Probability of stars in a multiverse

[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.

 

[rbj]

You say that, and yet you continually demand that people present evidence for one (and only one) of those options.

Noth, if you were to consider forensics (as in debate, like being on a debate team), you're going to have to avoid strawmen (misrepresenting your opponents' position and throwing it back at them) because they will call you on it. it's quite an ineffective way to argue a point unless the other guy is really dumb.

i wasn't talking about "options", but if you insist on articulating the "options" they are:

1. there is evidence of other universes not counting the universe we exist in.

2. there is not evidence of other universes excluding the universe in which we exist.

i don't think there is any dispute regarding evidence of existence of the universe we are in. we can point telescopes out there and see evidence of such.

it started with this:

... there is about as much evidence of the existence of these other universes as there is evidence of a transcendent God or of a flying spaghetti monster.

That is completely and utterly false.

so then i respond and you respond:

and that is a matter of opinion. your opinion.

Hardly. There simply isn't any comparison. One is a solid conclusion based upon broadly-supported scientific theory (in this case the standard model of particle physics).

so i am not equating "theory" to "evidence". if you are, you have to justify the semantics (and you'll lose that argument). and i am happy to stipulate that the observational or empirical evidence for a transcendental God or flying spaghetti monster is zero (but there is evidence, not conclusive, for fine-tuning, which motivates questions). i didn't say there is less evidence of other universes than that for theism or FSM. i said "there is about as much" of which you insist "is completely and utterly false."

somehow i doubt that your position is that there is far less evidence for the other universes, and presuming that, then what you have to do is propose or describe a falsifiable material observation of something consequential of the other universe(s) and you will then have more evidence for that than there is evidence of theism or FSM. because i think we both agree that conclusive material evidence of theism or FSM is the null set, {}.

but what i continue to wonder about if you're willing to apply scientific standards (and you don't get to define them, they are defined by others: what makes for science and what is not science) to your definite claim that there is more than zero evidence for the other universes. i didn't ask for theory (and by theory, i don't mean mere hypothesis), i asked for empirical, falsifiable evidence. because it is empirical and falsifiable evidence that is lacking for theism and FSM.

string theory and theorists and Ed Witten have some of the same problem. and they are being taken to task by the likes of Smolin and Woit. and that's fine. it's what Science is about.

you see, even though it was not offered as an explanation for the negative result for Michaelson-Morley, there was otherwise no material evidence offered by Einstein for either SR or GR when they were first presented. a theory gets to hang out there for a while without evidence and, if it's a good scientific theory, it can remain as plausibly valid for some time until there comes material observational evidence that falsifies it. that's why we don't believe in the existence of aether any more because, even when we tried to, we just couldn't measure it, and we expected to be able to at least some season of the year because we had no reason to expect that the aether moves around in space with the Earth as it orbits.

but, you never answered this question:

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?

these theories of Einstein made predictions of material consequence. that something in life differs from what Newtonian physics would say and we can check on that. do the physical observations look more like what Alfred said they would or do they look more like what Isaac said they would, and they are different. they are consequently different. because science is about what makes a consequential difference. that's why science is not about invisible pink unicorns or FSM or a transcendent God, none of which submit themselves to detection or measurement.

i'm trying to get you to submit to the requirement of science that it be of empirical consequence in order for it to be science. i don't think you're quite there yet.

Furthermore, you won't listen to evidence that isn't of your specific desired type.

that science must eventually be of empirical consequence and have evidence of empirical consequence in order for it to be science, is not about anyone's "specific desired type". if SR and GR made no falsifiable predictions of material consequence, predictions that were later empirically verified, time and again, they would likely have fallen by the wayside by now. it's why the "steady state model" of the universe has fallen by the wayside. and Witten and the string theorists have to worry about that string theory won't be forever accepted as physics if it just cannot be shown to have material consequence (which can be tested).

but you seem to think that the theory and claim regarding "the assurance..., the conviction of things not seen" (where do you think that quote comes from?) need not ever make a material, consequential difference indefinitely and that it's science.

i can (and others will) assure you that such is not the case. Science must eventually be empirical. if some purported science can never be empirical, it ceases to be science and is relegated to the discipline of philosophy. that is the case whether you like it or not, whether you deny it or not.

