—are arguably compatible with this theological vision.

    It may turn out that our world is fairly middling, one among the many universes that were good enough for God to create. And the idea of a multiverse consisting of disconnected spacetime universes may make it easier to believe that our world—our universe—is a part of a larger one that is on balance very good and created by a perfectly benevolent deity.

    Dean Zimmerman is a professor of philosophy at Rutgers University. Follow him on Twitter @deanwallyz.

    Rutgers smaller

    See the full article here .

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    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.

     
  • richardmitnick 11:55 am on September 2, 2016 Permalink | Reply
    Tags: , , , Multiverse theory,   

    From New Scientist: “Stars burning strangely make life in the multiverse more likely” 

    NewScientist

    New Scientist

    1 September 2016
    Jacob Aron

    1
    The answer’s in the stars. NASA, ESA, and E. Sabbi (ESA/STScI)

    Your existence depends on an improbable threesome. A delicate reaction within stars called the triple-alpha process, which creates carbon, is often used to support the idea of the multiverse. Now, two researchers argue that stars in other universes might have alternative ways of producing carbon, giving life as we know it a greater chance in multiple universes.

    The triple-alpha process gets its name from the three helium nuclei involved, which are also known as alpha particles. When the universe formed, it mostly consisted of hydrogen and helium, the simplest elements in the periodic table. Heavier elements were forged by the first stars, which fused the lighter nuclei together.

    There’s just one problem with this tidy model. Fuse two alpha particles together and you end up with a nucleus of four protons and four neutrons – namely beryllium-8, an isotope of the fourth element in the periodic table. But beryllium-8 is highly unstable and falls apart into two alpha particles within a fraction of a second. That means there isn’t much of it in our universe.

    “The natural stepping stone towards bigger elements is not present,” says Fred Adams of the University of Michigan in Ann Arbor.

    That’s no way to build a cosmos – yet puzzlingly, here we are. In the 1950s, astronomer Fred Hoyle figured out a solution. He argued that the abundance of carbon in the universe must be the result of a coincidence between the energy levels of alpha particles and carbon-12.

    Hoyle said that because the energy of three alpha particles creates carbon-12 with more energy than it needs, this extra energy must be equal to an excited state of carbon-12, allowing it to decay to its ground state and remain stable. This so-called “resonance” between the energy values makes it possible to form carbon by fusing three alpha particles together.

    Experiments later proved him right, but the resonance introduced its own problems. It occurs at a very particular value, 7.644 megaelectronvolts (MeV), and calculations show that the triple-alpha reaction is very sensitive to this value. Vary it by 0.1 MeV and the reaction will slow, producing less carbon, and a change of more than 0.3 MeV will halt carbon production altogether.

    Hoyle and others argued that this means our universe must have been fine-tuned for life. That resonance could have occurred at a range of energies, and the fact that it just happened to occur at the point we needed it to for our existence makes us astonishingly lucky.

    The odds of this happening at random are very low, and some argue that the only way to explain it is if our universe is just one of many in a multiverse. In that case, each universe could have slightly different values for the fundamental constants of physics. Life would arise only in suitable universes, meaning we shouldn’t be surprised to find ourselves in one of these.

    Another kind of universe

    But now Adams and his colleague Evan Grohs have argued that if other universes have different fundamental constants anyway, it’s possible to create a universe in which beryllium-8 is stable, thus making it easy to form carbon and the heavier elements.

    For this to happen would require a change in the binding energy of beryllium-8 of less than 0.1 MeV – something that the pair’s calculations show should be possible by slightly altering the strength of the strong force, which is responsible for holding nuclei together.

    Simulating how stars might burn in such a universe, they found that the stable beryllium-8 would produce an abundance of carbon, meaning life as we know it could potentially arise. “There are many more working universes than most people realise,” says Adams.

    These universes would arguably be more logical, he says, with stars steadily building elements along the periodic table without having to resort to the triple-alpha process. “We tend to think not only is our universe fine-tuned for us, we also think this is the best universe one could design,” says Adams. “In some sense, we’ve designed a better universe.”

    “It’s an interesting point, that there is another way of treating the physics that is no bigger than the tweaking you need to get rid of the carbon resonance,” says Martin Rees of the University of Cambridge.

    But Rees points out that we don’t really know if the multiverse exists, let alone if different universes would have different physics. “We need a measure of the relative probability of all those things to decide whether we should be surprised that we’re in the universe we are in,” he says.

    See the full article here .

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  • richardmitnick 5:46 pm on May 9, 2016 Permalink | Reply
    Tags: , , Multiverse theory,   

    From Science Alert: “WATCH: What’s outside the Universe?” 

    ScienceAlert

    Science Alert

    If the Universe is expanding, what’s it expanding into?

    22 APR 2016
    BEC CREW

    You’ve probably read about how the Universe is expanding, and has been expanding since the beginning of time. Over the course of 13.8 billion years or so, it’s stretched from the size of a billionth of a proton to the vast, unknowable expanse it is today.

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

    In fact, recent research suggests that it’s actually expanding faster than our current laws of physics can explain, and that’s kind of a problem.

    But all of that aside, whenever someone mentions our expanding Universe, we get a big, fat (turtle-surfing) elephant in the room. Because if the Universe is expanding, what exactly is it expanding into?

