Learn physics
This page is a staged plan for learning physics from scratch, built for someone whose last contact with the subject was a school classroom. It moves in a fixed order: first the vocabulary that every physics text assumes you already have, then the theories that organise that vocabulary into working frameworks, then the physicists who built those frameworks, and finally the papers and books they wrote. The order matters, because physics is cumulative in a way most subjects are not. Relativity only makes sense once you know what an inertial frame is, and quantum mechanics only makes sense once you know what a field and a wave are. Nothing here requires you to do the mathematics, though the sources will show it to you when you are ready. Every concept, theory, and physicist below links to real references, mostly English Wikipedia, the Stanford Encyclopedia of Philosophy, Britannica, and the Nobel Prize archive, so you can check any claim and read further.
Stage 1. Learn the vocabulary
Finish this stage able to define about eighteen core physical terms in your own words and say, in two sentences, what each one is used for.
Work through the concepts one at a time, in the order given. Read the definition here, then read one cited source for that concept. Close both and write the definition from memory. Pay attention to the terms that have an everyday meaning as well as a technical one, especially force, energy, momentum, and field, because the everyday meaning will mislead you. If you cannot restate a concept without looking back, reread the source before moving on.
Stage 2. Map the theories
Finish this stage able to name each theory's period, its core claims, the range of situations it describes correctly, and the point at which it breaks down.
Read each theory in the order listed, which is roughly the order in which they were built. For each one, write down two things: what it explained that nothing before it could, and what it failed on. Those failures are the entry points to the next theory. Classical mechanics fails at high speed, which is where special relativity starts. Classical electromagnetism plus thermodynamics fails on the radiation from a hot body, which is where quantum theory starts. Reading them as a chain of failures and repairs is more accurate than reading them as separate subjects.
Stage 3. Meet the physicists
Finish this stage with a working map of fifteen physicists: their dates, the result each one is known for, and which of their writings to read first.
Read each overview and note the recommended starting text. Read at least one cited source per physicist. Several of these people worked on the same problem within a few years of each other, so keep the dates in view: Planck in 1900, Einstein in 1905, Bohr in 1913, and Heisenberg, Schrödinger and Dirac between 1925 and 1928. Seeing how short that span was explains why the theories they produced overlap and contradict each other in places.
Stage 4. Go to the sources
Finish this stage having read one original physics text end to end rather than a summary of one.
Start with Galileo or Faraday. Both wrote for readers who had no formal training, both describe experiments you can picture, and neither requires mathematics to follow. Newton's Principia is the hardest text listed here and is best read in an English translation alongside a commentary. Einstein wrote Relativity: The Special and General Theory specifically for general readers, and it is the shortest route into relativity from the source. Every text in this stage with a Project Gutenberg id is available there in full, for free. The later texts are not on Project Gutenberg, so read those through the editions named in their overviews.
