Update (3/26): I should probably clarify that this post focuses on theories for new physics beyond the Standard Model. We certainly do have well-established theories that are absolutely spot-on within their regime of applicability, e.g. the Standard Model, quantum electrodynamics, general relativity… these have all been tested experimentally over and over and over again.
One our goals here on the US/LHC blog is to clarify a few public misconceptions about physics. One thing that the popular press seems to get consistently wrong is that people are married to their models—by which I mean “plausible, but speculative, frameworks for explaining natural phenomena.” Journalists will often write about a physicist’s pet model by starting with “Professor So-and-So believes that…,” as if Professor So-and-So goes to bed at night thinking of ways to explain to the world why his/her model is right and everyone else is wrong.
That’s not how science is done, not even speculative science. Just because someone spends some time developing a new idea, that doesn’t mean that they are doing so because they think it must be true. This may sound silly: if they don’t think its true, then why devote so much time to it?
One answer is that it could be true. Thus we should figure out what falsifiable implications it would have if it were true so that future experiments can cross it out. However, there’s a deeper reason to pursue ideas that one isn’t necessarily “married to.”
The point is that good ideas have value just because they’re good ideas, even if they are necessarily speculative. Certainly a “good” idea should be plausible, e.g. a model of “intelligent falling” would have a very hard time garnering serious interest. However, there are plenty of good ideas out there for open questions. Of course we really want to find the “right ideas,” but there’s no way to know which ideas, if any, will ultimately be reflected in nature. All we can know are which ideas fit present data and which have strong theoretical (somewhat subjective) motivation. Rigorously exploring these ideas, their implications, and their inter-relationships allow the field to move forward.
[An interesting side note: it's not even clear that there should be only one idea which is "right." Much of the modern progress in theoretical physics is based on the idea of "dualities," i.e. two totally different models describing the same physical phenomena in complementary ways.]
The value of “wrong” ideas is something that’s often under-appreciated in the popular press. In fact, theoretical physicists are usually interested in building up a tool-box of good ideas (independent of ‘correctness’ for a particular problem) that can be used as needed to solve open questions. One popular example is string theory.
- Our front-running speculative “theory of everything” wasn’t born with such grand aspirations: rather it was originally constructed as a potential model to explain the weird particles that were showing up at the old-school colliders of the 1960s. Later experiments showed that correct explanation (quantum chromodynamics) was something rather unrelated, and string theory (then known as “dual resonance models”) fell to the backs of everyone’s minds…
- … until some clever theorists realized that it could be used to give a quantum theory of gravity. This became a hip thing to study in the 80s and especially 90s, but since then has lost a bit of steam due in part to its lack of experimental predictions at accessible energies.
- But that’s okay: while people were playing with string theory as a “good speculative idea,” they discovered some very unexpected dualities between higher dimensional gravity theories (which are relatively well-understood) and lower dimensional models of strong coupling (which are notoriously difficult to work with). These ideas are usually referred to as the “holographic principle,” and have shown promise as models of, among other things, the very same kinds of particles that originally motivated string theory in the 1960s! (In coming full circle several new and rather deep insights were developed.)
Stories like this can be found all over the place in the history of physics. The extra dimensional models which became very popular in 1998 and 1999 are based on the Kaluza-Klein models from the 1920s, but adapted to solve new problems. The idea of electroweak symmetry breaking and a Higgs boson was built upon progress in understanding superconductivity. Good ideas never really die, they just lay dormant until the next big problem comes along.
In this sense, the measure of a theoretical physicist isn’t necessarily how many “right ideas” s/he has generated. (Indeed, in the past 30 years there hasn’t been enough experimental sources to definitively say anything about many good ideas.) Instead, the community values creative new ideas. And for what my two cents are worth, fostering this creativity—in multiple disciplines (arts, humanities, sciences, mathematics)—should be one of the main goals of primary and secondary education.
For what it’s worth, the ‘good idea’ that I personally think is most theoretically appealing is supersymmetry. But as evidenced by Cornell’s recent loss in the NCAA basketball tournament to #1 seeded Kentucky, most of the things that I cheer for don’t seem to benefit from my support. (PS, Big Red: we’re proud of you!)