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

[Ken G]

For someone that just spend lots of articles talking about how we should be skeptical and shouldn't rationalize, you are being remarkably uncritical about Popper.

The problem is his ideas are being badly mischaracterized, so we can't even get to the stage of a legitimate criticism. I don't want to get off topic, but the discussion about the shape of spacetime has taken us into the arena of whether or not multiverse ideas currently uphold a standard of empirical support we normally associate with physics, and Popper's views are of course intensely relevant.

Popper's ideas belong into a class of philosophies called logical positivism. One problem with those philosophies is that they state that we shouldn't make statements that are untestable, and then proceed to do just that.

I'm not sure where you are getting these ideas, but they are naive at best. Logical positivism is generally associated with a group of philosophers, physicists, and mathematicians called "the Vienna Circle." Here is what the Stanford Encyclopedia of Philosophy has to say about them:
"It included as members, besides Schlick who had been appointed to Mach's old chair in Philosophy of the Inductive Sciences at the University of Vienna in 1922, the mathematician Hans Hahn, the physicist Philipp Frank, the social scientist Otto Neurath, his wife, the mathematician Olga Hahn-Neurath, the philosopher Viktor Kraft, the mathematicians Theodor Radacovic and Gustav Bergmann and, since 1926, the philosopher and logician Rudolf Carnap. (Even before World War I, there existed a similarly oriented discussion circle that included Frank, Hahn and Neurath. During the time of the Schlick Circle, Frank resided in Prague throughout, Carnap did so from 1931.) Further members were recruited among Schlick's students, like Friedrich Waismann, Herbert Feigl and Marcel Natkin, others were recruited among Hahn's students, like Karl Menger and Kurt Gödel. Though listed as members in the manifesto, Menger and Kraft later wanted to be known only as as sympathetic associates, like, all along, the mathematician Kurt Reidemeister and the philosopher and historian of science Edgar Zilsel. (Karl Popper was never a member or associate of the Circle, though he studied with Hahn in the 1920s and in the early 1930s discussed its doctrines with Feigl and Carnap.) "

Later, we find about Popper: "He did not however, regularly attend meetings of the Vienna Circle and generally considered himself an outsider. Later he claimed to have “killed” logical positivism."

The Wiki on logical positivism makes this point even more clear, where we find:
"A well-known critic of logical positivism was Karl Popper, who published the book Logik der Forschung in 1934 (translated by himself as The Logic of Scientific Discovery, published 1959). In it he argued that the positivists' criterion of verifiability was too strong a criterion for science, and should be replaced by a criterion of falsifiability. Popper thought that falsifiability was a better criterion because it did not invite the philosophical problems inherent in verifying an inductive inference, and it allowed statements from the physical sciences which seemed scientific but which did not satisfy the verification criterion.

Popper's concern was not with distinguishing meaningful from meaningless statements, but distinguishing scientific from metaphysical statements. Unlike the positivists, he did not claim that metaphysical statements must be meaningless; he also claimed that a statement which was "metaphysical" and unfalsifiable in one century (like the ancient Greek philosophy about atoms) could, in another century, be developed into falsifiable theories that have the metaphysical views as a consequence, and thus become scientific."

From these quotes, we find several points are in evidence:
1) logical positivists are not just clueless philosophers who "got science wrong", as you say, but rather include active physicists and mathematicians, which was not untypical of the day.
2) Karl Popper's name does not generally come up under the heading of "logical positivist", and indeed he claimed that his approach led to the "death" of logical positivism.
3) Popper's main objection to positivism is that he did not feel the point was being positive about what we could verify, but rather being able to tell if we have tried hard enough to falsify our theories. This was a much more flexible view of a good scientific theory.
4) Popper seemed to agree with my characterization that an idea that can at first only be regarded as speculation can later on graduate to the status of a scientific theory, at such a time that falsifiability becomes a legitimate possibility.

