The Cosmos

06
Dec

Seeking Signs of the Multiverse

Is our universe just one of many? The “multiverse” has occupied the pages of theorists’ notebooks for decades. Now, astronomers are on the brink of testing this hypothesis as they begin the search for evidence of universes beyond our own.

Though the first test, using data from a satellite called WMAP, came up empty-handed, cosmologists are now turning their attention to fresh results from the European Space Agency’s Planck satellite, which is mapping the cosmic microwave background radiation and creating an all-sky temperature map with three times greater resolution than its predecessor. If other universes exist, it is possible that they have collided with our own universe. Physicists believe that such a collision would leave an imprint on the background radiation in the form of a disc-shaped region of very-slightly different temperature than the surrounding background. Planck’s improved resolution will sharpen the edges of any collision-induced disc in the background radiation.

Planck is also studying a property of the background radiation called polarization, which describes the angle at which the electromagnetic waves vibrate in relation to the direction they are traveling. (You encounter polarization every time you slip on polarized sunglasses; because sunlight reflected off the horizontal surface of a road or a body of water becomes polarized, these special lenses can selectively block it out, reducing glare.) Polarization is a sensitive probe of the conditions that prevailed when the photons were released. Though WMAP was not sensitive enough to see any patterns in the polarization of the photons, Planck, with three times more sensitivity, is expected to see such patterns, which just might contain the fingerprint of so-called “bubble collisions.”

What would such a signal look like? Matthew Kleban of New York University and his colleagues have shown that bubble collisions should leave two highly-polarized rings surrounding the temperature disc.

“According to our predictions for the probability of these bubble collisions, we are more likely to see larger discs than smaller discs,” says Kleban. “And it turns out that for larger discs, polarization is actually a very sensitive test. The signal is more distinctive, and it gets stronger as the disc gets bigger.”

So, if we did see such signatures in the Planck data, what would it prove?

“It would be conclusive of the fact that before our observable universe was formed, there was this precursor phase, and you could say with great certainty that that precursor phase still exists, somewhere, and that we are one small little pocket in a much, bigger multiverse,” says Matthew Johnson of the Perimeter Institute for Theoretical Physics. “It would be fairly direct evidence for the existence of a multiverse.”

That would be revolutionary. It would also focus attention on an unorthodox view of quantum mechanics which is already growing in popularity: the many-worlds hypothesis.

Proposed in the 1950s by physicist Hugh Everett, the many-worlds hypothesis takes a radical view of what happens to the wave function—the equation that spells out the probability of finding a quantum system in a particular state—when a measurement is made. In Niels Bohr’s Copenhagen Interpretation, any time we make a measurement, the wave function “collapses,” giving us one outcome from an infinity of possibilities. Everett argued that the wave function never collapses. Rather, every possibility exists in a parallel universe. This suggests a staggeringly large number of other worlds.

But are they the same “other worlds” predicted by eternal inflation? Recent work by Leonard Susskind of Stanford University and Raphael Bousso of the University of California, Berkeley, hints that the many worlds of quantum theory and the multiverse of eternal inflation might be two sides of the same coin. By linking eternal inflation with Everett’s many worlds, Susskind and Bousso hope to establish the physical meaning of the probabilistic predictions that have confounded quantum physicists for decades.

Yet even if bubble universes exist, the odds might be against spotting a collision. “Everyone thinks that we would have to be lucky,” says Susskind. “I would not try to estimate just how lucky, but at least somewhat lucky.” After all, our universe is much, much bigger than what we can see—so the collision may lie beyond our cosmic horizon.

Henry David Thoreau once wrote, “The universe is wider than our views of it.” That is true, of course. But the quest to find evidence of universes beyond our own shows that our “view” of the universe is a window that widens just as far as technology, theory, and the laws of physics can stretch it.

