[whatshisface]

>Saying "energy is conserved" is the moral equivalent of looking at Newton's laws and just ignoring GR.

If you're not expecting the spacetime background to be changing rapidly during your experiment, it's pretty moral to say energy is conserved.

[Iolaum]

By Noether's theorem as long as you don't have the laws of Physics change over time then energy will be conserved. The problem is that the definition of energy changes when you model a different system or change the way you model an existing system (ie Newtonian -> GR). A follow up problem is that the energy definition that results from applying Noether's theorem can get hard to translate in plain English.