Baloney. Hogwash. Garbage.
That’s what’s to be found in the phys.org news article claiming that “Scientists at Towson University in Towson, Maryland, have identified a practical, yet overlooked, test of string theory based on the motions of planets, moons and asteroids, reminiscent of Galileo’s famed test of gravity by dropping balls from the Tower of Pisa.”
Sounds too good to be true, right? And it is.
What the scientists have done (or at least claim to have done, and I’ll be happy to take their claims at face value, since I can’t easily check them) is carry out a technique to test the equivalence principle, a foundation stone of Einstein’s theory of gravity, which implies that all objects, no matter what material they are made of and no matter how heavy they are, will be pulled by gravity in the same way… with the same acceleration. This principle, in Einstein’s theory, lies behind why all objects on earth fall with the same acceleration (when air resistance can be neglected), and behind why astronauts float in their space stations.
By looking at the precisely measured orbits of different objects in the solar system, which are made from different materials, the authors (James Overduin, Jack Mitcham and Zoey Warecki of little-known Towson University) claim in their July 2013 paper to have provided new tests that the equivalence principle applies to different materials. That’s very nice work. The principle works to the precision reached by their tests — which aren’t as precise as some other types of tests, but do explore some domains that haven’t previously been explored.
But what’s that got to do with string theory? If you read their paper, you will notice that the word “String Theory” appears in only one obscure sentence in the introduction, referring to a very specific form of string theory [with an extremely light spin-zero field, called the dilaton], implying that their work might be relevant for string theory if we lived in a stringy universe that had such a field. Not even the conclusion, much less the bulk of the paper, mentions strings or string theory. That’s because the paper has nothing to do with testing string theory; it is merely testing Einstein’s theory of gravity.
The reason it can’t test string theory is
- String theory doesn’t make a precise prediction for how the equivalence principle will be modified, and among the many possible universes string theory can lead to, many have no measurable modification of the equivalence principle;
- Even if a violation of the equivalence principle had been detected, or is detected in the future, it isn’t necessarily due to string theory. It might be due to some other modification of Einstein’s gravity — in fact, the authors consider one such modification in their paper!
So here we have a nice little paper that tests Einstein’s theory of gravity and puts constraints on various alternatives to it — though none of those alternatives is unique to string theory nor is uniquely predicted by string theory. How did this get billed as a practical test of string theory?
You’ll have to ask the author of the phys.org article, which appears to be a Towson University press release. ["Provided by Towson University", says the last line of the phys.org article.] Or you’ll have to ask the scientists involved (unless one of them is the author) — who ought to be pretty darned embarrassed that their work was billed in this way. I hope they didn’t do this on purpose. It’s certainly great free advertising for Towson University; who cares if the article’s right if people are willing to read it? But a willingness to distort the facts to impress and mislead the public is not a worthy attribute.