Angular Momentum of the Solar System
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[edit] Introduction
The creationist argument may be stated as follows: "If, as you say, the solar system was formed by the action of gravity on a spinning disc of matter, then by the law of conservation of angular momentum, we would expect all the planets to revolve in the same direction and in the same plane, for all the planets to revolve in the same direction, with axes perpendicular to the plane of rotation, and all satellites to orbit their planets in the same direction and in the same plane as the Solar System, for much the same reason that a gyroscope at speed rotates in a single plane. But there are exceptions to these rules."
[edit] Discussion
There are indeed exceptions to these rules, though not as many as some creationists claim: no planet, for example, has a retrograde orbit, although some moons do.
Nonetheless, it is true as a general rule that we would expect to see the Solar System as described above. But we cannot expect the rule to have no exceptions, for it would only be true if the bodies in the Solar System never interacted with each other. But they can, and there is no reason to assume they have not: on the contrary, the rocky planets of the Solar System are pockmarked with the evidence of past collisions.
Now if two bodies collide, or get close enough for a significant gravitational interaction, then this will change the angular momentum of the two bodies. Of course, since such events take place in accordance with the laws of nature, they conserve the angular momentum of the Solar System as a whole, and are thus in accordance with the law of conservation of angular momentum.
We can test this hypothesis by observation. For if it is true, then retrograde moons should be debris which has undergone gravitational capture after planetary formation, rather than being the "regular" (spheroid) moons produced during the process of planet formation, which should all be prograde. This turns out to be the case. Indeed, not only are all retrograde moons irregular, but a very high proportion of irregular moons are retrograde, a phenomenon only recently understood.[1]
[edit] Chinese whispers
There are some Creationists who wish to make the argument above, but conflate the Big Bang with the formation of the solar system. We shall quote a few for comic effect:
- if all the matter in the universe was conpressed to a dot that exploded so X amount of years ago it would all follow that same rotation. [2]
- Law of Conservation of Angular Momentum: "if a spinning object explodes, the pieces are going to spin in the same direction". [3]
- Why do we have planets and moons spinning opposite to each other? If these all came from a "big bang" then they should all be spinning the same way! [4]
