## Wednesday, February 23, 2005

### Null energy condition

New paper! A bit too technical to discuss here. But for Sci-Fi fans, the following tidbit: wormholes and time machines generally require violation of the null energy condition. Our paper shows, among other things, that none of the particles or fields of the type generally considered in particle physics will allow construction of a (stable) wormhole or time machine.

For those familiar with the Einstein equations, they are of the form:

{Curvature tensor R, fn of spacetime geometry} = {matter energy-momentum tensor T}

The set of possible spacetime geometries (could there be wormholes? loops in time?) satisfying the Einstein equations is unconstrained without some information about the right hand side of the equation. Traditionally in general relativity, one assumes that the matter fields satisfy certain energy conditions, for example the null energy condition, which requires that the tensor T, when contracted with any null (lightlike) four-vector n, is positive: Tnn > 0. We show that when this condition is violated, the system is necessarily unstable to small perturbations.

Instabilities and the null energy condition
Authors: Roman V. Buniy, Stephen D.H. Hsu

We show that violation of the null energy condition implies instability in a broad class of models, including all gauge theories with scalar and fermionic matter as well as any perfect fluid. When applied to the dark energy, our results imply that $w = p / \rho$ is unlikely to be less than -1.

http://arxiv.org/abs/hep-th/0502203

Anonymous said...

Is there a way for me to visualize what you are proving?

Anne

maxkennerly said...

"Our paper shows, among other things, that none of the particles or fields of the type generally considered in particle physics will allow construction of a (stable) wormhole or time machine."

Well, gee, aren't you a downer.

Congratulations; does this improve your Erdos number?

Anonymous said...

Well, I went through the paper but I need more of a summary sense of what to visualize. What can a philosopher find through your finding? What should I "see?"

Anne

Anonymous said...

Steve

Why do you question the general ability and sincerity of researchers in the field of climate change? There is always poor and distorted research done in any applied field, but there are all sorts of clever and honest scholars. To slant an entire field is possible, but not simply to be expected.

Though I have no idea why, for I am not a climate researcher, I can tell you birds from New York to Massachusetts are changing behavior patterns in ways that surely seem to reflect climate change. Why though must be examined.

Anne

Anonymous said...