# Q & A: infinite mass-energy?

Q:
Now you’ve said that you cant move faster then the speed of light because (skipping a long explnation) your mass becomes infinite and then you would need infinite energy Now beacise of E=mc^2 we know that means mass is energy So if mass is energy and you had infinite mass that would mean you had infinite energy as well so thats means you would be able to go the speed of light or faster does this work?
- James
U.S
A:
One part of your argument is correct. If you had infinite inertial mass then you would also have infinite energy, since they are really just the same thing measured in diffefent units (E=mc^2). However, the second part, where you say 'hey that infinite energy is just what you need' is circular. Remember, the argument was that the energy would have to be infinite IF you were travelling at c. You can't use that to say that therefore you can get enough energy. The limits on where the energy comes from are still the usual ones, and there's no way you are going to get infinite energy.

Mike W.

In more modern language, E^2=(mc^2)^2 + (pc)^2, where p is the momentum, and m is an "invariant" mass (you can call it the rest mass). Increasing the speed of something towards the speed of light increases its momentum to infinity, and also its energy. Not only is there no such thing as infinite energy, there's also no such thing as infinite momentum.

Tom

(published on 10/22/2007)