    As Fraser Cain from Universe Today explains, one possibility is that it’s expanding into an unfathomable cosmic void called the multiverse, which harbours not just our own Universe, but a multitude of parallel universes.

    Multiverse. Image credit: public domain, retrieved from https://pixabay.com/
    Multiverse. Image credit: public domain, retrieved from https://pixabay.com/

    We kinda want this to be the right answer, because if parallel universes really do exist, shit’s about to get so weird.

    As the video above explains, the laws of physics as we know them wouldn’t necessarily apply in other universes. Things are fundamental to us and everything we know, such as the pull of gravity or the binding strength of atoms, that simply would not exist in other universes.

    “For each one of these basic constants, it’s as if the laws of physics randomly rolled the dice, and came up with our Universe,” says Cain. “Maybe in another universe, the force of gravity is repulsive, or green, or spawns unicorns.”

    For a universe to form with the right combination of physical laws to allow for life to evolve, it’s a monkeys and typewriters situation – roll the dice an infinite number of times, and you’ll eventually get it right.

    So let’s say there are multiple universes – what if our Universe actually expanded so close to a neighbouring universe, it bumped into it?

    Turns out, signs of such a ‘cosmic bruise’ do exist, and scientists have been trying to explain them for decades. In fact, there’s one region in our Universe that’s so confounding, scientists have literally called it the Axis of Evil.

    According to Cain, there are a bunch of explanations that could explain the weirdness of the Axis of Evil more reliably than it being the site of a great ‘meeting of the universes’, but we can’t throw that possibility out just yet. And if it really is the case, what’s happening to the poor aliens living in the universe that we’re so rudely overlapping?

    I’ll let the video above handle that one, but let’s just say it’s somewhere between whatever the average of seven and green is, and the sum of 26 and unicorn dreams. Thanks a lot, science.

    See the full article here .

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  • richardmitnick 2:46 pm on May 7, 2016 Permalink | Reply
    Tags: , , Multiverse theory,   

    From SPACE.com- “Parallel Universes: Theories & Evidence” 

    space-dot-com logo

    SPACE.com

    April 28, 2016
    Elizabeth Howell

    1
    Our universe may live in one bubble that is sitting in a network of bubble universes in space. Credit: Sandy MacKenzie | Shutterstock

    Is our universe unique? From science fiction to science fact, there is a proposal out there that suggests that there could be other universes besides our own, where all the choices you made in this life played out in alternate realities. So, instead of turning down that job offer that took you from the United States to China, the alternate universe would show the outcome if you decided to venture to Asia instead.

    The idea is pervasive in comic books and movies. For example, in the 2009 “Star Trek” reboot, the premise is that the Kirk and Spock portrayed by Chris Pine and Zachary Quinto are in an alternate timeline apart from the William Shatner and Leonard Nimoy versions of the characters.

    The concept is known as a “parallel universe,” and is a facet of the astronomical theory of the multiverse.

    Multiverse. Image credit: public domain, retrieved from https://pixabay.com/
    Image credit: public domain, retrieved from https://pixabay.com/ from Ethan Siegel, “The multiverse and the road not traveled”

    There actually is quite a bit of evidence out there for a multiverse. First, it is useful to understand how our universe is believed to have come to be.

    Arguing for a multiverse

    Around 13.7 billion years ago, simply speaking, everything we know of in the cosmos was an infinitesimal singularity. Then, according to the Big Bang theory, some unknown trigger caused it to expand and inflate in three-dimensional space. As the immense energy of this initial expansion cooled, light began to shine through. Eventually, the small particles began to form into the larger pieces of matter we know today, such as galaxies, stars and planets.

    Inflationary Universe. NASA/WMAP
    Inflationary Universe. NASA/WMAP

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

    One big question with this theory is: are we the only universe out there. With our current technology, we are limited to observations within this universe because the universe is curved and we are inside the fishbowl, unable to see the outside of it (if there is an outside.)

    There are at least five theories why a multiverse is possible, as a 2012 Space.com article explained

    1. We don’t know what the shape of space-time is exactly. One prominent theory is that it is flat and goes on forever. This would present the possibility of many universes being out there. But with that topic in mind, it’s possible that universes can start repeating themselves. That’s because particles can only be put together in so many ways. More about that in a moment.

    2. Another theory for multiple universes comes from “eternal inflation.”

    Into what is the universe expanding NASA Goddard, Dana Berry
    Into what is the universe expanding NASA Goddard, Dana Berry

    Based on research from Tufts University cosmologist Alexander Vilenkin, when looking at space-time as a whole, some areas of space stop inflating like the Big Bang inflated our own universe. Others, however, will keep getting larger. So if we picture our own universe as a bubble, it is sitting in a network of bubble universes of space. What’s interesting about this theory is the other universes could have very different laws of physics than our own, since they are not linked.

    3. Or perhaps multiple universes can follow the theory of quantum mechanics (how subatomic particles behave), as part of the “daughter universe” theory. If you follow the laws of probability, it suggests that for every outcome that could come from one of your decisions, there would be a range of universes — each of which saw one outcome come to be. So in one universe, you took that job to China. In another, perhaps you were on your way and your plane landed somewhere different, and you decided to stay. And so on.

