Multiverse Evidence Explanation?

[TheDemx27]

My friend keeps on harping on this sort of stuff. He says that there is a gravitational pull from other universes affecting the matter in this universe and creating imperfections in the cosmic background radiation. I find it hard to believe that any sort of boson would be able cross the nonexistent space between universes. Someone please explain.

Thanks.

 

[mfb]

My friend keeps on harping on this sort of stuff. He says that there is a gravitational pull from other universes affecting the matter in this universe and creating imperfections in the cosmic background radiation.

As far as I know, there is no sign of such an influence. Just ask him for a reference ;).

The temperature fluctuations can be explained with our own universe only - in fact, they fit very nicely to the model predictions.

 

[phinds]

My friend keeps on harping on this sort of stuff. He says that there is a gravitational pull from other universes affecting the matter in this universe and creating imperfections in the cosmic background radiation. I find it hard to believe that any sort of boson would be able cross the nonexistent space between universes. Someone please explain.

Thanks.

Tell him he's been watching too much TV "science".

 

[Chronos]

A recent claim of evidence for a multiverse was promoted by Kashlinsky in: A new measurement of the bulk flow of X-ray luminous clusters of galaxies, http://arxiv.org/abs/0910.4958. It has been frequently criticized by the mainstream, largely because it does not demand the existence of a multiverse to be explained. A paper in 2011 is regarded as refuting Kashlinsky's assertion: Measuring the cosmological bulk flow using the peculiar velocities of supernovae, http://arxiv.org/abs/1102.0800. Planck data also casts doubt on the significance of any bulk flow in the universe: On the Statistical Significance of the Bulk Flow Measured by the PLANCK Satellite, http://arxiv.org/abs/1303.6614. To date, there is no firm observational favoring the multiverse concept. If other universes are causally disconnected from ours, as usually suggested, it is unclear how such evidence could be gathered.

 

[Garth]

The problem is that any 'evidence' for the multiverse is likely to be able to be also explained by other less exotic causes.

It is interesting to see how keen some are to find evidence no matter how insubstantial; compare with the discovery of the Higgs boson that was not confirmed until it had reached 5 sigma significance.

Garth

 

[Nunchi]

Edit: Nevermind. I didn't read the cosmic background part. I'll still leave this here, these videos were more like standup comedy.

(What I meant: Start at 6:50)

 

[skydivephil]

The multiverse is not tv science. Its a serious proposal by serious cosmologists. It may well be wrong, and I'll come to that in a moment, but we should not dismiss it as as "Tv science".
There are several different multiverse concepts. The one that I think that should be taken the most seriously is eternal inflation.
You can read Alan Guth's case for a multiverse here:
http://arxiv.org/abs/hep-th/0702178
or watch his talk here:
http://pirsa.org/index.php?p=speaker&name=Alan_Guth

There are two questions then that the existence of the multiverse in this framework depend upon. Is there observational evidence that inflation happened and is it true that if inflation happened it is necessarily eternal or is it one time event only? If we want to know if a multiverse is real or not these are the questions we need to address.
On the first question the evidence seems so far to suggest inflation did happen, but we would still I think like to see the evidence from gravity waves to be more sure.
On the second question there are two possible routes. Explore Guth's maths that implies that if inflation happened once then it must happen again and again in other regions of the universe, creating a multiverse or look for evidence of bubble collisions in the CMB.
I think its possible that inflation did not happen and even if it did, Guth has his sums wrong.Or perhaps quantum gravity will help us understood the evolution of the inflaton field better. But these are issues to explored not written off as "tv science"
The issue of bulk flow can be read about here:
http://en.wikipedia.org/wiki/Dark_flow
I don't see how eternal inflation implies bulk flow but other less cited theories of the multiverse do, such as the one proposed by Laura Mersini-Houghton. Strangely seems to be making noise that its discovered by Planck even though Planck says not. I have no idea why she is saying this, it seems to be very wrong. maybe someone has seen her recent talk and can answer that.
http://www.math.columbia.edu/~woit/wordpress/?p=5907

 

[phinds]

The multiverse is not tv science. Its a serious proposal by serious cosmologists...

Yes, I'm aware of that. They include Lawrence Krauss, who is one of my favorite modern physicists because of his outspokenness and his entertaining presentation style. I've read his "A Universe from Nothing" and was disappointed to find that at the end he concluded that the multiverse is the only reasonable solution to some cosmological issues.

