Probability of stars in a multiverse

jimjohnson

Yes, Greene is definitly hedging in the introduction; the purpose of the book is to describe 7 multverses each developed via different logic.

Chalnoth

How do you know humans descended from apes? You weren't there! Nobody has done an experiment showing an ape give birth to a human!

Arbitrary restrictions on what sorts of conclusions we can draw based upon evidence are fundamentally anti-science.

Chalnoth

Well, right. For each symmetry breaking event it is possible that there was some interesting physical phenomenon that forced the symmetry breaking to happen in a very specific way. I wouldn't be horribly surprised if a few things, such as the electroweak symmetry breaking event, turned out to do this.

But I don't buy for an instant that this sort of thing can possibly explain how we go from E8xE8 down to SU(3)xSU(2)xU(1), for instance (or whatever the fundamental symmetry group happens to be).

rbj

not answering the question.

Noth, even when the theory is there, and even when the theory makes sense, when there are holes in the evidence, you have to be prepared for surprizes. like Homo floresiensis.

you're problem is, again, that you're so enamored by a theory, versions of which are quite elegant (i think the string landscape theory of other universes is pretty elegant), that you are confusing that with evidence. i like elegance, too, but Nature doesn't necessarily give a rat's @ss about elegance.


that's called "strawman".

so what would have happened to special relativity if experiments like the Rossi-Hall (muon decay time is dilated) or the many that followed had turned out differently? or what would have happened to GR if Eddington's trip to measure the perihelion precession of Mercury (or the many subsequent experiments or observations supporting GR) turned out differently?

you know as well as anyone else what the meaning of "falsifiable" is and we're waiting patiently for you to describe a falsifiable physical experiment that would turn out one way if another universe exists and would turn out another way if no other universe exists.

Chalnoth

So, you think reality will just play nice and only present itself so that every single aspect of it will be neatly-falsifiable in a trivial manner?

rbj

never said anything of the sort. so i am at a loss to why you would conclude that i think that.

please stop propping up strawmen and just answer the question posed to you.

julcab12

We can handle that. Its not even clear whether the product of such breaking can fully constitute to a whole new set of physical laws moreover an entire zoo of universes. When a quantum particle becomes larger, the symmetry of the system as a whole becomes more unstable against small perturbations signaled by a set of noncommuting limits. It led to the particles with nonzero masses remains symmetrical but appears to be/'could be' hidden by default observation. Besides, it is pointing towards a form of indirect mechanism that hides EWSB. And one thing is certain. The specific mechanism that hides EWSB remains an open question but they have reasons to believe that a positive suspect is 'much' closer to home^^.

Chalnoth

It depends upon what you mean by, "a whole new set of physical laws." There's not really any question that having the electroweak symmetry breaking event occur somewhat differently would have impact on the properties of the weak force, and maybe also the electromagnetic force. This would likely result in different particles having different masses, and various reactions having rather different cross sections or decay times.

But that's only the tip of the iceberg: there were also symmetry breaking events earlier that transformed from a higher-order symmetry down to the standard model. We don't know what those were yet, but those may also have resulted in significant differences. I think it will be interesting to see where high energy physics goes in the next few decades, to see if we make any significant progress towards uncovering this part of the mystery.

All that said, yes, quantum mechanics guarantees that every possible result of a symmetry breaking event occurs. And even if you have trouble buying that, all you need is a universe that is larger than the typical size of a domain with a typical value of the broken symmetry, and that is trivially easy to produce in most inflation models, and perhaps even easier given that the original event that started inflation is highly unlikely to be a unique, one-off event.

Chalnoth

My point is that you're making up legalistic restrictions on what sorts of things we should and should not conclude, but perhaps even worse you're jumping to the conclusion (without even bothering to argue the point) that the default assumption should be a unique universe.

But that's nonsensical: a unique universe requires more assumptions than a prolific one. Even if we knew nothing at all about physical law, but just knew a little bit about how math behaves, the default assumption should clearly be a prolific universe. To take a simple example, consider the following two situations:

1. The set of all integers with addition, negation, and multiplication operations defined. The set of all integers is closed under these operations.
2. A set of the integers from [0,5], with addition, negation, and multiplication operations defined, with the set of integers [0,5] closed under these operations.