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

again, i have never, ever, once said that. it's a strawman. it weakens your argument because it is evidence that while you cannot dispute what your opponent is saying then you'll dispute what your opponent is not saying.

it doesn't help you.

 

[Chalnoth]

Noth, if you were to consider forensics (as in debate, like being on a debate team), you're going to have to avoid strawmen (misrepresenting your opponents' position and throwing it back at them) because they will call you on it. it's quite an ineffective way to argue a point unless the other guy is really dumb.

If you're going to accuse me of presenting a strawman argument, you're going to have to stop proving me right again and again. You have continually compared the multiverse idea with obviously false notions like the FSM: you claim to say you don't know, your mind is open. And yet you insist on using language elsewhere that makes it absolutely, positively clear that you consider multiverse ideas to be the height of absurdity, worthy of no consideration whatsoever.

Aside from this fundamental contradiction in what you are saying, the truth is the exact opposite of the way you try to paint it. You're very much like a man who lives his entire life situated in the plains of the central United States, and then proclaims to be ludicrous any notion that there might be parts elsewhere on Earth that are very unlike those plains. This is very clear when you use the following overly-simplistic comparison above:

1. there is evidence of other universes not counting the universe we exist in.

2. there is not evidence of other universes excluding the universe in which we exist.

Because the fact of the matter is that our vision is limited by causality. We cannot see beyond the horizon. But just because we cannot see beyond the horizon this does not mean that the default assumption should be that nothing is there (or even that everything is the same as the part within our horizon).

In fact, the default should most certainly be that things are quite different far enough beyond that horizon. How different we cannot say, but it is highly unlikely that things are identical everywhere.

Furthermore, you have over-simplistically assumed that just because we are causally-limited in our vision that we cannot ever possibly obtain evidence in support of things that may lie beyond our horizon. To be fair, we will never be able to point at a specific region outside of our cosmological horizon and use that as an example. But that isn't necessary. What we do need is a coherent and well-evidenced model of high-energy physics, combined with a coherent and well-evidenced model for how universes like ours begin and evolve, that together unambiguously predict that there will be other regions with different low-energy physical laws.

In technical terms, what we need is for the vacuum to be metastable with multiple local minima, and an early-universe model which allows the universe as a whole to explore the multiple local minima. As I've pointed out, basic quantum mechanics essentially guarantees that all local minima will be explored, while the existence of spontaneous symmetry breaking makes multiple local minima highly likely. Further study of the details of the properties of the Higgs may confirm that we live in a metastable vacuum state.

 

[Mordred]

My take on multiverse is that its not only possible but also likely. Depending on how you define Universe we have examples of a multiverse even now. I know this is adding fuel to the fire but oh well.

Alternate Universe definition from Wiki.

According to a still-more-restrictive definition, the Universe is everything within our connected space-time that could have a chance to interact with us and vice versa.[citation needed] According to the general theory of relativity, some regions of space may never interact with ours even in the lifetime of the Universe, due to the finite speed of light and the ongoing expansion of space. For example, radio messages sent from Earth may never reach some regions of space, even if the Universe would live forever; space may expand faster than light can traverse it.

By that definition any region well beyond any means of interaction with our observable universe can be construed as a disconnected spacetime hence anothere universe.
Regions inside an event horizon can be construed as a separate spacetime. As we will never be able to gain any information from that region. Though the interaction of Hawking radiation and blackbody radiation could be used as a counteere argument.

Many of the models used in cosmology are open to the possibility of a multiverse. Until we have irrefutable evidence either way, Thinking that this universe is one of many or all that there is are both equally valid.

 

[rbj]

If you're going to accuse me of presenting a strawman argument, you're going to have to stop proving me right again and again.

i only take responsibility for the things that i say. i do not take responsibility for things that other persons say that i say. (nor, specifically, for what you say that i say.)

again, you cannot dispute what your opponent is saying so then you dispute what your opponent is not saying.

it doesn't help you.

