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First Principles
School

Every subject here is taught the way it was invented — starting from the question somebody could not stop asking, not from the answer printed in the back of a book.

Education is free.
Ignorance is expensive.

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This panel fills itself in as you go. Open a subject and it appears here with your percentage, your module count, and a link straight back to where you stopped. Subjects you have never touched stay out of it.

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A map of human invention

Not a list of who discovered what. A record of the questions — what each of these people refused to take on authority, and what cracked open when they pushed.

250 BCE — 1021

The First Questions

Argument stops being rhetoric and starts being measurement.

c. 250 BCEMechanics

Archimedes

Syracuse

The law of the lever, and buoyancy

Why does a small weight far from the pivot balance a large weight near it?

Forget the wood and the stone. Weigh only the distances. If the balance does not tip, then weight times distance on one side must equal weight times distance on the other — and that is true whatever the object is made of. The shape of the thing is a distraction. The ratio is the law.

Archimedes · reasoning, reconstructed

What broke open

Machines become calculable. You can now predict a crane before you build it.

1021Optics · Method

Ibn al-Haytham

Cairo

Book of Optics — and the experiment as arbiter

Does the eye reach out to the world, or does the world arrive at the eye?

Everyone from Euclid onward says rays leave the eye. But stare at the sun and the eye is hurt — the damage travels inward. So build a dark room with one small hole and let the world paint itself upside down on the far wall. The image arrives without any eye present at all. Light comes in. Settle it by making the world answer, not by arguing.

Ibn al-Haytham · reasoning, reconstructed

What broke open

Controlled experiment becomes the referee of physics. Every result after this owes it a debt.

1638 — 1877

The Machine of the World

The universe is shown to run on a handful of equations that do not care who is watching.

1638Mechanics

Galileo Galilei

Arcetri

Inertia and uniform acceleration

If I take friction away, what does a moving body do when nothing pushes it?

Falling is too fast to time with a pulse and a water clock. So dilute gravity: roll the ball down a shallow ramp and the same law plays in slow motion. The distances go as 1, 4, 9, 16 — the squares. And a ball rolling down one ramp and up another returns to its starting height, whatever the second slope. Flatten that second ramp to nothing and the ball must roll forever. Rest is not the natural state. Constant motion is.

Galileo Galilei · reasoning, reconstructed

What broke open

Motion needs no cause. Only *change* of motion does — which leaves an opening exactly the shape of Newton.

1687Mechanics · Gravitation

Isaac Newton

Cambridge

Principia — universal gravitation and the calculus of change

Is the force that drops an apple the same force that bends the Moon?

Fire a cannonball level from a high enough mountain and it falls the whole way — but the ground curves away beneath it just as fast, so it never lands. It is in free fall forever. That is all an orbit is. Then the Moon is simply falling, and falling is a single law that thins out as the square of the distance. One rule for the orchard and the sky. To write it down I need a mathematics of instantaneous change, so I will have to invent that too.

Isaac Newton · reasoning, reconstructed

What broke open

The heavens lose their special physics. One equation now covers everything with mass.

1789Chemistry

Antoine Lavoisier

Paris

Conservation of mass, and the death of phlogiston

When wood burns away to almost nothing, where did the rest of it go?

The books say burning releases a substance called phlogiston. But metals get *heavier* when they burn, and a negative weight is a confession, not an explanation. Seal the reaction in a closed vessel and weigh the whole vessel before and after. If the total never budges, nothing was created or destroyed — it only changed partners. The missing mass left as a gas I failed to catch.

Antoine Lavoisier · reasoning, reconstructed

What broke open

Chemistry becomes quantitative. Bookkeeping, rigorously applied, kills a century-old ghost.

1831Electromagnetism

Michael Faraday

London

Electromagnetic induction and the field

A current makes a magnetic field. Can a magnetic field be made to give a current back?

I have no mathematics, so I will think in pictures. Iron filings around a magnet arrange into lines — treat those lines as real things filling space, not as bookkeeping. A steady magnet next to a coil does nothing. But push the magnet *through* and the needle kicks, then dies. So it is not the field that drives the current, it is the *cutting* of those lines — the change. Nature charges for motion, not for presence.

Michael Faraday · reasoning, reconstructed

What broke open

Every generator, motor and transformer on Earth. Also: the field becomes a physical object in its own right.

1859Biology

Charles Darwin

Down House

Evolution by natural selection

Can design appear with nobody doing the designing?

Breeders reshape pigeons in a few decades simply by choosing who reproduces. Nature has no intention, but it has scarcity — more are born than can live. Give me only three things: offspring vary, some of that variation is inherited, and some variants survive a little better. Then the selecting happens on its own, and deep time does the rest. No aim is required. Only differential survival, repeated beyond intuition.

Charles Darwin · reasoning, reconstructed

What broke open

Purpose stops being an input to biology and becomes an output of it.

1865Electromagnetism

James Clerk Maxwell

London

A dynamical theory of the electromagnetic field

If Faraday's pictures are true, what do they look like as equations — and are they complete?

