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# Unpredictability

Unpredictability

Sometimes asteroids and comets stray from their expected orbits, so scientists can't predict where they're headed. But this unpredictable behavior isn't random. We'll talk with mathematician Curt McMullen about unpredictability - after this on Earth and Sky.

Date

DB: This is Earth and Sky, talking with Dr. Curt McMullen of Harvard University about an example of behavior in nature that's unpredictable - but not random.

(Tape 0:00:39-0:00:45) Traditional physics from the time of Isaac Newton on had to do with prediction. (Tape 0:01:20-0:01:33) In more modern times, we've realized that there are lots of systems which obey very definite laws like the law of gravitation, but which exhibit unpredictable behavior.

DB: For example, certain asteroids - rocky fragments hurtling through space - stray from their regular orbits, so scientists can't predict where they'll be in a hundred years. But even though the asteroid's motion is unpredictable, it isn't random. Again, Dr. McMullen:

(Tape 0:02:54-0:03:41) When one talks about, for example, the trajectory of a stray asteroid, it may be very difficult to predict where it will be a hundred years from now. But this unpredictability is not due to some sort of internal random behavior or â€˜dice-rolling' on the part of God, the asteroid is obeying perfectly well-understood and deterministic physical laws. The problem is that a very minor change in the position of the asteroid, undetectable to us at this time, can completely vary its location a hundred years from now -- in the same way that some minor event in your life five years ago might completely change what kind of job you have now, where you're living in the united states, something like that.

DB: Thanks to Dr. Curt McMullen for speaking with us. And with thanks to the National Science Foundation, I'm Deborah Byrd, for Joel Block, for Earth and Sky.

Author: Beverly Wachtel

Thanks to the following individual who aided in the preparation of this script:

Dr. Curtis McMullen
Department of Mathematics
Harvard University
Cambridge, MA
ctm@math.harvard.edu

If you enjoyed this program, you may be interested in the following:

Dr. Curtis McMullen's website:
http://www.math.harvard.edu/~ctm/

Mathematical Sciences Research Institute website:
http://www.msri.org