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Math Science

A Mathematical Answer To the Parallel Universe Question 566

diewlasing writes to mention that Oxford scientists have proffered a mathematical answer to the parallel universe question that is gaining some support in the scientific community. "According to quantum mechanics, unobserved particles are described by 'wave functions' representing a set of multiple 'probable' states. When an observer makes a measurement, the particle then settles down into one of these multiple options. The Oxford team, led by Dr. David Deutsch, showed mathematically that the bush-like branching structure created by the universe splitting into parallel versions of itself can explain the probabilistic nature of quantum outcomes."
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A Mathematical Answer To the Parallel Universe Question

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  • One question... (Score:4, Interesting)

    by StandardCell ( 589682 ) on Monday September 24, 2007 @01:39PM (#20732431)
    How does this reconcile with reality as we see it?

    From my perspective, even if this mathematical "proof" is true, it is only true in the ontological sense, i.e. that these branches can happen and maybe do happen, but not in reality. Then again, I believe the entire basis for the universe is ultimately ontological but that's a different matter.

    My point is that these alternate "universes" may only exist in infinitesimally-small times (possibly below the Planck time threshold) and then simply cease to exist again as compared with our reality in the next moment, moment after moment.
  • by Xtravar ( 725372 ) on Monday September 24, 2007 @01:54PM (#20732721) Homepage Journal
    Life is like a dream. You never die in your dreams. You never die in your observed life. You just die in alternate universes. This carries on until you reach the next plane of intelligence (wake up) whereupon you realize that there was no mind-body problem to begin with.

  • Where is the paper? (Score:4, Interesting)

    by kmac06 ( 608921 ) on Monday September 24, 2007 @01:59PM (#20732821)
    I would very much like to find the publication of this, or least more details given by the authors if anyone can fine a link.

    By the way, Deutsch is a well known physicist, not some crackpot. One of the first problems discovered to be theoretically sped up by a quantum computer is named after him (link []).
  • Re:Occam's razor (Score:3, Interesting)

    by MyLongNickName ( 822545 ) on Monday September 24, 2007 @02:17PM (#20733085) Journal
    Occam's razor is useless in situations like this. Basically Occam's razor comes down to a judgment call. 'Which "sounds more plausible"? 'is the question that is asked. To be honest when you get into this branch of physics, even things that have been damn well proven and the knowledge used to build workable devices... the concepts STILL sound impossible.
  • Re:Occam's razor (Score:5, Interesting)

    by hanssprudel ( 323035 ) on Monday September 24, 2007 @02:20PM (#20733151)

    So, which is simpler?

    (1) Shit happens.

    (2) Shit happens. Parallel universes are created.
    That isn't the choice. It is more like:

    (1) (Copenhagen) The act of "observing" a particle at some point between the particle, the measuring apparatus, and your mind, somehow magically causes the particle to collapse from a wave state to a fixed one, without any other action on your part. Nobody has ever explained exactly what an observation is (we are, after all, made of particles too) nor when this happens.

    (2) (Multiple worlds) Reality consists of particles in quantum waves of superimposed states. Period. When we observe a particles state, it's state becomes entangled with the state of the particles in our mind, and hence we observe the particle as collapsing to a single state "in each world".

    I don't know about everybody else, but the fact that all states can exist, yet I can only perceive them separately, is no stranger to me than that all moments of time exist, yet I can only perceive each one separately.
  • by pclminion ( 145572 ) on Monday September 24, 2007 @02:42PM (#20733459)

    My theory is that we actually ARE experiencing parallel universes. But the pressures of biological evolution have driven us toward brain structures which hide this fact. Maybe we actually ARE spread out across many different possibilities, but our conscious view of reality is as a single whole. Why? Because it made survival easier, perhaps. Or maybe, individuals with parallel awareness inevitably go insane and die out. Who knows.

    Sometimes this parallelism "leaks through," in the form of quantum strangeness. But it's not the universe which is strange, it's actually us. Our brains contradict reality by trying to condense everything and the result is "weird" physics. Is the electron here, or there? Maybe it's both, but our brains decide to interpret it as a concrete one-way-or-the-other, because doing otherwise would require us to be consciously aware of all of reality, something which is probably impossible.

  • by kebes ( 861706 ) on Monday September 24, 2007 @03:15PM (#20734025) Journal
    I'm not sure if you were already aware, but there is indeed a concept called "Quantum Darwinism []" which helps explain (using the results from quantum decoherence []) why we observe things "classically" (single outcomes of experiments, non-entangled macroscopic states, etc.) despite the universe being fundamentally quantum.

    Briefly, the theory shows (rigorously) how pseudo-classical states are the only ones that are robust against decoherence. Hence, those are the states that tend to persists for measurable periods of time. And those pseudo-classical states are the ones that give rise to other pseudo-classical states.