This last issue is the entire crux of the multiverse question-- is there legitimate falsifiability there, given what we already know what must be true (such as that we are here)? Is there really "risky predictions" being made, that one would expect to be wrong if the multiverse is not a good model? Personally, I have never seen a single one-- and the papers that report on predictions are usually talking about things that could be tested in principle, rather than legitimate tests we can expect to actually carry out, motivated by the theory. A theory that motivates falsifying observations is a good theory, but I just don't see the observations that the multiverse is motivating, that any cosmological picture would not motivate equally well. It's just a theory waiting for an actual purpose, beyond the "warm fuzzy feeling" of successful rationalization.

In regard to a more correct understanding of Popper's views, I would argue that they reveal just how insightful he really was, and how important of a "cautionary tale" he provided for helping keep scientists honest to others in how they sell their theories, and more importantly, honest to themselves.

 

[Haelfix]

That's a rather broad generalization. The possible inflation models that do not lead to multiverse all require a miracle. If a model does not lead to multiverse then it will be MORE contrived. That seems to be what you are trying to suggest.

Do you have a link to a source where some reliable expert makes such a statement?

So the fact that inflation has a finetuning problem has been pointed out many times by Roger Penrose (see the Road to Reality) and Steinhart and is common knowledge in the field. See this paper by Caroll for a summary and some speculations about the possible resolutions: http://arxiv.org/abs/1007.1417

It has been argued by a number of authors that eternal chaotic inflation ameliorates the problem. See:
http://arxiv.org/abs/hep-th/0702178

 

[Ken G]

That last paper seems like a nice summary of many of the issues we have been discussing, and note the abstract includes this:

Although the infinity of pocket universes produced by eternal inflation are unobservable, it is argued that eternal inflation has real consequences in terms of the way that predictions are extracted from theoretical models. The ambiguities in defining probabilities in eternally inflating spacetimes are reviewed, with emphasis on the youngness paradox that results from a synchronous gauge regularization technique. Although inflation is generically eternal into the future, it is not eternal into the past: it can be proven under reasonable assumptions that the inflating region must be incomplete in past directions, so some physics other than inflation is needed to describe the past boundary of the inflating region.

I translate that as saying that just as inflation is not really a theory, but more like a signpost to a theory capable of resolving many conundrums like the flatness and horizon problems, eternal inflation is also not really a theory, but more like a signpost to a theory, that could resolve even more purely metaphysical problems like the "youngness" problem. However, the paper seems clear that these problems have not yet been resolved (in particular, it seems the issue of getting constraints on the current "multiverse" distributionis a lot harder than constraining what the distribution is asymptotically evolving into in the future).

The paper stresses ways to connect with the standards of science in terms of changing our testable predictions, but I would still worry about Popper's "risky" element: a signpost to a theory that is a factory for making predictions that are capable of fitting anything we observe sounds a lot like fitting n independent observables with n theoretical degrees of freedom, i.e., not risky. It still sounds to me that the fundamental motivation for multiverse-oriented models is primarily metaphysical, and I think that should give us all pause as to whether or not the important line between science and metaphysics is being carefully respected in the more grandiose versions of claims on the multiverse.

 

[Haelfix]

Well that is just exactly the issue. Because you see, it is very much my impression that the case for the multiverse is just exactly how you framed it just one post ago-- that it is primarily based in a desire to be able to tell a good story, rather than actual experimental justification.

No! The case for the multiverse already have experimental support. These models were written down in the 80s, and already had a large amount of support by theorists. People only took them seriously after COBE and WMAP verified their detailed predictions. No one would believe them otherwise.

The problem is not that they don't make experimental predictions, its that there is an inverse problem. Namely that there is another model Y that makes the same or almost the same detailed predictions as Multiverse model X. Of course as we get better with understanding model X, the inverse problem diminishes as new predictions are able to be made and so forth.

But anyway the naive statement is then that you should prefer model Y b/c it doesn't include the same superstructure that model X does.

But this is not correct. The reason model X should be preferred over model Y, is that there is a great deal fewer miracles that must occur. The finetuning is considerably reduced and more 'natural', and the extra assumptions are quite reasonable:

Namely that if we believe in inflation to begin with, then we know that our universe is very large. If we believe in a very large universe, than an event that occurred by chance once, could in principle happen again somewhere else. Finally the event that happened once, has a parameter space of possible constants that very generically create a situation where inflation is eternal (the case where inflation is not eternal is of measure zero)!