    4. Another possible avenue is exploring mathematical universes, which, simply put, explain that the structure of mathematics may change depending in which universe you reside. “A mathematical structure is something that you can describe in a way that’s completely independent of human baggage,” said theory-proposer Max Tegmark of the Massachusetts Institute of Technology, as quoted in the 2012 article. “I really believe that there is this universe out there that can exist independently of me that would continue to exist even if there were no humans.”

    5. And last but not least as the idea of parallel universes. To go back to the idea that space-time is flat, the number of possible particle configurations in multiple universes would be limited to 10^10^122 distinct possibilities, to be exact [Please explain the derivation of this number.]. So, with an infinite number of cosmic patches, the particle arrangements within them must repeat — infinitely many times over. This means there are infinitely many “parallel universes”: cosmic patches exactly the same as ours (containing someone exactly like you), as well as patches that differ by just one particle’s position, patches that differ by two particles’ positions, and so on down to patches that are totally different from ours.

    Arguing against a parallel universe

    Not everyone agrees with the parallel universe theory, however. A 2015 article on Medium by astrophysicist Ethan Siegal agreed that space-time could go on forever in theory, but said that there are some limitations with that idea.

    The key problem is the universe is just under 14 billion years old. So our universe’s age itself is obviously not infinite, but a finite amount. This would (simply put) limit the number of possibilities for particles to rearrange themselves, and sadly make it less possible that your alternate self did get on that plane after all to see China. [Sorry, I do not get this argument at all. Especially the fact that our universe is finite means there could be others.]

    Also, the expansion at the beginning of the universe took place exponentially because there was so much “energy inherent to space itself,” he said. But over time, that inflation obviously slowed — those particles of matter created at the Big Bang are not continuing to expand, he pointed out. Among his conclusions: that means that multiverses would have different rates of inflation and different times (longer or shorter) for inflation. This decreases the possibilities of universes similar to our own [Why do they need to be similar?].

    “Even setting aside issues that there may be an infinite number of possible values for fundamental constants, particles and interactions, and even setting aside interpretation issues such as whether the many-worlds-interpretation actually describes our physical reality,” Siegal said, “the fact of the matter is that the number of possible outcomes rises so quickly — so much faster than merely exponentially — that unless inflation has been occurring for a truly infinite amount of time, there are no parallel universes identical to this one [same question.].”

    But rather than seeing this lack of other universes as a limitation, Siegal instead takes the philosophy that it shows how important it is to celebrate being unique. He advises to make the choices that work for you, which “leave you with no regrets.” That’s because there are no other realities where the choices of your dream self play out; you, therefore, are the only person that can make those choices happen [I really enjoy Ethan Siegel. He is a stellar (no pun intended) science communicator who obviously knows his stuff. But this last point is not Cosmology, Astronomy, or Astrophysics. It is Philososphy. Is Ethan also a philosopher?]

    See the full article here .

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  • richardmitnick 4:58 am on February 6, 2016 Permalink | Reply
    Tags: , , Multiverse theory,   

    From Ethan Siegel: “The Multiverse And The Road Not Traveled” 

    Starts with a bang
    Starts with a Bang

    2.5.16
    Ethan Siegel

    Multiverse
    Image credit: public domain, retrieved from https://pixabay.com/en/globe-earth-country-continents-73397/

    Is there an alternate Universe with a different version of you, and all the outcomes you didn’t choose?

    “Go then, there are other worlds than these.” –Stephen King, The Dark Tower

    The Multiverse is a word used by a great many people, yet not everyone means the same thing when they say it. Reader (and my former Lewis & Clark student!) Chris Olson wrote in and asked about two different meanings in particular:

    In what way, if at all, are the ideas of Everettian Quantum Mechanics and Eternal Inflation related? Can we distinguish between the multiverse as implied by each?

    There are a lot of different possibilities for what people might mean by Multiverse as opposed to Universe, so let’s go through them, starting from the least conservative (with the fewest new assumptions) and moving on through the increasingly more speculative.

    1.) The Universe beyond what we can observe. When we speak of “the Universe,” we often mean the Universe that we can observe. Because the Universe that we know and recognize began with an event we know as the hot Big Bang — where a hot, dense, matter-and-radiation-filled Universe emerged and began expanding, cooling and collapsing into clumps under its own gravity — some 13.8 billion years ago, we’re fundamentally limited in terms of what we can see. Signals may have emerged at exactly that instant and traveled, unimpeded, at the speed of light [in a vacuum] through the constantly expanding Universe all that time, and yet there’s a finite distance that signal could’ve traveled. In our Universe with normal matter, dark matter, dark energy, neutrinos, radiation and all we know, that corresponds to a distance of 46.1 billion light years, centered on us.

    But there’s no reason to believe there isn’t plenty more Universe out there. There simply hasn’t been enough time for all of what we know as the unobservable Universe to reach us. As time continues to go on, more and more of the Universe will be revealed to us at our vantage point, even factoring in dark energy. But how much more is out there? Based on the observed curvature of the space we can observe, what exists compared to what we can see is at least 250 times as much in all dimensions, meaning the Universe has (250³) or over fifteen million times the volume of space (and stuff) that we can see. It’s possibly even infinite, although we don’t know for sure. However, that’s just the most conservative version of the Multiverse out there: more stuff like us. But there could be…

    Inflation to gravitational waves derived from ESAPlanck and the DoENASA NSF interagency task force on CMB research
    Inflation to gravitational waves derived from ESA/Planck and the DOE/NASA NSF interagency task force on CMB research

    ESA Planck
    ESA/Planck

    2.) Different “pockets” of Universe where inflation ends. The Big Bang might have been the beginning of what we know as “our” Universe, but it’s not possible (nor accurate) to extrapolate backwards to an arbitrarily hot, dense state. Instead, we know (from the cosmic microwave background [CMB]) that the maximum temperature the Universe reached in the hot Big Bang was no greater than about 10³⁰ K.

