The Strangest Idea in Physics, One Front Page at a Time

In December 1900 a careful, conservative professor in Berlin fixed a stubborn problem about glowing ovens with a trick he hoped was only a piece of algebra. It wasn’t. Over the next century that trick grew into quantum mechanics, the most accurate theory science has ever produced, and the one its own founders argued about the hardest. It also happens to run the phone or laptop you’re reading this on.

The animation below tells that story as eleven front pages of The Quantum Gazette, from 1900 to today. It takes about twelve minutes. You can pause whenever you like, or jump straight to any chapter from “In this edition” below the player. Six times along the way the story stops and hands you the controls: heat an oven, fire electrons through two slits, try to beat Einstein’s hidden instructions. Twice it asks you to guess what happens next before it shows you.

LATE EDITIONAll the quanta fit to printWEATHERUncertainThe Quantum GazetteCENTURY EDITION1900 to todayPRICE: ONE QUANTUMThe QuantumCenturyHow a desperate trick about glowing ovens becamethe strangest, most successful theory in science.IN THIS EDITION1900Planck's act of desperation1905Light comes in lumps1913Bohr's quantum leaps1924Matter makes waves1925Two mechanics, one theory1927Dice and uncertainty1935The cat and the spooky link1948Taming the infinities1964Bell's test1982Aspect settles itTodayQubitsEngraved for the Gazette by our staff artist

The Quantum Gazette · Century Edition

More than a century of physics in eleven front pages. About twelve minutes, longer if you linger: six hands-on experiments and two predictions along the way.

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The Quantum Century

The Same Story, Without the Newspaper

Year Who What changed
1900 Max Planck Energy is exchanged in lumps, E = hf
1905 Albert Einstein Light itself comes in lumps, later called photons
1913 Niels Bohr Electrons sit on fixed steps and leap between them
1924 Louis de Broglie Everything that moves has a wavelength
1925–26 Werner Heisenberg, Erwin Schrödinger Two versions of quantum mechanics that turn out to agree
1926 Max Born The wave tells you the odds of where a particle turns up
1927 Heisenberg The uncertainty principle
1927 Clinton Davisson and Lester Germer, George Paget Thomson Electrons diffract like waves
1935 Einstein, Boris Podolsky, Nathan Rosen; Schrödinger Entanglement, and a cat in a box
1947–48 John Bardeen and Walter Brattain; Richard Feynman, Julian Schwinger, Sin-Itiro Tomonaga The transistor, and a working theory of light and electrons
1964 John Stewart Bell A test that could settle Einstein’s argument with Bohr
1972–82 John Clauser, Alain Aspect Experiments side with quantum theory
1981–94 Feynman, Peter Shor Quantum computers, first as an idea, then with a reason to build one
2015–today Labs in Delft, Vienna and Boulder, and the rest of the world Loophole-free tests, and the first working quantum machines

Lumps: 1900–1913

Planck’s quanta. Heat anything enough and it glows, first dull red, then orange, then white. By 1900 physicists at Berlin’s imperial standards laboratory had measured exactly how much light of each colour a hot oven gives off, and no theory matched the data across the whole range. On 19 October 1900 Planck presented a formula that did. On 14 December he explained where it came from, and to get there he had to assume the oven’s walls could only trade energy in fixed parcels, each worth a tiny constant h times the frequency of the light. Short, high-frequency waves need big parcels, so at any ordinary temperature they rarely get one. The physics of the day, applied honestly, would have handed those short waves nearly all the heat and made every warm oven blaze with unlimited ultraviolet. Paul Ehrenfest named that absurdity the “ultraviolet catastrophe” in 1911, well after Planck’s fix. Planck himself treated the lumps as a mathematical device. His famous description of it as “an act of desperation” comes from a letter he wrote in 1931, three decades later.

Photons. In March 1905 Einstein, then 26 and working at the Swiss patent office, took Planck’s lumps literally. Light, he proposed, travels as a stream of packets, each carrying energy hf. That explained a puzzle about the photoelectric effect: shine light on a metal and electrons can fly off it, but whether they do depends on the colour of the light, never on its brightness. A photon of red light doesn’t carry enough energy to free an electron from sodium, however many of them you send. A single violet photon does. Brightness only changes how many photons arrive, and so how many electrons come out. Few physicists accepted the idea for years. The 1921 Nobel Prize cited Einstein for this law of the photoelectric effect, and relativity went unmentioned.

Bohr’s levels. By 1911 Ernest Rutherford had shown that an atom is mostly empty space around a tiny, heavy nucleus. If electrons circled it like planets, classical physics said they would radiate away their energy and spiral inward in about sixteen trillionths of a second. Atoms plainly don’t collapse. In 1913 Bohr proposed that electrons can only occupy certain orbits, like the steps of a staircase, and that they leap from step to step without ever being in between. Each leap down releases one photon whose colour matches the size of the drop. That explained why each element glows with its own barcode of sharp spectral lines, and for hydrogen it predicted the lines’ positions exactly.

Try it: the oven stop lets you heat a glowing bar and flip Planck’s rule on and off to watch the classical curve run away. The lamp stop lets you mix colour and brightness to see which frees electrons from sodium. The staircase stop asks you to find hydrogen’s four visible lines: red, cyan, blue and violet.

