Relativity, quanta, and the strange edges.
Modern Physics
Modern physics breaks the classical picture: time bends with motion, particles behave like waves, and observation alters reality.
Chapter outline
Lessons in this chapter
Short, focused lessons. Each one ends with a worked example and a quick quiz.
Key concepts at a glance
The essential ideas, paired with their equations.
Mass–Energy Equivalence
01Mass and energy are interchangeable — a tiny mass holds enormous energy.
Time Dilation
02Moving clocks tick slower as seen from a stationary frame.
Schrödinger Equation
03The wavefunction's evolution — quantum mechanics' equation of motion.
Uncertainty Principle
04Position and momentum can't both be known exactly.
Photoelectric Effect
05Light delivers energy in discrete quanta — Einstein's 1905 insight.
Entanglement
06Quantum particles share correlations stronger than any classical signal allows.
Frequently asked
What is quantum mechanics?+
The physics of the very small — where energy comes in discrete packets and particles behave probabilistically.
Is time travel possible?+
Relativity allows forward time travel via high-speed motion or strong gravity; backward travel remains speculative.