Discovering the Shape of Spacetime from the Big Bang: A Scientific Exploration

[Ken G]

It would rule out certain *types* of multiverse cosmologies. Eternal inflation for example makes pretty specfic predictions about the CMB background.

I guess we've made our cases, there's no point in just repeating. All I want to know is, are you, or are you not, going to answer this question:
What is something that we have not yet observed, that we should expect to observe if the multiverse model is good, but which anyone skeptical of the multiverse idea would expect that we will not observe that?

All you have said is that, in your opinion, the multiverse doesn't need to do that to be considered something we have learned about our universe. I have pointed out the danger of rationalization in place of demonstration. If you cannot argue that the multiverse passes that criteria, then anyone inclined to see that as an important fact can reach their own conclusion.

There is a *particular* power spectrum that inflation predicts, and it's hardly a case of "fitting the parameters" because people made the prediction a few years before COBE went up.

I didn't ask about inflation, I asked about the multiverse associated with eternal inflation.

Predicting that there will be fluctuations isn't impressive. Predicting the exact spectrum of the fluctuations is.

I still await where you show that eternal inflation predicts something we would expect to be untrue if we were skeptical of eternal inflation. I'm skeptical of eternal inflation, and you have not showed me a prediction that I would have expected to fail.

Predicts that curvature is < 1e-5 and that CMB is gaussian at small scales.

I see those as predictions of any inflation model that works.

I can't say the leading candidate model since there are several hundred inflationary models, all with various predictions.

That is very much the problem. It raises the spectre of rationalization by simply building in enough theoretical degrees of freedom to fit anything necessary, which is exactly what Popper objected to about Freud, Marx, and Adler.

Also for an example of a *falsified* multiverse model, look at cosmological natural selection. Smolin made the prediction that there would be no pulsars with more than 1.6 solar mass, and when we found a 2.0 solar mass pulsar, that theory went bye-bye.

Yes, but of course the irony is, the only good candidate theory that the multiverse model has been falsified. That means Smolin deserves kudos for the effort, but it is certainly no selling point for the multiverse models that have not been falsified. For them, I await the answer to the above question.

 

[Haelfix]

Well, that description just does not seem at all accurate to me. That sounds more like what happened to the Big Bang model in the 60s, at which point it became the cornerstone of cosmology and began to be taught as "lesson one" in any introductory cosmology course. I don't see any of that as being true for the multiverse.

Yea, I am getting a little bored of this conversation b/c if we can't agree on this then it makes no sense to continue. Suffice it to say that it's true and readily confirmed if you read up on the history of inflation. Eternal and chaotic inflation were already textbook material at the time when the final papers from COBE were released, and both predictions had been spectacularly confirmed by the data.

When WMAP released its findings, its fair to say that it became the dominant paradigm in the field over and above most of the competitor models (and there are hundreds of them, some involving a MV some without). Incidentally, several specific and popular models of chaotic inflation were falsified at the time namely those with a minimal phi^4 potential.

Anyway, I simply cannot understand why you would think that making a very specific (and at the time an original prediction) --a Harrison-Zeldovich nearly scale invariant primordial spectrum-- with detailed values somehow doesn't count. It is and was about as risky a proposition that you can write down, and quite honestly was not accepted by large portions of the community.

 

[Haelfix]

I see those as predictions of any inflation model that works.

This is your problem.. The problem is you are being very unspecific. There are detailed values, and shapes of the spectrum that you are ignoring. Different versions of inflation make different predictions (even those with an almost gaussian spectrum + 10 e-5 anisotropy bounds) and all of these are subject to falsification and indeed some have.

Further, it would be like arguing that General Relativity is unconvincing simply b/c its accurate predictions of the perihelion of Mercury must be true of any theory that works and that there are other theories out there that make identical predictions (and there are).

Do you see how silly that is?

 

[Ken G]

Anyway, I simply cannot understand why you would think that making a very specific (and at the time an original prediction) --a Harrison-Zeldovich nearly scale invariant primordial spectrum-- with detailed values somehow doesn't count. It is and was about as risky a proposition that you can write down, and quite honestly was not accepted by large portions of the community.

What is perfectly obvious here is that you are overselling the case for the multiverse. If your argument was valid at all, then we would have a single wisely accepted model of the multiverse, instead, of what we actually have, which is a kind of factory for producing agreement with anything we want. To get some idea of the expanse of this factory, consider:

"Brian Greene, in his 2011 book The Hidden Reality, sums up the numerous proposals for a multiverse as follows (including some that are not mentioned above) [Greene2011, pg. 309]:

The "quilted multiverse" -- Greene's name for Davies' collection of "pocket universes".
The "inflationary multiverse" -- Greene's name for the Guth-Linde collection of universes spawned in the inflation era of the very early universe.
The "brane multiverse" -- a higher-dimensional expanse populated by other "branes" as defined in string theory.
The "cyclic multiverse" -- a theorized collection of universes, parallel in time, resulting from collisions between branes.
The "landscape multiverse" -- the collection of universes resulting from the huge number of distinct possible shapes (topology) of the universe's fundamental structure -- see above.
The "quantum multiverse" -- the vast ensemble of branching parallel universes suggested by the "many worlds" interpretation of quantum theory.
The "holographic multiverse" -- the observation, stemming from the "holographic principle" (see [Greene2011, pg. 238-273]), that our universe is mirrored by phenomena taking place on a distant bounding surface.
The "simulated multiverse" -- a collection of universes that potentially are created as simulations running inside futuristic super-powerful computer systems.
The "ultimate multiverse" -- the suggestion by Tegmark and others that every set of mathematical equations describing a possible universe is actually realized."

