Thursday, 4 June 2015

Is String Theory Bad Science and Misleading Hype?

String Theory has been around for 30 years, since the first superstring revolution which made it a contender theory for high-energy physics. It has yet to produce one testable prediction, and no-one is even talking about a decisive experiment that would confirm String Theory while refuting, say, Loop Quantum Gravity. They haven’t even derived the existing Standard Model from String Theory yet, and to understand how bad that is, deriving Newtonian Gravity from General Relativity is now left to the reader as an elementary exercise. It’s really, really serious that literally thousands of super-bright physicists, including the man said to be as smart as Einstein, haven’t shown how to get the current theory of elementary particles from String Theory. But a lot of families get fed off the back of String Theory professorships, and a lot of money gets made by publishers and authors from popularisations and textbooks - even I have both volumes of Polchinski.

I’m fairly confident that String Theory will take the same place in the history of science as epicycles do now. Or maybe phlogiston. (There’s a difference: epicycles can be seen as using a partial Fourier analysis of the planet’s observed orbit – it’s acceptable curve-fitting and inacceptable physics; phlogiston was acceptable but wrong physics.) For the moment, it’s creating enough problems for some people to want to re-define science so that String Theory, with its lack of actual predictions, is still science. Well, they don’t need to. Let’s look at the idea of testability.

Suppose the theory only makes predictions at energy levels that needed a lot of expensive kit, and then Governments cancelled the programme and used the money to save the banks (again). That doesn’t make the theory untestable. Now suppose that there simply isn’t enough money in the world, or ever will be, to build the kit to test the theory. This doesn’t make the theory untestable-in-principle, simply untestable-in-practice. Now suppose it simply wasn’t practically possible to build a piece of kit that would be able to test the theory, cost aside. Same thing: untestable-in-principle, simply untestable-in-practice. The theory is still making empirical predictions. Now suppose that there’s actually no piece of kit that will test the theory, because the kit would use all the energy in the Universe and there would be no-one around to see the results. That’s untestable-in-principle. None of these apply to String Theory.

What applies to String Theory is that the theorists just haven’t come up with a prediction, let alone the budget-busting kit to test it. This could mean
  1. The theorists aren’t as smart as they say they are
  2. The theorists are as smart as they say they are, but it’s really hard to get a prediction out of all those equations
  3. Actually, there aren’t any predictions to be gotten out of the theory. It just doesn’t touch the real world.
It’s worth noting that so far in the history of science, all the Hall-of-Fame theories came with novel predictions, often in the paper that first introduced the theory. I’m stretching the point a bit with electromagnetism, as Maxwell had three shots at it over a couple of decades, but once he embraced the field theory and dumbed the mechanical models for his 1865 paper, that prediction of light as electromagnetic radiation is as carefully contrived a throw-away as you could find. Some of this was, of course, because the pace of life was slower back then, and people could afford to hold back on publication until they had a good prediction. Because a good novel prediction is great for credibility.

Testability comes from Karl Popper’s Logic of Scientific Discovery. His original objection to Marxism and psychoanalysis was that, no matter what happened, the theorists could always interpret it post-hoc as a success, but not in a way that would make new predictions (that last clause was added by Lakatos). String theory would be untestable in this sense if there was always an ad-hoc way of re-jigging it to explain the result post-hoc. That shows up in the practice of the theorists or the structure of the theory itself. Woit has a few posts where he describes the dodges and retractions of String Theorists in response to actual lack of anything from CERN. Because their ability to feed their children and travel to conferences in exotic places depends on String Theory, it’s pretty clear that nothing would actually make these physicists give up their livelihoods reject String Theory. Until they have somewhere else to go.

Peter Woit’s point is that the String Guys have had enough time and should quit. Lakatos made the point that it is never irrational to carry on working on a degenerating programme, but what is irrational is to deny its track record and continue to hype it as the “only game in town”. The theory may yet yield a prediction that can be tested in this world, but the current bunch of theorists have failed to get it to do so. If they are sensible, they should give it break and go do something else on the taxpayer’s dime. What they do in their spare time is entirely up to them.

In summary:

Is String Theory science? Yes.

Is String Theory a good scientific theory? NO. (Though it might be)

Are String Theorists who carry on hyping it behaving like “good scientists”? NO

Are String Theorists who take on doctoral students fulfilling their duty to advise well? Tougher: we’re dealing with consenting adults here. But if the advisor waves visions of glittering careers in front of their student, I’d say we have a case of deception.

Does String Theory deserve taxpayers’ and institutional support? NO. No more grants. But give them a severance package or a sabbatical to find some more dignified profession or fruitful field of study.

Should some physicists work on it in their spare time? YES. Should it be taught in schools and at undergraduate level as the dominant theory of fundamental particles? NO.

Should academic publishers be wary of selling books touting String Theory as the Only Game In Town For A Final Theory? YES. Academic publishers have a minimal duty to filter for cranks and hype.

Should commercial publishers be wary of selling books touting String Theory as the Only Game In Town For A Final Theory? NO. Commercial printers are not intellectual gatekeepers and do not have the resources to be. Let ‘em print what they think will sell.

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