Built on facts: Light, up to 11

How many photons can you stuff into a box?

[I]f you stuff enough energy into the vacuum you’ll eventually start creating matter (electron/positron pairs in this type of circumstance) via Einstein’s famous E = mc^2 relationship. In nuclear weapons we’re used to seeing the m turn into E very dramatically, but of course the other direction works just as well. Get enough E and you’ll start making m.