A Tour of Space-time Foam

Narrator (April Hobart, CXC): At the smallest scales of distance and duration that we can measure, space-time - that is, the three dimensions of space plus time - appears to be smooth and structureless. Think of flying over the ocean in an airplane. From 30,000 feet or so, the ocean appears completely smooth. However, if your plane were to descend low enough, you could make out the waves and swells of the water. Certain aspects of quantum mechanics, the highly successful theory scientists have developed to explain the physics of atoms and subatomic particles, predict that space-time may act the same way. Instead of being totally smooth, it would have a foamy, jittery nature if we could look at small enough scales -- like those waves on the ocean. In these models, space-time would consist of many small, ever-changing, regions for which space and time are constantly fluctuating.

Since space-time foam, as it is called, is so tiny, scientists cannot observe it directly. However, they can hunt for evidence for its existence - or non-existence - in things we can see. By looking at the light from distant quasars in X-rays from Chandra as well as gamma-ray telescopes, a team of scientists set out to test some of the models of space-time foam.

What did they find? The researchers say their evidence can help rule out two different models of space-time foam. While their work does not eliminate the existence of space-time foam entirely, it does suggest that space-time is less foamy than some models predict. Scientists will continue to test the nature of space and time on the very smallest scales using every experiment they can think of, including using high-energy light from across the Universe.