There are at least two ways to convert a supply of matter, with no antimatter, to “pure energy” (light and such) with 100% efficiency, but neither is what I’d call easy. The first is to drop it into a black hole, and let the hole evaporate. Since it’ll produce equal amounts of matter and antimatter in the evaporation, you can then annihilate those particles to get what you need. Unfortunately, for any of the black holes ever discovered, this would take many times the lifetime of the Universe, and any black hole which did evaporate quickly enough would be very difficult to keep stable.
The second method would be to just wait for all of the protons to decay, which the Grand Unified Theories predict should happen… Eventually. Again, we’re talking many times the lifetime of the Universe here, although it may be possible to catalyze the reaction to a practical rate using, say, magnetic monopoles. Unfortunately, there’s estimated to be approximately one magnetic monopole in the entire visible Universe, so we’re not likely to get our hands on one.
E = MC[sup]2[/sup] is written correctly. Exponents don’t distribute themselves among coeficients unless it’s explicit (e.g. you have a parenthesized expression with an exponent). At least, that’s what Mrs. Irwin said in eighth grade, and she’s never wrong.
Antimatter has been created in small quantities in particle accelerators. I imagine they got quite a cool fireworks show shortly thereafter.
I call that an error in keeping significant digits. The original data (i.e. your body weight) is only known to 2 or 3 significant digits so the result shouldn’t have any more significant digits.
Anyway, yes e=mc^2 has been confirmed in many ways. For instance, a gamma-ray photon can turn into an electron-positron pair, and the photon energy required is the mass of two electrons times c^2. Also if you accelerate a particle in an accelerator, you will notice that it gets harder and harder to bend the path into a circle. Not just because of the greater speed, but also because of the greater mass. Those parameters can be measured.
Like scr4, I would call it an error in significant figures. Unless you had measured your mass and found that it was 75.0000000000000000000 kg. Otherwise, I would just call the number 5.1x10[sup]20[/sup].
Now you know where you screwed up, but maybe I should be the one to point out that a Joule (work, energy, quantity of heat) has units of kg m[sup]2[/sup]/s[sup]2[/sup], whereas your big number has units of kg[sup]2[/sup]m[sup]2[/sup]/s[sup]2[/sup].
