Where can I find another universe?
March 7, 2011 9:04 AM Subscribe
Physics: In the many-worlds interpretation, "there is a very large -- perhaps infinite -- number of universes." Where are they located?
If there's another universe with its own particles, where is it? Can it even be described as being "there," as in, a different physical location? Or is it like the Big Bang, where every particle was once located in the singularity, and hence every particle is in "the center of the universe."
If there's another universe with its own particles, where is it? Can it even be described as being "there," as in, a different physical location? Or is it like the Big Bang, where every particle was once located in the singularity, and hence every particle is in "the center of the universe."
Well, see, here's the thing. It's just an interpretation of the math. It's an attempt to rationalize what appears as an aberration in the mathematics. It's a metaphor more than anything.
So, conceptually, they're "there". But, "where" isn't an applicable question. We can't get "there" from here. From my understanding, there is no chance whatsoever of Sliders-like transportation between the different universes--in fact, there's a better chance of time travel than there is of inter-universe travel.
posted by Netzapper at 9:15 AM on March 7, 2011 [3 favorites]
So, conceptually, they're "there". But, "where" isn't an applicable question. We can't get "there" from here. From my understanding, there is no chance whatsoever of Sliders-like transportation between the different universes--in fact, there's a better chance of time travel than there is of inter-universe travel.
posted by Netzapper at 9:15 AM on March 7, 2011 [3 favorites]
This askme about a Radiolab podcast is related. (And recommended!)
In the discussion in the podcast, string theorist Brian Greene describes it like an infinitely large and ever-expanding block of swiss cheese: the holes are the various universes, and the cheese itself is the space between the universes. The catch is that the space between the bubbles is expanding faster than the speed of light, and thus information cannot cross from one universe to the next.
Yeah, I don't know either.
posted by sportbucket at 9:21 AM on March 7, 2011 [3 favorites]
In the discussion in the podcast, string theorist Brian Greene describes it like an infinitely large and ever-expanding block of swiss cheese: the holes are the various universes, and the cheese itself is the space between the universes. The catch is that the space between the bubbles is expanding faster than the speed of light, and thus information cannot cross from one universe to the next.
Yeah, I don't know either.
posted by sportbucket at 9:21 AM on March 7, 2011 [3 favorites]
My understanding of the math— which is pretty limited— is that the other universes are "here", part of ours, overlaid on ours. It isn't so much that there are other universes as that our own universe has a certain complexity we can't perceive or interact with. Or, perhaps more strictly… we do interact with it, but because QM is linear, the result of the evolution-over-time of the combined universe (including any measurements we could do) is the same as the results of the noncombined universes. So there isn't really a way to tell whether those other states exist in any meaningful sense. That's why it's called an “interpretation” of the math.
posted by hattifattener at 9:23 AM on March 7, 2011
posted by hattifattener at 9:23 AM on March 7, 2011
Note that membrane theory, which is Brian Greene's metier, postulates multiple real universes being literally parallel to each other, separated from ours in some much-higher dimension – suggesting, for example, that the speed of the expansion of our universe may be a little greater than it should be given the mass it contains not due to "dark matter" but because some of our mass's gravity is "leaking" into other universes.
This has little to do with the Many-Worlds Interpretation's multiplication of universes, which is in a sense the inversion forward in time of Feynman's path integrals, a hypothetical way of describing the superposition of possible universes so that you can add up their outcomes probabilistically, without worrying about "where" the many worlds "are".
posted by nicwolff at 10:13 AM on March 7, 2011 [1 favorite]
This has little to do with the Many-Worlds Interpretation's multiplication of universes, which is in a sense the inversion forward in time of Feynman's path integrals, a hypothetical way of describing the superposition of possible universes so that you can add up their outcomes probabilistically, without worrying about "where" the many worlds "are".
posted by nicwolff at 10:13 AM on March 7, 2011 [1 favorite]
"Where" is a question that implies a spatial relationship-- I am 120 miles Northeast of you, my neighbor is two stories above me, etc.
These other universes have no clearly defined spatial relationship to our own. I have heard them referred to them as "perpendicular" to our own, but I believe that just means that in one particular mathematical model you treat them as orthogonal when doing calculations.
