PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 539 May 15, 2001
By Phillip F. Schewe, Ben Stein, and James Riordon

(DE)CONSTRUCTING DIMENSIONS

What is space?

We generally take space for granted. We exist within it, we move about, make measurements of it. It's there before anything else and it seems to be continuous. Furthermore, extra dimensions, beyond the three spatial dimensions we perceive, are mandated by modern string theories in the process of bringing quantum mechanics and general relativity together in a single theoretical framework.

That we can't see these dimensions is usually explained by saying that they are curled up in some way. The customary prescription for discovering such dimensions is to study particle interactions at ever higher energies, which is equivalent to studying matter at ever smaller size scales.

Now, three physicists want to re-examine the whole concept of space by coming from the other direction. As higher energies are probed, say Nima Arkani-Hamed (LBL, 617/496-8188) Andrew Cohen (Boston Univ, 617/495-1988) and Howard Georgi (Harvard, 617/496-8293), dimensions may actually disappear, revealing themselves as only a property of particle forces at low energies.

Imagine, for the moment, a number of copies of our four-dimensional (three space plus time) universe. Without interactions between them, these universes are inaccessible -- we are ignorant of their existence. But further imagine a new set of forces, linking pairs of these universes. If these forces are similar to the strong nuclear (hadronic) force, which is strong at low energies but gets weak at high energies, relatively low energy experiments (although still high energy in the TeV range by today's standards) would detect these alternate universes while high energy ones would not. This connection between different universes at low energies, the ability to transfer information, and even travel among them, appears as a new dimension. This dimension was not present beforehand, but appeared dynamically. In other words, the new dimension comes into existence only through interactions among particles. At high energies these forces "melt" away, and the extra dimension disappears.

The theorists suggest that even our familiar three spatial dimensions might come about in this way. Evidence for this kind of dynamical dimension would be the discovery, amid high energy collisions, of a finite series of new particles with a very specific spectrum of masses.
(Arkani-Hamed et al., Physical Review Letters, 21 May 2001; get text at Physics News Select)

Dan