I'm also aware that I'm personally biased against the concept, BUT ... that bias is based on the total lack of any actual evidence in addition to my belief about how Occam's Razor should be applied to the concept (it's just too damned complicated!)

 

[Garth]

The multiverse is not tv science. Its a serious proposal by serious cosmologists. It may well be wrong

How exactly would you prove it wrong?

There may well be other universes 'out there' but leaving no evidence of their existence in our universe.

One objection to the multiverse concept is that it is unfalsifiable.

Just a thought...
Garth

 

[mfb]

"It might be wrong" and "we can show it is wrong" are not the same.

Unrelated:
A common statement about other universes is "if we have no way to test its existence, it is pointless to consider it at all".
I disagree. Consider quasars, for example: some of them are so far away that they are outside our observable universe now. We have no way to test if they still exist - but it would be foolish to propose that those galaxies just vanished!
If some theory requires that many universes exist, and if the same theory gives good predictions about our own universe, it can be a valid view that there are "probably" many universes.

 

[skydivephil]

The inflationary multiverse can be disproved by either showing inflaltion didn't happen or showing clearly the inflaton field doesn't evolve in the manner Guth claims.

 

[Chalnoth]

One objection to the multiverse concept is that it is unfalsifiable.

The claim of a unique universe is also unfalsifiable. It has the additional problem that it is patently absurd.

 

[TheDemx27]

Couldn't one argue that since there is hardly any evidence for it, that it is less of a matter of physics and more of belief or religion? Just a thought.

 

[skydivephil]

The inflationary multiverse comes from analysing the way the inflaton field evolves. That anaylsis might be wrong but i don't see how it has any similarity to religion.
Quanutm mechanics seems absurd to a lot of people so i don't think we should rule out anyything on those grounds. We should try and find out more about the dynamics of inflation and see if the claims made by Guth and other are right or wrong.

 

[phinds]

The claim of a unique universe is also unfalsifiable. It has the additional problem that it is patently absurd.

Interesting point of view. I hold the opposite --- the multiverse seems patently absurd to me. Since there's no evidence either way, I hold with Occam's razor and vote for one.

 

[skydivephil]

Interesting point of view. I hold the opposite --- the multiverse seems patently absurd to me. Since there's no evidence either way, I hold with Occam's razor and vote for one.

Have you read Guth's paper that I cited above? Of course his analysis might be wrong and his assumptions might be wrong but I am not sure why "patently absurd" is appropriate here. perhaps you can enlighten us?

 

[Nugatory]

The multiverse is not tv science. It's a serious proposal by serious cosmologists.

Everybody, serious cosmologists included, has a right to consider interesting propositions that are not currently considered falsifiable. It becomes "tv science" when the pop-sci crowd notices that a serious scientist is speaking, allows the prestige of the speaker to rub off on it, and starts overhyping it with phrases such as "exciting new theory".

When I hear someone talking about the multiverse, I presume that they've been victimized by the pop-sci crowd until shown otherwise - and this presumption is justified by a fairly straightforward application of Bayes' Theorem
I see no reason not to apply this presumption to someone who is identified only as a friend of the OP.

As an aside, it has happened that people have found ways of experimentally testing propositions once thought to be not falsifiable. Probably the most striking example is Bell's theorem, which pointed to experimental tests of the philosophical proposition of EPR realism.

 

[Chalnoth]

Interesting point of view. I hold the opposite --- the multiverse seems patently absurd to me. Since there's no evidence either way, I hold with Occam's razor and vote for one.

That's an invalid use of Occam's razor. The only way in which it makes sense is to base it off of the number of assumptions required. And a multiverse requires fewer.

 

[Nugatory]

Im not sure why "patently absurd" is appropriate here.

Absurdity, like beauty and other aesthetic judgements, is in the eye of the beholder.

So I have good news for you and bad news... The good news is that you cannot lose this argument; and the bad news is that you can't win it either.

 

[phinds]

Have you read Guth's paper that I cited above? Of course his analysis might be wrong and his assumptions might be wrong but I am not sure why "patently absurd" is appropriate here. perhaps you can enlighten us?

I'm just biased.

 

[skydivephil]

Everybody, serious cosmologists included, has a right to consider interesting propositions that are not currently considered falsifiable. It becomes "tv science" when the pop-sci crowd notices that a serious scientist is speaking, allows the prestige of the speaker to rub off on it, and starts overhyping it with phrases such as "exciting new theory".

