Parallel Universes?

Adam

A Scientific American article about the universe, parallel universes, stuff like that. I'd like some thoughts on it please.

http://www.sciam.com/article.cfm?cha...A5809EC5880000

jammieg

If there were infinite parallel universes right in our vicinity with infinite you's and me's next door then one of them would eventually find a way to break through to my universe, the fact that this hasn't happened leads me to the conclusion that it is irrelevant to consider since it can't be done or that this is science fiction sensationalism.

Eh

Not if our doubles are untold of light years away from us. They could never find us, even with the best possible technology. Hell, a photon probably couldn't either.

Adam

It seems very silly to me. The idea that there is another me (a horror in itself) simply because of the presumption that "in an infinite universe there are infinite possibilities" really requires, also, an infinite amount of matter/energy to make use of possibloy infinite variation. Since there is not infinite mass/energy, the whole thing is meaningless. Or so it seems to me.

LURCH

Agree. The necessary condition is an infinite universe. Although this possibility is not ruled out, it just doesn't seem very likely.

Eh

An infinite universe would have an infinite amount of energy and matter.

FZ+

No, at least for what the article terms level 3. From my understanding of Everett's theory, the key feature of the many worlds is that after the event that created it, all the universes are self-contained and non-interacting. While the theory allows anything possible - however unlikely - to exist, it does not allow the impossible to be done. The usefulness of Everett's theory is that it allows for a philosophically more consistent replacement to the Copenhagen interpretation in solving the "Schrodinger's cat paradox". The weakness of it is that it is too similar to in terms of observable results, so little reason is given to switch to it.

Adam

As I understand it (and I'm no expert), the universe is infinite area occupied by finite mass/energy. Which is why we have that "heat death of the universe" thing.

Eh

That's a common misconception. The universe is not a ball of matter expanding into infinite empty space. The space itself expands. If the cosmological principle holds true, space should look the same on average, everywhere you go. It may fail, but it doesn't make sense to have matter in only one small finite region of the universe.

Adam

This is no doubt based on my lack of reading in this field, but:

1) Why should there be any limit to the area of the universe?

2) Why should matter be evenly distributed? We know it isn't, simply by waving a hand around or looking up into the sky.

LURCH

But the theory described in the article does not appear to be Everett at all. The separate universes are proposed as extensions of a single continuum, separated merely by incredibly large distance, rather than overlapping universes separated by their different eigenstates.

Eh

There need not be, but a finite universe is possible. In such a universe, space is curved to the extent that if you were to travel in one direction for long enough, you would eventually return to your starting point.

The earth of course is a rare case, and the uneven distribution goes away once you get into space. From observations, it appears that on average, the universe is indeed the same from place to place, at least in terms of mass density. At least in the universe that is visible to us. However, there is no way to know if the cosmological principle is true on large scales, making any kind of matter distrubition possible. But as I said, it doesn't make much sense for matter to only be found in one infinitesimal point in an infinite universe, especially considering that matter/energy seems to be an inevitable property of space.

Eh

The article covered 4 different kinds of multiverses, did it not?

wimms

Indeed. Imo its as silly as thinking that because set of integers is infinite, every integer must repeat.

Of many ideas of parallel universes, one that seems most plausible to me is idea that parallel universes are potentialities, that either "come into existence" or don't. In them, there are infinite copies of every person in slightly different conditions. For eg. in one you cross the road and get run over by a truck, in other you don't cross the road, and continue to prosper. Which one of them is "real" is matter of perception, as there is really no reason for any preference and no one is any more real than other. Whenever you exercise act of free will or simply interact (eg. with truck), you basically move to other universe. In such swamp, there is no "another me", its still same you everywhere, and there is also no meaning in hoping that "another me" breaks into this universe and faces "real" me.

I wonder, by equivalence principle, isn't expanding universe equivalent to shrinking matter?

Eh

What, the equivalence between gravity and acceleration?

LURCH

Ah yes, I see that it does eventually get around to Everett. I must confess, however, that I've never seen the Everett interpretation as rational.