The Shape of Spacetime.

twofish-quant

To which I would respond, "and that's exactly why Popper gets science wrong."

Ken G

Not necessarily-- all physics requires is the statement that physics will use logic and seek naturalness (which as near as I can tell, is synonymous with unification, which is certainly the goal of physics to find). But none of this makes any claims on the universe, it makes claims on physics-- the other criterion of physics is that it must not make claims on nature prior to their empirical establishment. We certainly have found a great deal that is logical and somewhat natural, but we also have constantly made the error of overinterpreting this fact, throughout history.

But again those are just constraints on physics. We don't need to assume anything about the universe, we only need to define what our tools are going to be. One of those tools is going to be making theories that don't have evolving laws if we have no reason to do so.
I was mostly referring to the irony that if a lot of people believe something before it is tested, then it either did not need to be tested, or the people had no basis for their belief. People seem to want it both ways! (Think "Higgs boson.")
I certainly agree that ultimately these issues will come into the realm of experimental testing, at which point whatever works will rise to the fore, so it doesn't matter too much what our current opinions are. I'm really just saying "whoa, we don't really know these things yet, let's wait until we do have the experiments to justify our expectatons." There's a kind of irony in Popper's "risky prediction" idea-- the better theory is the one that makes the predictions that seemed least likely to be right, but ended up being right, than the one that made predictions that seemed inevitably true. So the signpost of a "good theory in the making" is that few are inclined to believe it prior to the experiments that establish it! So in that light, it isn't really saying anything all that good about eternal inflation that many theorists currently believe the predictions it makes will end up being true.
That is blatantly untrue. Philosophers of science are perfectly qualified to make judgements about what makes a good scientific theory, they are exactly the ones who worry about that sort of thing. Yes, some don't understand the laws of physics as much as we'd like, but Popper was not in that class, he was quite knowledgeable in those laws. His job, in a nutshell, was to keep scientists honest and grounded, when they might otherwise tend to enter into a kind of self-perpetuating flight of fancy. I always marvel at how little most physicists understand what philosophy even is, or what philosophers do-- and how often I see the attitude "it's truth if I agree with it, and philosophy if I don't." Indeed, philosophers think that physics is a subset of philosophy, which comes as a big surprise to most physicists but actually it has perfectly good historical precedent.
Good, then we have a common ground.
This is where it gets dicey. I agree with your basic point that science is not "one-stop shopping", it is actually a very diverse and complex interplay of different modes of discovery. So I don't want to cheapen it with some oversimplified template that it has to fit to count as science. I'm just siding with Popper that we should all see red flags when people start generating theories that can explain almost anything. A factory for theories that are flexible enough to make any outcome seem "natural" is not what we need, we need a single theory that makes seemingly unlikely predictions that end up being true. Such a theory does not rationalize what we already know to be true, it tells us something we didn't know we should expect. I don't rule out the possibility that eternal inflation or the multiverse might accomplish that, my objection is that what I mostly see is exactly what Popper warned against-- a stream of rationalizations that seem like they could easily rationalize any outcome at all.

What I want to know is, how is a universe that has life in it and is part of a multiverse, different from a universe that has life in it and is not part of a multiverse? If someone could answer that question for me, I could then test the concept scientifically.
Well, the discussion is evolving, and those more strident statements of mine or no longer of any particular usefulness. Instead, we are honing in on just what kinds of requirements we are going to need from the multiverse idea before we can really feel like we are following a scientific course, rather than getting swept away in a current of successful rationalization. I think your references to Popper have really helped crystallize that progress, because this was very much Popper's mission.
Here I'll defer to Wikipedia: "The spin 3⁄2 Ω−
baryon, a member of the ground state decuplet, was a prediction of the model. When it was discovered in an experiment at Brookhaven National Laboratory, Gell-Mann received a Nobel prize for his work on the quark model." I don't know chapter and verse of how many particle attributes the model was created to explain, versus how many it predicted and were later found, but I understand that the situation was not all the former-- meeting the criterion of making "risky predictions."
Then let them wait before they call the multiverse a scientific hypothesis. I have no crystal ball, I don't know what discoveries the idea will lead to or what risky predictions it might eventually make that hold true. I'm just saying that until it delivers on these important objectives, the jury is still out on whether or not the idea can be considered a scientific model, and not just a way to feel like we can rationalize what observations we already know to be true.