 

[Haelfix]

I translate that as saying that just as inflation is not really a theory, but more like a signpost to a theory capable of resolving many conundrums like the flatness and horizon problems, eternal inflation is also not really a theory, but more like a signpost to a theorye.

Sure its an infinite set of possible theories, with an infinite dimensional parameter space! The simplest versions (involving a solitary scalar field) still have several undetermined constants that basically must be fitted to experiment and to theoretical constraints (for instance, slow roll conditions).

The problem is experiment currently only gives 2 numbers, which still vastly undetermines the solutions.

Thus theorists have to ask questions about the space of all possible inflationary universes satisfying the experimental constraints.

 

[marcus]

...
Namely that if we believe in inflation to begin with, then we know that our universe is very large. If we believe in a very large universe, than an event that occurred by chance once, could in principle happen again somewhere else. Finally the event that happened once, has a parameter space of possible constants that very generically create a situation where inflation is eternal (the case where inflation is not eternal is of measure zero)!

This is the main weakness in the argument for MV. We do not know that inflation is initiated by a random fluctuation. (IOW, something that would spontaneously recur, given enough space and time.)

 

[Ken G]

No! The case for the multiverse already have experimental support. These models were written down in the 80s, and already had a large amount of support by theorists. People only took them seriously after COBE and WMAP verified their detailed predictions. No one would believe them otherwise.

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. I realize that we have much better constraints on the models now, and multiverse models have survived those better constraints, but as I said above, that may just be (and seems to me is) simply because the multiverse models were flexible enough to accommodate almost any outcome of WMAP. It was only the "risky" models that could not, but that's what made those models real scientific models in the first place. Ironically, it is that they were good science that made them get falsified, whereas the jury is still very much out on that in the case of the multiverse idea.

The problem is not that they don't make experimental predictions, its that there is an inverse problem. Namely that there is another model Y that makes the same or almost the same detailed predictions as Multiverse model X. Of course as we get better with understanding model X, the inverse problem diminishes as new predictions are able to be made and so forth.

Right, that's why Popper stressed the need for "risky" predictions. Adler had a model of how human psychology worked, and the problem with it was not that it made no predictions-- indeed, the whole point of the Adler model was to predict human behavior. The problem was that its predictions were not "risky", they were not predictions you would be inclined to expect to be wrong if you didn't already know they were already examples of human behavior. Hence, any outcome of any experiment on human behavior could be rationalized via Adler's model, but it wasn't granting us new insight, it is was preventing any real insight from being obtained (because the answer was viewed as already known, whereas the goal of scientific research is to find the answer that is being missed). It is the difference between prediction and rationalization-- there's that old joke that an observer shows their result to a theorist, and the theorist says "I can explain that, my theory must be good!" Then the observer says "oops, hang on, I was holding the graph upside down," to which the theoriest resplies "no worries, my theory is so good, I can explain that too." I have a hard time seeing how multiverse thinking is not similarly flexible, for the simple reason that we have so few a priori constraints on the attributes of the putative "distribution" of universes.

What's more, it is also not clear to me that embedding one universe in a distribution that cannot be observed but is said to exist anyway is not purely metaphysical to its core-- how would that model ever be distinguished from a model which simply asserts "any time we have prior knowledge X of the universe, and we want to make a prediction for unknown outcome Y, we can imagine there is some probability distribution Z, informed by X, that is pertinent to Y." I see nowhere in any of that which requires the existence of a multiverse, any more than playing a single hand of poker in a perfectly intelligent way requires that any other hands of poker have ever existed anywhere else. It's nothing but a probabilistic model for how unknowns in nature should be addressed, all else is metaphysics.

But this is not correct. The reason model X should be preferred over model Y, is that there is a great deal fewer miracles that must occur. The finetuning is considerably reduced and more 'natural', and the extra assumptions are quite reasonable:

But none of that requires the multiverse concept. This is getting too far off topic probably, so I am starting a new Cosmology thread on "is the multiverse cosmology or metaphysics?"

