Mute said:
And the chemical energy in a battery is still energy when it has been converted into electrical energy and heat, but the forms of energy are not equivalent.
In line with that, the energy of the electron/positron is still energy when it is converted to that of a couple of photons, but the form has changed.
Bare in mind that orbiting electrons can absorb/emit photons when changing shelves to increase/decrease their energy levels, so the form of the energy must be fairly compatible.
Except here there is no chemical reaction. The other properties of each particle cancel each other out.
The form of the energy changes without the addition of any energy or other particulate property. One moment it has mass, the next it doesn't (please note all previous posts about invariant mass - let's not go there again).
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When dealing with electrons/positrons annihilation, the only way to calculate the transition to gamma rays is using invariant mass. The reason for this is because if you don't use invariant mass, then the equation doesn't balance. The reason it won't balance is because on one side of the equation you have relativistic mass and on the other side you do not. To say that the mass was converted to energy takes you away from using invariant mass and into using relativistic mass which it appears to be quite widely agreed that you can't do. Relativistic Mass cannot be used to calculate the outcome of this process because photons have none and any reference to E=MC^2 is using the wrong math.
The reason that invariant mass must be used is because there is currently no method of manipulating Relativistic Mass into anything else. Sure, you can use E=MC^2 to determine the amount of energy your playing with, but that's as far as you can take it.
Whatever it is that is the root cause of, or at least has a part to play in Relativity is lost at the moment an electron/positron pair is annihilated. The requirement to add increasingly more energy to these particles to get them to travel at ever higher velocities no longer applies.
Whatever was preventing those particles from traveling at the speed of light was removed when the energy became photons, in fact traveling at the speed of light suddenly became mandetory.