    Cosmic Background Radiation Planck
    CMB per ESA/Planck

    Now, that’s a huge number, but it’s not hot enough to reach the Planck scale, a singularity, or to cause the laws of physics as we know them to break down. One of the things it tells us is that there was something else prior to the Big Bang, consistent with what we perceive as the initial conditions to set it up: cosmic inflation. Inflation is basically a period in the Universe prior to the Big Bang that sets it up by making it:

    stretched flat,
    empty of all relic particles created prior to the end of inflation,
    with the same temperature and energy density everywhere,
    that contains a uniform spectrum of fluctuations.

    Inflation is like a ball that rolls down a hill, only it’s a quantum ball, so there are probabilities in every location that it will (or won’t) roll down that hill.

    Inflation in quantum terms
    Images credit: E. Siegel. Inflation ends (top) when a ball rolls into the valley. But the inflationary field is a quantum one (middle), spreading out over time. While many regions of space (purple, red and cyan) will see inflation end, many more (green, blue) will see inflation continue, potentially for an eternity (bottom).

    In the places where inflation stays atop the hill, not rolling down, inflation continues, creating more and more (inflating) space. Where it does roll down the hill, inflation comes to an end, creating the hot Big Bang. While inflation came to an end in our region of space some 13.8 billion years ago, it’s unreasonable to expect it came to an end everywhere. Instead, some regions of space will continue to inflate forever. So long as the rate at which space inflates is greater than the rate at which pockets of inflation come to an end (which it is in all working models), there will both be an infinite number of “Big Bangs” that are disconnected from one another, and also inflation will continue in the regions where it doesn’t end for an eternity into the future.

    3.) Different versions of you in different sections of the Multiverse. There are some 10⁹⁰ particles (including photons and neutrinos) in our observable Universe, all having undergone interactions and collisions with many other particles. They have positions and momenta, they have their own unique history, and some ~10²⁸ of them combine, right now, to make each and every one of us. If we take the expected rate of space’s expansion during inflation, and allow that most of space has been expanding at that rate for the entire history of our Universe (13.8 billion years), we can calculate how many possible Universes there are similar to our own.

    Inflationary Universe

    It’s a big number! Realistically, we’re talking about at least (10¹⁰)^50 Universes that started off with initial conditions that might be very similar to our own. That’s 10¹⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰⁰ Universes, which might be one of the biggest numbers you’ve ever imagined. And yet, there are numbers that are bigger that describe how many possible outcomes there are for particle interactions; remember, if you want to get an identical you, you need for the entire Universe’s history to have unfolded the exact same way ours did, up until you decided one way or the other to:

    take that job,
    buy that house,
    kiss the person you like,

    or whatever other decision you did (or didn’t) make.

    Our Universe has a lot of particles in it: about 10⁹⁰. Every time two particles interact, there’s not just one possible outcome, but an entire quantum spectrum of outcomes. As sad as the case is, there are way more than (10⁹⁰)! possible outcomes for the particles in the Universe, and that number is many googolplexes times larger than a paltry number like (10¹⁰)^50. In other words, the number of possible outcomes from particles in any Universe interacting with one another tends towards infinity faster than the number of possible Universes increases due to inflation. You would have needed inflation to have been going on literally forever before our Big Bang for this to be possible, and that would violate the Borde-Guth-Vilenkin singularity theorem, which shows that inflation cannot be past-timelike complete. In other words, this one seems unlikely.

    4.) Entangled versions of you in different pocket Universes. This reaches for the second part of Chris’ question: the part about Everettian quantum mechanics. Assuming that option 3 is true, and that there are other versions of you in other pockets of the Multiverse, are they entangled? Quantum physics is open to interpretation, meaning that there are a number of different approaches to it (or ways of looking at it) that give the same answers. Quantum systems can either have wavefunctions that spread out over time and instantaneously collapse when an interaction occurs, for instance, or can have an ensemble of possible outcomes that one is selected from as we go down that path. Hugh Everett’s interpretation — the Many-Worlds Interpretation of quantum mechanics — holds that there are an infinite number of parallel Universes out there, and whenever a decision is made, we go down some of those paths and not others. So there are Universes out there where you did (and didn’t) take that job, where you did (and didn’t) buy that house, and where you did (and didn’t) kiss your love interest at the critical moment, among others.

    Even if a truly infinite number of Universes did exist, there is no way to create an entanglement between them that’s clear, although that doesn’t stop people from speculating. This is another untestable possibility, and one that requires a number of quite extraordinary assumptions. Yet, we can go even further down the Multiverse rabbit-hole, if we want.

