Stop me if you’ve heard this one before.

A physicist walks into a bar and says “Hey, I got this particle-wave duality thing all figured out”. And his buddies look over the numbers, and sure enough, they parse. “But it’s still bullshit,” one of them says. “It has to be.” And the others all nod in agreement.

“But the numbers,” the physicist says.

The naysayer takes a moment to butter his nose. “Look, according to those, those numbers,” he says, as the resident bar cat starts licking, “if you put this cat into that box over there, and put this radioisotope trigger in there with him, and closed the lid, why, why — according to your numbers the cat would be alive and dead at the same time!”

And everybody agrees that this is so fucking stupid that there must be something wrong with the numbers, even if they can’t find what it is.

But here’s the thing: almost a century later, they still haven’t. That cat’s still in there, in its indeterminate catly state, and the experts still don’t know what that even means for sure. Except that a reductio ad absurdum once put forth to discredit a model has instead become an icon for it.

And you know what’s even scarier? It’s happening again, only worse.

If I’m reading this NYT piece correctly (and I’m trusting you guys to set me straight if I’m not), a theoretical consequence of dark energy is that quantum fluctuations following universal heat death could seed the spontaneous and probabilistic reemergence of a bunch of new universes. This would be fine except that probabilistically, simple things are more likely than complex ones to arise spontaneously. (The analogy they use in the story is Scrabble letters, spilled randomly onto a table; a word is more likely to arise from that happenstance than is an entire sentence.) And any subset of a universe, by definition, is less complex than the universe as a whole, and therefore more likely to arise.

So yes, while the spontaneous reemergence of new universes is certainly called for in some cases, in far more cases you’d just be getting pieces showing up. Cats in Space. Fully-functional yet utterly disembodied brains, floating in the void. Very small rocks. And since such iterations are more likely — and hence, more numerous — then the likelihood is that I’m just a disembodied brain imagining a universe where none actually exists, and the rest of you are — well, no. The rest of you aren’t. Which makes me feel a bit better about not having got laid over the past few months, but a whole lot worse about pretty much everything else.

Of course, nobody takes this seriously. The whole Disembodied-Brain thing was cooked up specifically as a a reductio ad absurdum, to show how stupid the whole idea is. Everyone seems pretty much convinced that there’s something wrong with the numbers, even if they haven’t found what it is. And I think we should trust them, because after all they certainly figured out Schrödinger’s — oh, wait…

At this point I’ll just modestly clear my throat and suggest that the thematic punchline for the five-billion-year plot of Sunflowers (or Gerbils — still open to suggestions) will resolve the whole open-universe question much more elegantly, when I get around to it. In the meantime I can only invoke the spirit of the AI in John Brunner’s Stand on Zanzibar, “bathed in his currents of liquid helium, self-contained, immobile, vastly well-informed by every mechanical sense: Shalmaneser. Every now and then there passes through his circuits a pulse which carries the cybernetic equivalent of the phrase,

Christ, what an imagination I’ve got.

Illo credit to Holly Stevenson.

This entry was written by Peter Watts , posted on Wednesday January 23 2008at 07:01 am , filed under astronomy/cosmology . Bookmark the permalink . Post a comment below or leave a trackback: Trackback URL.

17 Responses to “Stop me if you’ve heard this one before.”

  1. This is a pretty natural consequence of the uncertainty principle, so I’m pretty sure this has been around for a while.

    Anyway, I’m not sure how exactly to run the math on this but it seems possible that a universe could actually be more likely than any macroscopic subsets of our current universe, because the creation of a new universe would just need a fuckton of energy. Everything else just sorts itself out after a while; no need for complex arrangements to form instantly.

    So I suspect you’d have small bursts of energy being most likely, with large bursts of energy being increasingly unlikely, with spontaneous creation of ordered, macroscopic objects being less likely than all but very, very large bursts of energy. This sort of stuff happens at very small scales, so it isn’t a problem of having enough energy spontaneous arise, because that would just be an explosion from a very small points. Instead, a very large number of very small energy bursts at many locations would be needed at the same time. I’m sure you can see how this would be far less likely than the creation of the equivalent total energy at a point.

    It’s possible that the only macroscoptic objects you would ever see created in this way before a new big bang would be hydrogen and helium gas clouds large enough to form small stars. Maybe I’ll run some math on this latter.

