Is Paul Steinhardt's Statement "Rather Pathetic"? Why?

[Chalnoth]

But we're not trying to establish the correctness of a given model, like quantum mechanics. We are trying to understand the nature of one of its predictions. Until you empirically verify the existence of other universes, I'm sorry, they do not correspond to any objective reality.

This attitude of yours is fundamentally anti-science. It is exactly like the creationists complaining that we don't have transitional fossils because we don't have a continuous line of fossils of every lineage. Or that evolution isn't science because it can't be repeated.

Models do not exist in a vacuum. Refusing to believe in a definitive prediction of a model, even though that model has been thoroughly vetted through other means, and even though this other prediction is a natural consequence of the parts of the model that has been vetted, is just plain anti-science.

 

[bapowell]

Refusing to believe in a definitive prediction of a model, even though that model has been thoroughly vetted through other means, and even though this other prediction is a natural consequence of the parts of the model that has been vetted, is just plain anti-science.

It's not a matter of belief (who sounds like the creationist?) I've stated above (which you didn't read because you were too busy planning your rebuttal) that I am agnostic to the existence of the multiverse because it has not been observed. Once evidence accumulates in favor of it, I will accept it as part of objective reality. <---- THAT is science. To do otherwise is to merely have faith in its existence. Which is precisely what you are doing whether or not you choose to accept it.

Another important point you missed, is that my argument is not so much about the purported existence of the multiverse, but of its character. The anthropic principle presupposes not just its existence, but makes assumptions about its character. Such assumptions I refuse to accept without evidence.

There's a little thing called inductive reasoning. You should google it.

 

[Chalnoth]

It's not a matter of belief (who sounds like the creationist?)

No, it's a matter of evidence. And refusing to take evidence at face value is the problem here.

 

[bapowell]

No, it's a matter of evidence. And refusing to take evidence at face value is the problem here.

OK. What evidence, taken at face value or otherwise, can you provide for the existence of mutliple universes?

 

[Garth]

Is not the force of Steinhardt's objection the next part of his sentence:

—regarding the existence of multiple universes, a random creation process, probability distributions that determine the likelihood of different features, etc.— none of which are testable because they entail hypothetical regions of spacetime that are forever beyond the reach of observation.

Garth

That's not a valid objection either, because a unique universe is also not testable, due to the inability to verify that uniqueness. Furthermore, there is no requirement that the universe accept our demands that it be testable.

Like I said, you can object to the specific ways in which multiverse ideas are applied. I see no problem with that. These ideas can certainly be applied very poorly in certain cases. But it is still, by far, most likely the case that we live in some sort of multiverse.

Let's get this quite clear.
In this argument no-one is trying to assert or prove that our universe is unique or to prove that other universes don't exist.

It is not the uniqueness of our universe that is to be tested but its existence, and I think that we have enough evidence to assert that it actually does exist in a scientifically verifiable way. (Fans of the Matrix not withstanding!)

Other universes may well exist, in fact as a theologian I might argue that if the total density parameter \Omega is just greater than unity, as some results suggest, so that this universe is bounded and finite, and if the creative power of God is infinite, then there has to be many (an infinite number?) such universes!

It is as a scientist that I have a problem. It is not the possibility of these other universes that is the question but their verification, or falsification, by scientific observation and testing. Garth

 

[Chalnoth]

OK. What evidence, taken at face value or otherwise, can you provide for the existence of mutliple universes?

I've already posted it.

 

[Chalnoth]

It is as a scientist that I have a problem. It is not the possibility of these other universes that is the question but their verification, or falsification, by scientific observation and testing.

And I have already posted the very good reasons to believe that other regions of space-time with different low-energy laws of physics are exceedingly likely. Far, far more likely than our universe being unique.

 

[bapowell]

I've already posted it.

If you are referring to your post about spontaneous symmetry breaking, such a discovery, in itself, is not direct evidence for the existence for a multiverse because of the additional, untestable assumptions that must be made (I pointed these out in response to your post). If you're referring to your comment regarding quantum mechanics, you make no mention of any direct observational evidence for the other branches of the wavefunction.

