[Stingy Jack]

Okay. First of all, a scientific "Theory" is different than the layman's "theory." In the language of science, a "Theory" is about as close to fact as you can get. An "hypothesis" (which is similar to the layman's term 'theory') is tested over and over and over again. When enough tests have been completed (and I mean MANY tests), and the results remain consistent with the hypothesis, only then does it become a scientific "Theory". Take the "Atomic Theory" as an example. A scientific theory isn't just a guess.

As far as the moon thing goes, here is a quote from my Astronomy text from college.

"Today, many astronomers favor a hybrid of the capture and fission themes. This idea -- often called the impacttheory -- postulates a collision by a large, Mars-sized object with a youthful and molten Earth. Such collisions may have been quite frequent in the early solar system (see Chapter 15). The collision presumed by the impact theory would have been more a glancing blow than a direct impact. The matter dislodged from our planet then assembled to form the Moon.
Computer simulations of such a catastrophic event show that most of the bits and pieces of splattered Earth could have coalesced into a stable orbit. Figure 8.27 shows some of the stages of one such simulation. If the Earth had already formed an iron core by the time the collision occurred, the Moon would indeed have ended up with a composition similar to the Earth's mantle. During the collision, any iron core in the impacting object itself would have been left behind in Earth, eventually to become part of the Earth's core. Thus both the Moon's overall similarity to that of the Earth's mantle and its lack of a dense central core are naturally explained. Over the past decade, planetary scientists have come to realize that collisions such as this probably played very important roles in the formation of all terrestrial planets".

That is from the text "Astronomy Today 2nd Edition" by Eric Chaisson and Steve McMillan (both of which hold doctorates in astronomy and astrophysics from Harvard.) Published by Prentice Hall in 1997 (ISBN 0-13-712382-5). Pages 189-190.