    5.) Different Universes with different laws of physics. This is an even more highly speculative one, predicated on an assumption: that when inflation ends, there are multiple ways for it to end, resulting in different laws of physics and/or fundamental constants from the Universe we presently inhabit. This would be a Multiverse where some pockets of it recollapse, others expand so rapidly that no stars or galaxies ever form; where some have no dark matter and others have all dark matter; where some have bigger or smaller or even negative cosmological constants. There may even be Universes out there that have entirely different particles and interactions from our own. There is no way to test this.

    From what we can observe, we are pretty sure that option 1 is true: there is more Universe out there than what we can see. From what we know of inflation, we’re pretty sure option 2 is also true: there are regions of space outside of our Universe where inflation ended at different times, each with their own hot Big Bangs, as well as regions where inflation is still ongoing, and where it will go on eternally into the future. And from what we know of different infinities, we’re pretty sure that number 3 isn’t true, and hence option four cannot be true either. Option five? Many entertain this, but there’s no evidence for it, it’s not testable, and the fact that inflation ends well below the Planck scale gives us serious reasons to doubt that this is even possible. (Yet many will continue to entertain it without ever giving this a second thought.) The Multiverse is almost definitely real beyond any reasonable doubt, but what version of the Multiverse you subscribe to makes all the difference in the Universe.

    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 5:23 pm on October 28, 2015 Permalink | Reply
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    From New Scientist: “Mystery bright spots could be first glimpse of another universe” 

    NewScientist

    New Scientist

    28 October 2015
    Joshua Sokol

    Light given off by hydrogen shortly after the big bang has left some unexplained bright patches in space. Are they evidence of bumping into another universe?

    1

    THE curtain at the edge of the universe may be rippling, hinting that there’s more backstage. Data from the European Space Agency’s Planck telescope could be giving us our first glimpse of another universe, with different physics, bumping up against our own.

    ESA Planck
    ESA/Planck

    That’s the tentative conclusion of an analysis by Ranga-Ram Chary, a researcher at Planck’s US data centre in California. Armed with Planck’s painstaking map of the cosmic microwave background (CMB) – light lingering from the hot, soupy state of the early universe – Chary revealed an eerie glow that could be due to matter from a neighbouring universe leaking into ours.

    Cosmic Background Radiation Planck
    CMB per Planck

    This sort of collision should be possible, according to modern cosmological theories that suggest the universe we see is just one bubble among many. Such a multiverse may be a consequence of cosmic inflation, the widely accepted idea that the early universe expanded exponentially in the slimmest fraction of a second after the big bang.

    Once it starts, inflation never quite stops, so a multitude of universes becomes nearly inevitable. “I would say most versions of inflation in fact lead to eternal inflation, producing a number of pocket universes,” says Alan Guth of the Massachusetts Institute of Technology, an architect of the theory.

    Energy hidden in empty space drives inflation, and the amount that’s around could vary from place to place, so some regions would eventually settle down and stop expanding at such a manic pace. But the spots where inflation is going gangbusters would spawn inflating universes. And even areas within these new bubbles could balloon into pocket universes themselves.

    Like compositions on the same theme, each universe produced this way would be likely to have its own spin on physics. The matter in some bubbles – the boring ones – would fly apart within 10-40 seconds of their creation. Others would be full of particles and rules similar to ours, or even exactly like ours. In the multiverse of eternal inflation, everything that can happen has happened – and will probably happen again.

    That notion could explain why the physical constants of our universe seem to be so exquisitely tuned to allow for galaxies, stars, planets and life (see Just right for life? below).

    Sadly, if they do exist, other bubbles are nigh on impossible to learn about. With the space between them and us always expanding, light is too slow to carry any information between different regions. “They could never even know about each other’s existence,” says Matthew Johnson of York University in Toronto, Canada. “It sounds like a fun idea but it seems like there’s no way to test it.”

    Bubble trouble

    However, if two bubbles started out close enough that they touched before expanding space pushed them apart forever, they could leave an imprint on each other. “You need to get lucky,” Johnson says.

    In 2007, Johnson and his PhD adviser proposed that these clashing bubbles might show up as circular bruises on the CMB. They were looking for cosmic dance partners that resembled our own universe, but with more of everything. That would make a collision appear as a bright, hot ring of photons.

    By 2011, they were able to search for them in data from NASA’s WMAP probe, the precursor to Planck.

    NASA WMAP
    NASA/WMAP

    Cosmic Microwave Background WMAP
    CMB per WMAP

    But they came up empty-handed.

    Now Chary thinks he may have spotted a different signature of a clash with a foreign universe.

    “There are two approaches, looking for different classes of pocket universes,” Johnson says. “They’re hunting for lions, and we’re hunting for polar bears.”

    Instead of looking at the CMB itself, Chary subtracted a model of the CMB from Planck’s picture of the entire sky. Then he took away everything else, too: the stars, gas and dust.

    With our universe scrubbed away, nothing should be left except noise. But in a certain frequency range, scattered patches on the sky look far brighter than they should. If they check out, these anomalous clumps could be caused by cosmic fist-bumps: our universe colliding with another part of the multiverse (arxiv.org/abs/1510.00126).

    These patches look like they come from the era a few hundred thousand years after the big bang when electrons and protons first joined forces to create hydrogen, which emits light in a limited range of colours. We can see signs of that era, called recombination, in the light from that early hydrogen. Studying the light from recombination could be a unique signature of the matter in our universe – and potentially distinguish signs from beyond.

