"Parallel Universes"

Qwerty 42 · Post by **Qwerty 42** » 2006-02-09 08:16pm

I was on GameFAQs and I posted in a topic about the limits of the Universe and I posted a "Flatland Theory" sort of thing in response to a thread derail about parallel universes. Would such a thing be even possible?

Qwerty FortyTwo wrote:
If Parallel universes exist, wouldn't that mean the Universe is finite?
Not necessarily. Imagine, if you will, a pair of two-dimensional worlds that extend forever, parallel to one another. These would be considered parallel universes, but the only way they would ever interact would be to skip across our third dimension. If a fourth dimension exists, then the only way for us to access our "parallel universes" would be to cross this fourth dimension.

If these parallel universes exist, they would bear no physical resemblance to our own. You wouldn't meet some parallel copy of yourself, it's improbable that humans as we know them even exist, since the two universes would be evolutionarily isolated. The odds of anything existing on the same coordinates as our Earth are infinitely small. It would be a truly remarkable discovery, but it wouldn't be anything especially weird like the mirror universe in Star Trek.

tharkûn · Post by **tharkûn** » 2006-02-09 08:42pm

Depending upon one's assumptions about the nature of spacetime, certainly. However to date we have witnessed no evidence of there being any new dimension orthogonal to the present 4 (3 spatial, 1 temporal). If more dimensions exist; then either something screwy happens to force propogation between the dimensions, so that gravity doesn't bleed through, or all the mass is sufficiently distant that it cannot be detected.

They might be out there, and some scientists think it is a good theory, zilch for evidence so far as I know.

drachefly · Post by **drachefly** » 2006-02-10 04:24pm

This categories of theory is called 'm-brane theory' and it's an elaboration on String theory. One variant of M-brane theory implies the Ekpyrotic theory cosmogenesis, which is one of the few reasonable alternatives to the Big bang.

We aren't exactly long on evidence for any of these, though. (read: there is none)

Pezzoni · Post by **Pezzoni** » 2006-02-10 05:14pm

I thought that it was generally agreed that if you carry on traveling in one direction in the universe, you will evenutally arrive back at the starting point, ergo the universe is finite.
The parralell universe theory has also been bandied around as an explanation as to where all the antimatter has gone, although I'm not sure how seriously it has ever been taken.

wolveraptor · Post by **wolveraptor** » 2006-02-10 05:18pm

That's the hypothesis that all space-time is curved, I believe. I haven't heard of any evidence of this, though, and considering that the universe is continually expanding, it must have a calculatable volume if one froze time. So I'm sure it's finite.

Dooey Jo · Post by **Dooey Jo** » 2006-02-10 05:54pm

Pezzoni wrote:I thought that it was generally agreed that if you carry on traveling in one direction in the universe, you will evenutally arrive back at the starting point, ergo the universe is finite.

Measurements of the background microwave radiation have shown that the universe seems to be very flat, so most likely you will not arrive back at the starting point. Note that you might not be able to do so even if the global geometry of the universe was curved, because the expansion rate could be much too high.

wolveraptor wrote:...considering that the universe is continually expanding, it must have a calculatable volume if one froze time. So I'm sure it's finite.

Imagine a ruler that is infinitely long. Now imagine that you increase the distance between the points on the ruler. It's expanding but also infinite. The observable universe is finite, though, but space beyond that isn't necessarily so...

wolveraptor · Post by **wolveraptor** » 2006-02-12 03:13am

But how can scientists say that all space time was condensed to the size of an atom? It should've had a volume at that point, right?

Winston Blake · Post by **Winston Blake** » 2006-02-12 04:33am

wolveraptor wrote:But how can scientists say that all space time was condensed to the size of an atom? It should've had a volume at that point, right?

I'm eager to hear from someone who knows this stuff, but it seems to me that you could say that the intervals on Dooey's Infinite Ruler were once a handwavillion times smaller, comparable to the size of an atom. In this sense, the universe was always infinite (i.e. you could keep driving forever), it's just that all space was filled with incredibly hot and dense matter that eventually turned into familiar matter as the Infinite Ruler of the Universe expanded.