    Moreover the main developer of these ideas (Wojciech Zurek []) describes in his papers how what we typically term "memories" are inherently classical states (it's either "a" or "b"--not a superposition of both). He explains how macroscopic states will tend to be pseudo-classical, so of course any biological (macroscopic) creature will evolve to assume that reality is classical (it's an adaptive advantage and a good approximation of reality).

    The point is that these larger-scale superpositions do indeed exist, but that local observers (e.g. instruments, or ants, or humans) can inherently only record/remember classical states, not quantum ones. So, our perception of reality (and memory of reality) is inherently a classical one.
  • Re:Why is this news? (Score:1, Interesting)

    by Anonymous Coward on Monday September 24, 2007 @03:23PM (#20734123)
    It's not just a statement of the many worlds interpretation. It's a claim of mathematical proof that the branching proposed by the many worlds theory gives rise to the wave equations as the branches are superposed. So it's equivalent to the "and only if" portion of an "if and only if" condition in mathematics. So in effect they've stated that "a universe that branches when quantum events are observed gives rise to the wave equations that define the undetermined state of quantum events in our universe." This means that the many worlds interpretation may just have graduated from hypothesis to theory.
  • Re:Occam's razor (Score:1, Interesting)

    by Anonymous Coward on Monday September 24, 2007 @04:38PM (#20735185)
    You (like almost everyone...) misinterpret the Copenhagen Interpretation. "Observer" in QM is ANY PROCESS WHICH IS AFFECTED by the collapse of the quantum wave function. That is if the photon can go left or right in the 2 slit experiment then it is 'observed' if any other particle in the universe CAN interact with it on its way to one or the other slit. If 2 WAVE FUNCTIONS interact, then they become entangled. That is ALL their possible states become related. So you could entangle 2 photons by passing one through either slit A or B, and another through either slit B or C, as long as neither one interacts with anything else in the universe (IE is observed). This leads to the neato 'action at a distance' behavior of entangled wave functions. Once one photon IS observed, the entire entangled waveform collapses...

    In any case, your comment about the CI doesn't apply. Nothing in QM makes people some special class of observers. In fact the idea of 'collapse' and 'observer' don't really precisely make sense. Given that an observer has another quantum wave function of its own how can you even say the observer observed anything? Its location at the point necessary to make the observation is ITSELF subject to localizing its own wave function. Beyond that consider the case of Schroedinger's Cat. Is the cat dead or alive? Well, if you're INSIDE the box, you can answer that question (IE the wave function has collapsed). If you're OUTSIDE the box, it hasn't. Thus the very notion of 'collapse of a quantum wave function' is meaningless in the general sense.

    In fact if you think about it the GENERAL case of the 'many worlds' interpretation is therefore also meaningless. There can be said to be many LOCAL "branches" of the universe, but the differences between them are all localized to one area of spacetime. One cannot say that 'the universe forks', one can only say that 2 versions of some localized portion of the spacetime continuum exist, and at whatever point they become indistinguishable they cease to have distinct existence.

    Both 'interpretations' are in all particulars indistinguishable.
  • Re:Ummm . . . (Score:2, Interesting)

    by Bryan Ischo ( 893 ) * on Monday September 24, 2007 @04:44PM (#20735269) Homepage
    Is the axiom that physical law is the same everywhere in the universe really unfalsifiable?

    I mean, practically speaking, we are unlikely to ever go to some other distant galaxy and to verify physics there. But there is nothing in the laws of science that prevent us from doing that. It is "practically" impossible to falsify the axiom, but not theoretically impossible.

    The many universes theory, is, on the other hand, impossible to falsify in every way (theoretically and practically). The universes are disjoint. We could never travel to them. We could never exchange information between two disjoint universes such to communicate the truth or falseness of the axiom of physical law.

    This I think is the real definition of non-falsifiable, and for this reason, I think that theories like the many universes theories are science fiction and not even remotely scientific. Also they're a ridiculous waste of time; I didn't read the comments to this Slashdot article because I think that many universes is an interesting theory, I just wanted to be amused by how the misinformed attempt to justify it.

    Don't take that the wrong way - your post was informative and interesting. But people who really believe in stuff like multiple universes and time travel and think it's all very scientific just really make me laugh out loud.
  • by TrailerTrash ( 91309 ) * on Monday September 24, 2007 @05:19PM (#20735713)
    My question would be, are the number of parallel universes countably infinite (same cardinality as the integers) or uncountably infinite (same cardinality as the real numbers)? If countable, this suggests that the number of quantum potential states in the universe are countable, and would seem to lend credence to the idea of an orderly deterministic universe. If uncountable, then the multiverse is infinitely deep - more satisfying, perhaps, in a religious worldview.

    Unless, of course, God(s)(ess)(esses) constructed the universe deterministically, to compute something. I suspect it is to create the question to which 42 is the answer.
  • Re:Ummm . . . (Score:3, Interesting)

    by lawpoop ( 604919 ) on Monday September 24, 2007 @05:23PM (#20735745) Homepage Journal
    I have another question, which might sound kind of naive. If we can accept that there are many universes, with new ones sprouting all the time, is there some constraint on how those universes are? That there might be an infinite set within a certain limit? Otherwise, if, in one of these other universes, the laws of physics are different, then those inhabitants or observers might be able to travel between universes -- just like in another universe where the speed of light follows different laws, they might be able to observe the whole universe.

