(1/3) The arrow of time is the distinction between past and future. Causes precede effects; we grow older; we remember the past. #aot
(2/3) Deep physical laws are reversible. Time's direction only arises macroscopically, because entropy/disorder is increasing. #aot
(3/3) Entropy is increasing because it started small near the Big Bang (and is still pretty low). Nobody knows why that's the case. #aot
Other 3-tweet Physics theory explain nations, In Quantum Field Theory, the Higgs Boson, and M-Theory can be found at Sean's original blogpost on the subject at Cosmic Variance: here.