  2. It sounds to me like a reedition of Nick Bostrom’s Simulation Hypothesis. The problem is that when dealing with the infinite probabilities break down and stop being meaningful. More exactly, all probabilities (except 0.0) turns to 1 and becomes a certainty. So there are infinite individual Brains floating around, but there are also infinite copies of me in this exact universe. That doesnt exactly make me feel any more lucky….

  3. Bloody hell!

    If:
    1) a simple universe is more likely than a complex one
    2) there are multiple universes

    Then it’s rather obvious that we should find ourselves in a universe just big enough to support life interesting enough to wonder why the universe is the size it is.

    But we aren’t. We’re in a staggeringly much huger universe.

    If I kill assumption 2, I am faced with the idea that the one universe that exists just happens to be hospitable. No way. Life isn’t typical in a monte-carlo multiverse, or if it is I’ll eat my shoes.

    So… maybe complex universes are, in fact, perfectly likely. Maybe instead of complexity it’s *energy* we should be looking at.

    If:
    1) a low-energy universe is more likely than a high-energy one
    2) there are multiple universes

    Then we should find ourselves in a universe where the matter-energy + the kinetic energy + the (negative) gravitational potential energy = 0. AKA a flat universe, or one so close to flat as to make little difference.

    And until 10 years ago we thought the universe was flat. Until dark energy.

    This makes no sense!

    Didn’t David Brin or somebody publish something in Analog where universes reproduced and evolved through black-hole-making?

  4. @Keith- I think that was from one or more of Stephen Baxter’s Manifold novels. Or they share the same idea anyways.

  5. “Christ, what an imagination I’ve got.”

    Peter,

    Using the Lord’s name in vain (or vein). And you call yourself a good atheist.

  6. Oh yeah, and your opening vignette is completely wrong. In the real world, Erwin Schröedinger worked out the numbers, and when other people, Niels Bohr and Werner Heisenberg specifically, interpreted the results in probabilistic terms while working together at Copenhagen, hence the term “Copenhagen interpretation of quantum mechanics,” Erin Schröedinger argued against this view with the, what he felt to be, reductio ad absurdum commonly called Schröedinger’s Cat.

    Obviously most people didn’t think this was really so absurd, as the Copenhagen interpretation is still, in some sense, the “standard” interpretation. A more serious criticism came from Einstein, Podolsky, and Rosen, who argued, with what was later called the EPR paradox, that either quantum mechanics is incomplete, or reality is non-local. Contrary to your claims, though, considerable advancements have been made, and it is now generaly agreed that the EPR paradox does not demonstrate that quantum mechanics is incomplete, but that reality is non-local. (To clarify, quantum mechanics is non-local in the intuitive sense defined in the EPR paradox, but is local in a more general sense. Although faster-than-light interactions are possible, they can never allow for actual faster-than-light signaling, so while QM does contradict intuition, it does not actually contradict special relativity.)

    Besides that, the original Copenhagen interpretation is only one interpretation of quantum mechanics. There are others, including the decoherence interpretation, which offers a mathematically consistent model for the appearance of wave-function collapse. Decoherence has since been incorporated into the modern Copenhagen interpretation, and others. The Schrödinger equation is also not the only theory of quantum mechanics consistent with observations, though the only other one that springs to mind at the moment is GRW theory, which includes Schrödinger mechanics and also models the mechanism of wave-function collapse itself. To my knowledge, this theory has not caught on because no experiments have yet been found that observably distinguish it from mainstream QM, but I’m sure they’re working on it.

    Also, the link to the article is broken.

  7. Perhaps this is too blindingly obvious, but if you can speculate about this going forward in time, why not backwards in time also? In other words, perhaps our universe is merely the less complicated remnant of a more complex prior universe. Just one of those little side whirlpools caused by something much larger moving down the river of time….

  8. Anonymous opined

    Using the Lord’s name in vain (or vein). And you call yourself a good atheist.

    I do, indeed, call myself that. But I was not actually taking anyone’s Lord’s name in vain; I was only quoting someone else. My integrity remains intact.

