String theory is dead

An exclusive interview with Peter Woit

Following Eric Weinstein’s interview on how String Theory culture has stifled innovation in theoretical physics, longstanding critic of String Theory, Peter Woit, takes aim at the theory itself. He argues that String Theory has become a degenerative research project, becoming increasingly complicated and, at the same time, removed from empirical reality. Even the remaining string theorists of the past have given up on the ontology of strings, as well as the original vision of the theory.


Your book Not Even Wrong: The Failure of String Theory and the Continuing challenge to Unify the Laws of Physics came out in 2006. Could you summarise the main argument against String Theory as put forward in that book?

The story of string theory is rather complicated, so the intent of the book was to fully examine some of those complexities. The main problem with the theory though has always been a simple one: it achieves unification by postulating six or seven unobserved extra dimensions, then tries to explain everything we see in terms of these. The initial hope of 1984-5 was that there would only be a few consistent ways of making those extra dimensions unobservably small, and one of these would give our universe. But all evidence now is that either:

1. There is no consistent way to do this.
2. There is an essentially infinite number of ways to do this (the "landscape"), giving almost anything you want, so unpredictive.

In either case, the idea of string theory unification is simply a failure.

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Has anything has changed since then about the way you think about String Theory?

I think that the arguments made in that book have aged very well and there is little that I would change if I were to rewrite it today.  Back when I wrote the book I was concentrating on trying to understand exactly what string theorists were doing.  In recent years they themselves have mostly given up on their original claims and the field has come to a standstill, so no reason to spend much time on it.

I heard you say in a recent podcast interview that it’s hard to pin down what String Theory even is today. What did you mean by that?

String theory has always suffered from the fact that it is only defined in certain limiting cases.  What has happened over the years is that hopes to find a unified theory using one of those limiting cases have collapsed as it became clear this didn’t work.  People working on string theory have mostly given up on work using these limiting cases, but they haven’t made any progress on finding a general theory. So, they have moved onto working on other topics, but oddly often still calling themselves “string theorists”.  To some extent people now refer to “string theory” as whatever this group of theorists is doing now, but since it’s a range of things, none of them involving strings, it’s hard to now know what the term means.

One aspect of what has happened is that since attempts at a unified theory have collapsed, the string theory community has fallen back on just thinking about quantum gravity, and only a small range of questions within that subject, mainly using techniques that historically have some origin in string theory research, but now have nothing to do with strings.

One of your main critiques of String Theory has been that it doesn’t make predictions that can be tested. Does this invalidate it as a scientific theory in your mind? If it isn’t science, what is it?

There’s no simple answer to the question of what’s “science” and what isn’t.  Having testable predictions is something to aim for, but more important for any speculative theory in its early stages is to see what happens as people explore its implications.  I believe there’s a concept in philosophy of science of evaluating a research program as progressive or degenerative. Even if a research program hasn’t yet made testable predictions, it could still be progressive in the sense that it looks like a better and better idea the more you work on it.  String theory is the opposite, a degenerative program.  The more people have learned about it, the more complicated, ugly and unpredictive it gets as an explanation of anything in the real world.  So, the problem isn’t so much not arriving at testable predictions, but 40 years of steadily moving in the wrong direction.


We’ve hit technological limits of what we can do experimentally in many directions, and that carries implications for what research is going to be fruitful


Is there a role for philosophy of science when it comes to answering this question about the status of a theory that has been developed by physicists, but doesn’t seem to make predictions we can test?

I do think philosophy of science has a role to play here, by helping to evaluate the string theory research program using a more historically and philosphically informed understanding of what is healthy science and what isn’t.  One big problem with this is that the details of the theoretical work in the subject are extremely complex, very hard for a non-expert to understand and evaluate.  Some of what I’ve seen philosophers of science (e.g. Richard Dawid) do is rather discouraging. Unable or unwilling to evaluate the theory according to usual standards (since the result would be very negative), they start arguing that failure by a conventional standard means that there’s a problem with that standard and it needs to be changed.

Eric Weinstein’s critique of String Theory is that it has dominated theoretical physics for far too long, thus not allowing any alternative attempts at a theory of everything to develop. Do you agree with this assessment?

Yes, very much so. I completely agree with Eric that the big issue in the field is that of how to get the research community out of the long blind alley it has worked itself down.  What’s most discouraging is that even convincing theorists of the obvious fact that they’re in a blind alley seems to be impossible.  The institutional pressures to keep doing what one has been doing for decades and not admit to failure are huge.

String Theory also had a strong grip not just within academic physics, but on the public imagination. Why do you think that is?

The sorts of questions about the nature of physical reality and its description by an exotic unified theory that string theory claims to successfully address are ones that many human beings naturally find compelling.  Looking at the public claims made for the theory, often in high profile TV specials, it would be strange if these didn’t attract significant interest from the public.

What would you say are the positives, if any, to have come out of String Theory research?

There have been some quite interesting mathematical spin-offs from string theory research. One of the most successful has been the concept of “mirror symmetry”. This was first discovered by string theorists looking at high-dimensional spaces. It’s something that turned out to have no use in a theory of physics but opened up a new perspective in geometry and topology.

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If String Theory has failed to live up to expectations, are there more promising candidates for unifying General Relativity with the Standard Model?

I believe so. In particular, for several years now, I’ve been looking at ideas which put together the symmetries of General Relativity and the Standard Model in a new way, using, among other things, the geometry of twistors. I’m quite excited by these ideas, although I have to admit I’ve had little luck getting others excited.

Could you say a bit more about the theory of twistors as a way of unifying General Relativity and Quantum Mechanics?

The idea of twistors was developed by Roger Penrose and others, going back to the 1960s and 70s. The new idea about unification is that of taking seriously the idea of formulating twistor theory in imaginary time, and noticing that when you do this, the usual space-time symmetry becomes a mixture of space-time symmetry and the internal symmetry of the electroweak theory, unifying these in an unexpected way.

Is it possible that the whole project of aiming for a theory of everything is misguided in the first place?

Anything is possible, but from all I’ve seen in a long career, there’s many reasons to believe we can do better than our best current unified theory.  We don’t know what the end of the road in this direction will look like, but to me it seems that while string theory is at the end of its road, there are promising other ones to go down.


String theory is a degenerative program. The more people have learned about it, the more complicated, ugly and unpredictive it gets as an explanation of anything in the real world


What are the questions in theoretical physics that you think future research needs to focus on?

We’ve hit technological limits of what we can do experimentally in many directions, and that carries implications for what research is going to be fruitful.  My own interest now is mainly at the boundaries of physics and mathematics, finding new ideas about math inspired by physics, and better understanding of fundamental physics by incorporating deeper and more sophisticated mathematics. Others should though follow whatever they see as possible ways forward.

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