E=mc² bugs the shit out of me.

This is what happens when I get bored at work.

So E=mc² has always bothered me. Because what it says is that not only are Energy and Mass really mostly the same thing but also every amount of m, regardless of the type of m, contains the same amount of E. And I was pretty sure that couldn't be the case until I read wikipedia:

So one gram of mass — approximately the mass of a U.S. dollar bill — is equivalent to the following amounts of energy:

89.9 terajoules
24.9 million kilowatt-hours (≈25 GW·h)
21.5 billion kilocalories (≈21 Tcal)
21.5 kilotons of TNT-equivalent energy (≈21 kt)
85.2 billion BTUs

So every gram of mass is equivalent to 24.9 million kilowatt-hours. That is pretty neat.

So then I start to wonder why we can't just turn our dollar bills into 24.9 million kilowatt-hours. And, again, wikipedia tells me things:
"One theoretically perfect method of conversion of the rest mass of matter to usable energy is the annihilation of matter with antimatter. In this process, all the mass energy is released as light and heat. However, in our universe, antimatter is rare. To make antimatter requires more energy than would be liberated."

While there are some other ways of doing this it seems to be the case that to convert a dollar bill to 24.9 million kilowatt-hours one has to fully change the matter to energy, which we can't do because it's, like, really difficult.

So with that little quizibuck settled I'm trying to figure out if Energy and Mass are fundamentally the same thing then are space and time, too, the same sort of thing. Because if Energy and mass can be fundamentally the same thing then time and space, too, would seem to have that same sort of relationship.