We started class by discussing eclipses, since Jared had seen the lunar eclipse this morning. We discussed the difference between solar and lunar eclipses. We then returned to the Big Bang, and I explained to Jared the interaction between elementary particles (protons, neutrons, electrons, quarks, etc) and radiation, and why the early Universe was opaque. We talked about particle accelerators and cloud chambers, and how through high speed collisions we can understand better the fundamental building blocks of matter. Using what we know today, we can work backwards and infer (with sophisticated mathematical tools) what physical processes dominated in the first 380,000 years of the Universe.