I just watched this interview about multiverse theories*,
and was surprised that both participants treated them as quite common among astrophysicists.

I thought multiverse theories were much less accepted...

*the interview is much longer, I'm only linking to the multiverse part

Multiverse theories are based on math...not scientifc observation.

They could be right, but unless we have a way of indirectly "observing" them, it will only remain math.

That would be math science. (Theoretical Physics - like what Michio Kaku does) - and Michio will tell you himself, that he is not a scientist.

Hmmm....physicists, such as Andre Linde or Lisa Randall, who work on these and related problems would be surprised to learn that they aren't physicists. These models are mathematically and (as far as I know) physically self-consistent, but as of yet do not have many testably observable consequences.

This is a good question, Clint, and an excellent and interesting interview between Sean Carroll and science writer John Horgan. Professional theoretical physicists work out at the edges of current knowledge. As Carroll admits, these various multiverse theories are speculative, and like Horgan, I am rather surprised that many of the top scientists have incorporated such things into their research programs that are unlikely to be empirically verified even in the near future.

But I think Sean Carroll gives an answer to this question of why these scientists seem to be leaving observational science behind and speculating about such things as multiverses. His answer? "We are forced to." What we do observe in our universe is forcing us to seek answers that explain our observations within a broader framework.

I happen to be reading Paul Davies The Cosmic Jackpot. I'm about in the middle of the book, and I'm not sure where he's going with this, but he is reporting on the long-standing question about the physical constants and why they seem to be so finely tuned to allow stars and galaxies and observers such as us to exist. If the relative masses of the proton and neutron were slightly different, our universe would be nothing like what we observe, and indeed, observers could not exist.

Yes, this is the Anthropic question, and Davies points out that historically scientists have considered this as tautological, unproductive, and unworthy of any scientific consideration. But in the last few years, several respected and very knowledgeable theoretical physicists and cosmologists have said, "Wait a minute. These cosmic coincidences are significant and too coincidental to ignore any longer." And the odd comparative strengths of the various constants? Why the heck is the electromagnetic force 10⁴⁰ times stronger than the gravitational force? (But as it happens, that's a good thing.) And the biggest miscalculation of all time, why does the vacuum energy appear to be 10¹¹⁹ times weaker than quantum mechanical calculations imply it should be? (Again, a darn good thing it is, too!)

I'm not sure if the relevance of the Anthropic question was laid bare by the recent discovery of the accelerating expansion or what, but obviously several top scientists feel this is one of those questions that they are being forced to confront, as Sean Carroll explains. And of course an appeal to the supernatural is not an option in science. Scientists seek natural explanations. And so several versions of multiverse theories have been proposed by theorists such as Susskind, Smolin, Vilenkin, Linde, Steinhardt&Turok, and I'm sure others I'm not aware of. But these theories are not "accepted" as you imply. They are proposed. The authors aren't saying, "This is how it is." They are saying, "This might be how it is, and this would explain why we observe what we do."

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Sean Carroll's article on the Anthropic Principle from back in 2004 is excellent and worth reading.

By the way, I meant to point out to KenG Carroll's remark in the interview linked above where he differentiated between the views of Steven Weinberg and David Deutsch regarding [paraphrasing] the fundamental reason for science. I have long sought some way to express what I have thought is wrong (or too one-sided) with what I suppose is Ken's philosophical view of science, and here Sean Carroll expresses it quite well in 5 or 10 seconds in this interview. Of course, being too "Weinbergian" is hardly a criticism that many people would be unhappy about, but I believe Carroll sided solidly with Deutsch on this point, as do I.

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I don't think they are ATM. They are just theories. Like evolution....or religion...

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In the Year 2525.

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I suppose Ken would reply that, although speculative, such theories have the potential to one day become testable, hence scientific. I hope he sees this thread and speaks for himself, though. I thought of him too as soon as I started to read it.

But that's the thing -- evolution is not just a theory. The TalkOrigins archive calls it "a fact and a theory". What they mean by this is that particular instances of evolution, observations that confirm evolution, have been made in persuasive amounts. The same, of course, cannot be said of multiverse theories. Unless one regards multiverses as mere heuristic "interpretations" of astrophysics.