    Another poster asked [] "Why am I experiencing this universe?" To which a poster replied [], "Because you are in this one. If you were in a different one you would wonder the same thing. That's the anthropic principle."

    So then, if the anthropic principle holds multi-versally, then each observer is trapped in a universe of singular experience. But logically, if anything can change in a forked universe, including the laws of physics, we might imagine a universe where the inhabitants could traverse one or more universes. They might ask, "Why do I experience these universes?" Furthermore, there might be a universe where the laws of physics are such that inhabitants can traverse *any* universe -- a universal universe, so to speak. They wouldn't wonder why they were having a singular experience -- their universe would contain *all* universes. They would be experiencing everything! "Why do I experience everything?"

    So what really is different between all the forking universes? They must have some commonality, at least in the laws of physics. If not, then there is the possibility of a universe where you can traverse universes. Am I off base here? Can the laws of physics be different in another universe, even if it is descendant of a universe with laws like ours?
  • by lawpoop ( 604919 ) on Monday September 24, 2007 @05:50PM (#20736095) Homepage Journal

    The absurd number of parallel universes that would have to be created is mind boggling, since, at the very least, an entire universe would have to be created every single time any atom decayed (one for the universe where that atom happened to decay at that instant, another for the case where that atom didn't happen to decay).
    What exactly is the absurdity scale you are using to measure the absurdity of this idea? Four parallel universes are okay, six are goofy, seven are silly, 10 are ridiculous, and 1000 or more are absurd?

    Strange that none of the wackos who advocate this, and I use the term very loosely, "theory", bother to expain where all of the mass and energy is coming from for all of these extra universes.
    That's like asking where the mass and energy in our universe came from. It's the same answer in all parallel universes -- it was there all along. When they talk about a new universe branching, it's not a big bang event, where a new universe is born, it's an altered copy its twin, identical up until the point where the quantum decision was made. It has a completely identical history after a certain point and therefore, the same mass and energy. Parallel universes do not 'share' energy, nor information, nor anything else. They don't 'seed' or 'give birth to' each other. They are totally out of contact with each other. We wouldn't even know about other ones, if not for the math.

    Note that we are talking about far more universes than atoms in our own universe. Absolute hogwash.
    I can't see why anyone modded you insightful here. You seem to be arguing from personal incredulity []. Not that I'm claiming that these guys are right or their theory is true, but your skepticism seems more emotional than rational to me.
  • Re:More links (Score:1, Interesting)

    by Anonymous Coward on Monday September 24, 2007 @06:13PM (#20736325)

    So now for the first time, the two traditional technical problems with the MWI have reasonably good solutions. Hence we are back to, as Tegmark says, "I hate it" as the main objection to the theory. Since that's not really a good argument, it can be said that the MWI should be considered the most compelling candidate for an interpretation of QM."
    That makes it a candidate. The trouble is, you can turn the same argument around. You "hate" the idea that the universe just inherently depends on probability, and so you find the many-worlds viewpoint more "compelling," even though they're identical from the viewpoint of every experiment we can do. If you resolve all the problems with the MWI then fine, we'll all have to admit it's possible. That doesn't make it better than the interpretation we already had, which had no problems to begin with! It just puts them on equal footing.

    It's a judgement call, is the bottom line. If all the kinks are worked out of the MWI for good, then out comes Occam's Razor. There will be interminable arguments between scientists over which one they consider "simpler," and therefore better. Is it better to postulate an invisible pair of dice in the sky, or an endless infinity of universes we can never observe? As I understand your post, you've chosen your side in that debate, for the present; that's fine. But nothing in your post, or the article from what I've seen, settles the debate. In fact, unless one or the other eventually leads to a deeper theory of physics that can't exist without a multiverse (or can't exist with it) and is experimentally testable, it can be argued that this debate lies outside the ability of science to settle.
  • Re:Occam's razor (Score:4, Interesting)

    by suv4x4 ( 956391 ) on Tuesday September 25, 2007 @12:00AM (#20738985)
    Reality consists of particles in quantum waves of superimposed states. Period. When we observe a particles state, it's state becomes entangled with the state of the particles in our mind, and hence we observe the particle as collapsing to a single state "in each world".

    Many people mix those up. Our "mind" doesn't have anything to do with it.

    The wave function collapses when a particle interacts with a macrosystem. When two macrosystems are separate from each other, we have to assume the other macrosystem is not coherent with us until contact.

    And remember contact *includes* photons reflected off the other macrosystem, so if we see it, otherwise put "observe" it, we're already in contact.

    This is why "observation" causes collapse. Not because we're smart.

When speculation has done its worst, two plus two still equals four. -- S. Johnson