## Is the Solar System Gravitationally Stable?

After centuries of hard work, mathematicians have finally arrived
at the definitive answer of whether or not the gravitational
perturbations of the planets will ever cause them to disrupt their
"fine and regular harmony". The answer is: Absolutely
maybe.

The problem, alas, is that there is a difference between the real
solar system and the mathematical one. The mathematical one deals
with n planets and a center of attraction that is so much more massive
than the others that its gravitation is the major influence in the
motion of the planets. This is *almost* the case in the solar
system.

Because universal gravitation is, well, **universal**,
*every* body in the universe attracts *every* other body. A
true model of the solar system would not only include the nine
planets, the sun, the thousands of asteroids, billions of comets, and
every spec of dust in the solar system, every space probe that has
ever been launched, and every passing atom of hydrogen, but it would
also have to take into account things like the gravitational
attraction of Alpha Centauri, M31, and the most distant quasar. In
this sense, we are qualitatively no better off than we are by assuming
that the planets are attracted by the sun alone. (Quantitatively, of
course, we can ignore the gravitational effects of just about
everything except for the larger planets and still get good matches
with observation)

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