Category: Physics

What is this? It seems this charmonium-like state is a bit of a mystery. Theoretical calculations for the possible identity of this particle are off by ~50 sigma. I’m betting the theory just needs tweeking, but who knows? Anyone want to take the bet?

Famously, classical general relativity tells us that black holes “have no hair”: the mass, electric charge, and angular momentum of the black hole are the only parameters about the black hole measurable by us “outside the horizon” observors. Silly me it was only today while exercising that I realized that it might be interesting to ask if black holes can carry a charge from a non-abelian gauge theory. While I was pondering this, the other thought I had was that maybe if the theory of nature has multiple gauge fields, not just just the U(1), SU(2), SU(3) we know, but other higher ones, then this the “hair” produced by these theories might help explain the information paradox for black holes. Amazingly, this is deeply related to the content of some ideas about string theory and black holes!
Update 11/14/03: and of course, embarrassingly, there is this famous paper as pointed out by Ben Toner in the comment section.

Sometimes papers on the ArXiv are crazy. From the amusing but more than a bit scary department comes this paper comparing astrophysics and prostitution.

Today I recieved a proof of a paper to be published with Ben Toner in PRL (quant-ph/0304076.) The APS has this neat little program which automatically checks your references. In the proofs we recieved the following error for our paper: “References [5,9] could not be located in the databases used by the system.” The references that were said to be incorrect were

J.S. Bell, Physics (Long Island City, N.Y.), 1, 195 (1964)

and

A. Einstein, P. Podolsky, and N. Rosen, Phys. Rev. 41, 777 (1935)

Funny, these entries are indeed correct and are two of the most famous papers in physics!

I’ve been reading The Present Moment in Quantum Cosmology: Challenges to the Arguments for the Elimination of Time by Lee Smolin of loop quantum gravity fame (phil-sci archive). Mostly I’m reading because I’m an addict for anything involving the notion of “the present.” In the article he discusses two questions raised by Stuart Kauffman in the context of biology and economics which Smolin has ported over to physics:

• Is it possible that there is no finite procedure by means of which the configuration space of general relativity or some other cosmological theory may be constructed?
• Even if the answer is no is it possible that the computation that would be required to carry out the construction of the configuration space is so large that it could not be complete by any physical computer that existed inside the universe?

I’m not much of a fan of the first, (Penrose-ish) question…I find it hard to imagine noncomputability being of any practical consideration because it seems to me that one always needs an “infinity” of sorts to make the noncomputable arguments. (Apologies to Michael Nielsen quant-ph 9706006.) How do I verify that the universe is doing something noncomputable with my finite means?
The second question also strikes me as a bit odd. What I like about the question is that it talks only about the construction of the “configuration space.” This is, in a way, a specific computational problem. But it also seems that it glosses over a lot because in order to use a physical theory one needs a lot more than just the configuration space. The way in which I present a configuration space has a lot to do with what I can do with this space. And even if the full physical configuration space is not tractable, this doesn’t render it useless…there are probably tractable configuration spaces. Indeed, in a beautiful universe, the tractable configuration spaces will correspond to the tractable experiments. But this is wrong in some way: we know that we can use a quantum computer to simulate a quantum experiment, but this doesn’t mean we can use a quantum computer to output the amplitude of a particular basis state: there are nontractable questions about the theory even though we can use the theory to simulate the system.

Today while shopping for books at Borders I notice that “The God Equation” was shelved right next one of Feynman’s books. Of course, I had to correct this and moved the God book a few spaces to the right (I hope no librarians are reading this.) Of course the irony of this is that Feynman is the place where I first saw how you could right a single equation to represent a theory of everything (assuming that such a theory can be written down in terms of our algebraic notation…something which I feel shows quite a bit of hubris!) To do this, first notice that all equations can be written as A=0 where A is some probably nasty equation. A theory of everything, i.e. a set of equations describing all physics, will just be a collection of such equations, say A_1=0, A_2=0, … A_n=0: it’s important to make sure all of these equations are over real numbers, but this is easy to do. Now we can combine all of these equations into one by specifying

A_1^2+A_2^2+…+A_n^2=0

which is true iff all of the A_i=0! I’m not sure if Feynman was the first to pull this little slight of hand, but it was the first place I saw this trick.

R. P. Feynman characterized his work in QED as

a scheme for pushing a great problem under the rug. Maybe it will stay under the rug and, then again, maybe it won’t.

If this quote doesn’t fill you with a nagging desire to go look under the rug, then don’t become a theoretical physicist. If it does, take some aspirin, read the quote again for inspiration and then start doing problems.

Edward Teller is dead. The first great era of physics has ended.
Continue reading “The First Great Era of Physics”