I'm new to all these concepts so sorry if i make any mistake in advance ! I watched a video on Nat Geo a few months ago it was about time travel into the future which is quite possible. They talked of building a track that goes around the earth. A train would go around the earth at a very high speed so hence slowing down time for the passengers. They said that 1 week in the train would be equal to 100 years on the earth. My question is regarding the energy for the train. I f you power it from the outside then you'll have to supply energy to the train for a 100 years and if you supply the energy from inside it would be just for a week! What am i missing here? Don't say change in mass!