Parallel Universes

May 12, 2003 3:55 AM

In an infinite universe there's a copy of you reading this post - in Latin. The Scientific American updates current cosmological thinking on Parallel Universes - The key question is not whether the multiverse exists but rather how many levels it has - and reaches some startling conclusions.
posted by grahamwell (40 comments total)

cool stuff, grahamwell. Definitely adds a new level of copmlexity to the infinite monkeys question.
posted by kaibutsu at 4:04 AM on May 12, 2003

Perfect ... just perfect. I'm stuck in the "Shrub-in-the-whitehouse" universe while my double is porking Sandra Bullock in a parallel one. Just swell.
posted by RavinDave at 4:41 AM on May 12, 2003

Exciting as it sounds, this view is not the only one - and I don't just mean in parallel universes. Once again, a particular interpretation of quantum physics is used to explain certain results while ignoring other less orthodox explanations. The article takes one of a number of "many worlds" interpretations and extrapolates while totally ignoring - which means failing to refute - some other equally persuasive interpretations. Take for example Bohm and Hiley's "The Undivided Universe". Back in the fifties J. Robert Oppenheimer said of Bohm's first version, "If we can not refute Bohm, we must agree to ignore him." So goes modern science.
posted by donfactor at 5:02 AM on May 12, 2003

This is an excellent article although it took some time to read and absorb it is accessible to the layperson to understand multiple universe theories without having to read a book. As donfactor says this is not a complete survey of all the multi universe theories, but it does help to understand some of the most commonly discussed theories and how they fit together and co-exist at the same time. It shows how we can not see other universes directly but infer they exist by direct observation of things we can see. Clever human brain, go brain, go.
posted by stbalbach at 6:12 AM on May 12, 2003

So if this theory proves that there were infinite numbers of Mickey Mice before Disney invented him, does that mean the copyright is null and void?
posted by Pretty_Generic at 6:36 AM on May 12, 2003

The idea of multiple universes I can handle, but the idea of parallel universes really bugs me. If the infinite possibilities of action of all organisms that ever existed are acted out in other universes, wouldn't that require (I'm no maths expert) something like infinity factorial by infinity factorial number of universes. It just seems too much like fantasy to me.
posted by hippyboy at 6:42 AM on May 12, 2003

Back in the fifties J. Robert Oppenheimer said of Bohm's first version, "If we can not refute Bohm, we must agree to ignore him." So goes modern science.

I find Bohm's viewpoint to be incredibly intuitive and explanatory, but I'm no quantum physicist. From my lay perspective, I hope I can understand what Oppenheimer was getting at though.

Bohm's idea of universal wholeness implies a singular entity with a depth of texture which is effectively infinite.

However, the nature of perception (and of science) is to establish and then test our theories via discrete sampling, Science can thereby never make conclusions about the (potentially) continuous nature of the data which is being sampled. Blind men touching the elephant, and all that.

So whilst science cannot refute Bohm (and it never shall), "we" (and I think Oppenheimer was using the Royal "we" here) can only ignore his ideas as a curious, but unverifiable, fantasy. However, speaking philosophically, I believe he was on the right track. Just like William of Ockham ...
posted by walrus at 6:44 AM on May 12, 2003

In an infinite number of parallel universes, I finished reading all of those pages before commenting, but in this one I only had time for the first couple. Still, I plan to finish it, and just wanted to pop in to say thanks, grahamwell, for posting this. It looks like a very well-put together explanation of a complicated topic that has interested me for a long time.
posted by soyjoy at 6:49 AM on May 12, 2003

Here's a link for Bohm (I think this covers the basics in a non-technical way).
posted by grahamwell at 7:15 AM on May 12, 2003

Fantastic, thought-provoking stuff, grahamwell. Thanks. I'm eager to read and digest both the article and the Bohm link later today when my brain is fully functional.

Also: what RavinDave said.
posted by eyebeam at 7:34 AM on May 12, 2003

I'm no stranger to wonder, but I have to ask what the usefulness of this theory is.
posted by divrsional at 8:01 AM on May 12, 2003

I'm no stranger to wonder, but I have to ask what the usefulness of this universe is.
posted by Pretty_Generic at 8:27 AM on May 12, 2003

I'm no stranger to wonder, but I have to ask what the usefulness of this universe is.

