[PQ]

Originally Posted by kdbolt70

Well, he's right and wrong, in a sense. I'll try to explain There is a very important mathematical equation that defines gravity:

F = GMm/R²

F is the Gravitational force
G is the Gravitational constant, 6.67*10^(-11) N-m²/kg².
M is the mass of object 1 (we'll say the earth)
m is the mass of object 2 (the moon)
R is the radius between the two object's center of gravity

The last part is important. Notice the equation says nothing about volume, or density. All that matters is mass (no pun intended :p). So, regardless of the earth's size, assuming it had the same mass, the moon would revolve around it at relatively the same distance. Whether the earth was the size of a basketball, or the size it is now. (granted if it was the former, it would probably end up as a black hole!)

Now, whats really interesting about the moon in this theory is its creation. Its believed that the moon was created from a very early collision between the earth and a meteor. A chunk of molten earth was blasted off in to space, and slowly coagulated into our modern day moon.

To do this, the meteor was pretty big in relation to the Earth, something like 1/4 the size of present day Earth. If earth had been much smaller, the metor would have had a much larger effect on our planet.

Also, why isn't the moon expanding?

Originally Posted by DGthe3

the claim was made that the earth has doubled in size? Did it double in radius? Area? Volume? Land area makes the most sense considering the topic that was discussed. Doubling in area means that the volume would be 2.83x larger. So density would then have to have gone down by an equal factor for mass to remain the same. So, given that the current density for the earth is ~5.5g/cc, it would have had to have a density of 15.6 g/cc before expansion. This is halfway between the density of lead and gold.

One other problem with this though, if the earth had to double in area while maintaining the same mass, the force of gravity at the surface would have been twice as strong before it grew. Unfortunately, this would have made dinosaurs impossible to stand.

If the earth had significantly less mass eons ago, the moon would never have maintained a stable orbit. Since we have a moon and dinosaurs fossils, I think that proves that this guy is talking out of his ass.

Ok, so did we establish that it would be unlikely that the moon could have remained in it's current orbit throughout the proposed theory or not?