One of the more popular crackpottish ramblings I run across concerns “pure energy” and an explanation of what it is. Here is a good counterpoint:
Pure Energy?
Energy is a property of “stuff”; that is a physical system. A configuration of a physical system will have a property that we can indirectly measure, which we call energy. One cannot have energy as some independent “thing”.
Cheers.
“If the mathematical description of the physical system does not alter upon changes in time then there is a conserved quantity that we call energy.”
If time is homogeneous, energy is conserved. The local mix of space and time varies with gravitational potential, e.g., GPS atomic clock correction for altitude. Does “conservation” of energy vary in kind?