You apparently are referring to just one of these, the Guth-Linde "collection of universes" (which means, sub-factory). Are you claiming none of the other ones are consistent with current cosmological data? Also, are you claiming there is no theory of inflation that does not invoke a multiverse that could explain that data?

What makes it even clearer that you are overselling the case for the multiverse is that if it were really true that the multiverse model made what we could view as "risky predictions" of what WMAP would observe, which no one who did not favor the multiverse picture would have expected that WMAP was going to observe, then it would be very clear that all astronomers and physicists would consider the multiverse the leading mainstream explanation for that data. Do you think that is true?

Here is a set of opinions, found at http://www.sciencemeetsreligion.org/physics/multiverse.php :

Paul Davies: Davies, a leading physicist, notes that the multiverse represents an inconceivably flagrant violation of Occam's razor -- postulating an enormous ensemble of essentially unobservable universes, just to explain our own. What's more, if the multiverse exists, then not only would universes like ours exist, but also vastly more universes where advanced technological civilizations acquire the power to simulate universes like ours on computer. Thus our entire universe, including all "intelligent" residents, are merely avatars in some computer simulation. In that case, how can we possibly take the "laws of nature" seriously? [Davies2007, pg. 179-185].
George F. R. Ellis: In a August 2011 feature article in Scientific American, Ellis addresses several multiverse proposals, and then concludes "All in all, the case for the multiverse is inconclusive. The basic reason is the extreme flexibility of the proposal: it is more a concept than a well-defined theory. ... The challenge I pose to the multiverse proponents is: can you prove that unseeable parallel universes are vital to explain the world we do see? And is the link essential and inescapable?" [Ellis2011].
David Gross: As a leading string theorist, he invokes Winston Churchill in urging fellow researchers to "Never, ever, ever, ever, ever, ever, ever, ever give up" in seeking a single, compelling theory that eliminates the need for anthropic/multiverse arguments [Susskind2005, pg. 355].
Stephen Hawking: In a 1999 lecture, Hawking declared, "I will describe what I see as the framework for quantum cosmology, on the basis of M theory [one formulation of string theory]. I shall adopt the no boundary proposal, and shall argue that the Anthropic Principle is essential, if one is to pick out a solution to represent our universe, from the whole zoo of solutions allowed by M theory." [Susskind2005, pg. 353].
Andrei Linde: "Those who dislike anthropic principles are simply in denial. This principle is not a universal weapon, but a useful tool, which allows us to concentrate on the fundamental problems of physics by separating them from the purely environmental problems, which may have an anthropic solution. One may hate the Anthropic Principle or love it, but I bet that eventually everyone is going to use it." [Susskind2005, pg. 353].
Juan Maldacena: Maldacena remarked, "I hope [the multiverse-anthropic principle] isn't true." However, when asked whether he saw any hope in the other direction, he answered, "No, I'm afraid I don't." [Susskind2005, pg. 350].
Joseph Polchinski: Polchinski is one of the leading researchers in string theory, but he sees no alternative to the multiverse-anthropic view [Susskind2005, pg. 350].
Paul Steinhardt: "I consider this approach to be extremely dangerous for two reasons. First, it relies on complex assumptions about physical conditions far beyond the range of conceivable observation so it is not scientifically verifiable. Secondly, I think it leads inevitably to a depressing end to science. What is the point of exploring further the randomly chosen physical properties in our tiny corner of the multiverse if most of the multiverse is so different. I think it is far too early to be so desperate. This is a dangerous idea that I am simply unwilling to contemplate." [Steinhardt2006].
Leonard Susskind: "The fact that [the cosmological constant] is not absent is a cataclysm for physicists, and the only way that we know how to make any sense of it is through the reviled and despised Anthropic Principle." [Susskind2005, pg. 22].
Gerard 't Hooft: 't Hooft, in response to a query by Susskind, wrote: "Nobody could really explain to me what it means that string theory has 10100 vacuum states. Before you say such a thing you must first give a rigorous definition on what string theory is, and we haven't got such a definition. Or was it 10500 vacua, or 1010000000000? As long as such 'details' are still up in the air, I feel extremely uncomfortable with the anthropic argument. ... However, some form of anthropic principle I cannot rule out." [Susskind2005, pg. 350].
Steven Weinberg: "For what it is worth, I hope that [the multiverse-anthropic view] is not the case. As a theoretical physicist, I would like to see us able to make precise predictions, not vague statements that certain constants have to be in a range that is more or less favorable to life. I hope that string theory really will provide a basis for a final theory and that this theory will turn out to have enough predictive power to be able to prescribe values for all the constants of nature including the cosmological constant. We shall see." [Weinberg1993, pg. 229].

