luvluv

Well, most of the multiverse ideas I've heard about have to do with black holes. To contend with fine-tuning though your hypothesis would have to include an infinite number of inflation epochs. It's still not clear to me how this helps the cases of other universes forming elsewhere.

I've always been told that there was no way to know whether or not there were other universes from our universe, and that this was not a technological or a developmental problem but an intrinsic one. This would mean, even if inflation in this universe were to be proven, that we would still have no grounds for claiming that there are other universes.

eh

You're thinking of other theories. Chaotic inflation isn't really about more universes, it just offers a way that different regions will evolve. The fine tuning issue would not need an infinite number to work.

You're probably thinking of the many worlds interpretation of QM, which is a very different theory. That is a true multiverse theory, where each universe would be completely isolated.

Inflationary cosmology is quite different. If we could prove that such inflation occurs (perhaps a labratory universe would concince you?) then the idea would be unavoidable. But we will need a better understanding of gravity to know whether the laws of physics could be different in each region.

luvluv

Not infinite, maybe, but an awful lot. Trillions and trillions and trillions of times to cover some of the more improbable anthropic coincidences.

eh

Based on what, are you making that claim?

luvluv

Based on the random probabilities of certain anthropic coincidences, and based on their combined probability.

eh

And how do you know what, if any of these random probabilities are truely random, and not fundemental? Like I've said before, it's gonna take a lot more understanding of gravity before we know what is random, and what is not.

If we find there are lots of these random variables, what does it mean the concepts discussed in this thread? Would the idea of billions of different regions of the cosmos really sound unlikely? It would be like astronomers of less than 100 years ago, claiming our galaxy is all there is to the universe. They were of course, infinitely wrong.

luvluv

eh:

Fine, but like I said some of the leading experts in the field say that a quantum theory of gravity will not solve all of the anthropic coincidences.

Well, firstly, there would need to be trillions for a few of them. It's hard to believe that taken together the anthropic coincidences would require less than a trillion. And frankly, yes, given that the universe has only been around for 15 or so billion years, one trillion different inflation epochs would seem a bit excessive. Even if we got down to a necessity of only a billion epochs, that's still one every fifteen years. Surely at that rate most of the universe throughout most of history would have laws different than ours, so most of our astronomy would have to be thrown out of the window. In all of our observations, so far as I am aware, we have not noticed any sort of variations in the laws of physics anywhere in the universe.

[ November 16, 2002: Message edited by: luvluv ]</p>

eh

But it would put a cap on the AP speculation. Until then, you don't know if you have hundreds of fine tuning issues, millions, or even more.

You're making wild speculations again.

Nothing is excessive in an infinite universe. Even in standard BB cosmology, the prediction for a flat universe is that the cosmos is infinite - and has been from the very beginning. Tell me why time would make any difference in an open universe.

Of course, the universe may actually be closed and finite, and appears flat locally because of the inflation epoch. But if this is the case, then what justification do we have to claim the age of the entire universe? We would only be able to know the age of our visible universe, created from the inflation. The rest of the cosmos could be older than we can possibly imagine.

You're billion of epochs requirement is pure speculation, and we only know the age of our visible universe. No one is suggesting the laws of phyiscs are different in our region, but beyond that, all bets are off.

luvluv

eh:

Okay, you're talking about stuff I have never heard of. I have never heard anyone say that the size of the universe was infinite.

As for it being infinite "from the begining", well, if you decide that the universe is "all there is" then you could argue it has infinite size even if it were the size of a pea. It would not be truly infinite, which it would need to be for inflation to account for all the anthropic coincidences.

Not really. I'll get some literature in front of me for next time, but there are several A.C.'s which ALONE have random probabilities in the trillions. I'll have specifics next time.

Do you have any links or any substantiation for this? I've never heard anyone seriously question the age of the universe.

In order to eliminate all of the anthropic coincidences, I think one billion is extremely conservative.

eh

I don't mean infinite in that sense. Infinite means the universe was said to be infinite in size, from the beginning. A singularity in such a situation is where each region of space reaches infinite density. Only closed universes shrink down to atomic sizes.


Again you're missing the point. We are missing a theory of gravity, which would certainly put a limit on the variables that could be changed.

But I think this deserves a topic on it's own. How about we come up with some of the strongest AP issues, and apply them to even an incomplete theory, like M theory? I think that would be a good thread on it's own.

No one seriously questions the age of our visible universe. But with inflationary theories, there is no limit on how old the universe as a whole can be.

This page has some more info on a self reproducing universe: <a href="http://www.eurekalert.org/pub_releases/1999-01/SU-DTUB-260199.php" target="_blank">http://www.eurekalert.org/pub_releases/1999-01/SU-DTUB-260199.php</a>

There is also a link to the homepage of the leading proponent for inflation. It should have more details.

Not without knowing how many of these coincidences only exist because we lack a working theory of gravity.

[ November 16, 2002: Message edited by: eh ]</p>