So, the question persists. What evidence am I being accused of refusing to take at face value?

 

[Chalnoth]

If you are referring to your post about spontaneous symmetry breaking, such a discovery, in itself, is not direct evidence for the existence for a multiverse because of the additional, untestable assumptions that must be made (I pointed these out in response to your post).

I don't see this in your response.

But no, it doesn't require any additional assumptions. Unitary quantum mechanics + spontaneous symmetry breaking is sufficient.

If you're referring to your comment regarding quantum mechanics, you make no mention of any direct observational evidence for the other branches of the wavefunction.

Except that you have to invoke magic to avoid them. You can invoke magic to avoid anything if you like.

 

[bapowell]

Except that you have to invoke magic to avoid them. You can invoke magic to avoid anything if you like.

But you can't observe these other branches of the wavefunction. I'm not denying their existence; I'm not trying to avoid them. I'm trying to say that you can't observe them which is absolutely necessary for empiricism.

 

[marcus]

Chalnoth I think you made a mistake in post #2, right at the start. It doesn't make it simpler to assume a patchwork of regions with different laws/constants.

Specifically, I object to this statement:

"The anthropic principle makes an enormous number of assumptions"

Except that in reality, it requires more assumptions to assume a unique universe than it does to assume a prolific universe-generation process: you still need a universe-generation process, except now it can only ever occur once. And forcing that universe-generation process to only occur once requires additional and completely unreasonable assumptions.
...

Don't know what you mean by "universe-generation process". Could be a shell concealing a fallacy in your thinking. It is not incumbent on me or anyone else to explain why existence exists. The universe exists, our job is to explain aspects of its behavior in testable ways, to arrive at the next deeper layer of explanation--the next deeper layer of testable natural law.

No one is expected to leap to some conclusion as to the ultimate Answer.

And BTW eternal inflation would not solve that problem either. If it could actually be determined that there really is a patchwork of assorted big bang regions then what "universe-generation process" established the field on which they blossom?

As for the various ideas about how expansion started, some are more complicated and some less. At this point we have no reason to presuppose it happened this way or that. I can't tell whether or not you are committed to the eternal inflation picture, you sometimes seem to be and this would explain why you think it is more complicated to assume a mechanism that prevents other inflations in some imagined elsewhere-land.

 

[salvestrom]

I assume he is suggesting that it is more likely that the process which caused our universe to exist was not a one off and happens regularly, much as the m-brane theory proposes.

Your comment, marcus, about the process that created the area into which the universes are expanding is very much why I am dubious about cyclic models and m-branes. Taking the process back a 'step' should be done cautiously.

 

[salvestrom]

That's not even necessary, though, as the nature of quantum mechanics guarantees that all of these different symmetry breaking events are realized right here as different branches of the wavefunction.

Does it? Unless a consensus is reached on the physical reality of the wavefunction then what happens when that wavefunction is collapsed is entirely debatable.

 

[Chalnoth]

But you can't observe these other branches of the wavefunction. I'm not denying their existence; I'm not trying to avoid them. I'm trying to say that you can't observe them which is absolutely necessary for empiricism.

Direct observation is not required for anything in science. You can't observe an electron either in the strong sense.

 

[Chalnoth]

Chalnoth I think you made a mistake in post #2, right at the start. It doesn't make it simpler to assume a patchwork of regions with different laws/constants.

It is automatically simpler because it requires fewer assumptions. Just taking the standard model, for example, it is simpler for the electroweak symmetry breaking to be spontaneous, and thus occur differently in different patches, than it is for it to be forced to take on the particular value we observe. This situation is only likely to get more extreme as we learn more about high-energy physics.

Don't know what you mean by "universe-generation process". Could be a shell concealing a fallacy in your thinking. It is not incumbent on me or anyone else to explain why existence exists. The universe exists, our job is to explain aspects of its behavior in testable ways, to arrive at the next deeper layer of explanation--the next deeper layer of testable natural law.

