The Feynman Lectures on Physics

Here's something that should change how you spend your evenings: the complete Feynman Lectures on Physics are available online, for free, in beautiful HTML5 with scalable vector graphics. Every equation renders perfectly at any zoom level. Every diagram is crisp.

This isn't some scanned PDF. In 2013, Caltech partnered with Michael Gottlieb to publish the "New Millennium Edition"—a version that corrects hundreds of minor errors accumulated over decades and converts everything to LaTeX for future-proofing. The result is arguably the most accurate physics textbook ever published.

The audio recordings of Feynman delivering these lectures are still sold separately (Audible has them), and they're worth it for his timing and humor alone. But the core intellectual content? Completely free.

In 1961, Caltech had a problem. Their introductory physics curriculum was boring students to death. The standard approach—mechanics, then thermodynamics, then electromagnetism—felt disconnected from the actual practice of physics. Students were memorizing formulas without understanding why the universe behaved this way.

Matthew Sands proposed a radical solution: bring in Richard Feynman, their Nobel laureate who had a reputation for explaining quantum electrodynamics to his barber. Feynman agreed, on one condition—he would teach it his way.

His way meant starting with atoms. Most physics courses save atomic theory for later. Feynman opened with it. "If all of scientific knowledge were destroyed," he told students, "the one sentence I would preserve is: all things are made of atoms." Everything else follows from there.

Robert Leighton transcribed every lecture. The resulting "red books" became instant classics—though ironically, the freshmen they were designed for often struggled with them. The lectures turned out to be better suited for faculty and graduate students who already had the mathematical background to appreciate Feynman's insights.

Volume I establishes the "atoms first" approach. Feynman spends the opening chapters building intuition about what matter actually is before introducing F=ma. By the time you reach Newton's laws, you understand why they work at the atomic level.

The most audacious move comes in Chapter 37: "Quantum Behavior." Most introductory physics courses save quantum mechanics for advanced study. Feynman introduces the double-slit experiment to freshmen, letting them confront the strangeness of reality before they've built up classical prejudices.

The volume also covers special relativity, treating it not as Einstein's strange theory but as the inevitable consequence of taking Maxwell's equations seriously. Time dilation and length contraction emerge naturally when you stop privileging any particular reference frame.

Volume II is where most physics students either fall in love with the subject or realize they should have majored in biology. Electromagnetism—the unified theory of electricity, magnetism, and light—demands genuine mathematical sophistication.

Feynman's key insight: magnetism is a relativistic effect of electricity. Move a charged particle past a wire carrying current, and special relativity explains why it feels a magnetic force. This isn't just a clever observation—it's the conceptual foundation that makes Maxwell's equations make sense.

The volume builds to a complete exposition of Maxwell's equations in differential form. By the final chapters, you understand how these four equations describe everything from radio waves to why the sky is blue to how your phone's GPS works.

Here's where Feynman does something no other introductory textbook attempts: he starts quantum mechanics with Dirac bracket notation instead of the Schrödinger equation. Most courses spend months building up to the mathematical formalism. Feynman begins with it.

The approach sounds backwards but works beautifully. By focusing on two-state systems like electron spin, students grasp superposition and uncertainty immediately. The wave function comes later, as a specific representation of something they already understand.

The famous two-slit experiment runs as a thread through the entire volume. Feynman returns to it repeatedly, each time revealing new implications. By the final chapters, you understand why "the observation of an electron changes everything"—not as mysticism, but as mathematics.

Feynman's lectures succeeded because he practiced what he preached: "If you can't explain it simply, you don't understand it." This wasn't false modesty. He genuinely believed that jargon was a warning sign—a symptom of fuzzy thinking, not evidence of sophistication.

Author Scott Young formalized this into the "Feynman Technique" around 2011:

1. Choose a concept you want to understand.
2. Teach it to a child (or rubber duck). Use plain language, no jargon.
3. Identify gaps in your explanation—places where you wave your hands.
4. Return to the source material, then simplify and use analogies.

The technique works because it forces you to confront what you actually know versus what you merely recognize. Feynman famously said there's a difference between "knowing the name of something" and "knowing something." The Feynman Technique is a tool for telling the difference.