Wednesday, October 12, 2005

Microstate Blackhole Production

I thought it important that some clarity be brought to this subject. So by bringing some information together that I had been thinking about, I would blog it.

Horatiu is referring to a mathematical similarity between the physics of the real world, which govern RHIC collisions, and the physics that scientists use to describe a theoretical, “imaginary” black hole in a hypothetical world with a different number of space-time dimensions (more than the four dimensions — three space directions and time — that exist in our world). That is, the two situations require similar mathematical wrangling to analyze. This imaginary, mathematical black hole that Horatiu compares to the RHIC fireball is completely different from a black hole in the real universe; in particular, it cannot grow by gobbling up matter. In other words, and because the amount of matter created at RHIC is so tiny, RHIC does not, and cannot possibly, produce a true, star-swallowing black hole.

Unfortunately, all of this is overstated. At RHIC we don't make a "real" black hole, in the sense envisioned by Einstein's General Theory of Relativity. Rather, Nastase's point of view is that RHIC collisions can be described by a "dual" black hole. But what does "dual" mean in this context? It's not "two-ness" in any sense, but rather indicates that one can write down a theory which describes the collision as a black hole, but in a completely different world than that we see around us. To make his model work, he (and many other researchers who are exploring this direction) make a calculation of a black hole in 10 dimensions in order to describe difficult (but gravitationally benign) aspects of the strong interaction in 4 dimensions.

This is not to undersell how interesting RHIC collisions are: if we in fact can use this "dual black hole" language to describe the collisions we are making daily, this may be a real advance in our understanding. But no-one I have ever spoken to has suggested that this black hole can or does act like a traditional black hole in our observed universe (although this possibility has been considered, and has been generally discounted as an implausible scenario).

Missing Energy

Given the dearth of knowledge about gravity in the subcentimeter range, the group is looking for any kind of deviation from expectations, not just extradimensional effects, he says. Nonetheless, the excitement about extra dimensions helps spur the group on, Price says.

If the strength of gravity takes a sharp turn upward at around 1 TeV, as the Stanford-Trieste scenario implies, an opportunity opens for testing this theory also in accelerators. Collisions at such energies could produce gravitons in large numbers, and some of these particles would immediately vanish into the extra dimensions, carrying energy with them. Experimenters would look for an unusual pattern of so-called missing energy events.

This and more subtle effects of extra dimensions could show up at existing accelerators, such as LEP and the Tevatron at Fermilab, only if the dimensions have scales nearly as big as a millimeter. The powerful LHC will greatly improve the chances for detecting missing energy events and other prominent extradimension effects.

In 1930 Wolfgang Pauli proposed a solution to the missing energy in nuclear beta decays, namely that it was carried by a neutral particle This was in a letter to the Tubingen congress. Enrico Fermi in 1933 named the particle the "neutrino" and formulated a theory for calculating the simultaneous emission of an electron with a neutrino. Pauli received the Nobel Prize in 1945 and Fermi in 1938. The problem in detection was that the neutrinos could penetrate several light years depth of ordinary matter before they would be stopped.

If you perform an experiment in which some of the energy you put in seems to disappear somewhere, unaccounted for, then yes, you have some explaining to do. Conservation of energy is not something we’d give up lightly; rewriting all those textbooks would be exhausting… but large extra dimensions would certainly not top the list of things to consider.

First of all, “missing energy” is a normal feature of collider experiments, since you can’t expect to catch all the stuff that comes out of them. You have two particle beams banging into each other inside a tunnel of finite width; any decay products flying off into the tunnel are lost. Around the collision point, you have detectors which, while huge and most impressive, also have blind angles and - most importantly - finite size.

Stanford’s Savas Dimopoulos: New Dimensions in Theoretical Physics

Our new picture is that the 3-D world is embedded in extra dimensions,” says Savas Dimopoulos of Stanford University. “This gives us a totally new perspective for addressing theoretical and experimental problems.

The machine, dubbed ATLAS (A Toroidal LHC ApparatuS), is one of four facilities to be located at a powerful accelerator, the Large Hadron Collider (LHC), now under construction near Geneva, in Switzerland

No comments:

Post a Comment