Re: Equivalence orinciple (was @ Adalat)
The point is that if you can't look outside the car you can't tell if the track is horizontal or not: there is nothing you can do which will allow you to distinguish running at constant speed on a track running up hill or being accelerated by the locomotive on a horizontal track. That's what I was trying to get at by the whole tilting thing: thinking of the rails running uphill is better really. And that fact (that there is no experiment you can do to distinguish those two cases) is the weak equivalence principle: the strong equivalence principle says that those two cases are therefore the same: the force of gravity is acceleration.
The equivalence principle really is (as far as we know) correct: if I've failed to convince you that it is then that's because my explanation hasn't been clear enough, and I'm sorry. It's worth (well, I found it worth) spending some time trying to think up experiments that would let you distinguish: you'll fibd you can't
Biting the hand that feeds IT
