There is the other sum:
E=MC2 (can't do superscript 2)
Essentially, our everyday Newtonian concept of the universe falls apart at the extremes. When things get very small, we throw out Newtonian mechanics in favour of Quantum theory (Heisenberg etc, see this link:
http://zebu.uoregon.edu/~imamura/122/feb9/hup.html).
When things get very large we throw out Newtonian mechanics in favour of General Relativity (see this link
http://archive.ncsa.uiuc.edu/Cyberia/NumRel/GenRelativity.html. As far as I remember, Hawking is in search of the big idea that unifies the theories.
Because we don't live in a world where we are aware of E=MC2 applying in our everyday lives, it is hard to picture that particular relationship between mass and energy. We just have to remember to throw out the rules whereby apples fall out of trees (v=u+gt) and think in a completely different way, the amazing thing to me is how clear it all seemed to Einstein.