Write down everything known about electricity and magnetism and the set is inconsistent: charge would not be conserved inside a charging capacitor. Patch it with one extra term — a changing electric field must itself count as a current. Now the equations close. And when I solve them in empty space, they give a wave whose speed is built from two numbers measured in a laboratory with no light in it. That speed is the speed of light. Light is not *like* an electromagnetic wave. It is one.

James Clerk Maxwell · reasoning, reconstructed

What broke open

Optics is absorbed into electromagnetism, and radio is implied two decades before anyone builds one.

1877Statistical Mechanics

Ludwig Boltzmann

Graz

Entropy as counting: S = k log W

Every collision runs fine backwards. So why does time only run forwards?

Stop tracking the particles; count the arrangements. There is exactly one way for every molecule to sit in the left half of the room, and an unthinkable number of ways for them to be spread evenly. Nothing forbids the gas from rushing into one corner — it is merely overwhelmed. Entropy is not a substance leaking away. It is a tally of how many microscopic states look the same from outside. The arrow of time is a statement about arithmetic.

Ludwig Boltzmann · reasoning, reconstructed

What broke open

Heat, probability and information are shown to be one subject — the seed Shannon harvests seventy years later.

1898 — 1928

The World Cracks Open

Continuity, absolute time and determinism all fail inside thirty years.

1898Radioactivity

Marie Curie

Paris

Radioactivity as an atomic property; polonium and radium

These rays never weaken. What reservoir are they drawing on?

Measure the rays with an electrometer rather than a photographic plate, so the answer is a number and not an impression. The intensity tracks only the quantity of uranium present — not its compound, not its temperature, not its crystal form. Chemistry cannot reach it. So the source is inside the atom itself, and the atom is therefore not indivisible. And pitchblende is more active than its uranium content allows, which means something far stronger is hiding in it.

Marie Curie · reasoning, reconstructed

What broke open

The atom acquires an interior, and with it nuclear physics, radiometric dating and medicine.

1900Quantum Theory

Max Planck

Berlin

The quantum of action

Why does classical physics predict infinite energy from a warm object?

Treat the walls of the oven as oscillators and classical theory says every mode gets an equal share — but there are infinitely many short-wavelength modes, so the oven should blaze with infinite ultraviolet. It does not. As an act of desperation, suppose energy can only be traded in whole lumps proportional to frequency. Then high-frequency modes are too expensive to excite and the infinity dies. I intended this as a mathematical trick. It refuses to go away.

Max Planck · reasoning, reconstructed

What broke open

Continuity fails. Energy turns out to be grainy, and the twentieth century starts.

1905 · 1915Relativity

Albert Einstein

Bern · Berlin

Special and general relativity

What would I see if I ran alongside a beam of light?

I should see a frozen wave standing still — but Maxwell's equations have no such solution, and no experiment has ever caught light moving at anything but c. So the fault is not in the light. It is in my assumption that time is the same for everyone. Keep the speed of light fixed and let simultaneity break instead. Ten years later, the falling man: a person in free fall feels no weight at all, so gravity is not a force pulling on him — it is the shape of the spacetime he is coasting through.

Albert Einstein · reasoning, reconstructed

What broke open

Space and time become one deformable object with mass as its sculptor. GPS, black holes, cosmology.

1918Mathematical Physics

Emmy Noether

Göttingen

Noether's theorem: symmetry ⟷ conservation

We keep discovering conservation laws one at a time. Why is anything conserved at all?

The conservation laws are not separate facts to be collected. Take any continuous symmetry of the action — a transformation that leaves the physics unchanged — and a conserved quantity falls out automatically. The laws not caring *when* you run the experiment gives you energy. Not caring *where* gives you momentum. Not caring which way you face gives you angular momentum. The bookkeeping was never fundamental. The indifference is.

Emmy Noether · reasoning, reconstructed

What broke open

Physics gains its deepest organising principle. Every modern field theory is built on it.

1928Quantum Field Theory

Paul Dirac

Cambridge

The relativistic electron — and antimatter

Schrödinger's equation is first order in time and second in space. Relativity will not accept that. Can I take the square root?

To make the equation first order in both, the coefficients cannot be ordinary numbers — they must be matrices that anticommute. Force that and two things fall out uninvited: the electron's spin, which nobody put in, and a second set of solutions with negative energy. I can either discard half my own equation or believe it. I will believe it. There is another particle, identical in mass and opposite in charge.

Paul Dirac · reasoning, reconstructed

What broke open

Mathematics predicts a particle before anyone sees one. Four years later, the positron shows up.

1936 — today

Information & Spacetime

Computation, information and geometry turn out to be the same subject wearing three coats.

1936Computation

Alan Turing

Cambridge

On Computable Numbers — the universal machine

What is the absolute minimum a machine needs in order to compute anything computable?

Watch a human clerk doing arithmetic. They look at one symbol, consult their state of mind, write a symbol, move their attention, change state. Strip it to that: an endless tape, one symbol at a time, a finite table of rules. Nothing else is necessary. And since the rule table is itself just symbols, one machine can read another machine's description and become it. Hardware and software are the same substance. Then ask whether a machine can decide in advance if a program halts — and the answer is no, provably, forever.

