Multiverses: Science or Science Fiction?

The September issue of Astronomy magazine is now out, with a cover story on Multiverses: Science or Science Fiction? The author Bob Berman does a good job of explaining both the arguments for various Multiverses, as well as the reasons for skepticism about some of these arguments. After quoting Max Tegmark as defending multiverse theory as science since it is a prediction of an “arguably testable” theory (inflation), Berman ends the piece in a way I have to agree with:

Given the current multiverse infatuation, it may be fairest to give the last word to a prominent skeptic. Columbia University mathematical physicist Peter Woit, who maintains the popular multiverse-critical blog Not Even Wrong, pulls no punches.

“Physicists had huge success in coming up with powerful compelling fundamental theories during the 20th century,” he explains, “but the last 40 years or so have been difficult, with little progress. Unfortunately, some prominent theorists have now basically given up and decided to take an easy way out. The multiverse is invoked as an all-purpose, untestable excuse. They allow theoretical ideas like string theory that have turned out to be empty and consistent with anything to be kept alive instead of abandoned. It’s a depressing possibility that this is where physics ends up. But I still hope this is a fad that will soon die out. Finding a better, deeper understanding of the laws of physics is incredibly challenging, but it’s within our capability as humans, as long as the effort is not overwhelmed by those selling a non-answer to the problem.”

Whoa, intense. We’ve got to toss the multiverse if we care about physics!

Of course, if an infinite multiverse does exist, some other Woit is out there saying the exact opposite.

The same issue of Astronomy has a “Web Extra” entitled What happens if string theory is wrong? It mentions the 2013 poll of theorists discussed here, which had a large majority (73%) answering the question “Do you think that String Theory will eventually be the ultimate unified theory?” with a “No”, then goes on to link to a 2007 article by Sten Odenwald. Some of that article includes quotes from an interview with Lenny Susskind, which Odenwald recently included here. It will be interesting to have an update on that material in a year or so once 13 TeV LHC results on supersymmetry are in.

Bonus material: Quanta magazine has a great interactive map of “Theories of everything”.

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59 Responses to Multiverses: Science or Science Fiction?

  1. Lucy M says:

    Peter Woit “Actually I think the multiverse is an opportunity for philosophers of science to show that their subject is relevant and useful. There’s a lot of material there to apply their best thinking about the demarcation problem to. Unfortunately I haven’t seen much of this happening.”

    the problem with deploying philosophy is that the very enactment of that effectively answers the central question that has been there from the start and still remains unanswered to this day. Is science unique, or is it a continuation of pre-scientific philosophy.

    If science were unique philosophy would not be able to see that uniqueness. All it would see would be the elements in which science is like philosophy.

    This happens to always be the conclusion of philosophy. The productivity gets played down, as well as every other unique feature. The special meaning of a whole range of words within science, are rejected out of hand by philosophers because they don’t understand the word in the first place. Words become like they are outside science; just instances of more general effects. Nothing can be a special case because nothing ever was before science. Prediction is just a special case of criticism. Or one of many ways to determine the truth value of a theory. Consensus is about dogmatic authority. And so on. Just exactly what those words and the effects they describe intractably always were before science.
    p.s. Popper on science that it had to be ‘falsifiable’ is a widespread misconception of the thrust of his work. In fact Popper thought science was an unprivileged domain of philosophy and Conjecture&Refutation would suffice there as everywhere else. In other words rational criticism replacing prediction.

  2. Peter Woit says:

    adrian,
    I don’t think the problems with the landscape require being an active researcher in the field to understand. The more general issue of what the problems are with string theory as a TOE and whether it is accurate to describe the situation there as “failure” are much more complex. I’ve wasted a lot of my life following that story since its beginnings when I was a graduate student, others quite sensibly may want to just ignore it.

    If you make that decision though, I think you forfeit both the right to complain about people criticizing this failure, as well as the right to justify your research as related to a promising path to a TOE. I do see a lot of string theorists these days claiming the TOE problems have nothing to do with what they do, but then their grant proposals start with a reference to string theory as a TOE. They’re also often unhappy about people criticizing string theory’s failures, while at the same time unconcerned about dubious TOE claims being made by their colleagues.

  3. student says:

    One of the general “landscape” goals is to find “top-down” constraints on effective field theories (EFTs). These give constraints on the landscape. Quite remarkably string theory predicts constraints on EFTs that aren’t immediately apparent from a purely EFT perspective. One example where string theory has provided insight into the structure of effective actions is dissipative relativistic fluid mechanics.

