How long for 2 particles to collide due to gravity?

[BruceW]

yeah... hopefully he will be back soon. I am curious about this 'original method'. I cannot guess how it would work from the short description you gave.

edit: I mean, that I can substitute r with u and dr with du. But then the integral it gives is not any nicer at first glance (maybe my brain works differently to whoever did the original method). But anyway, I can wait 'till the OP comes back.