When I hear someone talking about the multiverse, I presume that they've been victimized by the pop-sci crowd until shown otherwise - and this presumption is justified by a fairly straightforward application of Bayes' Theorem
I see no reason not to apply this presumption to someone who is identified only as a friend of the OP.

As an aside, it has happened that people have found ways of experimentally testing propositions once thought to be not falsifiable. Probably the most striking example is Bell's theorem, which pointed to experimental tests of the philosophical proposition of EPR realism.

"Of all objects, the planets are those which appear to us under the least varied aspect. We see how we may determine their forms, their distances, their bulk, and their motions, but we can never known anything of their chemical or mineralogical structure; and, much less, that of organized beings living on their surface ...
Auguste Comte, The Positive Philosophy, Book II, Chapter 1 (1842)

It was only a few years later that spectroscopy came on the seen.

 

[Nugatory]

"Of all objects, the planets are those which appear to us under the least varied aspect. We see how we may determine their forms, their distances, their bulk, and their motions, but we can never known anything of their chemical or mineralogical structure; and, much less, that of organized beings living on their surface ...
Auguste Comte, The Positive Philosophy, Book II, Chapter 1 (1842)

It was only a few years later that spectroscopy came on the scene.

Thank you - that's another seriously cool example. Maybe I should have credited Bell with the most striking example of the 20th century? And even then, I'll be the first to admit that this is another of those aesthetic judgements.

 

[Garth]

The claim of a unique universe is also unfalsifiable. It has the additional problem that it is patently absurd.

We observe one universe - there may well be others but unless there is a way of observing them their existence is pure conjecture.

Science is meant to be about what we observe and can make sense of, not about what we can imagine. If we do observe other universes with a significant certainty then the multiverse will be promoted into scientific fact, until then it is just intelligent conjecture.

A unique universe may well be absurd, but then so may life be!

Garth

 

[PhanthomJay]

Pardon my lack of knowledge in this area, but many years ago when M-Theory was relatively in its infancy, Hawking noted the possibility that dark matter in the form of E/c^2 could be high frequency gravitational waves penetrating our Universe from another brane universe by the way of Black Holes. I wouldn't discount this. Ahhh, Gravity! ...maker of all things both seen and unseen.

 

[DennisN]

FWIW, here's my brief opinion on the multiverse hypothesis: Is it reasonable? Yes. Is it probable? I don't know. Is there any good evidence pointing to it at the moment? I don't think so. But I can't rule it out. But I can't argue for it either. I need more data. Give me more data .

 

[Chalnoth]

We observe one universe - there may well be others but unless there is a way of observing them their existence is pure conjecture.

And why is it a reasonable assumption, then, that only observable things exist?

To take a trivial example, consider regions that lie beyond our observable horizon. Do you really think that the fact that we can't observe galaxies beyond this horizon means they don't exist, or that people would be engaging in wild speculation by proposing that they do?

 

[Garth]

And why is it a reasonable assumption, then, that only observable things exist?

To take a trivial example, consider regions that lie beyond our observable horizon. Do you really think that the fact that we can't observe galaxies beyond this horizon means they don't exist, or that people would be engaging in wild speculation by proposing that they do?

The Copernican Principle, that humans are not privileged observers of the universe, means that we may extrapolate our observations of the nearby observable universe to beyond our observable horizon.

Of course we might be wrong in doing so and there may be some range beyond which there are no galaxies, however there is no evidence to suggest that might be the case.

All such galaxies would be in the space-time continuum of our observable universe, the conjecture that there are other universes is a different concept altogether.

Garth

 

[Chalnoth]

The Copernican Principle, that humans are not privileged observers of the universe, means that we may extrapolate our observations of the nearby observable universe to beyond our observable horizon.

And how is that materially different from, for example, the suggestion that spontaneous symmetry breaking events in our past probably occurred differently in different regions?

 

[Garth]

And how is that materially different from, for example, the suggestion that spontaneous symmetry breaking events in our past probably occurred differently in different regions?

We observe other galaxies, we do not observe (yet) other regions of alternative spontaneous symmetry breaking events.

Garth

 

[Chalnoth]

We observe other galaxies, we do not observe (yet) other regions of alternative spontaneous symmetry breaking events.

We do not observe any galaxies whatsoever beyond our cosmological horizon.

 

[Garth]

We do not observe any galaxies whatsoever beyond our cosmological horizon.

