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Quote by: Stewbert  However, theres a theory that the earth will eventually be eaten up by the Sun. |
That's true, but not for the reasons you state.
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Quote by: Stewbert As you know, the Sun's gravitational forces cause the earth to orbit about it, slowly getting closer. Like a paper orbiting a drain, the Earth will eventually be sucked in. |
Nope. The degradation of the earth's orbit isn't fast enough to cause it to fall into the sun in the time the sun has left. The sun is about half way through it's life at 4.5 billion years. In another 4.5 to 5 billion years the sun will run out of hydrogen in its core. The sun isn't large enough to fuse the helium, so as the energy production at the core stops, the remaining helium contracts. The contraction causes the outer shells to also contract to the point that fusion of hydrogen outside the core is increased, which in turn causes the outer layers to heat up which expands the outer layers. The additional heating (and therefore brightness) is more than offset by the expansion and the sun would appear red (if anyone were there to see it) and become a red giant. The fusion in the outer shells will cause the sun to expand until it is the roughly the size of the orbit of earth. That's where the earth being eaten by the sun idea comes from. However, as time passes, the process of fusion is making the sun less massive and thus reducing its gravity. As a result, the orbit of earth will become larger, not smaller. It
may grow enough that the earth (a mere cinder by that time) will not be consumed by the sun and will eventually become a dead rock orbiting a brown dwarf.