There is a multiverse model that has other worlds like ours where this question makes sense: Max Tegmark's Level 1 multiverse.
posted by justkevin at 10:24 AM on March 7, 2011
These other universes have no clearly defined spatial relationship to our own. I have heard them referred to them as "perpendicular" to our own, but I believe that just means that in one particular mathematical model you treat them as orthogonal when doing calculations.
There is a multiverse model that has other worlds like ours where this question makes sense: Max Tegmark's Level 1 multiverse.
posted by justkevin at 10:24 AM on March 7, 2011
I good starting point for understanding this issue is to read Edwin Abbott's Flatland: A Romance of Many Dimensions. Unfortunately, there are editions of this book that lack illustrations, so I advise buying it from a brick-and-mortar bookstore rather than online.
posted by neuron at 10:36 AM on March 7, 2011
posted by neuron at 10:36 AM on March 7, 2011
Flatland is available with illustrations at project gutenberg.
posted by thsmchnekllsfascists at 10:44 AM on March 7, 2011
posted by thsmchnekllsfascists at 10:44 AM on March 7, 2011
The problem with thinking about this spatially is that... you can't. Sorry. For there to be parallel universes, there needs to be a 4th spatial dimension. It is manifestly impossible to visualize 4 dimensions. Our brains just don't have the hardware to do it. The flatland analogies above are apt.
You can really only speak of these things in the language of higher-dimensional math.
posted by auto-correct at 10:51 AM on March 7, 2011
You can really only speak of these things in the language of higher-dimensional math.
posted by auto-correct at 10:51 AM on March 7, 2011
They're all here, in the same place, but you can only see that if you're standing outside of all of them.
posted by Faint of Butt at 10:52 AM on March 7, 2011 [1 favorite]
posted by Faint of Butt at 10:52 AM on March 7, 2011 [1 favorite]
(Disclaimer: I am not a quantum physicist, this is just my layman's understanding. Corrections are welcome.)
There's a common misconception that "parallel universes" and "higher dimensions" are the same thing. This is sort of approaching the right idea, but not quite there.
Quantum mechanics relies heavily on the notion of phase space. Imagine the universe was one-dimensional and contained only two particles. If you wrote down the x-axis coordinates of both particles, you could plot the entire state of the universe as a single point on a two-dimensional graph.
In the real world, there are a huge (potentially infinite) number of particles, each with a 3D position and momentum, etc. You can imagine extending this phase space with a huge number of perpendicular dimensions, one for every measurable aspect of every particle. Just remember that one single point in this phase space represents — or, if you prefer, describes — the state of every particle in the universe. If there were additional spatial dimensions, they wouldn't be special; we'd just add more axes to our model of phase space.
Under a classical, deterministic model of the universe, this one point would be enough information to calculate the state of the world an instant in the future. Over time, the point would follow a path through phase space. But with quantum mechanics, the point becomes a fuzzy blob of uncertainty called a wavefunction, and the "path" it follows can split into branches. This is experimentally verifiable because of how the different paths can interfere with each other in certain specific circumstances.
All interpretations of QM agree on this much; they're based on the same math and make the same predictions. Many-worlds is simply the position that the branches continue their existence independently, instead of somehow being "collapsed" back down to a single possibility as the Copenhagen interpretation postulates.
So to finally answer your question: it doesn't really make sense to talk about "where" parallel universes are, in a spatial sense. But you could informally think about points in phase space as being "similar to" each other, based on how close together they are on each of the infinitely many axes.
posted by teraflop at 11:21 AM on March 7, 2011 [3 favorites]
There's a common misconception that "parallel universes" and "higher dimensions" are the same thing. This is sort of approaching the right idea, but not quite there.
Quantum mechanics relies heavily on the notion of phase space. Imagine the universe was one-dimensional and contained only two particles. If you wrote down the x-axis coordinates of both particles, you could plot the entire state of the universe as a single point on a two-dimensional graph.
In the real world, there are a huge (potentially infinite) number of particles, each with a 3D position and momentum, etc. You can imagine extending this phase space with a huge number of perpendicular dimensions, one for every measurable aspect of every particle. Just remember that one single point in this phase space represents — or, if you prefer, describes — the state of every particle in the universe. If there were additional spatial dimensions, they wouldn't be special; we'd just add more axes to our model of phase space.
Under a classical, deterministic model of the universe, this one point would be enough information to calculate the state of the world an instant in the future. Over time, the point would follow a path through phase space. But with quantum mechanics, the point becomes a fuzzy blob of uncertainty called a wavefunction, and the "path" it follows can split into branches. This is experimentally verifiable because of how the different paths can interfere with each other in certain specific circumstances.