Which of the two above requires fewer assumptions? Clearly the second: it requires all of the rules of the first set, but it also requires additional rules to determine how to deal with the fact that it only includes six numbers.

rbj

citation, please.

i am making the same requirement about what it means for something to be "science" that Woit and Smolin and these guys that are fond of the phrase "Not even wrong". i'm not a big fan of Wikipedia, but i'll quote it :

http://en.wikipedia.org/wiki/Observation

how do you plan to deal with step 5? or are you saying that at least one of these multiverse theories is immune to that requirement? that somehow your scientific theory need not be subject to falsifiable empirical testing? if it does not ever subject itself to such, then what difference does it make? (and my question is how long does it retain the status of "science"? Smolin and Woit would say the same thing about string theory, which is also nice and elegant, on paper.)

not for theists. i don't even know that this claim is true for materialists or physicalists, and i suspect there are even those who disagree with you.

the issue is not whether or not we know nothing about the physical law, but whether or not we know everything about it (and we don't, of course). you don't know what will be discovered or derived by our descendants 400 years into the future. but you are writing as if you do.

the reality regarding other universes does not give a rat's patootie about it.

i think you meant the first. but the greater reality (about the multiverse or lack thereof) still is unaffected by the argument.

julcab12

I'm referring to SSB resulting to different physical constant.

Well .I don't have any problem with explicit or spontaneous symmetry breaking occurring because it did happen in nature. Some scientists can 'agree' on the multiverse theory, they can't always agree on how the multiverse actually works. I also see possibilities on mutiverse as a clear/direct consequence (The best we could think of or/ the only thing we could postulate for now) but i'll remain skeptic of multiverse until sufficient evidence is presented. The multiverse scenario right now is problematic. It can neither be verified nor falsified as per standard. Given our current universe as basis. No form of selection process can be invoked. Maintaining a plausible hypothesis, a universe generating mechanism is needed. In conclusion, without a scientifically rigorous means by which a multiverse (not SB)can exist. The concept remains a conjecture and less satisfactory. On the other hand it is 'exciting'. They've taken a great deal of speculation in attaining an answer to fine tuning but i do hope they'll find something more cohesive Or it is!? We don't know..

Chronos

I feel constrained by observational evidence - which does not yet favor the multiverse conjecture. Until that changes, I remain skeptical.

Chalnoth

You don't see how continually demanding to see evidence for a multiverse is, by default, assuming a unique universe?

I demand you present evidence that a unique universe is the preferred conclusion.

Chalnoth

Why be more skeptical about a multiverse than a unique universe?

rbj

i don't see that. it is, in fact, not the case. i do not assume a single universe and i also do not assume there are other universes out there. and settling that question (which cannot be settled for mortals) does not affect my worldview. i don't require a single universe to support my worldview, nor do i require multiple universes. i guess i cannot wrap my head around it if the number of universes is not a real integer greater than zero, unless the reality we apparently live in is really a simulation in a universeless existence (but i don't give that any credibility).

well, i cannot. nor do i say it's the preferred conclusion.

i will say this: the universe we're in is pretty big and quite old. and we can see it pretty deeply (e.g. hubble deep space). it could be all that there is (and there is no evidence and no hope for evidence that it's not all that there is, materially), and if that is the case, the teleological question regarding fine tuning remains. anthropic reasoning and selection bias does not cut the mustard in explaining fine tuning of a single universe from a solely materialist POV.

if the universe is one of many (some have speculated as many as [itex]10^{10^{10000}}[/itex]), just having math that is compatible with such an existence does not, in itself, make for a mechanism for the generation of all these universes. physical law is not "stuff", but it governs the stuff that exists or emerged into existence. all adding the multiverse concept does is add another layer of turtles. from a material POV, it's still "turtles all the way down". just another step in this problem of infinite regress.

perhaps there is a multi-multiverse. that the multiverse we live in is just one of many multiverses. maybe it's even another layer deeper than that. perhaps our multiverse that has some reasonable set of common physical law (but different parameters for the different universes) is one of many multiverses where the other multiverses have a reality of magic, wizards, and pink unicorns. we don't know.

you might object and say that such a reality is ridiculous, and i might agree. but if, in order to avoid (in your mind) the teleological question, you construct the necessity of a gazillion other universes, just to answer the question for how is it that our universe seems so finely-tuned (both in fundamental constants and in initial conditions) for the existence of matter, astronomical structures, elemental diversity, or life as we understand it, and yet criticize theists as being silly for suggesting that maybe it's the consequence of design, i think that open-minded philosophers would be quite dubious of your position.

but there are both open-minded and close-minded philosophers. just as there are open-minded and close-minded comologists, physicists, electrical engineers, musicians, and parents.

Chalnoth

You say that, and yet you continually demand that people present evidence for one (and only one) of those options. Furthermore, you won't listen to evidence that isn't of your specific desired type.

Why do you act as if you have already assumed there is only one universe if you don't believe it?

Chronos

I think rbj is saying there is no compelling observational evidence suggesting the existence of parallel universes. To that extent, I agree. I do, however, agree there is theoretical support for this possibility.