peptoabysmal said:
The one point I got out of the show, in favor of string theory is that under the two current systems, the "fabric" of space is very dynamic and chaotic at very small sizes and very smooth at great big sizes. This can't be. So far, string theory is the only one which unifies the difference for gravity in both quantum mechanics and general relativity. Forgive my clumsy explanation here.
That's one of the reasons I was disappointed with the show. It seemed to me that it emphasized the wrong things.
The main problem providing an impetus to looking for a Theory of Everything is that gravity seems very different from the other three forces. The electric, strong, and weak forces are nicely understood a quantum forces mediated by an exchange of virtual particles. However, according to General Relativity (GR), which is a wildly successful theory, gravity isn't a force but rather the absence of a force. The presence of energy/momentum, of which mass is the most obvious kind since we have some big ones in the solar system, distorts space-time. The seemingly curved path that a planet or a thrown baseball follows is actually a "straight line" in spacetime (technically called a "geodesic"), so it's just plain old intertia. It only looks curved because we insist on separating time and space in our thinking.
So the desire is to find some sort of unifying principle, so that we don't have to remember as many theories. Just as in the 19th century it was discovered that mechanics and temperature were just two different ways of looking at the same thing, it would be nice if GR and QM should turn out to be different ways of looking at the same thing.
Of course, nature is in no way bound by our desires, but there are some tantalizing hints that this should be possible. Unfortunately, the show gave the impression that quantum behavior was only important at small scales. This is completely untrue. While the strong and weak forces do not appear to play much of a role over large distances, the electric force certainly does. The universe is full of light, and for most of its lifetime, light has played a significant role in its development. Our eyes are quantum devices, Schroedinger's Cat in miniature in the form of trans-retinal, a simple molecule that is instable enough that a photon coming in increases the probability that it will twitch into a different shape, which is "felt" by other molecules and converted into a perception of vision. The appearance of a sunset or the Mona Lisa is a quantum event. Of course, transistors and vacuum tubes are quantum devices, too.
We also have a perfectly good quantum theory for the electric force and light at large scales: Quantum Electrodynamics. It's elegant and simple; it has all the funny quantum behavior built in; and it fits GR like a glove. It even suggest a mechanism according to which objects travel along geodesics. Since Newton, inertia has just been taken for granted, but QED actually shows a mechanism.
Of course, one of the other parts of physics has involved trying to come up with something for the strong and weak forces. Part of this is investigating something called Quantum Chromadynamics, or QCD, which is a lot like QED except that the equations are much harder to solve. I did some work on QCD back in the early 90s, and at least then, we were bound by processor power. I don't know about the state of the art now.
But still, back to harmonizing GR and QM. Since GR and QM are both so successful and well supported, maybe they're both right. This suggests that it should be possible to view all four forces either as quantum events mediated by force carriers (in which case, there would have to be a graviton) or as distortions of the spacetime in which we live (in which case, there would have to be extra dimensions, because just gravity seems to "use up" the three ordinary dimensions of space). The show did have a nod to this, in the form of the old guy in black and white who was ticked off at Einstein, but it wasn't emphasized nearly enough.
Personally, I think that the Inflationary Universe and String Theory folks are on to something that will lead to the real "theory of everything".
I have some problems with the inflationary universe stuff. Perhaps this is because I don't understand it well enough, and I've had more than one astrophysicist call me a crackpot, which may very well be true. But I have a gut feeling that it is a false lead, resulting from trying to maintain an unstable blend of classical and relativistic thought.
For example, the universe looks like an expanding sphere with us at the center. I guess that any civilization anywhere in the universe would see exactly the same thing. However, when you look due North, say, to the 2.7 K background radiation, you're looking at a time when the universe was a lot smaller. I don't know exactly the size at which we could be expected to see photons, but it doesn't really matter very much. Let's call it basketball-sized. So then when you look due South to the 2.7 K background radiation, you're looking at an event in spacetime that wasn't any more tan a basketball away from due North. Extending to a singular Big Bang, in classical terms, the circumference of this sphere when time is ignored would have to be zero. But this suggests that in spacetime it isn't a sphere. Maybe it's a projective plane crossed with a sphere or a torus or somtheing like that. (ISTM that the extra dimensions in String Theory would have to be toroidal or projective planes themselves).
I can't think of a way to test this that doesn't involve some really, really long baseline interferometry.