If you want to get pedantic, the low-entropy initial conditions of our observable universe demand an explanation. Some sort of process is required to produce those low-entropy initial conditions, and there is no reason whatsoever to think that this process happened only once. And even if it did, quantum mechanics still guarantees that all or at least a great many outcomes occur even if it did only happen once.

And BTW eternal inflation would not solve that problem either. If it could actually be determined that there really is a patchwork of assorted big bang regions then what "universe-generation process" established the field on which they blossom?

I didn't say it did. But there has been some recent work in fixing the infinities by limiting the calculations to one Hubble horizon. No generality is lost due to the nature of unitary quantum mechanics, but the calculations are now finite and do not suffer from the measure problem that plagues eternal inflation.

 

[Chalnoth]

Does it? Unless a consensus is reached on the physical reality of the wavefunction then what happens when that wavefunction is collapsed is entirely debatable.

I have no sympathy whatsoever for those that would argue that they need to make up extra dynamics that do nothing but reduce the predictive power of quantum mechanics.

 

[salvestrom]

Direct observation is not required for anything in science. You can't observe an electron either in the strong sense.

But testability is. Gotta be able to measure it or an affect you expect it to have on something else you can observe. I think the sciency response is along the lines of: if they do exist they have no causal effect on us and are irrelevant. I think irrelevant is harsh, but if it has no effect on any system, it's not science. It's just cool.

 

[Chalnoth]

But testability is. Gotta be able to measure it or an affect you expect it to have on something else you can observe. I think the sciency response is along the lines of: if they do exist they have no causal effect on us and are irrelevant. I think irrelevant is harsh, but if it has no effect on any system, it's not science. It's just cool.

Right, and many of the models that lead to the multiverse are testable. Real consequences of a multiverse, by the way, have already been posted in this thread.

 

[bapowell]

Direct observation is not required for anything in science. You can't observe an electron either in the strong sense.

But I can directly detect it's presence, for example, viz. a track in a cloud chamber.

It looks like you have your own version of how induction is done, which differs significantly from my view. You seem to be saying the following:

There is a theory A that makes predictions B, C, and D. I've collected the appropriate data and verified, to some degree of significance, that B and C are true. I have no data to verify D. But, since it is predicted by the same theory that predicts B and C, and since I have adequate data to support predictions B and C, then D is true. Sort of like "true by association." I'm sorry Chalnoth, but I don't buy it. And I don't think Francis Bacon would either. Or really any empiricist for that matter.

EDIT: That's not to say that such a situation shouldn't compel one to strongly suspect the validity of D. Your allusion to the transitional fossils made earlier is an example. Yes, given the success of evolutionary theory and its sound logical framework, many pieces of which have been verified scientifically, it is especially likely that transitional fossils should exist (and they do, as I think we all know, but sake of argument here.) However, such a strong suspicion does not abdicate the scientist from his responsibility of finding them. Their absence in no way invalides the theory -- an argument I think you suspected I was making. I was not. But they do not become objective reality simply because they really, really should be there.

 

[bapowell]

I have no sympathy whatsoever for those that would argue that they need to make up extra dynamics that do nothing but reduce the predictive power of quantum mechanics.

But you apparently have just the right amount of sympathy for those that would argue for a vast and wasteful proliferation of alternate universes. I don't see why you don't simply admit that you are following a sense aesthetic that helps guide which physical theories you deem most relevant to the universe. That's not a criticism -- we all do this. But it's ultimately just a hunch, not something you've verified with data.

This is not a rhetorical question: how does doing away with many-worlds reduce the predictive power of QM? If you can convince me that many-worlds is the way to go, then I will agree to upgrade my agnosticism regarding the existence of a multiverse to an "I strongly suspect..."

 

[salvestrom]

Thinking on the topic's title: accidental versus...?

I read the article about non-uniformity in the CMB. Anyone know if they've looked at that spiffy knew pink one we've got now?

