Sam Harris interviews Brian Greene in this two-hour video.
Greene is indignant when Harris says that string theory has failed to deliver the goods. Greene says that the theory has made great progress, and has merged gravity and quantum mechanics. The only trouble is that we do not know what that merged theory is, and it has made any testable predictions. That is not much of a criticism, he says, because no quantum gravity theory will ever make any testable predictions.
Someone asked about Bohr saying that physics is about observables. Greene prefers a wider view, and says that physics should look behind the curtain and tell us what is really going on.
So Greene can justify a string theory with no testable predictions.
Greene also defended many-worlds theory and Bohmian mechanics, altho he has not fully adopted them because the measurement problem is unsolved.
Harris points out that Bohmian mechanics is nonlocal, so doing something in one place can have an instantaneous distant effect. Greene agreed, but said that quantum mechanics is nonlocal anyway.
Greene is very misleading here. It is true that in textbook QM, if you make a measurement and collapse the wavefunction, then your knowledge of some distant particle can be immediately affected. You can say that is nonlocal, but classical mechanics is nonlocal in the same way. Bohmian mechanics is different in that it says that an electron is in one place, but its physical effects are in another place. That is a fatal flaw, since no such nonlocality has ever been observed in nature.
And any defense of many-worlds is nutty.
He gives this argument, common among many-worlds advocates, that it is a simpler theory, and thus preferable under Occam's Razor. He gives an example. Suppose a simple quantum experiments results in an electron being in one of two places, symbolized by his left hand and right hand. Suppose you then find the electron in his left hand. Under Copenhagen, you would deduce that the electron is not in his right hand. But that deduction is an extra step, and the many-worlds theory is more parsimonious because it skips that step and posits that the electron is in his right hand in a parallel universe.
It is amazing to see an educated man make such a silly argument with a straight face. The argument really doesn't even have much to do with quantum mechanics, as you could use it with any theory that makes predictions, and concoct a many-worlds variant of the theory that does not make any predictions.
Besides many-worlds, Greene defends physical theories in which anything can happen. If you assume infinite space, infinite time, infinite universes, etc., then pretty much anything you can imagine would be happening somewhere, and happening infinitely many times. In particular, Jesus rose from the dead.
Greene agrees with Harris that humans have no free will. Greene rejects Harris's determinism, but says that the laws of physics have no room for free will.
At least Greene did not go along with Harris's wacky consequentialist vegetarian philosophy.
It is too bad that Physics does not have better spokesmen.