## Saturday, January 02, 2010

### David Gross and the 60th birthday of Israel

If you have want to know what David Gross said in 2008 at Technion (posted in October 2009) about the future of physics, the Jewish achievements in science, and the current politics in Israel, see this one-hour talk:

As you may expect, I would probably subscribe to every word he said, with some exceptions of his criticism of the current Israeli government etc.

Gross reviews the achievements of various disciplines of physics in recent decades (one of the unusual physics disciplines studied at the KITP is "physics of climate change": is that really necessary, David?) and says that the greatest progress is that we gained the informed ignorance: we can ask certain fundamental questions intelligently.

So he asks various questions about the unknown features of the Universe - about the Planckian physics, future of the Universe, dark matter, dark energy, and about the "preposterous" anthropic Universe (is physics really an environmental science?).

David Gross is also surprised how it's possible that some physicists still believe that quantum mechanics will ultimately fail. I am shocked by it, too. It can't fail in a simple way, it shouldn't fail for large systems (although some people annoyed by Schrödinger's cat want to believe it) although it's "worth testing". Roger Penrose says that QM fails due to consciousness: Gross doesn't think so, either.

Others like 't Hooft believe that QM has to fail in the Planckian regime. Again, Gross uses string theory to prove 't Hooft wrong: all the paradoxes that lead to the Planckian quantum doomsday have been smoothly resolved in string theory so there's no reason to think that the doomsday is needed.

Another question is how do the forces unify. The answer is given by string theory. The followup question is whether all particles are vibrations of the same string. It could be. Gross omits this "incredibly rich, marvelous subject" because he would need an extra hours. We're on the right track and Gross wants to be around when the questions answered.

Are there more 3 spatial dimensions? He shows a nice stringy Calabi-Yau manifold. The features of such manifolds determine the properties of elementary particles. And what is the nature of space and time? A new radical revision awaits us. Gross quotes Nati Seiberg (space and time are illusions) as well as one of his students called Edward Witten (space and time may be doomed). ;-) By an "illusion", we mean it's emergent. For space, string theory gives us a lot of evidence for that. For time, which is kind of different, we don't have any examples. What is time made of?

Finally, Gross jumps at theoretical biology - a term that physicists like but biologists hate, much like the word "theory" itself (theoretical biology is probably what they call systems biology). The distinctions between physics and biology are artificially created by bureaucrats. Is there a theory of biology? Can physicists help? Is new maths needed?

Unlike normal physics, biology doesn't allow the separation of timescales. Neurons are fast but they can give you long-term memory etc. I don't quite understand these arguments. The rewriting of the memory and its preservation are different processes that are as separated as atomic physics from QCD, aren't they? The only difference I see is that the scales in biology are mixed up and more random.

Genomics: can the theory of evolution be predictive? Can you predict the future evolution? Gross believes that at least much improvement is possible. Can you reconstruct the shape of an organism from its genome? ;-) That's the exam in Genomics 101, year 2106, draw a picture of the animal with ATCGAG....CG. ;-) If you couldn't solve it, it's a grossaurus.

Which principles are responsible for self-organization such as memory and consciousness? Can you make a machine with free will and teleonomic (or ethical) behavior? Can you measure the rise of consciousness in infants? Is it continuous? I hope so, whatever the function is.

Dangers are that the traditional routes for progress - bigger colliders, sharper telescopes - will become unrealizable due to the costs and the time needed to build them. So he ends up with a question he can answer. Will physics continue to be important? Yes.

And that's his memo.