All interpretations of QM agree on this much; they're based on the same math and make the same predictions. Many-worlds is simply the position that the branches continue their existence independently, instead of somehow being "collapsed" back down to a single possibility as the Copenhagen interpretation postulates.
So to finally answer your question: it doesn't really make sense to talk about "where" parallel universes are, in a spatial sense. But you could informally think about points in phase space as being "similar to" each other, based on how close together they are on each of the infinitely many axes.
posted by teraflop at 11:21 AM on March 7, 2011 [3 favorites]
It is manifestly impossible to visualize 4 dimensions. Our brains just don't have the hardware to do it.
I really, really, really doubt this.
I'm pretty sure that parallel universes don't have a "where" in any sort of sense that we think of. It's like asking "where is tomorrow?".
posted by It's Never Lurgi at 12:02 PM on March 7, 2011 [3 favorites]
I really, really, really doubt this.
I'm pretty sure that parallel universes don't have a "where" in any sort of sense that we think of. It's like asking "where is tomorrow?".
posted by It's Never Lurgi at 12:02 PM on March 7, 2011 [3 favorites]
I really, really, really doubt this.
We can visualize shadows that higher dimensions leave in the three-dimensional world our brains can perceive.
posted by Blazecock Pileon at 12:39 PM on March 7, 2011
We can visualize shadows that higher dimensions leave in the three-dimensional world our brains can perceive.
posted by Blazecock Pileon at 12:39 PM on March 7, 2011
It is manifestly impossible to visualize 4 dimensions. Our brains just don't have the hardware to do it.
I really, really, really doubt this.
I'm curious why you think that. Visualizing 4D objects is a very active area, especially for mathematicians and high energy physicists. Here's a brief blog post about it. To my knowledge, everyone who works in this area only visualizes the 3D projections of higher dimensional objects - like this projection of a hypercube. I remember reading that even Penrose gave up trying to picture 4D objects [citation needed].
Anyways, the point with regards to multiple universes is that using words like "where" when talking complex objects like this might not really work. Concepts that come from the world of every day experience do not necessarily translate to cutting edge physics. Brian Green and Stephen Hawking both discuss this topic in their popular works with a lot more skill than I can.
posted by auto-correct at 12:53 PM on March 7, 2011 [2 favorites]
I really, really, really doubt this.
I'm curious why you think that. Visualizing 4D objects is a very active area, especially for mathematicians and high energy physicists. Here's a brief blog post about it. To my knowledge, everyone who works in this area only visualizes the 3D projections of higher dimensional objects - like this projection of a hypercube. I remember reading that even Penrose gave up trying to picture 4D objects [citation needed].
Anyways, the point with regards to multiple universes is that using words like "where" when talking complex objects like this might not really work. Concepts that come from the world of every day experience do not necessarily translate to cutting edge physics. Brian Green and Stephen Hawking both discuss this topic in their popular works with a lot more skill than I can.
posted by auto-correct at 12:53 PM on March 7, 2011 [2 favorites]
I'm curious why you think that.
I'm not saying it's easy and we might well lack the imagination to do it, but that's a far cry from saying that the brain lacks the fundamental hardware.
posted by It's Never Lurgi at 2:30 PM on March 7, 2011
I'm not saying it's easy and we might well lack the imagination to do it, but that's a far cry from saying that the brain lacks the fundamental hardware.
posted by It's Never Lurgi at 2:30 PM on March 7, 2011
This isn't a "math" answer, but I tend to imagine this in terms of vibration or frequency. I think of it as the way different radio stations share the same dial, but are separate. I suppose this means that the whole thing is observer-dependent. (i.e. You can't see one while "in" another, because you are inherently a part of it. You can only hear about others, and possibly change "levels" to observe the others from within.)
posted by skypieces at 5:38 PM on March 7, 2011
posted by skypieces at 5:38 PM on March 7, 2011
This thread is closed to new comments.
Now imagine that there is another piece of paper, half an inch above the first, with another ant on it. Again, the ant can travel the whole length of the paper; but neither can go the mere half an inch to the other's paper. They don't have access to that dimension; they can't move in that direction.
In other words, they're right here, but in a direction you can't go.
posted by spaltavian at 9:15 AM on March 7, 2011 [4 favorites]