A quick tally gives that 5/11 are highly skeptical of the scientific value of the multiverse concept, and at least 2 more still hope for an alternative to anthropic selection from a multiverse-- leaving only 4/11 who are happy that this is a good scientific theory which we can consider to give a satisfactory account. Note also that the view presented by Ellis is almost a carbon copy of the things I have been saying above. The dates on these quotes are generally around 2005, which means they have been informed by WMAP data. Finally, I point out the simple fact that on the WMAP website, http://map.gsfc.nasa.gov/, we find a "top ten" list of important discoveries-- none of which mention a multiverse in the slightest way. There is no question that some top cosmologists take eternal inflation very seriously, but that is a far cry from saying that it is widely accepted. More importantly, it also quite unclear that it survives the tests suggested by Popper to help us avoid mistaking rationalization for good theory.

I'm sorry that you are getting "bored of the conversation"-- I guess everything seems boring when you simply pretend to know the truth of something that is extremely subtle, and above all, highly controversial, despite your claims to the contrary.

 

[Haelfix]

I'm sorry but its really annoying when you keep changing the conversation topic.

First of all, almost all of high energy physics is a 'theory factory'. The standard model is an example of a theory that was curve fit to experiment, and there are many possible theories that go beyond the standard model where those parameters have not yet been measured. That is very much how science progresses.

Second of all I happen to know some of those individuals, and I know their opinions are rather more subtle than what can be subsumed in a sentence.

Thirdly, please distinguish between the case for level 1 of the multiverse and level 2-4 (using Tegmarks classification) and indicate which one you are talking about.

If you asked me to take a straw poll of people that I know and work with, I would say (anecdotally) at least one out of 3 people believe in level 1, with mostly undecided remaining, and I don't know many people who still hold out against inflation in general.

I'll give you a fact. I was present for a rather important conference in Chicago back in 1999, where a lot of famous cosmologists were presenting the case for inflation and what to make of a positive cosmological constant. A straw poll at the conference showed that approximately 60% believed in inflation. Of those that did, approximately 50% believed in some sort of chaotic/eternal inflation.. I daresay the percentages have increased significantly since then.

Incidentally, you haven't asked my opinion.. So I will volunteer it. Does it surprise you that my answer is 'I don't know'? There exists a strong theoretical argument against the multiverse that has to do with something called horizon complementarity and I am unsure what to make of it.

But the point is whether the mv exists or not will be decided by a mix of empirical data, and theoretical arguments. Philosophy of the sort you have presented, convinces nobody. Worse, the idea that there is no empirical or theoretical support for the MV and that it is pseudo science is basically an absurd proposition that has shown up in laymen topics on the internet, but is decidedly absent from any discussion amongst physicists.

 

[Ken G]

First of all, almost all of high energy physics is a 'theory factory'. The standard model is an example of a theory that was curve fit to experiment, and there are many possible theories that go beyond the standard model where those parameters have not yet been measured. That is very much how science progresses.

If you believe that, then I guess you missed the whole bit about Popper's challenge to scientists. To summarize, there is no issue with selecting a theory from a range of possibilities, the issue is that one cannot use all the data one has, and can likely expect to get, in the process of choosing, because if one does, one is simply rationalizing that data. If instead one wants to make a discovery about how the universe works, one must take the selected theory, and use it to make a "risky prediction", in reference to data that was not used to select the theory (or may not yet have even been observed, but which can motivate an observation to falsify the theory).

A theory that never does this is a very poor excuse for a scientific theory, that was Popper's point in the context of theories by Adler, Marx, and Freud, and this point is widely accepted as an important insight into doing good science. I don't claim categorically that the multiverse never does this, instead I challenge people to show that it does-- and the challenge has gone largely unmet, on this thread and on the one specifically set out to deal with that challenge. You came the closest yet, in referring to certain aspects of the quality of the fluctuations in the CMB, but fell short of demonstrating that the prediction was "risky", in the sense that someone disinclined to accept the actual existence of a multiverse should not expect that outcome on entirely different grounds.

Second of all I happen to know some of those individuals, and I know their opinions are rather more subtle than what can be subsumed in a sentence.

I can't help notice that you fell way short of claiming they were not skeptical of the multiverse idea. Are you now claiming that I misrpresented their skepticism, and they would agree with your blanket statements that WMAP data "spectacularly confirms", as you put it, that model?

Thirdly, please distinguish between the case for level 1 of the multiverse and level 2-4 (using Tegmarks classification) and indicate which one you are talking about.