You have continually compared the multiverse idea with obviously false notions like the FSM

only that we cannot measure either nor hope to ever measure either.

but if you replace "FSM" with "God", you might have some dispute with some very authoritative people about how "obviously false" the notion is.

you claim to say you don't know, your mind is open. And yet you insist on using language elsewhere that makes it absolutely, positively clear that you consider multiverse ideas to be the height of absurdity, worthy of no consideration whatsoever.

again, you cannot dispute what your opponent is saying so you dispute what your opponent is not saying.

it doesn't help you.

try to read what i wrote (most of which you don't respond to at all). and respond to what i wrote, not to what i didn't.

Aside from this fundamental contradiction in what you are saying, the truth is the exact opposite of the way you try to paint it.

so you have a special hook on "the truth"? and we should accept that based on what? your authority?

Because the fact of the matter is that our vision is limited by causality. We cannot see beyond the horizon.

might be that FSM is hiding behind that horizon. don't worry, he/she/it can't get you because that would mean that you can measure him/her/it (and you can't).

But just because we cannot see beyond the horizon this does not mean that the default assumption should be that nothing is there (or even that everything is the same as the part within our horizon).

why must there be a default assumption? why can't the position taken be that we don't know nor cannot know what is beyond the horizon?

In fact, the default should most certainly be that things are quite different far enough beyond that horizon. How different we cannot say, but it is highly unlikely that things are identical everywhere.

maybe God or FSM or Santa Claus is back there. that's quite different.

 

[rbj]

My take on multiverse is that its not only possible but also likely.

i feel approximately the same way about it as i do about the likelihood that there are E.T.'s out there on some exoplanet that supports life. i would be very surprized if somehow someone could prove that Earth can be the only planet supporting life in the Milky Way. i accept the results of the Drake equation and think that there could be presently thousands of other civilizations in the Milky Way. but distributed among 400 billion stars, the likelihood we'll get an EM transmission from any that is not drowned out by stellar radiation, that likelihood is pretty small.

but one big difference is that while it's possible (and that possibility is exciting and deserves some funding and effort) for us to detect the presence of some E.T., i have absolutely no expectation that humans will ever measure or detect either God (setting aside accounts of miracles), the Flying Spaghetti Monster, nor anything coming from another universe.

Many of the models used in cosmology are open to the possibility of a multiverse. Until we have irrefutable evidence either way, Thinking that this universe is one of many or all that there is are both equally valid.

it is for me, but not for Noth.

 

[julcab12]

Ok. Let's give a brief case of multiverse. What are the arguments and evidence for existence of a multiverse:(Study of George Ellis)

Argument 1: "There are plausibly galaxies beyond the horizon, where we can’t see then; so plausibly many different expanding universe domains where we can’t see them."

Untestable extrapolation; assumes continuity that may or may not be true. Outside where we can see, there might be (a) an FRW model, (b) chaotic inflation, (c) a closed model, (d) an island universe. No test can be done to see which is the case.

If each step in a chain of evidence is well understood and inevitable, then indirect evidence carries nearly as much weight as direct evidence. But not all the steps in this chain are inevitable.

If employed leads to the old idea of spatial homogeneity forever (`The Cosmological Principle’) rather than the multiverse of chaotic cosmology with domain walls separating phases.

CASE 1: 2 Implied by known physics that leads to chaotic inflation

The key physics (Coleman-de Luccia tunneling, the string theory landscape) is extrapolated from known and tested physics to new contexts; the extrapolation is unverified and indeed is unverifiable; it may or may not be true. The physics is hypothetical rather than tested!
Known Physics → Multiverse ??
NO!
Known Physics → Hypothetical Physics → Multiverse
Major Extrapolation
It is a great extrapolation from known physics.
This extrapolation is untestable: it may or may not be correct.

ARGUMENT 2: The String Landscape is a fantasy(scientifc standard). We actually have a
plausible landscape of minimally supersymmetric AdS4solutions of supergravity modified by an exponential superpotential. None of these solutions is accessible to world sheet
perturbation theory. If they exist as models of quantum gravity, they are defined by conformal field theories, and each is an independent quantum system, which makes no
transitions to any of the others. This landscape has nothing to do with CDL tunneling or eternal inflation.

"Points is whether one agrees or not: this analysis shows that the supposed underlying physics is certainly not well established."

