# Q & A: does energy cause gravity?

Q:
According to Einstein theory of relativity, Mass and Energy are different manifestations of basically the same thing. Both distort the curvature of space-time. From Newtons equations we can know the gravity between two different objects with a specific mass. Is it possible to just substitute the Mass in newtons equation for M=E/c2? If this can be done, does that means that energy attracts each other the same way that mass does? Even if this equation can not be arrange this way since Newtons equations deals primarily with resting mass instead of mass as a result of Energy and momentum; can Energy bend the curvature of space-time in a way that Energy can attract other Energy and end up with more energy? The same way that resting mass does even if Newtons Equation can not be used?
- David Rivas (age 33)
Costa Rica
A:

The general (accidental pun) answer to your question is yes. General Relativity says that any form of energy is a source of gravity. Think of light, which has energy but no rest mass. Imagine a bag of light, traveling all directions so it has no net momentum. From the outside, that bag has energy but no momentum, exactly like a particle with rest mass that's not moving (in our frame). Its gravitational field looks just like that of a rest mass.

We've got more thorough background on this here: http://van.physics.illinois.edu/qa/listing.php?id=16351.

Mike W.

(published on 12/02/2014)