/sci/ - Science & Math

I was mulling over some GR equations, when something hit me. We often say in physics that certain things can't be possible because they would violate causality, but just how well-founded is the invocation of causality to constrain a physical theory anyway?

Starting from classical physics, [math]F = ma[/math] really doesn't say anything, except to provide a meaning to the word "force", until we start attaching the implication that a force *causes* a mass to accelerate. Otherwise it, and everything else in Newtonian physics, is just a bunch of acausal couplings between expressions.

The problem gets hairier under relativity, because simultaneity now goes out the window. Two observers in different inertial frames cannot agree on the simultaneity of events, yet it is asserted that they can still agree on a partial ordering of some events, so long as a lightlike or timelike interval seperates them.

(cont.)