I was flicking through various posts on the interwebs this morning while I was having my breakfast and came across one that nearly made me choke on my muesli. *What it’s like to be a theoretical physicist* is a piece in Stanford University news. In it I found the following quote:

String theory feels like a little superpower that I have, this physical intuition that enables me to make connections and have insights into things that by rights I should not be able to say anything interesting about.

I’ve tried many times that in a way that doesn’t come across as arrogant, but I’m afraid I’ve failed – especially because (speaking as a physicist) I don’t think string theory has so far given us any profound insights into physics at all.

Now I’m mindful of the fact that many mathematicians thing string theory is great. I’ve had it pointed out to me that it has a really big influence on for example geometry, especially non-commutative geometry, and even some number theory research in the past 30 years. It has even inspired work that has led to Fields medals. That’s all very well and good, but it’s not physics. It’s mathematics.

Of course physicists have long relied on mathematics for the formulation of theoretical ideas. Riemannian geometry was `just’ mathematics before its ideas began to be used in the formulation of the general theory of relativity, a theory that has since been subjected to numerous experimental tests. It may be the case that string theory will at some point provide us with predictions that enable it to be tested in the way that general relativity did. But it hasn’t done that yet and until it does it is not a scientifically valid *physical* theory.

I remember a quote from Alfred North Whitehead that I put in my ~~PhD~~ DPhil thesis many years ago. I wasn’t thinking of string theory at the time, but it seems relevant:

There is no more common error that to assume that, because prolonged and accurate mathematical calculations have been made, the application of the result to some fact of nature is absolutely certain.

My problem is not with string theory itself but with the fact that so many string theorists have become so attached to it that it has become a universe in its own right, with very little to do with the natural universe which is – or at least used to be – the subject of theoretical physics. I find it quite alarming, actually, that in the world outside academia you will find many people who think theoretical physics and string theory are more-or-less synonymous.

The most disturbing manifestation of this tendency is the lack of interest shown by some exponents of string theory in the issue of whether or not it is testable. By this I don’t mean whether we have the technology at the moment to test it (which we clearly don’t). Many predictions of the standard model of particle physics had to wait decades before accelerators got big enough to reach the required energies. The question is whether string theory can be testable *in principle*, and surely this is something any physicist worthy of the name should consider to be of fundamental importance?

P.S. This rant reminded me of the time I got severely told off by a very senior British physicist (who shall remain nameless) when I was quoted in Physics World as saying that I thought that in a hundred years time string theory would be of more interest to sociologists than physicists…

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