Namely that if we believe in inflation to begin with, then we know that our universe is very large. If we believe in a very large universe, than an event that occurred by chance once, could in principle happen again somewhere else. Finally the event that happened once, has a parameter space of possible constants that very generically create a situation where inflation is eternal (the case where inflation is not eternal is of measure zero)!

That was flawed logic, because you used the largeness of the universe after inflation as a reason to expect inflation, but then assumed a largeness of the universe before inflation as a reason to expect inflation to occur many times. The argument makes assumptions that are not in evidence in observational fact, and is therefore metaphysics, not physics.

 

[Ken G]

Sure its an infinite set of possible theories, with an infinite dimensional parameter space! The simplest versions (involving a solitary scalar field) still have several undetermined constants that basically must be fitted to experiment and to theoretical constraints (for instance, slow roll conditions).

I'm glad we agree on this point, and I think this is exactly the place where the insights of Popper are most poignant.

The problem is experiment currently only gives 2 numbers, which still vastly undetermines the solutions.

I can just see what Popper's reaction would be to this: "so you are saying that now we have 2 reasons to believe the theory, but when experiment gives us 100 numbers, and we choose the parameters of our theory to fit those 100 numbers, then we will have 100 reasons to believe our theory."

Thus theorists have to ask questions about the space of all possible inflationary universes satisfying the experimental constraints.

Yeah, my point exactly.

 

[twofish-quant]

The problem is his ideas are being badly mischaracterized, so we can't even get to the stage of a legitimate criticism.

I don't think that I'm badly mis-characterizing his ideas. He seems to think that general relativity is more falsifiable than Marxism and psychoanalysis, and that "tweaking a theory" to make it fit reality weakens it.

I don't agree,

I don't want to get into the situation which happens with Marx in which anytime someone argues that Marx is just wrong, people argue that he is misquoted.

1) logical positivists are not just clueless philosophers who "got science wrong", as you say, but rather include active physicists and mathematicians, which was not untypical of the day.
2) Karl Popper's name does not generally come up under the heading of "logical positivist", and indeed he claimed that his approach led to the "death" of logical positivism.
3) Popper's main objection to positivism is that he did not feel the point was being positive about what we could verify, but rather being able to tell if we have tried hard enough to falsify our theories. This was a much more flexible view of a good scientific theory.
4) Popper seemed to agree with my characterization that an idea that can at first only be regarded as speculation can later on graduate to the status of a scientific theory, at such a time that falsifiability becomes a legitimate possibility.

Points taken, but the way that science was done in the 1920's is very different that the way that it's done today, and people have rather different philosophical assumptions about the world.

Also, I've actually tried to minimize philosophy, because I think that you vastly underestimate how falsifiable the models that have been proposed really are, and if I can convince you of that, then the philosophy is irrelevant.

The other thing is that if someone comes up with reasons to think that multiverse models are *inherently* unfalsifiable, then yes we do have a problem, but I don't think that's the situation.

This last issue is the entire crux of the multiverse question-- is there legitimate falsifiability there, given what we already know what must be true (such as that we are here)?

Too vague.

I think it could be argued that talking about the "multiverse concept" is not a proper scientific theory because it is *too vague*. The "multiverse concept" is probably much too vague to falsify, but it can (and has been used) to generate specific theories that are clearly falsifiable. Most of the time multiverse ideas have been invoked in the professional literature, they refer to "multiverses generated by string theory" and those are subject to falsifiablity (i.e. if string theory is wrong, then those models are wrong).

The same goes with the anthropic principle. For it to work, you have to be in a situation where life is impossible under some set of physical constants. This is not obviously true. For example, if you double the FSC, then human life may be impossible, but if it turns out that you can create something else intelligent, then the anthropic principle is dead.

Personally, I have never seen a single one-- and the papers that report on predictions are usually talking about things that could be tested in principle, rather than legitimate tests we can expect to actually carry out, motivated by the theory.

I've seen several.

Max Tegmark's paper on dimensionality for one. Also, it's an interesting paper, because even though the final result is not highly testable, the fact that dimensionality has this effect is interesting.