Alan Turing · reasoning, reconstructed

What broke open

Computation gets a definition, universality, and a hard limit — all in one paper, before a computer existed.

1948Information Theory

Claude Shannon

Bell Labs

A Mathematical Theory of Communication

How much of a message is actually information, and how much is noise the channel can be made to ignore?

The meaning of a message is irrelevant to the engineering problem. What matters is how surprised the receiver is. A symbol you could have predicted carries nothing; a symbol you could not carries a lot. Measure that surprise in bits and the whole thing becomes arithmetic — and the same formula Boltzmann wrote for a gas reappears, unchanged, for English text. Then the shock: a noisy channel still has a hard, finite capacity, and below it you can push the error rate to as near zero as you like.

Claude Shannon · reasoning, reconstructed

What broke open

Every modem, disk, deep-space probe and compression format. Information becomes a measurable physical quantity.

1949Quantum Electrodynamics

Richard Feynman

Cornell

Path integrals and the diagram

Why should a particle pick one route? What if it takes every route and they vote?

Assign every conceivable path from A to B a little rotating arrow whose spin rate depends on the action along it. Add all the arrows. Wild paths disagree with their neighbours and cancel; the classical path is simply where neighbouring arrows agree and pile up. Least action stops being a mystical principle and becomes interference. Then draw the interactions as cartoons — a line, a vertex, a squiggle — and the cartoons *are* the integrals. Bookkeeping you can see.

Richard Feynman · reasoning, reconstructed

What broke open

The most precisely tested theory in science, and a visual language physicists still think in.

1952Biophysics

Rosalind Franklin

King's College London

Photograph 51 — the geometry of DNA

What shape must a molecule have if its job is to copy itself?

Do not guess the structure and then look for support. Control the humidity, get the fibre to hold one crystalline form, and let X-rays report the geometry directly. The pattern comes back as a cross of spots — the diffraction signature of a helix — and the spacings fix the pitch and the diameter. The phosphate backbone is on the outside, where the water is. Whatever the bases do, they do it facing inward, in pairs.

Rosalind Franklin · reasoning, reconstructed

What broke open

Heredity becomes a readable, copyable string. Molecular biology starts here.

1964Quantum Foundations

John Stewart Bell

CERN

Bell's theorem — the end of local hidden variables

Is quantum randomness just ignorance of instructions the particles carried all along?

Einstein's objection was that the particles must leave the source with their answers pre-agreed. That sounds untestable — but it is not. Suppose the answers are predetermined and no influence travels faster than light. Then correlations between distant measurements must obey an inequality, and I can write that inequality down. Quantum mechanics violates it. So this is no longer philosophy. It is an experiment, and the universe gets to answer.

John Stewart Bell · reasoning, reconstructed

What broke open

Metaphysics becomes measurable. Experiment says the world is not locally real — and quantum cryptography follows.

1989Systems Engineering

Tim Berners-Lee

CERN

The World Wide Web

Why must you ask permission before one document can point at another?

Every system here wants to own its own data and impose its own hierarchy, so knowledge sits in silos and dies with the project. Drop the hierarchy. Give every document a single global address, let any document link to any other without the target's consent or knowledge, and accept that some links will break. The tolerance for broken links is the feature — it is what lets the thing grow without a coordinator. Then give it away, unpatented.

Tim Berners-Lee · reasoning, reconstructed

What broke open

A permissionless global commons for text. Then for everything else.

1994Quantum Computation

Peter Shor

Bell Labs

Polynomial-time factoring on a quantum computer

A quantum computer explores many states at once — but you only get one reading. How do you make the wrong answers cancel?

Superposition alone buys you nothing, because measurement collapses it to a random branch. The resource is interference, not parallelism. So recast factoring as finding the period of a function — a classical reduction that has been sitting there for years — and let the quantum Fourier transform arrange for every wrong period to interfere destructively while the right one adds up. You do not search the haystack. You make the hay cancel itself out.

Peter Shor · reasoning, reconstructed

What broke open

Public-key cryptography acquires an expiry date, and quantum computing acquires a reason to be funded.

2015Gravitational Physics

LIGO Collaboration

Hanford · Livingston

Direct detection of gravitational waves

If spacetime is a physical thing, it should be able to ripple. Can we feel one pass?

A passing wave stretches one direction while squeezing the perpendicular one — so build an L, send the same laser down both arms, and watch the interference pattern breathe. The catch is the size of the effect: a thousandth of the width of a proton over four kilometres. Everything else on Earth is louder. So build two detectors three thousand kilometres apart and accept only signals that arrive at both within the light-travel time. A century after the prediction, two black holes merge and both arms ring.

LIGO Collaboration · reasoning, reconstructed

What broke open

Astronomy gains a second sense. We can now hear events that emit no light at all.

And now it is your turn

Everything above
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62 modules and 240 lectures across physics, mathematics, computer science and finance. Every resource is free, and every one was chosen because it is among the best in the world — not because it was convenient.

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