Does God play dice with the world? Einstein didn't like Quantum Mechanics because he thought that Quantum Theory (QT) implied God did play dice. But that is a wrong interpretation, and Einstein had good reason to reject QT based on that framing.
A game of "chance," like dice play, is a category of probability Physics, and one that can be reduced to determinism if one knew all the initial conditions of the thrown dice.
Quantum Theory (or QT) is probability Physics that (1) can't be reduced to Determinism, and (2) is not in the same category as dice play.
Proving the Relativistic Energy-Momentum relation, the hard way and the easier way.
This adds the proof for the relativistic mass effects from motion, proving that gravity causes it.