Thursday, March 22, 2007

An Interview With Brian Greene

Brian Greene does not need any more publicity. But still, we have a Q&A with him on MSNBC.COM.

It's an interesting interview, but I'm really puzzled at a few things. Let's start with this:

Well, I think string theory in many ways is much easier to understand than relativity. Relativity challenges your basic intuitions that you’ve built up from everyday experience. It says your experience of time is not what you think it is, that time is malleable. Your experience of space is not what you think it is, it can stretch and shrink. These things are so counter to experience that it is very difficult even for professional physicists to take these ideas on board in a deep, intuitive way.

When it comes to string theory, though, it’s a very natural idea. It’s saying that those particles that we imagine making up everything in the world around us, that we previously envisioned as being little dots — now we’re saying if you examine them with a sufficiently powerful microscope, that dot will actually not be a dot. When you magnify it, you'll say, "Oh, it's actually a little filament, it's a little string."

So from that point of view, it's not a difficult idea to grasp. Of course, there are features of the theory that are hard to grasp, like extra dimensions of space and things of that sort. But from a rock-bottom standpoint, I think string theory's easier to grasp than relativity and also easier to grasp than quantum mechanics.

Now, I don't know about you, but a stringy object living in many dimensions is NOT "easier to grasp than quantum mechanics" in my book. Furthermore, Relativity is certainly easier to understand even when the concept of "time dilation" and "length contraction" appears a bit strange in the beginning. The proof? We teach undergraduates, some time in their 2nd year, of Special Relativity, and they seem to be able to grasp it quite well. Last time I checked, we don't teach these kids String Theory at that stage.

When asked the the length scales in String theory, this is what he has to say:

That's certainly the case. But that was the case also in the early days of quantum mechanics. Now we have technologies that allow us to probe directly to the small distances where quantum mechanics really comes into play. But in the early days, you were trying to find indirect signatures of this strange picture of the microworld.

Now the difference here is that I don't think we'll have equipment that can measure these tiny distances in 30, 50 or 100 years. It could be 500 or 1,000 years, or maybe we'll never be able to probe the tiny distances that string theory shows as the relevant arena for its new ideas. But that's the framework of science: You put forward fundamental ideas, and you try to work out their consequences in a manner that can be accessed with the equipment that you have.

Wow! I'm not sure how he could have said that with a straight face. Considering that macroscopic phenomena such as superconductivity are direct manifestation of quantum mechanics (i.e. we don't have to go to "small distances") mean that QM did not need such "indirect signatures" to signify that its description is valid. The same cannot be said about String Theory. There aren't any yet at measurable scales. So the comparison with QM here isn't quite valid.

The one part that is disappointingly missing from the question is the backlash against String theory. The reporter failed to asked him about Woit's and Smolin's recent books and attacks on String theory. I thought this was a rather strange thing not to have been brought up.


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