This is why I think that *requiring* falsifiablity to label something science is a bad idea. There are clearly things that scientists do that are science that don't involve creating falsifiable models.

In regard to a more correct understanding of Popper's views, I would argue that they reveal just how insightful he really was, and how important of a "cautionary tale" he provided for helping keep scientists honest to others in how they sell their theories, and more importantly, honest to themselves.

The trouble is that if we are really honest, then I'd have to say that some of the things that Popper considers "science" (i.e. general relativity) are in fact harder to test than some of the things that Popper consider "non-science" (i.e. Marxism).

 

[twofish-quant]

Also it would help if you named some names.

I do agree that some popular science writers (Lawrence Krauss, Michio Kaku, and Stephen Hawking) are *way* overselling what is currently being investigated, and part of the problem is that someone that makes scientifically ground claims is going to get less attention that someone that makes extravagant claims.

I *don't* think that this is a problem in the professional literature. Something that I find interesting is that nothing that Krauss has mentioned in his public speeches is part of his professional publication record, and when I read is peer-reviewed papers, it's almost like reading some one else.

 

[twofish-quant]

When experiment gives us 100 numbers, and we choose the parameters of our theory to fit those 100 numbers, then we will have 100 reasons to believe our theory."Yeah, my point exactly.

At which point the theorist will ask for several billion dollars for telescopes that will give them 10000 numbers to fit 100 parameters. This is one reason the CMB *spectrum* is so important. You aren't fitting to a number, you are fitting to a curve, which gives you a huge number of numbers to fit to.

 

[twofish-quant]

I said above, that may just be (and seems to me is) simply because the multiverse models were flexible enough to accommodate almost any outcome of WMAP.

That's not the situation. If you had zero CMB fluctuation, you have a problem. If you have large non-Gaussian CMB fluctuation, you have a problem. If you have unexplained anisotropy, you have a problem. If you have unexplained polarization, you have a problem.

This is a teaching issue, because I don't think that most intro astronomy courses for non-major really go into sufficient detail about the empirical evidence for cosmological models. Part of the problem is that to lots of people, they are *boring*.

Right, that's why Popper stressed the need for "risky" predictions.

Predicting the CMB *spectrum* seems to be a very risky prediction.

I have a hard time seeing how multiverse thinking is not similarly flexible, for the simple reason that we have so few a priori constraints on the attributes of the putative "distribution" of universes.

We can impose constraints, and eliminate *classes* of models.

I see nowhere in any of that which requires the existence of a multiverse, any more than playing a single hand of poker in a perfectly intelligent way requires that any other hands of poker have ever existed anywhere else.

In the case of inflationary models, there is a reason. Inflation asserts that the universe expanded very quickly so that a small region of space expanded to a volume larger than the current observed universe. Eternal inflation asserts that the scalar field is such that most areas are still expanding.

So in the case of eternal inflation, you are *required* to have a large volume outside the observed universe.

Again, I think the reason we are even talking metaphysics is that we aren't being specific enough. We aren't talking about *all possible multiverse models*, we are talking about a *specific* model.

That was flawed logic, because you used the largeness of the universe after inflation as a reason to expect inflation, but then assumed a largeness of the universe before inflation as a reason to expect inflation to occur many times.

It's a testable assumption. If the characteristics of the pre-inflationary universe wasn't uniform, we'd see it in CMB.

 

[Ken G]

At which point the theorist will ask for several billion dollars for telescopes that will give them 10000 numbers to fit 100 parameters. This is one reason the CMB *spectrum* is so important. You aren't fitting to a number, you are fitting to a curve, which gives you a huge number of numbers to fit to.

Not if the curve covers its tracks, which is exactly what a thermal spectrum does, except for the fluctuations-- a much lower-dimensional set of constraints.

 

[Ken G]

That's not the situation. If you had zero CMB fluctuation, you have a problem. If you have large non-Gaussian CMB fluctuation, you have a problem. If you have unexplained anisotropy, you have a problem. If you have unexplained polarization, you have a problem.

