But, he said, it took a lot of energy to turn energy into mass. And as such, it took just as much energy to turn mass into energy.
This is part of what the formula E=mc² was supposed to represent.
What he didn't say was whether or not you could use mass to turn mass into energy, or if you could use mass to turn energy into mass.
If, as he said, these two things were just variations on the same theme, then this second option should be just as valid as the first.
String theory suggests that perhaps all matter is made up of tiny bits of energy (pretty close to what Einstein was getting at). These "strings" of energy are so small (we typically define a unit of energy as a photon, but this is energy that is released by matter, not what that matter is made up of), that even one tiny electron can contain thousands upon thousands.
Supposedly, these strings of energy vibrate at different "tones", and the combination of different tones is what creates different objects (an electron, a proton, or even a graviton!).
String theory also suggests multiple dimension, not just the up/down forward/backward/ left/right of what we perceive, but also curved dimensions, possibly folded dimesions, and other shaped dimesions. It also suggests of multiple universes.
But let's not go that way.
In this theory, energy and matter wouldn't just be different variations on a theme, they would, in fact, be the theme itself. That is, these tiny particles ("strings") of energy actually make up particles of mass (protons, neutrons, etc).
String theory, at this time, is also considered to be the hopeful theory that can unite the basic theories into one grand-unifying theory. Einstein's theory of relativity, which concerns gravity, stars, soalr systems and galaxies doesn't work on the small scale of atoms, where the Strong Force theory (that which holds the neutrons and protons together), the Weak Force theory (holds the electrons to the protons, or causes radioactive decay), and the Electromagnetic Force theory (light, electricity, and magnetism). At the atomic level, these other three theories reign free... the gravitational theory doesn't seem to hold up at this level... and likewise, the W, S, and EM theories don't hold up and the galaxy level.
Apparently, String theory holds up on both sides.
String theory also hints at one other phenomenon.
A massless particle, thought, perhaps to be a graviton.
My next (and hopefully final post) we'll delve a little bit more into gravity.