It is the only viable alternative to a belief in a designed universe. And, by almost automatic extension, it is the only alternative to a belief in God. When people say that the multiverse is an established scientific fact, as near as I can tell, this is all they mean: "if there is no God, then this single universe is immensely improbable. Since there is no God, then there must be parallel universes."
posted by gd779 at 9:00 AM on May 12, 2003

Really? I got the impression that this was based on a multitude of physics experiments, not on theological posturing.
posted by Pretty_Generic at 9:24 AM on May 12, 2003

This may come as a surprise to you, gd779, but most people don't waste a lot of time worrying about the existence of god(s)...
posted by Mars Saxman at 9:40 AM on May 12, 2003

yeah, nice try gd779, but the author did specifically point out that he's speaking of physical rather than metaphysical reality: in other words, only things which are testable and falsifiable.

What I don't understand though is the first version of parallel universes based on infinite space: this must mean that the big bang is not the beginning of the universe, since the universe of the big bang can only be 14 billion light years across unless space-time can travel faster than light (- but even then, unless it travels at an "infinite" speed, that universe couldn't be infinite). So if we're talking about an infinite space-time, what's the big bang? Just some random explosion within this greater eternal space time?

I haven't finished all ten pages of the article, but he moved on to multidimensional universes, which i'm more familiar with and which don't need to posit eternity to make sense.
posted by mdn at 9:44 AM on May 12, 2003

My question stands.
posted by divrsional at 10:18 AM on May 12, 2003

I find the infinite different versions of me part to be a little flimsy. It doesn't seem that that would be the result of an infinite variety of universal starting situations. Although I guess it could.

So, there's one universe where I apply vigilante justice to bad drivers? I wonder how that's working out.
posted by mblandi at 10:46 AM on May 12, 2003

the author did specifically point out that he's speaking of physical rather than metaphysical reality: in other words, only things which are testable and falsifiable.

He claimed that, right up front in fact, but I didn't see any support for that assertion. Then again, it was a long article - maybe it's in there somewhere, and I missed it? Or maybe the science is too technical for a popular article - in which case, does anybody know where one would find support for that claim?

In other words, what exactly is testable and falsifiable about the multiverse theory? Because the only "evidence" I've ever seen relies on the anthropic principle - that is, there must be a multiverse because the universe we inhabit is immensely improbable in certain ways. This, as I pointed out earlier, takes as a presupposition that the universe originated by chance.
posted by gd779 at 11:36 AM on May 12, 2003

yeah, nice try gd779, but the author did specifically point out that he's speaking of physical rather than metaphysical reality: in other words, only things which are testable and falsifiable.

But presumably, mdn, there will be universes where metaphysical reality is testable and falsifiable? I dunno; it all sounds very Douglas Adams to me.
posted by carter at 11:39 AM on May 12, 2003

So, there's one universe where I apply vigilante justice to bad drivers? I wonder how that's working out.

You know, all of this seems interesting in considering various strains of determinism. If there are infinite universes, then by definition anything possible will happen in one of them. This is easier to determine in an infinite set of numbers, since what is and isn't possible for numbers is determinate (eg, there are infinite prime numbers, but not all numbers are primes; although there are infinite primes, we can name infinite possibilities that cannot belong to this set).

What is and isn't possible for "you" might be a different story, though. If we think of "you" as an infinite set, it still doesn't mean every possibility for a human could be true of "you" in one universe or another. Could your genetic equivalent in another universe have become a pathological serial killer? Could s/he have been a scientist or an artist or a mountain climber? Could s/he have had different religious / sexual / mood (depressive, manic, etc) orientations? What are the limits of possibility on a genetic level, in other words...
posted by mdn at 11:46 AM on May 12, 2003

But presumably, mdn, there will be universes where metaphysical reality is testable and falsifiable?

oop, shoulda caught that on preview: no, at least not if we assume the word "metaphysical" means the same thing in all these universes, since the meaning of the word is that "beyond the physical" - testable, falsifiable - universe.