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I didn't say they weren't physicists. I said that theoretical physics is not science in the way we use the term. It is indeed math science, in that you can test the math. As I stated, they do no actual physical experimentation.
Real scientists take the math and do the real science to see if the mathematical predictions hold up in the real world.

A scientific theory is not the same as the general usuage of the word.

A scientific theory follows the facts, it doesn't precede them.

You know that gravity is there, and you form a hypothesis. You test the hypothesis using the facts you already know, and when you have shown your predictions to be true over and over again, you have a theory. Your theory can then be tested and proven correct, incorrect, or adjusted.

Here is a snippet from it:
Actually, both of those objections seem irrelevant to me. The problem here is that apparently everybody is imagining that science is something other than what it is! Is there any question that what science is is a prescription for obtaining demonstrable knowledge about our universe (as opposed to a warm fuzzy feeling of understanding that is untestable)? So does that not mean that science is about motivating new experiments and organizing the data of existing ones? That just seems perfectly obvious to me. So the problem with speculating about variations in the vacuum energy is not that it is "giving up" on the problem (what demonstrable solution is being given up on there?), and it is not that the other values are known to be inherently unobservable (what other values can we know we can't observe?)-- it is simply that we have not observed them, nor is this approach giving us any clever ideas about how to observe them. That's sufficient, right there, to say it isn't science!

One does not invoke a contrary philosophy to argue against anthropic philosophy, one simply defines what science is and demonstrates that anthropism does not provide any of the proven benefits of science. To me, the crucial point is that the whole reason we invented science was to provide one mode of inquiry into truth that we could actually demonstrate, whose goals were testable and whose primary purpose was not simply to allow us to pretend we know more than we do. The latter is the hallmark of unscientific modes of inquiry-- including anthropic thinking. Why wouldn't Carroll count that as the main argument against it?

Carroll instead sets up the strawmen and shoots them down thusly:

I must agree that science does not first decide how reality works, and then force it to conform. But I would point out that this is precisely what anthropic thinking does, because it first posits that there has to be a reason that the variables are what they are, and then says the only we reason we can think of is anthropic. Both of those steps involve an unscientific fallacy-- the first is to state that it is part of a scientific principle to say we have to be able to understand something, and the second is to say that the only possibility we can think of is the correct one. Fortunately, real science does not rely on weak natural philosophy like that, it relies on experiment.
The problem here is that Weinberg is clearly wrong, and in just the way that Deutch's "black box" image suggests. But that doesn't make Deutsch right about multiverses as science! Yes, we don't just want predictions, we want understanding. I've always said that, I've said that Occam's razor is the beating heart of science, I've pointed out the inadequacy of "google science" (quite analogous to Deutsch's black box) where we just interpolate every answer from a body of stored existing data. But none of that suggests we need multiverses. The flaw in multiverse "science" has nothing to do with the idea that we only want to make predictions, it has to do with what we are going to call understanding, and how science can tell when and if we really do understand something.

This is not to suggest that scientific understanding is all that matters, it just says it is all that is science. I typically find Weinberg (like Dawkins) to be hopelessly positivist (the only truth worth having is the scientific truth, in effect). I did like Deutsch's point about the weakness of "selfish gene" approaches, and I have also asked the question, how do we know a gene wants to survive? Maybe they all crave oblivion, and the ones that don't achieve it are the failures. But I felt there were a few problems with "Deutch's Law:"
The first problem with it is that it would not seem to support his view of science as being forced to look for philosophical explanations. I would challenge him to cite even one single problem, even one, that was ever "solved" by philosophy! To me, his law states that no philosophical questions are interesting, which seems to contradict the way his view on science is being described here. Unless, that is, he will define "solved" as "convinced himself, in the absence of any actual experimental data on the subject".

The other problem with his "law" is, how do we know if a problem is soluble or not? Are there any examples of a problem that was known to be soluble before it was solved? Even one? If not, I claim that the only way we know if a problem is soluble is by solving it. But then the only problems we can know are interesting are ones that are already solved, and an already solved problem is no longer a problem at all. So the intersection of what is known to be interesting, and what is known to be a problem, is the null set using Deutch's Law. That's not a very useful law!

