Chad Orzel has made some comments on my post about the relative importance of physics and biology in the 21st century. Chad writes:
The crucial thing about physics in the middle of the last century was not the intellectual revolution that went on in the field, with Relativity and Quantum Mechanics supplanting the classical theories, but rather the material consequences of that revolution. Quantum Mechanics is important not because it forced scientists to re-think our relation to the universe, but because an understanding of quantum theory makes it possible to build devices like transistors and lasers. Relativity is important not because it transformed our understanding of space and time, but because understanding the theory makes it possible to build atom bombs and nuclear power plants. Everything that happened in the latter half of the twentieth century, from the Cold War to the Internet, is in some sense a result of the revolution in physics that took place in the first few decades of that century.
Seen in that way, none of the problems Michael mentions look like they stack up. Yes, a working theory of quantum gravity would be a major revolution in physics. But it doesn’t seem likely to have material consequences for the average person, unless some quirk of the theory makes either free energy or levitation possible. Quantum measurement and cosmology are fascinating topics, and the people who nail them down will richly deserve their Nobel Prizes, but I don’t think either is likely to have results that will re-make the world in the way that the transistor and the atomic bomb did.
The rub is in that phrase: “it doesn’t seem likely to have material consequences”. Neither did problems like resolving the ultraviolet catastrophe (which set in train the events leading to quantum mechanics), or the fact that the symmetry properties of Maxwell’s equations are different from those of ordinary Newtonian mechanics (which helped lead to relativity). However, resolving these problems caused the fundamental changes to our view of the world that enabled all the new technologies that Chad mentions.
It is, of course, an article of faith on my part that understanding quantum gravity, say, or quantum measurement, would have similar unexpected consequences. At present, I can no more predict those consequences than I could have predicted the laser before Planck discovered the first hints of quantum mechanics.
The rub is in that phrase: “it doesn’t seem likely to have material consequencesâ€. Neither did problems like resolving the ultraviolet catastrophe (which set in train the events leading to quantum mechanics), or the fact that the symmetry properties of Maxwell’s equations are different from those of ordinary Newtonian mechanics (which helped lead to relativity). However, resolving these problems caused the fundamental changes to our view of the world that enabled all the new technologies that Chad mentions.
I don’t think I agree with this, at least in the case of quantum theory. While it wouldn’t’ve been possible to predict the specific consequences of quantum theory, I think that the problems it was invented to solve loomed much larger than the current issues with quantum gravity.
Classical physics completely failed to explain a large number of relatively simple phenomena: blackbody radiation, the photoelectric effect, spectral lines of atoms. These aren’t esoteric phenomena, this is everyday sort of stuff, and classical theory isn’t even close.
I don’t think that the problems with quantum gravity and high-energy physics are on the same scale. Yes, it’s a large and glaring hole in the theory, but I don’t think anybody really expects the solution, whatever it may be, to fundamentally change our approach to physics at room temperature. The theory we have now does a much better job of describing the world than the theory we had before quantum mechanics.
I think you’re using the benefit of hindsight a bit too much. In particular, I’m not sure that for physicists at the turn of the twentieth century stuff like the photoelectric effect really “loomed large”, or was just regarded as a slight anomaly, doubtless to be cleaned up in due course without major changes to physics. I think it’s likely only with the benefit of hindsight that we can see how important and critical all these things were.
There are heaps of pretty basic things we don’t understand now that _might_ play the same role in the 21st century – stuff like high temperature and organic superconductors, dark energy, the pioneer anomaly, and so on. Not to ention very basic questions – why do we get infinite energies in quantum field theory unless we resort to hokey tricks; why is quantum measurement so screwy – that arguably are just as all-enveloping as something like the ultraviolet catastrophe.
As you say, on an absolute scale many of these are (somewhat) more esoteric than things like the photoelectric effect. But relative to today’s technology, I’m not sure that’s true. At the turn of the 20th century there was no household electricity, and the atomic hypothesis was still controversial…