    “This signal is one of the fingerprints of our own universe,” says Jens Chluba of the University of Cambridge. “Other universes should leave a different mark.”

    Since this light is normally drowned out by the glow of the cosmic microwave background, recombination should have been tough for even Planck to spot. But Chary’s analysis revealed spots that were 4500 times as bright as theory predicts.

    One exciting explanation for this is if a surplus of protons and electrons – or something a lot like them – got dumped in at the point of contact with another universe, making the light from recombination a lot brighter. Chary’s patches require the universe at the other end of the collision to have roughly 1000 times as many such particles as ours.

    “To explain the signals that Dr Chary found with the cosmological recombination radiation, one needs a large enhancement in the number of [other particles] relative to photons,” Chluba says. “In the realm of alternative universes, this is entirely possible.”

    Of course there are caveats, and recent history provides an important reality check. In 2014, a team using the BICEP2 telescope at the South Pole announced another faint signal with earth-shaking cosmological implications.

    BICEP 2
    BICEP2 on the right, South Pole telescope on the left

    The spirals of polarised light, spotted in the cosmic background, would have provided more observational evidence for the idea of inflation and helped us understand how inflation occurred. But it turned out that signal came from dust grains within our galaxy.

    Gravitational Wave Background
    Theorized gravitational waves

    2

    Princeton University’s David Spergel, who played a major role in debunking the BICEP2 finding, thinks dust may again be clouding our cosmological insights. “I suspect that it would be worth looking into alternative possibilities,” he says. “The dust properties are more complicated than we have been assuming, and I think that this is a more plausible explanation.”

    Joseph Silk of Johns Hopkins University in Baltimore, Maryland, is even more pessimistic, calling claims of an alternate universe “completely implausible”. While he thinks the paper is a good analysis of anomalies in Planck data, Silk also believes something is getting in the way. “My view is that they are almost certainly due to foregrounds,” he says.

    Chary acknowledges that his idea is as tentative as it is exciting. “Unusual claims like evidence for alternate universes require a very high burden of proof,” he writes.

    He makes an effort to rule out more prosaic explanations. If it is dust, Chary argues, it would be the coldest dust we’ve ever seen. It’s probably not noise masquerading as a signal. It could be carbon monoxide moving toward us, but we don’t usually see that. It could be faraway carbon, but that emission is too weak.

    “I am certain he made every effort to ensure that the analysis is solid,” says Chluba. Even so, foregrounds and poorly understood patterns could still be the source of the signals. “It will be important to carry out an independent analysis and confirm his finding,” Chluba says.

    Sensitive solutions

    One obstacle to checking is that we’re limited by the data itself. Planck was hyper-sensitive to the cosmic microwave background, but it wasn’t intended to measure the spectral distortions Chary is looking for. Johnson’s team also plans to use Planck to look for their own alternate universes, once the data they need is released to the public – but they estimate that Planck will only make them twice as sensitive to the bubble collisions they’re looking for as they were with WMAP.

    An experiment that could help might be on its way. Scientists at NASA’s Goddard Space Flight Center plan to submit PIXIE, the Primordial Inflation Explorer, to be considered for funding at the end of 2016.

    NASA PIXIE
    NASA Goddard PIXIE

    PIXIE’s spectral resolution could help characterise Chary’s signals if they really are there, Chluba says. But even if they aren’t, reconstructing how inflation happened could still lead us once again back to the multiverse – and tell us what kind of bubble collisions we should look for next.

    __________________________________________________________________________

    Just right for life?

    If our universe is just one of many, that could explain why it seems so exquisitely tuned for our existence.

    If dark energy, the repulsive influence hiding in empty space that speeds up the expansion of the universe, were just a little stronger, matter would be flung apart before galaxies could ever form. If it were attractive instead, the universe would collapse. But it is shockingly puny, and that’s weird, unless our universe is one of many in the multiverse.

    Compared with what we might expect from quantum theory, dark energy is 120 orders of magnitude too small. So far, no compelling explanation for that discrepancy has emerged. But if the multiverse exists, and dark energy varies from bubble to bubble (see main story), that might not seem so strange.

    That’s because our own universe might be an oddball compared to most bubbles. In many, dark energy would be too strong for galaxies, stars and planets to form, but not in all. “Plenty of them would have energies as small as what we observe,” says physicist Alan Guth of MIT.

    That still leaves us struggling to explain why our universe is one of the special ones. Our best answer so far, Guth says, is a philosophical headache: our universe has to be special because we are alive in it. In a more average region, where dark energy is stronger, stars, planets, and life would never have evolved.

    That could mean life only exists in a sliver of the multiverse, with any conscious beings convinced their own slice of space is special, too.

    __________________________________________________________________________

    See the full article here .

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  • richardmitnick 12:00 pm on October 19, 2015 Permalink | Reply
    Tags: , , , Multiverse theory   

    From Don Lincoln at FNAL: “What the heck is a Multiverse? ” Video 

    FNAL II photo

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

    10.16.15

    The idea of a multiverse (short for multiple universes) can seem absurd. After all, the definition of universe means everything, so what does it mean to have multiple universes? In this video, Fermilab’s Dr. Don Lincoln lists a couple possible definitions for a multiverse. The reality in which we live might indeed be a very strange place.

    Watch, enjoy, learn.