Sure, but those would be problems for any cosmology, not just multiverse cosmology. It doesn't single out the multiverse, I wouldn't expect any of those things prior to their being detected. Now, if the multiverse did predict one of those things, then at least it would have been falsifiable. The bottom line is, you really never have any idea if a theory is good until it makes a prediction that you didn't already expect without that theory, and then you test it. When the multiverse idea does that, I will agree it has evidential support. If it never does that, then it will never have evidential support, it will always just be a way to rationalize what we already knew to be true.

This is a teaching issue, because I don't think that most intro astronomy courses for non-major really go into sufficient detail about the empirical evidence for cosmological models. Part of the problem is that to lots of people, they are *boring*.

Possibly there could be more details on the models. But I think the real reason you don't see that is they are just too speculative. That's putting it quite mildly, in fact, for the case of the multiverse.

Predicting the CMB *spectrum* seems to be a very risky prediction.

It was indeed risky to predict a thermal background, and that is a prediction of the Big Bang. Any Big Bang, with our without multiverses. Predicting the fluctuations does not seem to be a risky prediction-- it seems to just be fitting the parameters, knowing that we would be able to fit them given the flexibility to invoke dark matter, dark energy, and any arbitrary scalar potential for the inflation.

Eternal inflation asserts that the scalar field is such that most areas are still expanding.

Which makes the risky prediction that ______? (fill in the blank.)

So in the case of eternal inflation, you are *required* to have a large volume outside the observed universe.

This is a natural feature of the inflation phenomenon, it does not adjudicate multiverse existence. I am inclined to disbelieve the multiverse, yet I'm also inclined to believe in a large universe. It's evidence for inflation, not the multiverse.

Again, I think the reason we are even talking metaphysics is that we aren't being specific enough. We aren't talking about *all possible multiverse models*, we are talking about a *specific* model.

Which specific model? What predictions does it make that are going to get tested any time soon? Can you say "the leading candidate model is X, which makes risky prediction Y, which will be tested by experiment Z, so we'll soon have an answer if just wait"? If you can say that, please do, and if you cannot, isn't that trying to tell you something?

 

[twofish-quant]

Sure, but those would be problems for any cosmology, not just multiverse cosmology. It doesn't single out the multiverse, I wouldn't expect any of those things prior to their being detected. Now, if the multiverse did predict one of those things, then at least it would have been falsifiable.

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

The bottom line is, you really never have any idea if a theory is good until it makes a prediction that you didn't already expect without that theory, and then you test it.

But there are times in which a theory is good even if it predicts nothing new. If you are able to turn something into a small set of parameters, that's a good thing to do even if nothing is predicted.

The other thing is that sometimes the universe doesn't cooperate. What do you do if general relativity happens to be right?

Possibly there could be more details on the models. But I think the real reason you don't see that is they are just too speculative.

There are different levels of speculative. Anything inflation related has something is dealing with real data so it's not as speculative as supersymmetry or string theory.

Predicting the fluctuations does not seem to be a risky prediction-- it seems to just be fitting the parameters, knowing that we would be able to fit them given the flexibility to invoke dark matter, dark energy, and any arbitrary scalar potential for the inflation.

Except that you can't. No matter how arbitrary the scalar potentials are and no matter how much dark matter, and dark energy you have, you are going to end up with a power spectrum that is roughly Gaussian. 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.

Inflation is inconsistent with zero fluctuation because you can't send information faster than the speed of light. This means that two regions that are outside of the light cone, can't talk with each other and they can't come up with the same temperature.

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

Which specific model?

Eternal inflation (which is a class of models)

What predictions does it make that are going to get tested any time soon?

Predicts that curvature is < 1e-5 and that CMB is gaussian at small scales. Also makes predictions for scalar potentials, which will have HEP effects.

Can you say "the leading candidate model is X, which makes risky prediction Y, which will be tested by experiment Z, so we'll soon have an answer if just wait"? If you can say that, please do, and if you cannot, isn't that trying to tell you something?

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

Also "risky prediction" is rather subjective. If you have no clue what the result is going to be then all predictions become risky, because you have zero expectation of what you are doing to expect.

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.

 

[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.