Theorem or Conjecture? I understand the definitions "theorem" and "conjecture" in mathematics, but I wasn't sure for physics. I mean, if it's proved mathematically, it's a theorem, otherwise it's a conjecture. But for physics (i.e. when the idea is meant to correspond to a physical reality - and - can only said to 'true' if tested experimentally), how does one make a distinction?
 A: In physics a theory is a mathematical model that provides a description of the real world in some limited circumstances. That is, it is a computational framework that allows us to feed in initial conditions and calculate what will happen.
All theories are approximate because they are based on assumptions that apply only within certain bounds. For example Newton's Theory of Gravitation gives a description of the Solar System that is pretty accurate (precession of Mercury apart). However we know that it fails at high speeds and energy densities and needs to be replaced by Einstein's Theory of general relativity. In turn we expect GR to fail at short distances and need to be replaced by some theory of quantum gravity.
As far as I know theorem means much the same in physics and maths, though the physics community is more pragmatic in the proof of theorems. I'm not sure that the word conjecture is used in any other than a casual way. In a sense all our theories are conjectures since they're not based on any rigorous mathematical proof.
