What non-fiction are you reading now?

[Quantum]

For example, ancient Greek history, contemporary Russian history, modern British history, business, the military-industrial complex?

I'm reading . It sure is mind-bending, but Kaku makes it mostly comprehensible. For example, what are strings?

The string is extremely tiny, at the Planck length of 10 ^-33 cm, a billion billion times smaller than a proton, so all subatomic particles appear point like.
...
If we were to pluck this string, the vibration would change; the electron might turn into a neutrino. Pluck it again and it might turn into a quark. In fact, if you plucked it hard enough, it could turn into any of the known subatomic particles.
...
Strings can interact by splitting and rejoining, thus creating the interactions we see among electrons and protons in atoms. In this way, through string theory, we can reproduce all the laws of atomic and nuclear physics. The "melodies" that can be written on strings correspond to the laws of chemistry. The universe can now be viewed as a vast symphony of strings.
(p.196-197)