Tell us what you think on Twitter, Facebook, or email.

aananthaswamy-big

Anil Ananthaswamy

    Anil Ananthaswamy tries to exist in a quantum superposition of lives in Berkeley, CA, and Bangalore, India. A former deputy news editor and now consultant for New Scientist magazine, Anil is also the author of The Edge of Physics, an extreme physics travelogue. He studied electronics and electrical engineering at the Indian Institute of Technology, Madras, India, and the University of Washington, Seattle, and trained as a journalist at the University of California, Santa Cruz.

    • Larry Rosenthal

      Is there another example of two macro systems colliding, or bumping, without spectacular damage done to one or both of those systems? Are there reasons to presume that the extreme limits of our otherwise infinite universe would behave differently than the entire contents of that universe? Even the prediction of discs presupposes universes that are round. At least observable evidence supports that prediction, so Bravo. It all sounds wonderful. It just doesn’t sound like science.

      • http://www.facebook.com/people/Pam-Uphoff/1533576376 Pam Uphoff

        It’s definitely science. They’ve made a prediction and now have an instrument that ought to be sensitive enough to test it. It’s the testing that makes it science, whether the results suport or demolish the theory.

        • Larry Rosenthal

          But the prediction has no basis in scientific observation. The theories upon which the predictions appear to have been predicated fail to address anything observable – they’re guesses, which have been sanctified as predictions and which will now be tested. And if the tests fail, they will say they don’t have strong enough equipment yet.

    • PeterKinnon

      The popular portrayal of such speculations as science is very inappropriate and misleading to the general public, who all to easily fall for such hype.

      The proponents of string theory, have, over the years adjusted their parameters in an ad hoc manner to accommodate internal consistency for a paradigm that has no basis in observed physical reality. I agree with the comment of Larry Rosenthal and would point out that there are many others who share this view. Here are some examples:

      Philip W. Anderson observes:

      “String theory is the first science in hundreds of years to be pursued in pre-Baconian fashion, without any adequate experimental guidance. It proposes that Nature is the way we would like it to be rather than the way we see it to be; and it is improbable that Nature thinks the same way we do.”

      Richard Feynman, for whose thinking I have enormous respect, put it this way:

      “I don’t like that they’re not calculating anything. I don’t like that they don’t check their ideas. I don’t like that for anything that disagrees with an experiment, they cook up an explanation-a fix-up to say, “Well, it might be true.” For example, the theory requires ten dimensions. Well, maybe there’s a way of wrapping up six of the dimensions. Yes, that’s all possible mathematically, but why not seven? . . . So the fact that it might disagree with experience is very tenuous, it doesn’t produce anything; it has to be excused most of the time. It doesn’t look right.”

      Here’s Sheldon Glashow:

      “Superstring physicists have not yet shown that theory really works. They cannot demonstrate that the standard theory is a logical outcome of string theory. They cannot even be sure that their formalism includes a description of such things as protons and electrons. And they have not yet made even one teeny-tiny experimental prediction. Worst of all, superstring theory does not follow as a logical consequence of some appealing set of hypotheses about nature.”

      Well, at last, by more mathematical smoke and mirrors, by further unwarranted assumptions, string theorists have come up with an experimental straw to clutch at.

      Kris Sigurdson, an assistant Professor at University of British Columbia, picked up the idea previously mooted several years previously by other researchers at UBC as a test for a multiverse and, it would seem, grafted this into the string framework. Which can, in keeping with tradition, and with no requirement to conform to physical reality, always be jiggled to fit. Sigurdson proposed that, providing the wake of any collision of multiverse components during inflation was sufficiently great, a characteristic double peak of single state photon polarization might be observable. A prediction which is, in principle, testable within the context of CMB missions to be carried out using the Plack observatory.