We are talking about the version with cosmological implications, obviously, so that's level 1. All the same, Tegmark might argue that similar kinds of reasoning goes into constructing all those multiverses, so if a "level 1" model ever becomes the mainstream consensus (indeed you have claimed it already is), at the very least this opens the door wide for the other levels (and at least one poster on this very thread has already connected the cosmological multiverse to the many worlds of quantum mechanics).

If you asked me to take a straw poll of people that I know and work with, I would say (anecdotally) at least one out of 3 people believe in level 1, with mostly undecided remaining, and I don't know many people who still hold out against inflation in general.

That statement neither surprises me in the least, nor contradicts a single thing I said, nor addresses the challenge that I have put for proponents of the multiverse to meet. Now let me tell you a fact. I move among more "rank and file" astronomers (who tend to adopt highly empiricist approaches to science), rather than cosmological theorists (who tend to adopt highly rationalistic approaches to science), and I cannot name even a single one who would be comfortable describing the multiverse idea as "textbook science" to any of their classes, and I would wager that the majority view it is primarily a metaphysical view. That may partly be because they are underinformed, but more likely it is mostly due to the simple fact that a good case has not been made that it isn't primarily metaphysics.

Since rank and file astronomers should certainly be the skeptical audience that cosmological theorists need to be able to "sell" their ideas to, I would say that the latter group are not doing a terribly good job making their case. I'll accept that work is advancing on someday, perhaps, being able to make that case, but it just isn't there yet. This speaks to the idea that the multiverse maybe making legitimate inroads into not being pure metaphysics, but it doesn't make the case that it isn't still fundamentally metaphysics, and I connect that to the way the Popperian challenge that I presented has not been met.

I'll give you a fact. I was present for a rather important conference in Chicago back in 1999, where a lot of famous cosmologists were presenting the case for inflation and what to make of a positive cosmological constant. A straw poll at the conference showed that approximately 60% believed in inflation. Of those that did, approximately 50% believed in some sort of chaotic/eternal inflation.. I daresay the percentages have increased significantly since then.

And you think those numbers (for chaotic/eternal inflation) would be similar in a general audience of astronomers, say an American Astronomical Society meeting? I strongly doubt it. Cosmological theorists are the most knowledgeable about their models, but they are also the most likely to be taken in by rationalization, which is Popper's whole point.

Incidentally, you haven't asked my opinion.. So I will volunteer it. Does it surprise you that my answer is 'I don't know'? There exists a strong theoretical argument against the multiverse that has to do with something called horizon complementarity and I am unsure what to make of it.

There's a separate thread on whether the multiverse is physics or metaphysics, and these issues are kind of getting crossed here. I think your explanation of that issue would be quite interesting, but might be more appropriate on that thread.

But the point is whether the mv exists or not will be decided by a mix of empirical data, and theoretical arguments. Philosophy of the sort you have presented, convinces nobody.

I fear you have missed the point-- what you just said is what I am arguing for as well. The arguments in favor of the multiverse almost always have a highly metaphysical quality to them, so they are already philosophy. The challenge presented by Popper is the path to arguing they are not metaphysics, but are rather science, and that's why I find it so significant that this challenge has not been met. In other words, I am not using philosophical arguments to say the multiverse doesn't exist, I'm pointing out the dearth of non-philosophical arguments that the multiverse does exist.

I'll give you a more concrete version of the objection. Let's say you favor some multiverse theory factory, which creates a multiverse model for every letter of the alphabet. Let's say model X, makes predictions x, which motivate the next set of observations. That's all good science to motivate observations, but still says little about the existence of the multiverse, for two reasons:
1) Getting outcome x does not lead us to suspect model X is correct, because every outcome could have been obtained by one of the models in the "factory", and
2) Even if we are inclined to increase our belief in model X, having observed x, this still does not provide non-metaphysical evidence for the existence of the multiverse because I can simply introduce theory X', which is mathematically identical to X so makes all the same predictions x, but merely refers to our uncertainties about our own universe-- and casts them in terms of some kind of probability distribution, much as quantum mechanics does. Then observing x does nothing to distinguish X from X', so does not say that the multiverse actually exists-- it continues to be a primarily metaphysical issue.

Worse, the idea that there is no empirical or theoretical support for the MV and that it is pseudo science is basically an absurd proposition that has shown up in laymen topics on the internet, but is decidedly absent from any discussion amongst physicists.

"Pseudoscience" is something very different, had I intended that word I would have used it. The choice is "metaphysics". When people feel the need to change the words to make their case, it always raises a red flag. But again, whether the multiverse is physics or metaphysics is more appropriate for that other thread, there's a lot of crossing over so it's hard to know which arguments were presented in which thread.

 

[twofish-quant]

If you believe that, then I guess you missed the whole bit about Popper's challenge to scientists.

We didn't miss it. We just think it's silly.

To summarize, there is no issue with selecting a theory from a range of possibilities, the issue is that one cannot use all the data one has, and can likely expect to get, in the process of choosing, because if one does, one is simply rationalizing that data.

The problem is that sometimes, you don't have much data. Sometimes, you don't have *ANY* data. In that case, you just do the best with what you have.