Also our known universe is only 13.7 billion lightyears in radius, so that sphere could have been 'condensed to the size of an atom'.

Dooey Jo · Post by **Dooey Jo** » 2006-02-12 07:55am

wolveraptor wrote:But how can scientists say that all space time was condensed to the size of an atom? It should've had a volume at that point, right?

As Winston suggested, it is our observable universe that they mean when they say that.

When scientists say "the universe", they usually mean "the observable universe", which is quite natural and correct, since that which is unobservable is irrelevant for us. However, one needs to make a distinction between the two when discussing multi-verse hypotheses...

Lord Zentei · Post by **Lord Zentei** » 2006-02-12 11:04am

Qwerty 42 wrote:
Qwerty FortyTwo wrote:If these parallel universes exist, they would bear no physical resemblance to our own. You wouldn't meet some parallel copy of yourself, it's improbable that humans as we know them even exist, since the two universes would be evolutionarily isolated. The odds of anything existing on the same coordinates as our Earth are infinitely small. It would be a truly remarkable discovery, but it wouldn't be anything especially weird like the mirror universe in Star Trek.

This is not neccesarily the case as long as you have an infinite (or at least very large) number of universes with identical physical laws. The number of constituent particles in a solar system, galaxy or galactic supercluster is finite and the number of configurations they can occupy is also finite. Thus, inevitably, identical configurations would have to occour.

wolveraptor · Post by **wolveraptor** » 2006-02-12 11:41am

What's considered the "observable universe" changes as you move throughout space, though, doesn't it? If you can only see things 15 billion lightyears away, what happens when you move 15 billion light years in a random direction? Shouldn't you be able to see things that were unobservable from your previous position?

Lord Zentei · Post by **Lord Zentei** » 2006-02-12 12:30pm

wolveraptor wrote:What's considered the "observable universe" changes as you move throughout space, though, doesn't it? If you can only see things 15 billion lightyears away, what happens when you move 15 billion light years in a random direction? Shouldn't you be able to see things that were unobservable from your previous position?

The universe expands, so the position of the horizon shifts with respect to the objects that are in it. There is aslo the matter of accellerating expansion to consider. So the set of objects in the observable universe changes even if you are stationary.

A person in another galaxy would see other objects that we cannot: his observable universe overlaps ours.

wolveraptor · Post by **wolveraptor** » 2006-02-12 12:51pm

Okay, I think I understand now.

10^-50 bagillion seconds after the Big Bang, the volume of everyone's observable universe would've been about the size of an atom. However, the actual space (unobservable included) was not of such a small volume. As the universe expanded, the amount of universe we could observe has increased, but the total amount has always been infinite.

Am I correct?

Dooey Jo · Post by **Dooey Jo** » 2006-02-12 01:40pm

wolveraptor wrote:10^-50 bagillion seconds after the Big Bang, the volume of everyone's observable universe would've been about the size of an atom. However, the actual space (unobservable included) was not of such a small volume. As the universe expanded, the amount of universe we could observe has increased, but the total amount has always been infinite.

Am I correct?

Yes. It's not quite certain that the "whole universe" really is infinite though, but if it is, you're correct.

drachefly · Post by **drachefly** » 2006-02-13 11:38am

drachefly wrote:This categories of theory is called 'm-brane theory' and it's an elaboration on String theory. One variant of M-brane theory implies the Ekpyrotic theory cosmogenesis, which is one of the few reasonable alternatives to the Big bang.

We aren't exactly long on evidence for any of these, though. (read: there is none)

I neglected to say that this theory is a theory of parallel universes. Oops.

B5B7 · Post by **B5B7** » 2006-02-17 04:39am

Whilst I find parallel universe stories fun, it's just fiction - I believe there is only one universe, finite and unbounded (created in a 'big bang').
If parallel universes existed, and if they were infinite, one still could not have a universe that duplicates our own - for the simple reason that infinity is not big enough.