You misunderstood me, of course I agree that we do not observe other galaxies beyond our cosmological horizon, however we do observe other galaxies and using the Copernican Principle extrapolate beyond our horizon.

Inflation, Eternal Inflation and alternative spontaneous symmetry breaking events are all conjecture, none of which have been demonstrated in physics.

Garth

 

[Haelfix]

There are galaxies just beyond our current horizon. No serious scientist suddenly doubts their existence just bc we can't currently observe them. That point of view could be said to be falsified every additional second when a new piece of evidence occurs.

Anyway, The evidence for the multiverse comes from the existence of inflation itself as well as rudimentary logic.

What you have is the following situation. Most natural and phenomenologically viable potentials for the inflation field involves one of two things. Either it is eternal, or it is generic. If it is generic, then you have a real problem explaining why it happens once, and only once when we know that quantum mechanics is about probabilities. This is particularly harsh given that we are forced to consider very large volumes in the early universe given the inflationary paradigm (so lots of places where an additional bout can occur). if it is eternal, then either we are at a very unique point of time (the initial bout) or inflation has already occurred multiple times.

Now this isn't ironclad in the sense that you can conceive of cases where this is not the case, however it really does involve more assumptions.

 

[Chalnoth]

You misunderstood me, of course I agree that we do not observe other galaxies beyond our cosmological horizon, however we do observe other galaxies and using the Copernican Principle extrapolate beyond our horizon.

Then why can't we use the same principle to extrapolate known physical laws beyond our horizon?

 

[Chronos]

Why ponder an effective theory that lacks observational evidence? It might be mathematically attractive, but, is that really sufficient?

 

[skydivephil]

Why ponder an effective theory that lacks observational evidence? It might be mathematically attractive, but, is that really sufficient?

Sufficient for what ?
I do not think we have sufficient reasons to say the multiverse exists, that its a fact like the mass of Jupiter if a fact.
But I do think we have sufficient reasons to "ponder an effective theory" as you say. Some people seem to imply the multiverse is simply an arbitrary assumption like its some sort of religious belief or a sci-fi plot device. That is not the case.
We do evidence for inflation. I agree the evidence is no iron clad, but it looks pretty good at the moment.
I also agree that Guth's argument is not iron clad. It may be possible to get an inflationary potential that is not eternal. But consider this form inflatioan biggest critics, Paul Steinhardt in SCIAM:
"Some suggest trying to construct theories of inflation that are not eternal, to nip the infinity of universes in the bud. But
eternality is a natural consequence of inflation plus quantum physics. To avoid it, the universe would have to start off in a very special initial state and with a special form of inflationary ener- gy, so that inflation ended everywhere in space before quantum fluctuations had a chance to reignite it. In this scenario, though, the observed outcome depends sensitively on what the initial state is. That defeats the entire purpose of inflation: to explain the outcome no matter what conditions existed beforehand."
The fact that both the critics and the defenders of inflation agree it leads to eternal inflation and the experimenters think inflation happens means there is some indirect evidence for the multiverse.
I agree its indirect, there is still the possibility that the experimenters who say the data supports inflation are wrong. They haven't measured the gravity wave spectrum yet , so we should wait for that . Its also possible the theorists have bungled things too. But i don't think that has really been shown to be the case. the fact that theorists who defend the theory like Guth, Linde, Vilenkin, Aguirre and those that attack it like Steinhardt and Turok all agree inflation is eternal does not mean it is right. but its hard for those of us sitting on the sideline to simply dismiss it is science fiction or religion. It's a very real possibility that its implied by a convincing and well supported theory.
We don't have to give up in a despair and claim we can never falsify this view. I think there is clear path ahead of us that could falsify this view.
1 measure the gravitational wave spectrum this can give us information on wether inflation really happened, what its energy scale is and may even help verify quanutm gravity theories like LQC and so on.
2 from this information we may getter a better understanding of how the inflaton evolves and we will be able to be more confident of whether it is eternal or not.
3 the above 2 are most likely long term. we might get lucky and see bubble collisions in Planck data. I know here are teams looking at this , a few months have gone by and they haven't realed any results yet, either positive or negative. From talking to theorists they think even if eternal inflation is true, we would have to be pretty lucky to see such collisions, but its not impossible.

I say let's wait and keep an open mind, maybe there are many universes, maybe only one. We don't need to let our prejudices decide. Science can make progress on this issue.