Also getting to the point where you come up with a model that fits the data is hard work.

A theory that never does this is a very poor excuse for a scientific theory, that was Popper's point in the context of theories by Adler, Marx, and Freud, and this point is widely accepted as an important insight into doing good science.

You believe it. No one else on this thread (including several people with astrophysics background) thinks it is. Personally, if you had to ask me whether or not Marxism or Freudian psychoanalysis are sciences, I'd say yes.

Again, you are lecturing science to scientists. Rather than telling scientists what their philosophical beliefs *should* be, it might be useful in this discussion to just listen and find out what scientist's philosophical beliefs really are. No one is requiring you to accept anything. You might thing that cosmologists are idiots.

I don't claim categorically that the multiverse never does this, instead I challenge people to show that it does-- and the challenge has gone largely unmet, on this thread and on the one specifically set out to deal with that challenge.

****You are not doing science.****

If you were doing science you would either:

1) state categorically that any theory involving a multiverse model leads to unprovable and untestable conclusions and then back up that claim with a airtight chain of logic, or

2) come up with a specific well-posed multiverse model that we can discuss

Also, challenges are awful in science. Just because I can't figure out how to do it in a few months, doesn't mean that it can't be done.

As it you have a vague model, and vague claims about that model. This is not how science works.

Since you've been making lots of claims about how science works and what is or isn't science, I thought you might be interested in seeing *science in action*, and what a ***scientific argument looks like***. If you aren't, and you'd prefer to lecture physicists about physics, then I'm losing interest.

Now let me tell you a fact. I move among more "rank and file" astronomers (who tend to adopt highly empiricist approaches to science), rather than cosmological theorists (who tend to adopt highly rationalistic approaches to science)

Name some names. I'm very skeptical of your claims because there are lots and lots of astronomers in this forum, and no one has particularly defended your views. I should also point out that I'm not a cosmologist. My specialty is supernova and financial mathematics, and a lot of the philosophical issues about reproducablity and falsifyiable are things I have to think about daily.

Also I know first hand, that the reason one famous cosmologist warmed up to anthropic ideas was in talking with planetary scientists. The assumption before 1990 was that most star systems would look like the solar system, and it was a major surprise when it didn't.

The other thing is that cosmologists are pretty "data-driven." It's the string theorists that people think are nuts.

2) Even if we are inclined to increase our belief in model X, having observed x, this still does not provide non-metaphysical evidence for the existence of the multiverse because I can simply introduce theory X', which is mathematically identical to X so makes all the same predictions x, but merely refers to our uncertainties about our own universe-- and casts them in terms of some kind of probability distribution, much as quantum mechanics does.

You can do this for QM. You can't do this for inflation. The physics behind inflation is that there are indeed causally separated regions. It's got nothing to do with mathematical uncertainties. In the eternal inflation model, multiverses end up being "real" in the same way that exoplanets are real.

This is why you have to talk about the specific theory under discussion. Inflationary models involve a rapid expansion of the universe, and so a patch of space that is outside of our "event horizon" is every bit as "real" as Alpha Centauri.

But again, whether the multiverse is physics or metaphysics is more appropriate for that other thread, there's a lot of crossing over so it's hard to know which arguments were presented in which thread.

I'm about to tune out, but

The "multiverse model as Ken G defines it" is not physics or multiphysics. It's nothing.

 

[twofish-quant]

Second of all I happen to know some of those individuals, and I know their opinions are rather more subtle than what can be subsumed in a sentence.

So do I. Also believe it or not, people change their minds. I've become much less hostile to anthropic ideas, because I can see ways in which it might actually be useful.

If you asked me to take a straw poll of people that I know and work with, I would say (anecdotally) at least one out of 3 people believe in level 1, with mostly undecided remaining, and I don't know many people who still hold out against inflation in general.

There's also "level 0" multiverse (my invention) which can be trivially shown to exist. Today I can see out to X billion light years. Tomorrow I can see out to X billion + 1 light day. Therefore assuming we don't get weird readings tomorrow, there is a universe outside of our cosmic horizon. Now if we take as a reasonable premise, that the parts of the universe we can't see are similar than the parts that we can, then we can use empirical data to show that the actual universe is quite a bit larger than the part that we can see.

Incidentally, you haven't asked my opinion.. So I will volunteer it. Does it surprise you that my answer is 'I don't know'?

That's also my answer. Some people have trouble with that answer. I once got into a conversation in which someone asked me if I thought aliens existed, and they were rather surprised that "I don't know" and then I keep insisting "I don't know."

There exists a strong theoretical argument against the multiverse that has to do with something called horizon complementarity and I am unsure what to make of it.

Either multiverses exist or they don't, and having multiverses *not* exist would be as wild has having them exist.

The basic question is what is

(the universe we can see) / (the universe we can't see)

That's a number. Mathematically, it's a number that's greater than 0 and less than or equal to one. I think that best empirical data is that that number is less than 10%.

It would be a wild universe if it was a large number. It would also be a wild universe if it was a very small small number.