      That even this is, to use Glashow’s expression, “teeny-tiny” is underlined by Charles Bennett, who is the principal investigator on NASA’s Wilkinson Microwave Anisotropy Probe. He expresses the opinion that “the detection of a cosmic wake would nonetheless be “extremely unlikely”. The amplitude of a wake would have to be just right: too small and we wouldn’t see it; too big and it would probably have had severe consequences for our universe’s structure. The number of collisions would also have to be “fine-tuned”

      Incidentally, the notion of a multiverse did not spring from string theory, It has been around for a very long time in various forms before having been being taken aboard and tailored to fit within the string/brane scenario.

      Regarding the requirement for evidence as a prerequisite for admission to the domain of science:

      Dan Friedan has this to say:

      “The fact that certain beautiful mathematical forms were used in the period 1905-1974 to make the presently successful theory of physics does not imply that any particular standard of mathematical beauty is fundamental to nature. The evidence is for certain specific mathematical forms, of group theory, differential geometry and operator theory. The evidence comes from a limited range of spacetime distances. That range of distances grew so large by historical standards, and the successes of certain specific mathematical forms were so impressive, that there has been an understandable
      psychological impulse in physicists responsible for the triumph, and in their successors, to believe in a certain standard of mathematical
      beauty. But history suggests that it is unwise to extrapolate to fundamental principles of nature from the mathematical forms used by
      theoretical physics in any particular epoch of its history, no matter how impressive their success. Mathematical beauty in physics cannot be separated from usefulness in the real world. The historical exemplars of mathematical beauty in physics, the theory of general relativity and the Dirac equation, obtained their credibility first by explaining prior knowledge. . . General relativity explained Newtonian gravity and special relativity. The Dirac equation explained the non-relativistic, quantum mechanical spinning electron. Both theories then made definite predictions that could be checked. Mathematical beauty in physics cannot be appreciated until after it has proved useful.
      Past programs in theoretical physics that have attempted to follow a particular standard of mathematical beauty, detached from the requirement of correspondence with existing knowledge, have failed.The evidence for beautiful mathematical forms in nature requires only that a candidate theory of physics explain those specific mathematical forms that have actually been found, within the range of distances where they have been seen, to an approximation consistent with the accuracy of their observation.”

      Personally I will stick to the understanding that phenomena for which there is no evidence have no place withing the realm of science.

      I also subscribe to the principle (Carl Sagan, I believe) that “Extraordinary claims require extraordinary evidence.”

      “Physics starts from experience and ends in it.” Albert Einstein

    • Hakuin Suso

      “In Niels Bohr’s Copenhagen Interpretation, any time we make a measurement, the wave function “collapses,” giving us one outcome from an infinity of possibilities. Everett argued that the wave function never collapses. Rather, every possibility exists in a parallel universe. This suggests a staggeringly large number of other worlds.”
      _____________________________

      I must admit these items can, at times, be very confusing. For instance,“Everett argued that the wave function never collapses”. Yet elsewhere I read about wave function collapse when physicists measure position as opposed to momentum. So wave function does collapse in spite of what Everett said.

      But Everett said it doesn’t collapse and that instead every possibility exists in a parallel universe. Well. Isn’t “possibility” another word for “potential”? So how can what is essentially “potential” also be “actual”?

      And if all potential states are actualized in one universe or the other, does that not mean that everything exists all at once? Forget free will in such a scenario. What does that mean for time? If everything is happening all at once then there is no time!

      If there is no time. Then there is no space-time continuum. No universe. No multiverse. Yet I’m clearly experiencing something. So I’m back to the one universe I’m in.

      FYI: I did say I was confused, didn’t I?

      • PeterKinnon

        I think that you will find that the concept of “collapse of the wave function” predated Bohr and that he was rather the proponent of the idea that it occurred as the result of an observation. That is my understanding, anyway, and that rather metaphysical interpretation is still kicking around, having been taken up and popularized with those having a penchant for the supernatural.

        As you point out, to avoid this scenario, Everett rather ingeniously proposed the Many Worlds hypothesis. A rather very extravagant and it would seem, untestable way out. The speculative “many worlds”, by the way, are postulated as parallel entities and do not correspond to the presently trendy notion of an infinity of universes, each with different physical parameters arising from the “Big Bang” so there is no question of collisions during the standard model of inflation arising in this picture.

