Compress almost anything to great densities and electrons react with protons to make neutron rich matter. This material is at the heart of many fundamental questions in Nuclear Physics and Astrophysics. What are the high--‐density phases of Quantum Chromodynamics? Where did the chemical elements come from? What is the structure of many compact and energetic objects in the heavens, and what determines their electromagnetic, neutrino, and gravitational--‐wave radiations? We describe the Lead Radius Experiment (PREX) that is using parity violating electron scattering to measure the neutron radius in 208Pb. This has important implications for neutron rich matter, neutron stars, and their crusts. We model neutron rich matter using large--‐scale molecular dynamics simulations and show the complex nuclear pasta phases intermediate between isolated nuclei and uniform nuclear matter. We find neutron star crust to be the strongest material known, some 10 billion times stronger than steel. It can support large mountains. These concentrated masses, on rapidly rotating stars, can generate detectable gravitational waves.