Philosophy of the sort you have presented, convinces nobody.

Yup. If I worshipped Popper, then having Popper say that it isn't science would convince me. But I don't, and I don't care very much about what Popper thinks.

Worse, the idea that there is no empirical or theoretical support for the MV and that it is pseudo science is basically an absurd proposition that has shown up in laymen topics on the internet, but is decidedly absent from any discussion amongst physicists.

Yup. One problem is that the people that tend to talk the most about things ideas to the general public are usually the worst people to do it. The general public has a *terrible* idea of what ideas are being talked about and why.

That's why I'd prefer to talk about specific scenarios which can be scientifically analyzed rather than the "multiverse concept" which is too vague to be worth discussing.

In case anyone is interested, let me explain why people are thinking about the multiverse.

Space is not empty. There are particles popping in and out. All sorts of fields and forces. Etc. Etc. So you can think of moving through a "vacuum" like moving through air. Just like when you are moving through air, you end up with all sorts of particles hitting you, the same sort of thing happens when you move through a vacuum. It turns out that some of the basic physical constants (like the fine structure constant) change based on how much energy is in the vacuum.

Now the problem is that there is no natural "zero" level for the vacuum. We can mark "zero" as the number we see in our vacuum, and then you can pump energy into or take energy out of the vacuum, and then you can see the physical constants change when you add or remove energy from "zero energy". (If you want to see an experiment when you take energy out of a vacuum, see Cashmir effect).

But "zero" is just where the universe ended up after inflation. It's not a real "zero". You could have had the universe expand in a way that "zero" was somewhere else, and in that universe the physical constants turn out to be different.

 

[Ken G]

We didn't miss it. We just think it's silly.

All I can tell is not a single thing you've said about Popper's views has seemed even remotely close to Popper's actual views. I know you don't care, you're happy with your misconceptions there.

Personally, if you had to ask me whether or not Marxism or Freudian psychoanalysis are sciences, I'd say yes.

Of course you would, that's because you still haven't understood Popper at all.

Again, you are lecturing science to scientists. Rather than telling scientists what their philosophical beliefs *should* be, it might be useful in this discussion to just listen and find out what scientist's philosophical beliefs really are.

All you can do is change my arguments so you can refute them. I have never told anyone what their philosophies should be, please quote where you think I did.

This is pointless, I'm afraid. You cannot meet the challenge I gave you, all you can do is make excuses for why you cannot meet that challenge. That's fine, you don't think you need to meet that challenge, and you don't understand Popper. I get it. This discussion has become pretty much exclusively about eternal inflation and the multiverse, so it should really be on the other thread anyway.

If you were doing science you would either:

1) state categorically that any theory involving a multiverse model leads to unprovable and untestable conclusions and then back up that claim with a airtight chain of logic, or

2) come up with a specific well-posed multiverse model that we can discuss

Wrong. It is not the job of a scientist to prove that a theory is a bad theory. Rather, it is the job of a scientist to say why a theory is good. You have failed to do that, choosing instead to shoot the messenger who is pointing out to you that you have failed to do that.

 

[twofish-quant]

Of course you would, that's because you still haven't understood Popper at all.

I know quite a few Christians that happen to believe that if you would "understand" the teachings of Jesus Christ that it would be so self-evidently obvious that he is correct that you'd accept Christianity.

The possibility that someone might understand the New Testament without accepting it as self-evidently true is something that has never occurred to them. If the only evidence that you have that I don't "understand" Popper is that I happen to think that he is wrong about certain things (i.e. claiming that Freudian psychoanalysis is non-science), that's not going to get us very far.

This is pointless, I'm afraid. You cannot meet the challenge I gave you, all you can do is make excuses for why you cannot meet that challenge.

The problem is that you haven't posed a proper scientific question, and you aren't acting according to the rules of scientific argumentation.

Wrong. It is not the job of a scientist to prove that a theory is a bad theory. Rather, it is the job of a scientist to say why a theory is good.

If you (or someone else) is interested in learning what scientists do from real scientists, that's one thing. If you are merely going to lecture science to scientists, we aren't going to get anywhere.

It's *precisely* the job of a scientist to show why a theory is bad. You normally do it by showing that it results in a big problem.

You have failed to do that, choosing instead to shoot the messenger who is pointing out to you that you have failed to do that.

But failing to come up with a theory doesn't mean anything.

If you challenge me to come up with a theory as to how type II supernova work, I can't do it. I tried for seven years, and I couldn't come up with a way to make them go boom. Now, what I was able to do (which got me a Ph.D.) is to show that certain things *won't work*.

 

[twofish-quant]

As far are telling what people what their philosophies should be. You keep making statements that scientists should do X or science involves Y. A is science and B isn't. That's imposing a philosophy of science on scientists.

 

[Ken G]

If you challenge me to come up with a theory as to how type II supernova work, I can't do it. I tried for seven years, and I couldn't come up with a way to make them go boom. Now, what I was able to do (which got me a Ph.D.) is to show that certain things *won't work*.

