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Universe not accidental: Is this Steinhardt statement rather pathetic ? If so, why? 
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#55
Jan2612, 08:26 AM

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I think your example above goes back to what I was saying, that really there is a grey area between what is science and not science. So lets suppose theory A predicts B, C and D. As you say B and C have veen verified. Should we accept D as true without verififcation? I think I would agree that we should not accept it to the same extent as we accept B and C. However neither should we classify it as the same level of non science as something silly like creationism. Take gravity waves for example, although there has been indirect evidence from binary pulsars there has never been a direct detection despite LIGO being operational for something like 10 years (?). Now lets suppose the pulsar observation had not been made, what should we say about gravity waves? Well I think they would be in this grey area, they are precited by GR and Gr si well verified. Not somehting silly like creastionsim, but neither somehting verified such as time dilation. 


#56
Jan2612, 09:18 AM

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2. Manyworlds makes the fewest assumptions. I don't see how there can possibly be any argument about this point. 


#57
Jan2612, 09:22 AM

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#58
Jan2612, 09:35 AM

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#59
Jan2612, 11:11 AM

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PF Gold
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The way I slice it, the appropriate question to be asking at this point is how did the "big bang" come about. How did the expansion begin and why does it have the observed characteristics? Bounce theories of how this happened seem to depend on fewer assumptions. They simply have the U extend back further in time, and be in a contracting mode. No different laws from those operating now. Here's a current survey that briefly describes various approaches to understanding "big bang". It is an invited review for Modern Physics Letters: http://arxiv.org/abs/1201.4543 Not all the approaches sketched here are "multiverse" and it seems to me some are simpler (as well as more testable.) So I don't think your claim stands. 


#60
Jan2612, 11:43 AM

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#61
Jan2612, 12:29 PM

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Brian, hope it's OK to interject. I think the main agenda here is to resolve the cosmological singularity and provide either for inflation or for a substitute mechanism.
Renaldi, in the invited review article I mentioned, mentions string cosmology, loop cosmology, Horava, Jacobson's Einsteinaether, and various others. He gives a brief historical account of the earlier attempts which preceded and led up to these approachesparticularly the first two. In one form or another, most of these involve a bounce. You might want to glance at the relevant section, which is just 2 pages long. It is section 2 "Lines of Research" and begins on page 2. Here's an excerpt. ==Rinaldi review article http://arxiv.org/abs/1201.4543 page 3== There are several other models that offer alternatives to the direct quantization of gravity. Recently, Horava has proposed a powercounting renormalizable theory of gravity, based on an anisotropic scaling at high energy ^{20}. Essentially, the fundamental hypothesis is that time and space do not scale in the same way, according to the scheme t → b^{z}t, x^{i} → bx^{i}, where z is called critical (Lifschitz) exponent and b is an arbitrary constant. By adding higher spatial curvature terms to the standard EinsteinHilbert action, one can construct a model where, at high energy z ≥ 3, which makes the theory powercounting renormalizable, while at low energy z = 1. Local Lorentz invariance is preserved in the infrared (IR), and it is broken in the UV. The original formulation of this model suffered from un unwanted ghost scalar field, that persisted also in the IR ^{21,22}. To remove this anomalous degree of freedom one needs to add new terms in the action, that are basically formed by combination of a vector field, orthogonal to constant time surfaces, and its derivatives ^{23}. In this form, the HoˇravaLifschitz theory becomes very similar to the “Einsteinaether” theory proposed by Jacobson many years before as a vectortensor theory of gravity 24. Both theories offer nonsingular solution to the cosmological equations ^{25,26} and the horizon problem is solved without recurring to inflation ^{27}. ==endquote== 


#62
Jan2612, 01:51 PM

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#63
Jan2612, 01:54 PM

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A tangential point that I'd make is that the way highenergy physics is progressing, it is seeming increasingly unlikely that you could ever achieve the conditions for life with a model that only started one region of spacetime with one set of physical laws. 


#64
Jan2612, 02:20 PM

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PF Gold
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Just to be clear, I am addressing the claim of simplicity or fewer assumptions that you made in post #2. It simply is not true.
It is your opinion that the 4 or 5 quantum cosmology approaches discussed briefly in that invited review article are "highly unlikely". Since it happens they are all bounce type. Your opinion could be right or wrongthis is not relevant. You cannot rightly say that multiverse scenarios require fewer assumptions than other theories being studied that resolve the cosmo singularity. I don't think you even know what the possible alternative theories are, so it is ridiculous to claim that multiverse theories need fewer assumptions than all the others. Logically I think what you need to say is that in your opinion the approaches Renaldi covers in his review article (string cosmology, loop, Horava, Einsteinaether...) are "highly unlikely" and if these approaches are excluded then multiverse requires fewer assumptions than whatever theories you know of that resolve the initial singularity. 


#65
Jan2612, 02:25 PM

P: 38

I think there is multiple meanings of the word multiverse being used here.
The problem I have with Steinahrdt's statement is the basis of his argument, in that he beleives the universe was not accidental. Other than that statement. I agree with the rest, in so much as to say that it's equally possible that galaxies are the largest structures or that there is possibly more than one isolated 'universe' existing at the same time. I agree with Chalnoth in that the universe is not a singular event. More time and a bounce scenario can explain the astronomical probabilities for the conditions of life (as we know it!) just as well as more space. 


#66
Jan2612, 02:36 PM

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#67
Jan2612, 02:41 PM

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#68
Jan2612, 03:14 PM

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PF Gold
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A scientific theory is supposed to explain observations and make testable predictions, this is what we apply the Occam criterion of simplicity to, and fit to data. A bounce cosmology has no place for some grandiose philosophical speculation about some other completely disconnected realm. Makes no assertion either way. this is how to get a really simple resolution of the initial singularity. 


#69
Jan2612, 03:58 PM

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#70
Jan2612, 04:14 PM

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#71
Jan2612, 08:37 PM

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#72
Jan2612, 08:39 PM

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