I also looked up wave-function collapse. The wikpedia article general says that the Copenhagen Interpretaton is the standard one, but contains no direct mention of what happens to the other probabilities. Many worlds is an extension of that and then, further down it mentions Many Minds. There were nearly a dozen, in all. I've been left with the clear impression that the nature of the wavefunction is quite open to debate and is not unambiguous evidence of a multiverse.

http://www.nature.com/news/quantum-theorem-shakes-foundations-1.9392

The above link (gotta love the over-stated title and leading line) has a further link to a preprint of the paper. They are in agreement with challnoth's view as far as I can tell.

I think I'm sort of with Einstien. He considered the wavefunction statistical, but with an as yet undiscovered underlying reality. My own personal view is the same. I view the wavefunction as a desription of something real, but that what it describes isn't quite what we think it to be.

 

[Chalnoth]

But I can directly detect it's presence, for example, viz. a track in a cloud chamber.

No. What you can do is test the predictions of a model of the electron. Many of the models which include a multiverse are testable in the exact same way.

There is a theory A that makes predictions B, C, and D. I've collected the appropriate data and verified, to some degree of significance, that B and C are true. I have no data to verify D. But, since it is predicted by the same theory that predicts B and C, and since I have adequate data to support predictions B and C, then D is true. Sort of like "true by association." I'm sorry Chalnoth, but I don't buy it. And I don't think Francis Bacon would either. Or really any empiricist for that matter.

This is the normal way that science is done. Every single prediction of a theory cannot possibly be verified. So we test what we can, and the more ways that we can test a theory, the more confident we are in its overall correctness.

With models of the universe that include a multiverse, even if it turns out to be impossible to observe the multiverse component of those models directly, there are most definitely other aspects of those models that can be tested. And even just the standard model plus unitary quantum mechanics makes a multiverse nearly certain.

EDIT: That's not to say that such a situation shouldn't compel one to strongly suspect the validity of D. Your allusion to the transitional fossils made earlier is an example. Yes, given the success of evolutionary theory and its sound logical framework, many pieces of which have been verified scientifically, it is especially likely that transitional fossils should exist (and they do, as I think we all know, but sake of argument here.) However, such a strong suspicion does not abdicate the scientist from his responsibility of finding them. Their absence in no way invalides the theory -- an argument I think you suspected I was making. I was not. But they do not become objective reality simply because they really, really should be there.

And there are many scientists working on creative ways to test for the impact of various multiverse ideas more directly. I don't hold much hope that this will prove to be fruitful. But it does, at least, avoid the useless work of trying to avoid such multiverse hypotheses as a matter of principle.

 

[Chalnoth]

But you apparently have just the right amount of sympathy for those that would argue for a vast and wasteful proliferation of alternate universes.

Why is it wasteful? What does that even mean?

It's exactly this knee-jerk reaction that I have such a big problem with. No matter which way you slice it, multiverse theories require fewer assumptions. It is easier for a theory to be prolific than not. Demanding that the default hypothesis be proven is ludicrous. The default hypothesis needs to be disproven, not proven.

 

[bapowell]

This is the normal way that science is done. Every single prediction of a theory cannot possibly be verified. So we test what we can, and the more ways that we can test a theory, the more confident we are in its overall correctness.

But you still haven't said why you've chosen to accept many-worlds over other interpretations, outside of from what I can tell are purely aesthetic reasons. Unless you have some Bayesian prior on your model space that you aren't telling anyone about.

EDIT: This discussion has actually been helpful because I understand now what we disagree about. It's not so much about the implied correctness of untested predictions or axioms. It's about your staunch acceptance of a version of quantum mechanics based solely on its relative simplicity that I'm not quite in agreement with. Occam's razor is an indispensable guide for selecting the most favored model out of a bunch; but it does not exclude those models it doesn't select.

 

[skydivephil]

But I can directly detect it's presence, for example, viz. a track in a cloud chamber.

