Particle in free fall problem

1. Apr 9, 2007

"Under what conditions does a geodesic represent a possible wordline for a particle in free fall, parametrized by proper time."

I can only think of one conditions - the fact that the metric ds squared is positive. Is this enough?

2. Apr 9, 2007

Dick

Possibly something like, "if acted on by no nongravitational forces". GR only absorbs gravitational forces into the metric. Though possibly that violates the condition of 'free fall'.

Last edited: Apr 9, 2007
3. Apr 9, 2007

Dick

Nope. I think you are basically right to begin with. 'Free fall' should exclude nongravitational forces. But I think the condition that they might be looking for is that the particle is massive. Otherwise proper time=0 is quite acceptable.