    See the full article here .

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    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 11:20 am on July 28, 2015 Permalink | Reply
    Tags: , Multiverse theory,   

    From Symmetry: “Is this the only universe?” 

    Symmetry

    July 28, 2015
    Laura Dattaro

    1
    Artwork by Sandbox Studio, Chicago with Ana Kova

    Human history has been a journey toward insignificance.

    As we’ve gained more knowledge, we’ve had our planet downgraded from the center of the universe to a chunk of rock orbiting an average star in a galaxy that is one among billions.

    So it only makes sense that many physicists now believe that even our universe might be just a small piece of a greater whole. In fact, there may be infinitely many universes, bubbling into existence and growing exponentially. It’s a theory known as the multiverse.

    One of the best pieces of evidence for the multiverse was first discovered in 1998, when physicists realized that the universe was expanding at ever increasing speed. They dubbed the force behind this acceleration dark energy. The value of its energy density, also known as the cosmological constant, is bizarrely tiny: 120 orders of magnitude smaller than theory says it should be.

    For decades, physicists have sought an explanation for this disparity. The best one they’ve come up with so far, says Yasunori Nomura, a theoretical physicist at the University of California, Berkeley, is that it’s only small in our universe. There may be other universes where the number takes a different value, and it is only here that the rate of expansion is just right to form galaxies and stars and planets where people like us can observe it. “Only if this vacuum energy stayed to a very special value will we exist,” Nomura says. “There are no good other theories to understand why we observe this specific value.”

    For further evidence of a multiverse, just look to string theory, which posits that the fundamental laws of physics have their own phases, just like matter can exist as a solid, liquid or gas. If that’s correct, there should be other universes where the laws are in different phases from our own—which would affect seemingly fundamental values that we observe here in our universe, like the cosmological constant. “In that situation you’ll have a patchwork of regions, some in this phase, some in others,” says Matthew Kleban, a theoretical physicist at New York University.

    These regions could take the form of bubbles, with new universes popping into existence all the time. One of these bubbles could collide with our own, leaving traces that, if discovered, would prove other universes are out there. We haven’t seen one of these collisions yet, but physicists are hopeful that we might in the not so distant future.

    If we can’t find evidence of a collision, Kleban says, it may be possible to experimentally induce a phase change—an ultra-high-energy version of coaxing water into vapor by boiling it on the stove. You could effectively prove our universe is not the only one if you could produce phase-transitioned energy, though you would run the risk of it expanding out of control and destroying the Earth. “If those phases do exist—if they can be brought into being by some kind of experiment—then they certainly exist somewhere in the universe,” Kleban says.

    No one is yet trying to do this.

    There might be a (relatively) simpler way. Einstein’s general theory of relativity implies that our universe may have a “shape.” It could be either positively curved, like a sphere, or negatively curved, like a saddle. A negatively curved universe would be strong evidence of a multiverse, Nomura says. And a positively curved universe would show that there’s something wrong with our current theory of the multiverse, while not necessarily proving there’s only one. (Proving that is a next-to-impossible task. If there are other universes out there that don’t interact with ours in any sense, we can’t prove whether they exist.)

    In recent years, physicists have discovered that the universe appears almost entirely flat. But there’s still a possibility that it’s slightly curved in one direction or the other, and Nomura predicts that within the next few decades, measurements of the universe’s shape could be precise enough to detect a slight curvature. That would give physicists new evidence about the nature of the multiverse. “In fact, this evidence will be reasonably strong since we do not know any other theory which may naturally lead to a nonzero curvature at a level observable in the universe,” Nomura says.

    If the curvature turned out to be positive, theorists would face some very difficult questions. They would still be left without an explanation for why the expansion rate of the universe is what it is. The phases within string theory would also need re-examining. “We will face difficult problems,” Nomura says. “Our theory of dark energy is gone if it’s the wrong curvature.”

    But with the right curvature, a curved universe could reframe how physicists look at values that, at present, appear to be fundamental. If there were different universes with different phases of laws, we might not need to seek fundamental explanations for some of the properties our universe exhibits.

    And it would, of course, mean we are tinier still than we ever imagined. “It’s like another step in this kind of existential crisis,” Kleban says. “It would have a huge impact on people’s imaginations.”

    See the full article here.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 1:57 pm on January 28, 2015 Permalink | Reply
    Tags: Multiverse theory, , ,   

    From NPR: “The Most Dangerous Ideas In Science” 

    NPR

    National Public Radio (NPR)

    January 27, 2015
    Adam Frank, University of Rochester

    1
    Some physicists are pushing back against ideas like string theory and the multiverse. Here, we see a computer-generated image of a black hole, which might, ultimately, be explained by ideas like string theory.

    There’s a battle going on at the edge of the universe, but it’s getting fought right here on Earth. With roots stretching back as far as the ancient Greeks, in the eyes of champions on either side, this fight is a contest over nothing less than the future of science. It’s a conflict over the biggest cosmic questions humans can ask and the methods we use — or can use — to get answers for those questions.

