01
The equivalence principle
Can I tell the difference between gravity and acceleration from inside a sealed box?
Advanced · Module 13
General Relativity
Gravity is not a force. It is the geometry of spacetime, and matter tells that geometry how to bend. The mathematics is demanding; the central idea fits in one sentence about a falling man.
By the end of this module
You can read the Einstein field equations and explain what each side means.
0%0 / 6 complete
02
Curved spacetime and the metric
What replaces the Pythagorean theorem when space bends?
ReadingFree
Lecture Notes on General Relativity ↗Sean Carroll
The standard free introduction. Became the textbook.
03
Tensors and geodesics
How do I write laws that no choice of coordinates can corrupt?
VideoFree
Relativity by eigenchris ↗eigenchris
The most patient tensor-calculus series available free. Start here if the index notation is fighting you.
04
The Einstein field equations
What is on each side of G = 8πT, in plain language?
Primary source★ LandmarkFree
The Foundation of the General Theory of Relativity (1916) ↗Albert Einstein
The Collected Papers of Albert Einstein, free online in translation.
05
Black holes, waves, and cosmological solutions
What does the theory predict that nobody expected?
Primary source★ LandmarkFree
Observation of Gravitational Waves from a Binary Black Hole Merger ↗LIGO & Virgo, PRL 2016
A century-old prediction confirmed. Open access.
Check yourself
End-of-module quiz
Every answer comes with the reasoning, not just a verdict. Getting one wrong and reading why is the point.
01The equivalence principle states that:
02In general relativity, a freely falling object moves along:
03The right-hand side of Einstein's field equations contains:
Answer all 3 to finish the module.