ARGUMENT 2: Implied by inflation, which is justified by CBR anisotropy observations.
- it is implied by some forms of inflation but not others; inflation is not yet a well defined theory.
- Not all forms of inflation lead to chaotic inflation.
- For example inflation in small closed universes.

Two central scientific virtues are testability and explanatory power. In the cosmological context, these are often in conflict with each other.

The extreme case is multiverse proposals, where no direct observational tests of the hypothesis are possible, as the supposed other universes cannot be seen by any observations whatever, and the assumed underlying physics is also untested and indeed probably untestable.

In this context one must re-evaluate what the core of science is: can one maintain one has a genuine scientific theory when direct and indeed indirect tests of the theory are impossible? If one claims this, one is altering what one means by science.
One should be very careful before so doing. There are many other theories waiting at the door –wanting to be called science (astrology, Intelligent Design, etc).

The multiverse proposals are good empirically based philosophical proposals for the nature of what exists, but are not strictly within the domain of science because they are not testable. There is nothing wrong with empirically based philosophical explanation, indeed it is of great value, provided it is labeled for what it is. But, cosmologists should be very careful not make
methodological proposals that erode the essential nature of science in their enthusiasm to support specific theories as being scientific, for if they do so, there will very likely be
unintended consequences in other areas where the boundaries of science are in dispute.

It is dangerous to weaken the grounds of scientific proof in order to include multiverses under the mantle of `tested science’ for there are many other theories standing in the
wings that would also like to claim that mantle.

What must be done?

- Determine a viable set of criteria/ procedures for what makes a theory scientific
- Find what methods can adequately justify unobservable entities
- Apply to the multiverse case
- Apply to other contentious cases (astrology, Intelligent Design) to see how they pan out
- Put the enterprise on a solid philosophical basis.

[G F R Ellis (2006): “Issue in the Philosophy of cosmology”
In Handbook in Philosophy of Physics, Ed J Butterfield
and J Earman (Elsevier, 2006), 1183-1285.
http://arxiv.org/abs/astro-ph/0602280 ]

The multiverse: conjecture, proof, and science
George Ellis

arXiv:1208.5715

http://www.aei.mpg.de/~axkl/HermannFestProceedings/Ellis.pdf

 

[Mordred]

I thoroughly enjoyed those papers you posted. They are being added to my collection. Thanks for linking them

 

[Chronos]

George Ellis is a well known critique of the multiverse hypothesis and his underlying objection is sensible - lack of testability. It is, however, unclear if the multiverse hypothesis is truly untestable. That remains to be seen. Gurzadyan and Penrose are still promoting CCC, which is a sort of temporal variant of the multiverse idea - On CCC-predicted concentric low-variance circles in the CMB sky, http://arxiv.org/abs/1302.5162

 

[Chalnoth]

George Ellis is a well known critique of the multiverse hypothesis and his underlying objection is sensible - lack of testability. It is, however, unclear if the multiverse hypothesis is truly untestable. That remains to be seen. Gurzadyan and Penrose are still promoting CCC, which is a sort of temporal variant of the multiverse idea - On CCC-predicted concentric low-variance circles in the CMB sky, http://arxiv.org/abs/1302.5162

I generally don't think that they have anything to offer here. Their first attempt at doing this was shockingly-bad. I didn't look at this attempt in too much detail, but I don't see how it's much better.

This was a much better, and better theoretically-motivated, search:
http://arxiv.org/abs/1210.2725

They didn't find anything definitively, but they did the analysis properly. I don't know if Planck will help or not for this sort of thing, however.

The discovery of cosmic strings would be another signature of a multiverse, because cosmic strings would be direct relics of a past spontaneous symmetry breaking event.

 

[Chronos]

I agree Gurzadyan and Penrose is a stretch. Strictly an opinion, but, it appears cosmic strings are a long shot at present.

 

[Chalnoth]

I agree Gurzadyan and Penrose is a stretch. Strictly an opinion, but, it appears cosmic strings are a long shot at present.

Well, I don't know how much of a long shot they are. They are certainly very rare, given current observational evidence. There's no question about that. But it would be a very interesting discovery if we found even one in the visible universe.