As above, something infinite can still exclude possibilities.
posted by mdn at 11:49 AM on May 12, 2003

Divrsional's question depends, as Bill Clinton might have asked, on what you mean by useful. It seems to me that any theory of the universe provides a context without which it would be meaningless to speak of any values. We each, either tacitly or overtly, have a world-view, a way of understanding the world. Some of us prefer a world-view backed by science and this gives us our particular sets of values and meanings and there are many others. So any such theory, especially one that purports to describe the totality of our universe or universes, has some usefullness - for better or worse. Take your pick.
posted by donfactor at 11:54 AM on May 12, 2003

I find the infinite different versions of me part to be a little flimsy. It doesn't seem that that would be the result of an infinite variety of universal starting situations. Although I guess it could.

I think they're basing this on "the distribution of outcomes in a Hubble volume", which is much more than just the starting situations. That is, they're saying that we live inside a Hubble volume with, say, x possible outcomes (based on the number of possible quantum states it contains). And they're also saying that there are many Hubble volumes out there, each with some number of possible outcomes.

Then they figured out how many different possibilities are actually feasible inside a given Hubble volume (that is, how many outcomes you could have if there was a Hubble volume entirely filled by protons, thus allowing for the maximum number of outcomes in a single universe). They got a number, and then extrapolated to get how much space you'd need to have enough Hubble volumes to hold that many possibilites, assuming one Hubble volume for each possible outcome. Let's call this amount of space n.

Since n isn't infinite, there must be some amount larger than n. Outside of n, the different possible configurations of Hubble volumes must necessarily to start to repeat, because all of the possible Hubble volume configurations already exist inside n. Since the evidence points to space being infinite, this suggests that there is also infinite space beyond n, and therefore infinite repetitions of each and every possible configuration.

I'm not a physics person, so somebody else might want to corroborate this for me... but I think this is roughly the way that they arrived at the Level I multiverse theory.
posted by vorfeed at 11:58 AM on May 12, 2003

It is the only viable alternative to a belief in a designed universe. And, by almost automatic extension, it is the only alternative to a belief in God.

Where do you Creationists cut-and-paste this stuff from?

Also, I'm pretty sure this is a double post, but I can't find it, sooooo.....carry on. :)
posted by dgaicun at 12:21 PM on May 12, 2003

Also, I'm pretty sure this is a double post, but I can't find it, sooooo.....carry on. :)

...or perhaps this the "multiverse" in action!
posted by dgaicun at 12:23 PM on May 12, 2003

Perhaps we move between them all the time? I often wake up with the feeling that the universe has become slightly crazier overnight, which could be explained by having moved into a parallel reality. Now, if only I could be moving progressively towards saner universes, rather than crazy ones ... say one where Bush is a gas station attendant, English teachers make as much money as sports stars do here, and no one has ever heard of Tom Robbins. Or Rumsfeld. Or Ayn Rand.
posted by jokeefe at 12:37 PM on May 12, 2003

If multiverse theory implies infinity and that by extension it means, somewhere, everything is possible, I would like to locate that universe in which everything is exactly the same regarding events throughout history but for the fact that the only sound by which humans ever communicate sounds like "spaftiblarf". The location of this universe will irrevocably prove the fundamental belief that infinity is absurd and not a little trite and must be destroyed. Thank you.
posted by WolfDaddy at 12:45 PM on May 12, 2003

He claimed that, right up front in fact, but I didn't see any support for that assertion. Then again, it was a long article - maybe it's in there somewhere, and I missed it? Or maybe the science is too technical for a popular article - in which case, does anybody know where one would find support for that claim?

I don't know what the evidence for the infinite space part would be (that's my q above) but regarding the multiple dimensional universe, I know that interference experiments were one way that researchers came to see the multiverse as the only explanation. These were experiments where they shined light through slits and found that certain interference patterns were found - so if the light went through one slit, it would land X, but if it was shone through four slits, instead of landing 4X there would be interference that resulted in new patterns.

The weird part is that they then found that individual photons acted the same way: when faced with one slit, they landed X, but when faced with four slits - even though there was only ONE photon - it would always land in the interference pattern. The explanation was shadow particle interference with photons in shadow universes.