Yes, and that's exactly why I would say it is perfectly good science to show what kinds of multiverse theories are ruled out by current observations. Popper would be thrilled.

 

[Drakkith]

If you challenge me to come up with a theory as to how type II supernova work, I can't do it. I tried for seven years, and I couldn't come up with a way to make them go boom. Now, what I was able to do (which got me a Ph.D.) is to show that certain things *won't work*.

Twofish, is there a link to your paper or something that explains all the mechanisms you worked out that don't cause a type 2 supernova?

I would have sent you a private message, but your box is full.

 

[denism]

I think the general consensus is that it's shape is similar to a black hole , hyperbolic. Geometry is dependent on which model universe we are speaking of.. there are open/close systems...

P.S: Open system ( hyperbolic) has the following condition : k<1 , on the other hand a closed system (k>1) would collapse back to a singularity over the passage of time (cyclic universe model).

I think that only one of these possibilities fulfills the 3 following conditions for universe: 1) homogeneous, 2) finite and 3) unbounded: the closed version, or 3-sphere.
Am I wrong? thanks in advance

 

[bapowell]

I think that only one of these possibilities fulfills the 3 following conditions for universe: 1) homogeneous, 2) finite and 3) unbounded: the closed version, or 3-sphere.
Am I wrong? thanks in advance

The torus is homogeneous, finite, and unbounded (although not globally isotropic). It has a flat geometry.

 

[denism]

although not globally isotropic

as you say, and in addition this form of organization would require some justification because it does not comply with the minimal-sufficiency principle. To my knowledge n-spheres are the highest entropy shapes

 

[bapowell]

as you say, and in addition this form of organization would require some justification because it does not comply with the minimal-sufficiency principle. To my knowledge n-spheres are the highest entropy shapes

Maybe, but the universe could still exhibit toroidal topology, and it satisfies your three criteria.

 

[denism]

Maybe, but the universe could still exhibit toroidal topology, and it satisfies your three criteria.

OK, I forgot a fourth criterion: minimal sufficiency. In absence of possible verification, no weird proposal of universe shape can be formally rejected, raising the risk of degeneration of this subject. Hence, in an attempt to maintain some rigor in this field, a principle of minimal sufficiency should be observed by rejecting imaginative but supererogatory hypotheses.
I am not aware of data supporting torus

 

[bapowell]

OK, I forgot a fourth criterion: minimal sufficiency. In absence of possible verification, no weird proposal of universe shape can be formally rejected, raising the risk of degeneration of this subject. Hence, in an attempt to maintain some rigor in this field, a principle of minimal sufficiency should be observed by rejecting imaginative but supererogatory hypotheses.
I am not aware of data supporting torus

There is no data supporting any global geometry/topology -- period. But, data does indicate a local universe consistent with flatness, which is evidence consistent with toroidal topology.

Could you articulate your minimal sufficiency principle?

EDIT: I'm not advocating for a toroidal universe, just pointing out that it's a perfectly viable possibility.

 

[denism]

There is no data supporting any global geometry/topology -- period. But, data does indicate a local universe consistent with flatness, which is evidence consistent with toroidal topology.

Could you articulate your minimal sufficiency principle?

EDIT: I'm not advocating for a toroidal universe, just pointing out that it's a perfectly viable possibility.

it is simply making the effort to not introduce hypotheses that are not strictly riquired by new observations. Are you sure that the torus does not cumulate positive and negative curvatures? n-spheres are locally flat as well
(but I ackowledge that the torus is prettier for graphical representations)

 

[bapowell]

Are you sure that the torus does not cumulate positive and negative curvatures?

It has positive and negative principle curvatures, but the Gaussian curvature is zero.

n-spheres are locally flat as well

They are not -- they are positively curved everywhere.

it is simply making the effort to not introduce hypotheses that are not strictly riquired by new observations.

Right, but none of your criteria are strictly required by observations. We have no data supporting the size (finite vs. infinite) of the universe, whether it is globally compact or bounded, or whether it is globally homogeneous. What we know from observations of the observable universe is that it is approximately homogeneous and close to flat locally. Empirically, all three manifolds of constant curvature -- Euclidean (including toroidal and other flat geometries), spherical, and hyperbolic spaces -- are equally in the running.

 

[denism]

It has positive and negative principle curvatures, but the Gaussian curvature is zero.

My feeling is that this curvature is more mathematical than concrete, but it is just a feeling

They are not -- they are positively curved everywhere.

to faint to be mesurable. Sir Eddington calculated that for a small circle with a radius of 5 m with a mass of 5 tonnes at its center, one would deviate from pi only at the level of its 24th decimal..

Right, but none of your criteria are strictly required by observations. We have no data supporting the size (finite vs. infinite) of the universe, whether it is globally compact or bounded, or whether it is globally homogeneous. What we know from observations of the observable universe is that it is approximately homogeneous and close to flat locally. Empirically, all three manifolds of constant curvature -- Euclidean (including toroidal and other flat geometries), spherical, and hyperbolic spaces -- are equally in the running.