  9. AR, after some of those nifty cosmological insights for which we are happy to keep him on the payroll, grumbled…

    Oh yeah, and your opening vignette is completely wrong. In the real world, Erwin Schröedinger worked out the numbers, and …

    (snippage)

    …Erin Schröedinger argued against this view with the, what he felt to be, reductio ad absurdum commonly called Schröedinger’s Cat…

    And I’m pretty sure Bohr didn’t put butter on his nose for the resident cat, either. The intent wasn’t to report on any actual meeting, of course, but to paraphrase years of debate. And when dealing with such parables, “wrong” is so harsh a word. (Or as Monty Python once put it, “It’s not meant to be taken literaly; it obviously refers to any purveyer of dairy products…”)

    Besides that, the original Copenhagen interpretation is only one interpretation of quantum mechanics. There are others, including the decoherence interpretation, which offers a mathematically consistent model for the appearance of wave-function collapse…

    Is “decoherence” synonymous with many-worlds? And am I right in understanding (remember, these ain’t my claims, this is just what I’ve read) that many-worlds is actually gaining the upper hand amongst physicists these days?

    Also, the link to the article is broken.

    Oops. Thanks. Fixed.

  10. DavidK said…

    … if you can speculate about this going forward in time, why not backwards in time also?

    I actually get the sense that people speculate about that all the time. It’s the whole increasing-entropy thing: the laws of physics go both ways, so technically nothing’s actually stopping the shattered teacup from spontaneously reassembling beyond the universal tendency towards increasing disorder.

    In other words, perhaps our universe is merely the less complicated remnant of a more complex prior universe. Just one of those little side whirlpools caused by something much larger moving down the river of time….

    That actually sounds pretty good to me. Of course, I hardly ever know what I’m talking about…

  11. And I’m pretty sure Bohr didn’t put butter on his nose for the resident cat, either. The intent wasn’t to report on any actual meeting, of course, but to paraphrase years of debate.

    Understood, but the character rolls are off. Literally, the person who came up with the numbers (the Schrödinger equation) and the person who said, “but… but… cats!” are the exact same individual. I get the idea, but it could have been done better.

    Is “decoherence” synonymous with many-worlds?

    All the interpretations are synonymous, in that they cannot be experimentally differentiated. In this way, none of the interpretations of QM are actually science, per se. Any “interpretation” that makes testable predictions is not strictly an interpretation of quantum mechanics, but is a quantum theory in its own right. This includes the discredited hidden variables “interpretation.”

    I do not know which interpretations are most popular among physicists, but I do know which position is most popular in general, which is that quantum mechanics does not necessarily need an interpretation, a state of mind best captured by the phrase, “Shut up and calculate.”

  12. Opps. Minor misstep there: local hidden variable theories have been discredited. Non-local hidden variable theories are still at least logically possible under current observations, although the one I am at least somewhat familiar with, the de Broglie-Bohm theory, certainly do violate parsimony in that it contains elements that can be discarded entirely without influencing observations at all. Doing so removes the determinalism of the theory and simply returns orthodox quantum mechanics.

  13. Kieth: Didn’t David Brin or somebody publish something in Analog where universes reproduced and evolved through black-hole-making?

    Personalmathgenius: @Keith- I think that was from one or more of Stephen Baxter’s Manifold novels. Or they share the same idea anyways.

    Lee Smolin, Physicist at that big Physics thing in Waterloo sponsored by Blackberry’s creator. He talked about that, in his book The Life of the Cosmos, now with 50% less math.

  14. Personalmathgenius:
    I read that long ago! That explains it then.

    TheBrummell:
    Interesting… does he talk at all about Hawking radiation and the information paradox? I’ll have to keep an eye out, thank you.

  15. Interesting… does he talk at all about Hawking radiation and the information paradox? I’ll have to keep an eye out, thank you.

    Smolin talks about Hawking radiation, yes. I can’t remember if he talks about the information paradox, but I assume yes. I read the book about 4 years ago and have forgotten much.

  16. Hmmm… so our big bang is a supernova in some higher universe? Meanwhile, accretion should show up as slow mass creation in here?

    I have got to read that book.

    Rindler geometry might be helpful here. An accelerated frame sees half the universe swallowed up by an event horizon that disappears once the acceleration stops. Equivalence principle says that’s a valid frame to do physics in, and apparently that information makes it across both ways just fine. But there’s a difference between an temporary event horizon and a full-blown black hole.

    I get dizzy. I go lie down now.

  17. AR said…

    Literally, the person who came up with the numbers (the Schrödinger equation) and the person who said, “but… but… cats!” are the exact same individual.

    Ah. I did not know that. I was, of course, just kinda making it up as I went along.

    As for the rest of the posts on this thread — dudes, you are all way beyond me. I’m just sitting back here hoping some of these ideas sink in through osmosis…