Is there a real chance that there is a multiverse?

[Alex K]

You mean if we had a complete TOE written down which explains all observations but also entails a multiverse?

yis

Let's say we have never observed a multiverse and let's say it's impossible to. Would the mathematics of a ToE with a 100% certainty confirm if a multiverse exists or not?

Ordinarily I'd say that's not how science operates - a mathematical construction is always a theory that needs to be tested, and some of its predictions may be inaccurate even if most others are correct. So I'd say no, it can be a strong hint if a otherwise very successful theory predicts something like that, but not a proof.

That being said, I've seen an actual talkby a philosopher of science who tried to construct something like statistical for string theory from the argument that there aren't any other theories or something. But I don't think this is widely accepted.

[Arkilogue]

yis

Let's say we have never observed a multiverse and let's say it's impossible to. Would the mathematics of a ToE with a 100% certainty confirm if a multiverse exists or not?

Ordinarily I'd say that's not how science operates - a mathematical construction is always a theory that needs to be tested, and some of its predictions may be inaccurate even if most others are correct. So I'd say no, it can be a strong hint if a otherwise very successful theory predicts something like that, but not a proof.

That being said, I've seen an actual talkby a philosopher  of science who tried to construct something like statistical for string theory from the argument that there aren't any other theories or something. But I don't think this is widely accepted.

I found this statement by the physics department at Oregon U to be enlightening. http://abyss.uoregon.edu/~js/ast123/lectures/lec17.html

Physics of the early Universe is at the boundary of astronomy and philosophy since we do not currently have a complete theory that unifies all the fundamental forces of Nature at the moment of Creation. In addition, there is no possibility of linking observation or experimentation of early Universe physics to our theories (i.e. it's not possible to `build' another Universe). Our theories are rejected or accepted based on simplicity and aesthetic grounds, plus their power of prediction to later times, rather than an appeal to empirical results. This is a very difference way of doing science from previous centuries of research.

Our physics can explain most of the evolution of the Universe after the Planck time (approximately 10-43 seconds after the Big Bang).

[bennyboy]

Is there enough inspiration about this tuning stuff to start a real thread on it?

[Alex K]

Is there enough inspiration about this tuning stuff to start a real thread on it?

Ok I hope I didn't F this up...

http://atheistforums.org/thread-45185.html

[Mister Agenda]

And you know the parameters of the universe can be tinkered with how? Not disputing, but I thought it was as yet unknown whether the cosmological constants could have been different from what they are.

To me it doesn't matter so much whether they can actually be tinkered with - after all what would that even mean. Whether they could have been different, the meaning of that question seems similarly hard to nail down, and depending on how I answer it, I find different related questions. So I don't think that distinction matters to me a lot. The physical parameters as we observe them seem to lie not entirely at random choices but such that matter can form, chemistry can exist, there are stars that actually work.

If that's not the only way they can be set, the question is, why were we so lucky that there is a universe at all where they are set in a sweet spot where there is chemistry and stars.

If for some reason the way they are set is the *only* way they can possibly be, the question becomes - why are we so lucky that the only way the universe can be is such that there is matter, and chemistry, and stars?

Conceptually, the latter is even more problematic than the former if you ask me...

I'm only a layman, but I thought Krauss made a somewhat compelling case that if the origin of the universe is due to a vacuum fluctuation, the 'energy budget' of the universe would need to be at or extremely close to zero, a 'flat' universe (and we have some evidence that this is the case). It doesn't seem more problematic to me that a universe that essentially has to 'add up to zero' would be extremely limited in the range of possible values its constants can have.

That's only one specific origin scenario; but I think it illustrates that we shouldn't be surprised to find ourselves in a universe so much like ours before we know how likely or unlikely a universe like ours is.

[Alex K]

Yes, the problem is that Energy, as we learn the concept in school or even college, is not conserved contrary to popular opinion, because of cosmic expansion. A photon travelling from A to B gets redshifted and obviously loses energy. One can rescue energy as a conserved quantity if one assigns an energy to space itself. It then turns out that the energy of the photon, and of space as a whole, and the spacetime ripples the photon causes due to its gravity, taken together, can be considered conserved. If you then add up the energy of the matter and radiation and dark energy in a flat expanding universe+plus the energy assigned to spacetime itself, you can get zero, i.e. this gives the compelling picture that all energy of the contents of space is borrowed from spacetime itseld, which carries negative energy due to its expansion.

[Mister Agenda]

That is the most comprehensible to a layman explanation for how the energy of the universe can be zero that I have ever read.

[Alex K]

I'm happy to hear that my explanations are helpful, as I'm writing physics textbooks and pop sci articles as a sidejob, so I better be good at it...