I'm happy with a "wait and see" attitude, as with string theory. What I object to is how all these "in fashion" theories tend to get oversold before they have really delivered on any of the promises we associate with them.
I don't think the issue here is whether or not it is possible to discover if Marxism is a viable theory to base an economy on, because Popper wasn't saying Marxism was a bad scientific theory because there was no possible way to falsify it. He was saying that the people who were using Marxism as their theory of choice for interpreting what was happening in the world were not doing so in an honest way-- they had the system rigged such that anything that happened could be interpreted as a confirmation of the theory. No doubt such people could interpret the fall of the Soviet Union as a confirmation of Marxist theory as well, they would point to some flaw in how the Soviet Union was applying Marxism or some such thing! Rationalization is easy, which was Popper's point.

So it's not so much the theory itself, it is the way it is used. I think what Popper was mostly cautioning against is rationalization-- the tendency to interpret facts in the light of a preconception. Instead, the scientist must take the opposite approach, the skeptical approach-- disbelieve everything, and fervently so, and attempt as hard as possible to falsify every theory. Only the theories that survive the onslaught can then be considered good, but it must be clear that the theory could have failed, even should have failed, had it not been onto something crucially important. But we're talking now about eternal inflation, and the multiverse. In my view, it's fine to expect a generic outcome subject to whatever strict sampling requirements are established by what you already know to be true. That is what we might call the weak anthropic principle.

Ken G

To that I would point out that he is generally regarded as one of the few most influential figures in the philosophy of science in the last century, so he couldn't have gotten it that wrong. More likely, it is actually the oversimplified accounts of Popper's views that are what has been gotten wrong.

twofish-quant

Physics does indeed make claims on the universe. These become more obvious when you are in situations where those claims happen to be false. One reason that the "string theory" approach has hit something of a dead end is that it turns out that extreme high energy physics isn't amenable to "naturalness" arguments. That also is why inflation is as complex as it is.

I don't see what's wrong with making claims about the universe.

And if I do, what's going to happen? Is someone going to revoke my Ph.D.? Are they going to revoke my AAS membership if I do that?

The whole point of theory is to make claims on the universe before you've done empirical work establishing them. It may turn out that those claims are false, but onward or upward.

There's a difference between making a claim and *believing* a claim. Sometimes appeals to naturalness work. Sometimes they don't. But when you have no idea what to do, then logic and naturalness help you create theories, and if you don't come up with theories (and *wrong* theories) then scientific progress comes to a halt.

That's not true. Just because I believe something to be true doesn't mean that I don't think it shouldn't be tested. Guess what. I've been known to be wrong. One thing that makes science different from religion is that science admits that it is falliable.

For example, I happen to believe that if you drop a proton and an anti-proton, they will fall at the same rate. That doesn't mean that I don't think we shouldn't do the experiment. Same with the FTL neutrinos. I didn't think that we'd discover FTL neutrinos, but I'm glad that someone checked it. My first reaction to the results was "experimental error" however if you have another group do a different experiment that measures the same thing, that goes out the window.

I believe lots of things. I also believe that much of what I believe is wrong.

Part of the reason I believe things without empirical data is that i have to in order to get through the day. I happen to believe that there isn't a man eating Bengal tiger outside my office door. If I believed that there was a Bengal tiger, I'd behave very differently.

But you have to make decisions based on current data, and you have to make decisions on *what experiments to make*? Much of the jobs of theorists is to give observers some ideas what to look for. Without some expectation as to what you will find, you can't set up the experiment.

Name names. You have this habit of making general statements about "many theorists" without naming them.

You are mistaking assumptions with belief. Just because a theorist writes a paper that outlines the predictions of eternal inflation, doesn't mean that they *believe* it. There are religions that are based on the idea of *belief*, but *belief* in science doesn't work the same way that it does in Protestant Christianity.

The papers on eternal inflation are usually, if you assume X, you'll see Y. That's got nothing to do with *belief* in the religious sense.

I don't see what makes them more qualified than the Pope or the President.

But the examples he gave were bad. Marxism had huge difficulty explaining the collapse of the Soviet Union, and Freudian psychoanalysis would have problems if people turned into vampires and zombies because of it. For that matter, if Jesus Christ came down from the heavens and said that "God is Lutheran" the Pope would have some explaining to do.

The other thing is that you don't know if you can explain almost anything until you do the math. It turns out that string theory has this problem in that it doesn't constrain the value of fundamental constants. This wasn't obvious in 1980. It takes years to work through a theory to figure out exactly what it predicts.

Sometimes the universe doesn't cooperate with you. You take what you can get.

