From: utzoo!decvax!harpo!duke!unc!jqw Newsgroups: net.physics Title: Equivalence of Mass and Energy Article-I.D.: unc.3792 Posted: Mon Aug 9 02:56:42 1982 Received: Mon Aug 9 06:23:12 1982 It has recently been shown (experimentally) that two beams of light have gravitational attraction for each other. All forms of energy have mass and some additionally have rest mass. The sum of the masses of all the particles in the fusion reaction are equal before and after (if you include photons and neutrinos.) The center of mass (and of gravity) of a supernova explosion remains in the same place whether or NOT there are asymmetries. If a greater mass goes in one direction, it will have a lower velocity and hence the center of gravity will not move. This is a rather general principle: if a rocket explodes in flight, the center of gravity of all the pieces will follow a parabolic path. Centrifugal acceleration IS the same thing as gravitational acceleration. The force is created by the mass of the entire universe that you are rotating with respect to. If you are the only object in the universe (*ego*), then when you rotate, there is no force. You also aren't rotating, since there's nothing to rotate with respect to, but that's the whole point. If there are only a few, relatively low mass objects in the universe, the centrifugal force will be small. Linear acceleration is also the same as gravitational acceleration. You are accelerating with respect to the entire universe (as represented by your local space-time), and hence the force. The same effect would be accomplished if every other object in the universe accelerated in the opposite direction. (Actually, because of the aforementioned center-of-mass-in-same-place effect, this couldn't really happen.) If, again, you were in a relatively empty universe, this time positioned between 2 hundred-foot diameter boulders, you could easily cause a large acceleration between these rocks with little force, because they would mass very little.