  Recent cutting-edge experiments have provided $in\,situ$ structure
characterization and measurements of the pressure ($P$), density ($\bar{\rho}$)
and temperature ($T$) of shock compressed silicon in the 100 GPa range of
pressures and up to $\sim$10,000K. We present first-principles calculations in
this $P,T,\bar{\rho}$ regime to reveal a plethora of novel liquid-liquid phase
transitions (LPTs), making the interpretation of these experiments very
challenging. The short-ranged ionic structure of the fluid is preserved under
collective adjustments of many distant atoms when subject to compression and
heating, with surprisingly little change in electrical and thermal
conductivities $\sigma$ and $\kappa$. We match the experimental X-Ray Thompson
scattering and X-ray diffraction data theoretically, and provide pressure
isotherms, ionization data and compressibilities that support the above picture
of liquid silicon as a highly complex LPT-driven ``glassy'' metallic liquid.
These novel results are relevant to materials research, studies of planetary
interiors, high-energy-density physics, and in laser-fusion studies.