I don't remember offhand other experiments, but there are a lot of good pop science books that attempt to explain these kinds of things. Michio Kaku & D. Deutsch come to mind for me as authors who try to explain how these ideas have come to be taken seriously when they sound so strange.
posted by mdn at 12:55 PM on May 12, 2003

Does infinite universe theory imply that "free will" is a fiction, since all possible actions will occur regardless of the intent of any single actor? Anyone want to tackle that?
posted by mr_crash_davis at 12:57 PM on May 12, 2003

Here's my understanding of the infinite space bit. (I could be wrong, so take this with a grain of salt.) Inflation theory says that in the very early universe, the state of the vacuum was slightly different from what it is now... a bit of extra energy caused the fabric of spacetime to expand with amazing speed. (Such speed, in fact, that regions of spacetime would seem to zoom away from each other faster than the speed of light.)

At some point, about 10^-32 seconds after the big bang, the vacuum state suddenly changed in our region of the universe and a bubble of spacetime "crystallized" into the vacuum state it is today. Our hubble volume resides within this bubble. However, this bubble does not span the entire "universe" -- in some regions, inflation kept going... and even as different bubbles crystallized and inflation ceased, in other regions of the universe, inflation kept going strong. Basically, inflation can keep going eternally in the "universe" as a whole, even though it has long since ceased in our local hubble volume. If everything works out properly, this means that there's an infinite number of bubble hubble-volumes constantly spawning throughout the universe as a whole, separated by ever-expanding regions where inflation continues.

I don't think this is *required* by inflation theory, but it's favored by some scientists because it's fairly spare in its assumptions compared to other scenarios.

As for the finite quantum states of any given hubble volume, I don't follow the arguments precisely, but I think it's based upon something Alexander Vilenkin published a few years ago.

Finally... *if* the universe has infinite hubble volumes and *if* those hubble volumes each have finite possible quantum states and *if* the configuration of any given hubble volume is relatively random, then it follows that there are multiple copies of any given configuration. (It follows from the same logic of infinite monkeys & Shakespeare -- or more technically, from the Borel-Cantelli lemma, IIRC.)

Oh... and mdn, multiverses are not *necessary* to explain quantum mechanics, but they are one possible way of explaining it.
posted by ptermit at 1:34 PM on May 12, 2003

Does infinite universe theory imply that "free will" is a fiction, since all possible actions will occur regardless of the intent of any single actor?
Interesting question - if we have no choice over what will happen to us, as everything will happen to us in one universe or another, then what about *head explodes*
posted by dg at 3:52 PM on May 12, 2003

dg, wouldn't that be your brane exploding??

At any rate, if the version of you that I'm addressing actually made it through the article you'll find the author's personal site, and you'll discover he's actually kinda cute for a cosmologist, and that his page has many many links to other worlds.
posted by WolfDaddy at 5:05 PM on May 12, 2003

What if the number of realities isn't actually infinite, but when it reaches a certain number, everything explodes and we start all over again? Wouldn't it be possible that this could happen at any time?
posted by Poagao at 8:15 PM on May 12, 2003

It could also be possible that this has already happened.
posted by dg at 10:49 PM on May 12, 2003

This is an annoyingly non Sci-Am article. It fails, on rhetoric mainly, as it gives the impression to someone not acquainted with the area that it describes something that has scientific consensus behind it. It doesn't. It's been a while since my General Relativity / Cosmology days but, my limited attempts to keep up with developements in the area, allow me to opine that f.e. the statement:

Infinite models fit the data, and strong limits have been placed on the alternatives.

isn't so much untrue as misleading - especially since the author avoids referring to a source. The source he does give does not support this statement at all (except in the trivial way that the accuracy of observations is such that we cannot yet measure whether our universe is "doughnut-shaped" or not). Indeed the crucial fact worth mentioning would be the statement of these limits as (I'm willing to wager) "10 to the 10 to the 28 meters" is probably not inside them.
This for level-I multiverses. For Level-II (by far the least controversial of the four BTW though not encapsulating a definitive cosmological consensus by any means AFAIK), there is no empirical support. This statement by the author:

Although we cannot interact with other Level II parallel universes, cosmologists can infer their presence indirectly, because their existence can account for unexplained coincidences in our universe.