I believed that night would not have been black in an infinite universe? (necessarily forever..)

 

[phinds]

I believed that night would not have been black in an infinite universe? (necessarily forever..)

No, that was dealt with conclusively quite some time ago as not being the case. I don't have a reference offhand but I assure you it is true. It has to do with the expansion of the universe. For one thing, it is irrelevant whether the universe is infinite since the only light that reaches us is from the OBSERVABLE universe.

 

[denism]

No, that was dealt with conclusively quite some time ago as not being the case. I don't have a reference offhand but I assure you it is true. It has to do with the expansion of the universe. For one thing, it is irrelevant whether the universe is infinite since the only light that reaches us is from the OBSERVABLE universe.

OK thanks. The observable universe is the part for which the redshifted wavelengths remain in the visible range?

 

[bapowell]

I believed that night would not have been black in an infinite universe? (necessarily forever..)

In addition to phinds' response, I'll add that the finite age of the universe also resolves this paradox.

 

[denism]

In addition to phinds' response, I'll add that the finite age of the universe also resolves this paradox.

something infinite has necessarily always been infinite. The finite age proves that the euclidean 3D space cannot be retained

 

[phinds]

something infinite has necessarily always been infinite. The finite age proves that the euclidean 3D space cannot be retained

You are talking about infinite in space, which may or may not be true. The post you were commenting on was referring to the finite AGE of the universe.

 

[phinds]

OK thanks. The observable universe is the part for which the redshifted wavelengths remain in the visible range?

Technically, that is exactly correct. In practise, "visible" requires extraordinarily strong telescopes for a long period (see the Hubble Deep Field).

 

[bapowell]

something infinite has necessarily always been infinite. The finite age proves that the euclidean 3D space cannot be retained

By finite age, I mean finite time since the big bang. Obviously, if the big bang occurred 13 billion years ago, then there are still CMB photons, as well as starlight, that have simply not had time to reach us yet. This is why the finite age resolves the paradox. It has nothing to do with the size of the spatial geometry.

 

[denism]

By finite age, I mean finite time since the big bang. Obviously, if the big bang occurred 13 billion years ago, then there are still CMB photons, as well as starlight, that have simply not had time to reach us yet. This is why the finite age resolves the paradox. It has nothing to do with the size of the spatial geometry.

OK I understand

 

[denism]

Technically, that is exactly correct. In practise, "visible" requires extraordinarily strong telescopes for a long period (see the Hubble Deep Field).

I asked this question because I read an other interpretation (with which I have some concerns) that the unobservable universe located behind the horizon, corresponds to galaxies for which the recession velocities exceed light speed. Is it erroneous according to you?

 

[phinds]

I asked this question because I read an other interpretation (with which I have some concerns) that the unobservable universe located behind the horizon, corresponds to galaxies for which the recession velocities exceed light speed. Is it erroneous according to you?

Not only is it NOT erroneous, it is an understatement in that galaxies IN the observable universe are "now" ("now" gets a bit tricky) are already receding from us FTL. In fact, those at the edge of the OU are receding at about 3c

 

[denism]

Not only is it NOT erroneous, it is an understatement in that galaxies IN the observable universe are "now" ("now" gets a bit tricky) are already receding from us FTL. In fact, those at the edge of the OU are receding at about 3c

I definitely cannot understand this point. My intuitive expectation was that the expansion rate cannot exceed c because it it was the case, everything would disconnect at once, even between the sun and Earth and between your eyes and your screen..

Did you read the problem of the ants on a rubber rope <http://en.wikipedia.org/wiki/Ant_on_a_rubber_rope>

 

[phinds]

I definitely cannot understand this point. My intuitive expectation was that the expansion rate cannot exceed c because it it was the case, everything would disconnect at once, even between the sun and Earth and between your eyes and your screen..

Did you read the problem of the ants on a rubber rope <http://en.wikipedia.org/wiki/Ant_on_a_rubber_rope>[/QUOTE]

The first thing you need to do when studying either cosmology or quantum mechanics it TOTALLY get rid of the concept that your intuition is worth squat. It is not. It's something we all have to get used to.

What you are not understanding is that nothing is traveling FTL in the same reference frame. The universe is expanding. The recession rate has nothing to do with c.

 

[Drakkith]

I definitely cannot understand this point. My intuitive expectation was that the expansion rate cannot exceed c because it it was the case, everything would disconnect at once, even between the sun and Earth and between your eyes and your screen..

Did you read the problem of the ants on a rubber rope <http://en.wikipedia.org/wiki/Ant_on_a_rubber_rope>[/QUOTE]

The expansion is a rate, meaning that the recession velocity increases over distance. The further away something is the faster it recedes. So a galaxy can receded from us at 0.01c that is relatively nearby while another that is very very far away can recede at 2c or 3c or whatever. Note that this also includes light emitted from those galaxies. A galaxy receding from us at 2c that emits light away from us would NOT catch up to the light. In the galaxies frame of reference it is stationary and the light moves at 1c away from it.