Is GPS the only practical application of General Relativity?

[petergreat]

I guess GR is also needed to accurately coordinate space flight, but I highly doubt without GR the space shuttle will have any problem finding its way back home. Gravitational lensing doesn't count as practical application.
Maybe a subject with even fewer applications is quantum chromodynamics. Even though QCD is in principle needed to describe nuclear physics, effective theories such as nuclear shell model and liquid droplet model have guided scientists well enough to detonate a nuclear bomb in 1945, well before the completion of QCD in the 1970s. It seems to me that by the time QCD comes out, nuclear physics is already more or less finished. Or I could be wrong.

 

[bcrowell]

I guess GR is also needed to accurately coordinate space flight, but I highly doubt without GR the space shuttle will have any problem finding its way back home. Gravitational lensing doesn't count as practical application.

This is an interesting question. SR is a different story. Every time you stick a magnet to your fridge, you're arguably applying SR, since magnetism is a relativistic effect. Explicit relativistic corrections are important in technologies as old as cathode ray tubes. Historically, GR was a poorly tested theory (relative to the other fundamental theories of physics) until the 1970's, so any practical applications of GR would probably have to be later than that. Although I doubt that you need GR for navigating the space shuttle, there are certainly detectable GR effects when you're dealing with space probes. Some of the best tests of GR are from Cassini. However, it's possible that those missions could have been carried out without understanding GR, just by carrying out course corrections on the fly, or taking GR effects into account as empirical fudge factors, without knowing that they originated in GR.

It seems to me that by the time QCD comes out, nuclear physics is already more or less finished. Or I could be wrong.

I assume you mean "more or less finished" in terms of practical applications? Nuclear physics is a big and diverse field. QCD is very nearly irrelevant in low-energy nuclear structure physics. It's central in relativistic heavy-ion physics.