Also, what is a theory. I take cold dark matter. It doesn't work. I add the cosmological constant. Is this the same theory or a different one?

But it *doesn't* rationalize any outcome at all. I remember the excitement when COBE went up and for the first month, they weren't reporting fluctuations. This was exciting because if we didn't detect CMB fluctuations then means we got something *very* wrong. Then we find those fluctuations. Bummer.

Also, you are missing the Dyson paper that argues that eternal inflation is inconsistent with a curvature more than 1e-4. If we find 1e-3 then eternal inflation is dead.

Now it wouldn't kill the general inflation concept. That would require addressing the CMB microwave background and the horizon problem.

First let's try to eliminate different *classes* of multiverses.

A universe that's in a multiverse has cosmological parameters set up so that if you apply those parameters to other universes that have the same class of physical laws and observers, that you end up with the same numbers.

For example

http://arxiv.org/pdf/1202.5037v1.pdf

If eternal inflation is true that most universes will end up with large amounts of inflation, and hence a very small curvature. Which means that if you pick a generic universe, you'll see no curvature. If you do see any curvature, then this is extremely, extremely unlikely, and since there are *no* anthropic reasons why curvature of 0.0000 is preferable to curvature of 0.001, the conclusion is that if you see small curvature than eternal inflation is dead to very high probability.

I think that part of the problem is that you are getting your impressions about what cosmologists are working on from the popular press rather than the professional literature. A lot of the books in the popular press are "GEE WHIZ, aren't multiple universes *COOL*!!!!"

In order to actually do something "real" you have to make long and technical arguments that 99% of the people in popular books will fall asleep reading. A lot of the professional literature is about trying to figure out what can we say, and what we can't from multiverse arguments.

It wasn't that risky. What happens is that if you put all of the particles in a chart, you end up with a "hole" in it.

You are putting the cart before the horse. You state the hypothesis *before* you try to figure out if it's testable.

One thing that *is* known from quantum mechanics is that you get the right numbers if you *assume* that there are multiple universes. Now for most of QM you can end up arguing that these is just a "mathematical trick" and that the alternative universes don't "really" exist. You can call this an "interpretation"

The trouble is that if you argue that the universe is the result of a quantum fluctuation, then you have problems figuring out what's going on.

Oversold to whom? There *is* a huge problem with people like Lawerence Krauss and Stephen Hawking spouting off before things are firmed up, but that's a "how science is popularized" issue and not a "science" issue. One problem is that people that say *I've discovered the secrets of the universe* get more press coverage.

1) But then that makes the problem with the people that interpret the ideology rather than the ideology itself.
2) OK, you are a Marxist in 1910, and the revolution hasn't happened and you are clearly wrong. What do you do? You tweak the theory to explain what happened with the minimum of changes. The reason I can't argue that this is a bad thing is that this is exactly what scientists do, when their theories get disproven.

1) Some people do but most people don't. There aren't too many Marxists in Vienna today.
2) I don't think that scientists are less immune to rationalization than other groups.

Again this *MUST*. This isn't how scientists behave, and I think that it's wrong and even dangerous to think that they do behave this way. If someone argues that they've discovered FTL neutrinos, I'm going to ask for a *LOT* more evidence than if they argue something that's consistent with relativity.

It's a bad idea to pretend that scientists are even-handed or less prone to belief than other people. Interpreting data in light of a preconception is not necessarily a bad thing, and I think it's impossible to interpret data without preconceptions. Pretending that scientist *can* interpret data without preconceptions is bad, because that means that the preconceptions just go underground.

Something that I have seen (although not in physics) is uneven skepticism. If someone assert something you agree with, you let the thing pass, whereas if you assert something they disagree with, they will argue the issue to death and demand evidence that isn't available.

Disagree. No theory is going to match data completely, and it's better to have a theory that's *known to be inaccurate* than something whose predictions are uncertain. There are about half a dozen current observations that LCDM has trouble with, and it's better to know what they are, and than to reject it completely.

Also, bad theories are sometimes good. You figure out that it's X by eliminating A, B, and C.

One reason I dislike Popper is that things are either true or false. That's not the way science works. If something turns out to be "true if you add a fudge factor" that could be useful.

twofish-quant

Yes he could. It's not as if he is Jesus Christ or the Prophet Muhammed.

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.

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.

Ken G

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.
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

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:
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

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 occured 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

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

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

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 accomodate 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.
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 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?"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

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

twofish-quant

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.

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.

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.

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.

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

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

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*.

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

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

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.

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