[JaimeThompson]

The rate at which the moon moves away from the Earth isn't constant. I can't find the details right now so I could be totally wrong.

[soliton4]

thats true, however the author explicitly stated that the collision point of earth and moon at 1.5 billion years was calculated by assuming the moons CURRENT rate of recession

[zenexer]

At no point does the author make any assertion that the rate was constant. Presumably, the current rate of recession is just one variable that gets plugged into an equation.

[soliton4]

"If we take the moon's current rate of recession and project it back in time" is a very straight forward way of saying, lets assume the moon receeded from the earth at the current rate.

[snowwrestler]

No it’s not because you are projecting backward in time in the presence of a gravitational field that varies with square of radius.

The path of the moon away from the Earth is not a straight line, it is a tightly wound spiral.

[soliton4]

given your insight in the matter, would you care to post the correct calculation then?