is seriously lacking logically unless he can demonstrate that it is the only way to account for these coincidences (it isn't).
Level III (Everett's parallel universes) multiverses are just one out of many hermeneutical schemata in quantum mechanics. There are other (much more acceptable within the physics community) interpretations that "explain" QM just as well (or bad depending on your views).
The idea that level IV is in any way experimentally decidable is not very convincing. The author can do much better than: "A hint that such a multiverse might not be just some beer-fueled speculation is the tight correspondence between the worlds of abstract reasoning and of observed reality." This is actually rather lame. Especially if one takes the author's initial statement seriously:
"It is grounded in well-tested theories such as relativity and quantum mechanics, and it fulfills both of the basic criteria of an empirical science: it makes predictions, and it can be falsified."
This "Level-IV" philosophical point is way beyond falsification and ignores to the point of annoyance a rather large corpus of discussion and debate about the "unreasonable effectiveness of mathematics".
All this doesn't mean that this isn't legitimate science or worthwhile,for what is worth, personally I find Level II (and when intoxicated even Level III) multiverses plausible. It does mean however that I expect from such an article, on such a topic, published in Scientific American to include a brief description of the criticism of the (speculative) theories presented. I would also find a less "inflated" rhetoric and some understatement appropriate.
A final point: on level I universes, the author seems to believe that an imaginable universe is a possible universe. The fact that I can imagine a perfectly square continent or a civilization of two headed penguins does not make the possibility of their occurrence any other than zero.
Finally this part I don't understand: how is a (level-I) infinite universe compatible with any sort of big bang theory? Are level-I and -II parallel universes mutually compatible?
posted by talos at 2:58 AM on May 13, 2003

If the universe is infinite, it was always infinite, from the time of the big bang onwards. It may have been infinitely dense (or simply unimaginably so), but it would still have been infinite in size. I and II aren't incompatible; each level I multiverse may be infinite, but that doesn't mean they're all connected with each other, any more than I can expect to start shooting spaceships after the last tetris brick finally falls.

As for evidence -- admittedly, level IV is incredibly speculative and seems to have been included mostly just for mind-expanding fun. Occam's razor seems to do the trick for level I, though -- the article (a sidebar, I think; I read the print version) explains how it's (conterintuitively) quite a lot simpler to stipulate the paramaters for an infinite universe than a finite one.

Oh, and the article also references one of my favorite science fiction books.

Yeesh; it seems like all I do on metafilter anymore is plug Greg Egan.
posted by Tlogmer at 2:52 PM on May 13, 2003

on level I universes, the author seems to believe that an imaginable universe is a possible universe. The fact that I can imagine a perfectly square continent or a civilization of two headed penguins does not make the possibility of their occurrence any other than zero.

On the contrary -- in an infinite level I multiverse, every possible arrangement of particles will eventually occur, thanks to quantum effects, as will every possible temporal arrangement of those arrangements -- that means that in some universe, your left nipple will spontaneoously begin composing a geopolitical opera. In another, all the events portrayed in the HitchHiker's Guide to the Galaxy will appear to play themselves out (of course, our physics will still be in play -- the elevators won't actually predict the future, they'll just think they can and guess right every time; Zaphod Beeblebrox, in his two-headedness, may only be staying alive through the continuous intervention of a quadrillion ludicrously improbably coincidences involving quantum effects inside his body. Though, come to think of it, that's just as satasfying.)

Anyway, since I'm being an Egan fanboy, I might was well link to Oracle (an alternate history semi-biography of Alan Turing that adds several new twists on the level III multiverse).
posted by Tlogmer at 3:03 PM on May 13, 2003

Donfactor: Thanks for understanding my question. If one's world view includes wanting the world to be other than what it is (the essence of human suffering), this theory is tailor-made. If you struggle (like a recovered alcoholic, or a Buddhist, or even a few physicists) to see things as they really are, then I suspect other, more meaningful (as defined by Wittgenstein: useful) theories might evolve.

I do not deny the multiverse; I accept that other people are living in other places; and I struggle to know my own.

I also look forward to hearing reports back from other universes.
posted by divrsional at 9:26 AM on May 14, 2003

Great thread. Thanks grahamwell and others!
posted by MiguelCardoso at 10:22 PM on May 14, 2003