It looks like you have your own version of how induction is done, which differs significantly from my view. You seem to be saying the following:

There is a theory A that makes predictions B, C, and D. I've collected the appropriate data and verified, to some degree of significance, that B and C are true. I have no data to verify D. But, since it is predicted by the same theory that predicts B and C, and since I have adequate data to support predictions B and C, then D is true. Sort of like "true by association." I'm sorry Chalnoth, but I don't buy it. And I don't think Francis Bacon would either. Or really any empiricist for that matter.

EDIT: That's not to say that such a situation shouldn't compel one to strongly suspect the validity of D. Your allusion to the transitional fossils made earlier is an example. Yes, given the success of evolutionary theory and its sound logical framework, many pieces of which have been verified scientifically, it is especially likely that transitional fossils should exist (and they do, as I think we all know, but sake of argument here.) However, such a strong suspicion does not abdicate the scientist from his responsibility of finding them. Their absence in no way invalides the theory -- an argument I think you suspected I was making. I was not. But they do not become objective reality simply because they really, really should be there.

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 let's 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 let's 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.

 

[Chalnoth]

But you still haven't said why you've chosen to accept many-worlds over other interpretations, outside of from what I can tell are purely aesthetic reasons. Unless you have some Bayesian prior on your model space that you aren't telling anyone about.

EDIT: This discussion has actually been helpful because I understand now what we disagree about. It's not so much about the implied correctness of untested predictions or axioms. It's about your staunch acceptance of a version of quantum mechanics based solely on its relative simplicity that I'm not quite in agreement with. Occam's razor is an indispensable guide for selecting the most favored model out of a bunch; but it does not exclude those models it doesn't select.

1. Many-worlds makes more predictions as to how the universe behaves. Specifically, it makes definite predictions about the nature of collapse. Most other interpretations sweep the nature of collapse under a rug and make no predictions at all about it. Considering that the nature of collapse is becoming more and more important as we try to take advantage of quantum mechanics for computing, this really is an essential feature and can no longer be considered up to personal choice (not that the nature of reality ever was up to personal choice).
2. Many-worlds makes the fewest assumptions. I don't see how there can possibly be any argument about this point.

 

[Chalnoth]

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 (?).

This is kind of off-topic, but I just wanted to point out that the upgrade to advanced LIGO is now under construction, and is expected to be up and running somewhere around 2015. The sensitivity is expected to be great enough that it will be guaranteed to detect gravity waves from a number of known sources, barring some unforseen systematic errors.

 

[martinbn]

2. Discoveries in high energy physics point to the existence of spontaneous symmetry breaking, which would lead to different regions of space-time realizing different low-energy laws of physics.

Why? I mean, the spontaneous symmetry breaking does not say that there are universes where each vacuum state is realized. Or am I wrong? I just don't see how spontaneous symmetry breaking is related to many universes!

 

[marcus]

... No matter which way you slice it, multiverse theories require fewer assumptions. It is easier for a theory to be prolific than not. ...

I think this is mistaken. (BTW it's a claim you already were asserting in post#2)
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.

 

[bapowell]

1. Many-worlds makes more predictions as to how the universe behaves. Specifically, it makes definite predictions about the nature of collapse. Most other interpretations sweep the nature of collapse under a rug and make no predictions at all about it. Considering that the nature of collapse is becoming more and more important as we try to take advantage of quantum mechanics for computing, this really is an essential feature and can no longer be considered up to personal choice (not that the nature of reality ever was up to personal choice).
2. Many-worlds makes the fewest assumptions. I don't see how there can possibly be any argument about this point.

OK. So as I understand it you favor many-worlds due to its parsimony and predictive strength relative to alternatives. This is precisely the way one would go about weighing the relative merits of competing statistical models. But at the end of the day, we are not considering statistical models; we are interpreting the candidate theories as representing objective physical reality. The more complicated, less predictive model may well be correct! Again, these considerations suggest a preference, statistically speaking, for the simpler model. I do not, however, think this is adequate to furnish the kind of certainty and correspondence to objective reality that you are advocating.