Energy in special relativity Imagine a spaceship travelling near the speed of light relative to observer on the ground. a candle is burning inside the spaceship and it takes 3 hours for the candle to burn completely relative to the spaceship. but for the observer on the ground it takes many years for the candle to burn since there is Time dilation. so how a single candle with little energy stored burns for years?
 A: I might be wrong but it seems like the underlying assumption in this question is that one frame has the information about the original energy of the candle, and the other frame has an excess/deficit of energy.
Energy is a frame dependent quantity. So if one moves between references frames which are distinguished by a uniform relative velocity, then the energies of a body as viewed in those two frames will in general be different, and that is okay. This is true in simple classical mechanics as well - a person moving in a car has no kinetic energy in the car's frame, but from the road, they do.
The conserved quantities are the momentum 4-vector and the energy momentum tensor, in special relativity.
Therefore, viewed from this framework, there is no need for the 'stored energy' of the candle to be the same when viewed by two different observers.
A: The answer is simply that the candle can burn for years because it burns at a slower rate.
A: The chemical reaction by which the candle burns is itself slowed down, as are any and all physical processes occurring inside the speeding spaceship. In fact, if the spaceship had a clock attached to its outside, as it zooms by us the clock would appear in our frame of reference to be running very, very slowly.