This is the crux of the issue right here. I would argue that the huge breakthrough in modern science came about the time of Galileo, where science started to depend more on experiment and observation than on natural philosophy. From that point forward, "math science" and "experimental science" worked hand in hand, and accomplished far more than either could alone. Tycho handed data to Kepler who found ellipses in it, and handed it to Newton who explained them, who handed the means to make an observational prediction to Halley, and so forth. Faraday handed experiments to Maxwell who handed a theory to Michelson-Morely who handed the data to Einstein, and on it goes. I see the new issue as being whether or not they should turn their back on all that success and go back to the realm of natural philosophy where theory and controlled experiment were highly uncoupled and even in competition (as in the ancient debates between Greek schools of natural philosophy). What an awful step backward for science, in the name of advancing it!
Well, they do the math with the intention of supporting those who do the experiments, it is not necessary that they carry out the observations themselves to be counted as scientists.

Thanks, Ken. I appreciate, and largely agree with, your responses.

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I have no argument here. All I was saying is that a theory is not just an idea. That would be a hypothesis. The theory comes after the experiments. A scientific theory is a falsifiable fact.

And all I was saying is that some of the various theoretical models under discussion here are more that just "ideas" or simple hypotheses, in that there is a lot of (physical) theoretical "meat" in them. So I was emphasizing that these are not simply mathematical exercises, which your post seemed to imply, but maybe I just misunderstood.

I also concur with KenG, that the scientific process does not flow in such a linear fashion ("theory comes after experiments"). Theoretical models (which are often much more developed than a simple hypotheses) often guide experiment and observation (e.g., they make testable predictions or tell us where/how to look for phenomena), which when done then put the models to the test. Theoretical models often advance way ahead in the vacuum of data. When the data eventually flood in, whole branches of models whither in the bright illumination. Likewise, experiment and observation are often find themselves way ahead of the theoretical development to properly explain the "facts". As progress is made in this hand-in-hand dance-like fashion, a successful scientific theory emerges.

One might argue that General Relativity was a theory developed without any data but one - this lone exception being the unexplained part of the precession of the perihelion of Mercury. However, to the best of my knowledge, that is not the reason Einstein pursued it, but rather it was "forced on us" by what else we (thought we) knew to be true about the world. It made many testable predictions, many of which are only recently being tested.

And to quibble a bit more, "scientific theories" are not considered to be nor do they become "facts". "Facts" are the data, the observations of nature (albeit, some level of interpretation is involved in these "facts"). Theories are models of the natural world that explain these "facts" and predict phenomena, including (and especially) those yet undiscovered. (Caveat emptor - theories or models that are explicitly/specifically constructed to explain a certain "fact" cannot then use their prediction of that fact to claim validity. I'm sure there is a better way to say that.)

Clint, thanks for the link to Horgan’s interviews.

Horgan made the comment in his interview with Sean Carrol that a more insightful question than the question “ Are Multiverse theories ATM?”

Is the sociological question: Why and how do people become convinced that one line of reasoning is “ATM” and should be attacked as heretical, where another is accepted?

Why would a person spend their life discussing and creating multiverse models? Assume it is a fact that multiverses do not exist. Why do we, allow significant intellectual latitude in one direction and not in another?

There is an emotional response to the label of “ATM”. A heretic is group attacked, where certain beliefs of a group are considered to be sacrosanct. Why is that so? Why do certain observations and discussions make people angry?

There is an unsolved sociological problem which is part of the scientific process. How does a person present and discuss anomalous observations and analysis, without promoting the emotional response?

Why for example do we (members of this forum) have an emotion response when the observations of Arp and Bell are discussed? Observational anomalies are not ATM. How can those observations be presented and discussed without causing conflict? Arp has obviously failed. Why?

Horgan stated that he and other scientific writers are searching for a heretic whose views lead to a breakthrough. Horgan differentiates between a heretic and a crank, supporting heretics, but not cranks.

Your thoughts concerning this problem would be welcome.

Comment:
I was particularly impressed with Bell's work and analysis.