    Cosmology is the study of the universe as a whole: its structure, its origins and its fate. Fundamental physics is the study of reality’s bedrock entities and their interactions. With these job descriptions it’s no surprise that cosmology and fundamental physics share a lot of territory. You can’t understand how the universe evolves after the Big Bang (a cosmology question) without understanding how matter, energy, space and time interact (a fundamental physics question). Recently, however, something remarkable has been happening in both these fields that’s raising hackles with some scientists. As physicists George Ellis and Joseph Silk recently put it in Nature:

    “This year, debates in physics circles took a worrying turn. Faced with difficulties in applying fundamental theories to the observed Universe, some researchers called for a change in how theoretical physics is done. They began to argue — explicitly — that if a theory is sufficiently elegant and explanatory, it need not be tested experimentally, breaking with centuries of philosophical tradition of defining scientific knowledge as empirical.”

    The root of the problem rests with two ideas/theories now central for some workers in cosmology (even if they remain problematic for physicists as a whole). The first is string theory, which posits that the world is made up not of point particles but of tiny vibrating strings. String theory only works if the universe has many “extra” dimensions of space other than the three we experience. The second idea is the so-called multiverse which, in its most popular form, claims more than one distinct universe emerged from the Big Bang. Instead, adherents claim, there may be an almost infinite (if not truly infinite) number of parallel “pocket universes,” each with their own version of physics.

    Both string theory and the multiverse are big, bold reformulations of what we mean when we say the words “physical reality.” That is reason enough for them to be contentious topics in scientific circles. But in the pursuit of these ideas, something else — something new — has emerged. Rather than focusing just on questions about the nature of the cosmos, the new developments raise critical questions about the basic rules of science [scientific method] when applied to something like the universe as a whole.

    Here is the problem: Both string theory and the multiverse posit entities that may, in principle or in practice, be unobservable. Evidence for the extra dimensions needed to make string theory work is likely to require a particle accelerator of astronomical proportions. And the other pocket universes making up the multiverse may lie permanently over our “horizon,” such that we will never get direct observations of their existence. It’s this specific aspect of the theories that has scientists like Ellis and Silk so concerned. As they put it:

    “These unprovable hypotheses are quite different from those that relate directly to the real world and that are testable through observations — such as the standard model of particle physics and the existence of dark matter and dark energy. As we see it, theoretical physics risks becoming a no-man’s-land between mathematics, physics and philosophy that does not truly meet the requirements of any.”

    What they, and others, find particularly worrisome is the claim that our attempts to push back frontiers in cosmology and fundamental physics have taken us into a new domain where new rules of science are needed. Some call this domain “post-empirical” science. Recently, for example, the philosopher of physics Richard Dawid has argued that in spite of the fact that no evidence for string theory exists (even after three decades of intense study), it must still be considered the best candidate for a path forward. As Dawid puts it, such arguments include “no-one has found a good alternative to string theory. Another [reason to accept string theory is] one uses the observation that theories without alternatives tended to be viable in the past.”

    Sean Carroll, a highly respected and philosophically astute physicist, takes a different approach from Dawid. For Carroll, it is the concept of falsifiability, which was central to Sir Karl Raimund Popper’s famous philosophy of science, that is too limited for the playing fields we now find ourselves working on. As Carroll writes:

    “Whether or not we can observe [extra dimensions or other universes] directly, the entities involved in these theories are either real or they are not. Refusing to contemplate their possible existence on the grounds of some a priori principle, even though they might play a crucial role in how the world works, is as non-scientific as it gets.”

    Thus, for Carroll, even if a theory predicts entities that can’t be directly observed, if there are indirect consequences of their existence we can confirm, then those theories (and those entities) must be included in our considerations.

    Other scientists, however, are not convinced. High-energy physicist Sabine Hossenfelder called Dawid’s kind of post-empirical science an “oxymoron.” More importantly, for scientists like Paul Steinhardt and collaborators, the new ideas are becoming “post-modern.” They use the term in the sense that without more definitive connections to data, the ideas will not be abandoned because a community exists that continues to support them.

    This is the possibility that troubles Ellis and Silk most of all:

    “In our view, the issue boils down to clarifying one question: What potential observational or experimental evidence is there that would persuade you that the theory is wrong and lead you to abandoning it? If there is none, it is not a scientific theory.”

    String theory and the multiverse are exciting ideas in and of themselves. If either one were true, it would have revolutionary consequences for our understanding of the cosmos. But, as debates about post-empirical science and falsifiability demonstrate, critics of these untested theories fear they may be leading the field down a difficult — and ultimately damaging — path. That’s why, one way or another, they may be science’s most dangerous ideas.

    See the full article here.

    My indebtedness to Don Lincoln of FNAL for pointing out this article using a Facebook post. Thanks, Dr Lincoln

    Please help promote STEM in your local schools.
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    Stem Education Coalition

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    • s7hummel 1:48 am on January 29, 2015 Permalink | Reply

      was a little empty without YOU! Welcome back!

      Like

    • richardmitnick 3:51 am on January 29, 2015 Permalink | Reply

      I don’t understand your comment. I approved it just to ask you what you mean. I have been posting constantly.

      Like

    • s7hummel 2:03 am on January 30, 2015 Permalink | Reply

      seemed to me that a few days there was no your entries. But maybe i missed something. Indeed, what can YOU expect from a stupid Pole. Sorry!

      Like

    • richardmitnick 4:34 am on January 30, 2015 Permalink | Reply

      Hey, no problem. I am glad to have you aboard. I hope that you continue to find articles interesting.

      Liked by 1 person

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