Endless Universe: Beyond the Big Bang by Paul J. Steinhardt & Neil Turok

Author:Paul J. Steinhardt & Neil Turok [Steinhardt, Paul J. & Turok, Neil]
Language: eng
Format: epub
Tags: Science, Cosmology
ISBN: 9780385523110
Publisher: Broadway
Published: 2007-05-29T00:00:00+00:00

A New Start with Braneworlds

The plan for the workshop at the Newton Institute was to bring together as many leading string theorists and cosmologists as possible, with the hope of stimulating progress in connecting M theory with real-world cosmology. The political backdrop was distinctly unpromising. Just before the workshop, NATO entered the war in Kosovo, creating potentially dangerous divisions across Europe. Because the workshop was funded in part through a NATO-sponsored scheme, several scientists pulled out at the last minute. After some debate, the decision was made to go ahead. There is a strong school of cosmology in Eastern Europe, but there are few opportunities for personal interaction with cosmologists from the rest of the world. If the workshop were canceled, all the participants would have missed a rare chance to exchange ideas and build better links.

We asked Burt Ovrut, a highly respected string theorist and long-standing colleague of Paul’s from his years at the University of Pennsylvania, to deliver a set of lectures on M theory that would be accessible to cosmologists. Ovrut is a leading expert in some of the most mathematically formidable aspects of string and M theory. On this occasion, he stepped back from the technicalities and presented an inspiring overview of the theory’s essential elements.

He began by reminding the audience that M theory unifies the five versions of string theory by showing they are all just different limits of a single master theory. Furthermore, the master theory includes a sixth regime involving branes but no strings. Then, for the remainder of his talk, he concentrated on this sixth regime, the remarkable new geometrical picture discovered by Hořava and Witten. He asserted that this version deserves special attention because it offers new insights into fundamental physics and may provide the most direct way to relate M theory to laboratory experiments.

Ovrut is one of those physicists with artistic talent, so he was able to draw evocative pictures to illustrate Hořava and Witten’s theory. He began with a drawing of two closely spaced parallel sheets. Although the sheets appeared two-dimensional, Ovrut asked the audience to imagine that the sheets were really nine-dimensional. (Time is an additional dimension, but, for simplicity, we will restrict ourselves to counting only the dimensions of space here.) The gap between the two sheets lies along the tenth dimension, the extra dimension that distinguishes Hořava-Witten theory from the other five string theories.

The sheets, Ovrut explained, are branes, but not ordinary ones. Branes normally have space on either side. The branes that Ovrut drew, though, are the boundaries of the extra dimension so that space only exists between the branes, not outside the gap. To emphasize his point, Ovrut called them “end-of-the-world” branes. As an analogy, consider a double-glazed window. The window itself consists only of two panes of glass and the air space between them. The two panes are like the branes and the gap between them is like the extra spatial dimension.

Ovrut then described a simplification of the Hořava-Witten picture that he and his collaborators had been exploring.

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