        The interpretation of Richard Feynman, on the other hand, requires no collapse of the wave function simply because no waves are posited.
        Photons, for example are always treated as particles in his formalism so there just ain’t no wave to collapse.

        Now it is the calculations of those who accept this school of thought that have provided the prolific predictions upon which such things as the laser, the tunnel diode and innumerable other advances in technology have depended..

        The beauty of this pragmatic approach is that it works.

        It works even though a “cheat” had to be included in the calculations to make it do so. The practice of “renormalization” which Feynman himself described as “a rather dippy procedure”.. Never mind. The fact that “shut up and calculate” works, and works so well, suggests that it cannot be too far removed from reality.

        It may be that our minds are simply not capable of visualizing these phenomena. Or it may be that within the context of a radically different world-view they will become more intuitively comprehensible.

        Personally, I have a hunch that Einstein’s affirmation of a space-time continuum should be taken far more literally than is the present fashion.
        In such a model “particles” can perhaps be better thought of as deformations of that all-pervading substance?

        Who knows? Feynman himself observed “Nobody understands quantum mechanics”. So, in your confusion, Hakuin, you are in very good company.

        Feynman’s little book “QED” is, for the most part, very accessible to the thoughtful layman and I strongly recommend it as a “must read”.

        • Hakuin Suso

          Metaphysics is a philosophical enquiry of a non-empirical character into the nature of existence. Non-empirical does not denote the supernatural but that which lies outside of scientific study. For instance, science can tell us that elements are created at the core of stars and in supernovas and that the human brain is comprised of these elements. But science cannot tell us how these elements combine to create consciousness or, for that matter, what consciousness is. Consciousness, then, is more a metaphysical pursuit of study and a scientific one.

          Because, properly speaking, science excludes consciousness, it is only natural that a strict “scientific” explanation of a universe excluding consciousness would evolve, such as that proposed in the “many worlds” hypothesis. This exclusion is a type of “renormalization”, a concept I’m the first to admit is not one I as of yet entirely understand. But to the effect that renormalization seems to be a treatment of equations that is designed to omit infinities, so, too, is the “many worlds” hypothesis designed to exclude consciousness. And as already noted, in this sense it seems to be eminently “scientific”.

          This is not to say that exclusion does not produce results, such as those you’ve noted that come from Richard Feynman’s calculations that exclude waves, e.g., lasers. But Newton’s work also produces results, as long, that is, as we remain in the realm of classical physics. But if that’s where we remained then the marvels of our present technology would never have come to pass.

          In order to conclude whether there are multiple universes or just one, it may be that a radically different world-view that makes this more intuitively comprehensible will evolve but not out of physics; but out of an interaction between physics and metaphysics. Perhaps the solution lies in not excluding what is now metaphysical, but in including what we all inherently know exists by virtue of the fact that we all have it, that is, consciousness.

          Having said that, I thank you for your clear and intelligent response to my original comment. I hope to soon read Feynman’s little book now that you’ve brought it to my attention.

          • PeterKinnon

            “Metaphysics is a philosophical enquiry of a non-empirical character into the nature of existence. Non-empirical does not denote the supernatural but that which lies outside of scientific study.”

            I have no quarrel with that, Hakuin.

            My remark merely reflected that it it is not uncommon for those who embrace “supernatural” notions to have have a habit of senselessly using terminology derived from QM for their irrational ramblings. As no doubt you would agree.

            However, I would certainly take issue with your statement to the effect:

            “Because, properly speaking, science excludes consciousness”

            It is, of course, a very common misconception, as reflected in a recent New Scientist issue as follows:

            “In a 1992 issue of The Times Literary Supplement, the philosopher Jerry Fodor famously complained that: “Nobody has the slightest idea how anything material could be conscious. Nobody even knows what it would be like to have the slightest idea about how anything material could be conscious.” In 2011, despite two decades of explosive advances in brain research and cognitive science, Fodor’s assessment still rings true.?”

