Is string theory the answer to the last big questions in physics, or a dead end? While some physicists believe that string theory could lead to a unifying 'theory of everything,' detractors say that string theory is sloppy and founded on unwarranted assumptions. One new book calls string theory 'not even wrong.' In this hour of Science Friday, we'll look at the pros and con of string theory, with physicists Lee Smolin and Brian Greene.

Plus, astronomers are set to vote on whether Pluto should remain a planet. A proposal under debate at the current meeting of the International Astronomical Union calls for a change in the definition of 'planet,' to include objects that have enough gravity to have formed into a spherical shape and that orbit a star (while not being stars themselves.)

Under that definition, our local neighborhood would suddenly include 12 planets -- Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Charon and 2003 UB313. However, many more bodies in our solar system could meet that definition, potentially expanding the planetary count in our Solar System by dozens more. The proposal is a topic of intense debate. We'll get the latest from the meeting of the International Astronomical Union, and find out whether astronomy textbooks might soon need to be rewritten.

Call in with your questions and comments at 1-800-989-8255 (3-4 Eastern). Teachers, find more information about using Science Friday as a classroom resource in the Kids' Connection.

Guests:
Mike Brown
Professor of Planetary Astronomy
Division of Geological and Planetary Sciences
California Institute of Technology
Pasadena, California

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Lee Smolin
Author, "The Trouble with Physics: The Rise of String Theory, The Fall of a Science, and What Comes Next" (Houghton Mifflin, 2006)
Faculty Member, Perimeter Institute for Theoretical Physics
Toronto, Ontario, Canada

Brain Greene
Author, "The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory" (WW Norton and Co., 2003); "The Fabric of the Cosmos: Space, Time, and the Texture of Reality" (Knopf, 2004)
Professor of Mathematics and Physics
Columbia University
New York, New York

Books/Articles Discussed:

"The Trouble with Physics: The Rise of String Theory, The Fall of a Science, and What Comes Next," by Lee Smolin. Houghton Mifflin, 2006.

"The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory," by Brian Greene. WW Norton and Co, 2003.

"The Fabric of the Cosmos: Space, Time, and the Texture of Reality," by Brian Greene. Knopf, 2004.

"Not Even Wrong: The Failure of String Theory And the Search for Unity in Physical Law," by Peter Woit. Basic Books, 2006.

(find books discussed on previous broadcasts)

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This segment produced by Annette Heist