For instance, take the positive integers - I can by selecting any particular category eg 1,2,3,4 ..., 2,4,6,8 ..., 2,3,4,5..., 1,1,2,3,5,8,13 ..., etc create an infinite different patterns, but in not a single one of those series is there the common fraction 1/2.
This is the case just with simple numbers, and a physical universe is even more complex.

And as for string theory - this involves entities that are intrinsically unobservable, and therefore no evidence.

His Divine Shadow · Post by **His Divine Shadow** » 2006-02-17 07:38am

drachefly wrote:This categories of theory is called 'm-brane theory' and it's an elaboration on String theory. One variant of M-brane theory implies the Ekpyrotic theory cosmogenesis, which is one of the few reasonable alternatives to the Big bang.

We aren't exactly long on evidence for any of these, though. (read: there is none)

Isn't also the "gravity bleedthrough" tharkün mentioned one of the theories of m-theory? Gravity is so much weaker because it extends into other dimensions as well.

drachefly · Post by **drachefly** » 2006-02-17 11:07am

Yea, but I don't know if all variants of m-theory have that feature.

Dooey Jo · Post by **Dooey Jo** » 2006-02-17 11:27am

B5B7 wrote:For instance, take the positive integers - I can by selecting any particular category eg 1,2,3,4 ..., 2,4,6,8 ..., 2,3,4,5..., 1,1,2,3,5,8,13 ..., etc create an infinite different patterns, but in not a single one of those series is there the common fraction 1/2.

That is because you have defined the series not to include fractions of numbers. The universe is not like that. If there is a finite number of particle configurations in the visible universe, and the whole universe and also the number of particles in it is infinite, then the particular configuration of particles that makes up our visible universe will eventually repeat itself. Infinity is in fact large enough for an infinite number of duplicates...

And as for string theory - this involves entities that are intrinsically unobservable, and therefore no evidence.

Not necessarily. String theories makes other predictions that can be tested. If they hold true, it would lend some credence to the other predictions that are harder to test.

B5B7 · Post by **B5B7** » 2006-02-18 06:55am

Ah, but the universe is like that. Quantum states.
Even if have finite quantity of particles, spatially they can occupy any of an unduplicatable infinite number of positions.

However, you have a valid point that even if a thing can not be directly observed, it can be observed by its effects. However, I am not aware of any such successful predictions for string theory.

Dooey Jo · Post by **Dooey Jo** » 2006-02-18 07:53am

B5B7 wrote:Ah, but the universe is like that. Quantum states.
Even if have finite quantity of particles, spatially they can occupy any of an unduplicatable infinite number of positions.

However, differences in positions that are less than the Planck length would be meaningless. There might not be universes that are quantum mechanically identical, but even at atomic scales, that wouldn't matter...

However, you have a valid point that even if a thing can not be directly observed, it can be observed by its effects. However, I am not aware of any such successful predictions for string theory.

No successful predictions that are unique to string theory has yet been produced, but theoretically at least, predictions of the existance and nature of supersymmetrical particles could be tested. Of course, it is a problem that there isn't yet a "complete" string theory, but several different ones...

drachefly · Post by **drachefly** » 2006-02-18 05:11pm

'Several' string theories? There are about a googol string theories (times or divided by a factor of a trillion to the power of several)

If we were to out 99% of them every year we would finally get one string theory in 50 years.

Furthermore, it may be that in the end those that remain have such similar properties we can't tell them apart except by building a particle accelerator stretching from here to Alpha Centauri.

String theorists are rather hoping this will not happen; but it is not vanishingly unlikely.

Zero · Post by **Zero** » 2006-02-19 10:49am

If you have infinite space to work with, and there's even the most minor of probabilities, say 1/(10^2000000), wouldn't there be infinite chances for it to happen anyways? I don't get why infinity wouldn't be big enough. It's infinity. Infinity times anything is infinity. Even the most minor probability should be able to happen infinite times.

StarDestroyer.Net BBS

"Parallel Universes"

"Parallel Universes"

Re: "Parallel Universes"