            My response is pasted below:

            What nonsense!

            It is saddening to see so many workers in the sciences becoming tied up in knots with what, in the light of present understandings, is a very easily explained phenomenon.

            In their attempts to cope with the mystical overtones generated by the traditional introspective approaches to the subject, with the consequent recursivities, all manner of quite unrelated or pseudo-scientific concepts are brought to bear..

            Examples in this case are “emergent dynamics”, information theory and autocatalysis.

            Phenomena blithely invoked by others include quantum effects, fractals and “complexity theory”

            “What is consciousness” when stripped of the metaphysical baggage generated by introspection, is seen to be entirely accounted for by our current understanding of biology.
            It is, in fact, an evolutionary necessity.

            Simply the navigational facility which enables an organism to interact optimally with its environment.

            The level of interaction of our species being inordinately high and the extent of consciousness correspondingly sophisticated.

            A point I have frequently made in various writings over the years is reflected in a far more more down-to-earth article in this same issue: We must remember this facility can be inactivated rather easily by a whiff of anaesthetic.

            The topic is discussed rather more fully in chapter 16 of “The Goldilocks Effect: What Has Serendipity Ever Done For Us?”, a free download.

    • Jeffrey Michals-Brown

      ;alsdfjalksdjfal

    • Graybear

      Like fireflies in a vast night sky, this vision of the multiverse just seems intuitively obvious somehow – if something could actually “see” this vision of universes winking in and out of existence. Do they ever touch at all – are we looking for something that doesn’t exist because they are so very far apart that matter evaporates before it reaches the next bubble? Time may tell.

    • http://www.facebook.com/people/Lorraine-Ingersoll/100000981831240 Lorraine Ingersoll

      WHY MUST SCIENCE PROBED INFINITY TO DENY GOD? I PROVED MEMORY (C) 1977: BECAUSE SCIENCE DENIED “WHERE THE ORIGINAL MATTER CAME FROM”! MEMORY RESEARCH PROVED “THOUGHT” CREATED THE BIG BANG! NOW , A 50/50 CHANCE OF BLASTING PLANET EARTH BUT THE LHC FIOUND NO BOSON: WHEN “THE MIND OF GOD IS EVERYWHERE”, PROVEN BY MY RESEARCH ON “DIVINE THOUGHT ENEREGY” SCIENCE MUST REALIZE NOTHING WILL CREATE GOD BECAUSE THE ALMIGHTY CREATOR IS “LIGHT” WHICH CANNOT BE REACHED WITHOUT PERMISSION TO
      “END ALL CREATION”!

    • http://www.facebook.com/people/Lorraine-Ingersoll/100000981831240 Lorraine Ingersoll

      WHY DOES GOD NOT SOLVE ALL PROBLEMS ? PEOPLE PRAY TIME AND AGAIN ,BUT WHY NO ANSWERS? IF MAN’S FREEDOM TO CHOOSE RIGHT FROM WRONG BECOMES PROBLEMS HE’S RESPONSIBLE TO FIX OF TOLERATE CONSEQUENCES OF HIS ACTIONS WHICH MAY CAUSE PROBLEMS. “GOD IS LIGHT” THE BIBLE SAYS”! “DIVINE LIGHT ENERGY” IS THE MIND OF GOD WHICH IS EVERYWHERE”! GOD IS GOODNESS AND LOVE! EVIL IS THE DEVIL’S HATRED! IF THE ABSENCE OF LIGHT IS DARKNESS THEN WHY CHOOSE EVERLASTING SERVITUDE TO THE PRINCE OF DARKNESS FOR HELP WHEN YOU MUST PRAY AND ABIDE BY “THOUGHT CONSEQUENCES” OF GOODNESS AND LOVE TO RECIEVE ANSWERS FROM THE CREATOR?