    Another example where “top-down” constraints were found first from string theory is the classification of 6d (1,0) SCFTs. Recently the “landscape” of 6d (1,0) SCFTs has been nearly tamed into a complete classification. Of course this is a far ways away from the landscape problem being discussed here, but it seems quite plausible that many of the general lessons will apply.

    The work on the landscape might be interesting or not, but without serious effort it would be difficult to say anything intelligent about a narrow sub-field. It is perfectly fine if this blog doesn’t care to maintain such a standard, but it is completely unfair to criticize others for not going “on record” about papers they haven’t studied in depth.

    Hopefully the media will eventually follow the example of Quanta Magazine and there will be a much richer and diverse discussion of contemporary research.

  4. Peter Woit says:

    student,
    I’ve no idea whether, as you claim, string theory provides insight into fluid mechanics. I do know though that the classification of 6d (1,0) models provides nothing at all in terms of the basic problem of getting a prediction about observable physics out of string theory.

    This is a very good example of the problem: the question of what is known about supposed “string vacua” is an infinitely complex one, so people can attack anyone who points out the disastrous nature of the landscape problem as just insufficiently expert on the technicalities of “string vacua” research. By invoking irrelevant calculations you’re just misleading people, claiming “progress” that isn’t there, and doing your best to obfuscate the failure of the whole research program.

    I agree that many of the writers at Quanta are doing a great job of covering diverse topics of current research, in particular by avoiding what the science media has done far too much of for 30 years, which is promoting misleading claims about string theory as a TOE (like the one you’re trying to make…).

  5. student says:

    Peter,
    The only claim that I made is that without serious effort, one can’t say anything intelligent about a research program. I think your post illustrates this nicely. The classification of 6d (1,0) SCFTs might pave the way for classifying 4d N=1 SCFTs and eventually give constraints on the possible 4d SUSY quantum field theories (or their SUSY-breaking cousins) or it might not. Without hard work, it is hard to say if this approach will succeed or fail. Independently if this is interesting for the landscape or string theory as a TOE (which I am agnostic about contrary to claims otherwise) it is certainly interesting as a vast generalization of the geometric Langlands program.

  6. Peter Woit says:

    student,
    I have no idea who you are or if you actually are a student, but if you are I’ll just point out that you probably lack the experience to know what “serious effort” is relevant to understanding the issues behind getting the SM out of string theory. This is a problem that a huge number of smart people have worked on for over thirty years, and almost all of those people have decided to work on something else. Back in 1985 there were specific proposals of how to compactify string theory and get the SM. After much effort, there are now well-understood reasons why those proposals don’t work. The history of the subject is that of continually finding new possible ways to construct “string vacua”, getting farther and farther away from the goal of a predictive framework. The fundamental problem with “string phenomenology” is not just the current state of the subject (which is dismal), but the derivative: things just get worse and worse every year and this has been going on now for three decades. This is both at the theory and experimental level (no SUSY, no evidence for GUTs). If you had been following the subject since 1984 and paying attention to the results being claimed (as opposed to the technicalities of how they were achieved), I think you would understand a lot better the current situation, as well as how ridiculous are the claims you are making about classifying possible string vacua using 6d superconformal field theories. Far more promising ideas than that have foundered long ago on basic problems that such superconformal theories have nothing to say about. You can do anything you want and claim that “maybe a miracle will happen and those problems will go away”, but that’s wishful thinking, not science.

  7. student says:

    Peter,
    Your reply has almost nothing to do with what I wrote. The only relevant statement you make

    > how ridiculous are the claims you are making about classifying possible string vacua > using 6d superconformal field theories.

    is manifestly false. The statement is that the classification of specific string vacua also classifies ALL 6d superconformal field theories. Again, I’m not saying anything about “string phenomenology” besides the fact that not having studied it, I can’t say anything meaningful about it.

    Do you still do research anymore? In thinking about prospective research topics, it seems that there are many fascinating areas of string theory that you completely ignore. However, despite your criticisms, you don’t really offer any program or vision that a student could work on besides some notes summarizing some basic mathematical results from the 70’s.

  8. Peter Woit says:

    student,
    “I’m not saying anything about “string phenomenology” besides the fact that not having studied it, I can’t say anything meaningful about it.”
    OK, this makes things clear. Obviously I was discussing string vacua possibly relevant to the real world, and you have no interest in that.
    “some basic mathematical results from the 70s”
    You’re changing the subject, but that too makes some other things clear.

  9. Curious Mayhem says:

    It’s scary to think about an infinite number of universes, each with a copy of Peter Woit saying something slightly different.

    It’s comforting to realize that this universe seems to instantiate at least a local maximum of verificationism in our incarnation of Peter.

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