Waves and dice: 1924–1927

Matter waves. In his doctoral thesis of November 1924, Louis de Broglie turned Einstein’s idea around. If light waves can behave like particles, perhaps particles can behave like waves. He gave every moving object a wavelength: Planck’s constant divided by its momentum. For a cricket ball that wavelength is absurdly small. For an electron it’s about the spacing between atoms in a crystal, which meant a crystal could act as a diffraction grating. In 1927 two teams confirmed it. At Bell Labs in New York, Davisson and Germer bounced slow electrons off a nickel crystal and found a strong peak at 50 degrees, right where de Broglie’s wavelength said it should be. In Aberdeen, George Paget Thomson fired faster electrons through thin films and got rings on photographic plates. The rings in the animation are Thomson’s; Davisson and Germer measured their peak with a detector swung around the crystal. Thomson’s father, J. J. Thomson, had won a Nobel Prize for showing the electron was a particle. George shared the 1937 prize with Davisson for showing it was also a wave.

The two mechanics. In June 1925 Werner Heisenberg, aged 23, fled hay fever to the island of Helgoland. There, and in the weeks before and after, he worked out a theory using only quantities that could actually be measured: the frequencies and intensities of the light atoms emit. His numbers came in tables that obeyed a strange rule. Multiplying a by b did not give the same result as b by a. Back in Göttingen, Max Born and Pascual Jordan recognised the tables as matrices, and the result became matrix mechanics. Over Christmas 1925 in the Swiss resort of Arosa, Erwin Schrödinger found a different route: an equation for the electron’s wave. Confined inside an atom, the wave can only vibrate in whole patterns, the way a guitar string only plays certain notes, and those allowed patterns reproduced Bohr’s steps without anyone having to impose them. The two theories looked nothing alike and each author disliked the other’s picture. In 1926 Schrödinger (and independently Carl Eckart) showed that they gave the same answers. A fully rigorous proof of their equivalence came a few years later, with John von Neumann’s work in the early 1930s.

Born’s probabilities. Schrödinger’s equation left open what the wave actually was. In 1926 Max Born proposed that it is a wave of probability. Where the wave is large, the particle is likely to be found. Where it’s small, it rarely turns up. Individual outcomes are genuinely random, and only the odds are predictable. Einstein never accepted it. In a letter to Born in December 1926 he wrote that he was convinced God “does not throw dice”. Born received the Nobel Prize for this interpretation in 1954.

Uncertainty. In early 1927 Heisenberg showed that quantum mechanics sets a limit on how sharply a particle’s position and momentum can be defined together. Squeeze the wave into a small space and its spread of speeds widens. Narrow down the speed and the position smears out. The limit comes from the wave nature of matter itself. Better instruments can’t get round it.

The double slit. The front page for 1927 asks whether an electron can pass through both slits at once. At the time that was a thought experiment. Nobody sent electrons through a double slit until Claus Jönsson did it in Tübingen in 1961, and the one-electron-at-a-time version the animation shows was first done in Bologna in 1974 and, more famously, at Hitachi in 1989. Each electron lands as a single dot, yet over thousands of them the dots build up interference stripes, as though each one had gone through both slits as a wave. Add a detector that tells you which slit each electron used and the stripes disappear. The animation draws that watched pattern as two neat bands, one behind each slit. That’s a simplification: on a distant screen the two single-slit patterns overlap into one broad smear, and the two separate bands only show up close to the slits.

Try it: before the electron-diffraction reveal, you’re asked to predict what a beam fired at a crystal will produce. The double-slit stop lets you fire electrons one at a time, then switch on the detector and watch the stripes vanish.

In October 1927 the leading physicists met in Brussels for the fifth Solvay Conference. Seventeen of the 29 people in the famous photograph had won, or would go on to win, a Nobel Prize. Einstein reportedly brought Bohr a new objection at breakfast each day, and Bohr had a reply by evening. The argument that started there ran for the rest of their lives.

The spooky argument: 1935–1982

Entanglement. In May 1935 Einstein, Boris Podolsky and Nathan Rosen published a paper arguing that quantum mechanics must be incomplete. The New York Times got hold of it early and ran it under the headline “Einstein Attacks Quantum Theory”. They imagined two particles that interact and then fly far apart. Measure one, and you can immediately predict what the same measurement would show on the other, however distant. Einstein concluded that each particle must have carried hidden instructions all along, since the only alternative was an instantaneous link between them, which he later mocked as “spooky action at a distance”. Schrödinger coined the word entanglement for this connection the same year.

The cat. Also in 1935, Schrödinger mocked the theory with a thought experiment: a cat sealed in a box with a radioactive atom, a Geiger counter, a hammer and a flask of poison. If the atom decays, the flask breaks. Taken at face value, quantum mechanics says the atom is in a blend of decayed and not decayed until someone looks, so the cat would seem to be both alive and dead. Schrödinger called the setup “quite ridiculous”. The question behind it, of when and how a blend of possibilities becomes one definite result, is still debated. It’s called the measurement problem.

Bell’s test. For almost thirty years the argument looked unanswerable by experiment. Then in 1964, at the University of Wisconsin in Madison, the Belfast-born physicist John Stewart Bell proved that any theory based on local hidden instructions must obey a statistical limit that quantum mechanics predicts will be broken. In 1969 Clauser, Michael Horne, Abner Shimony and Richard Holt recast Bell’s argument into a form that could be tested in a lab, known as the CHSH inequality. The animation turns that version into a game with two players: hidden instructions can win it at most 75% of the time, while entangled particles can win about 85% (more precisely cos² 22.5°, or 85.4%).

Aspect’s experiment. Clauser and Stuart Freedman ran the first test in 1972 at Berkeley, and quantum mechanics won. The obvious objection was that the detectors might somehow “know” their settings in advance. In 1982 Aspect’s team at Orsay, near Paris, switched the settings while the photons were already in flight, too late for any signal travelling at light speed to warn the other side. Their switches changed on a regular rhythm rather than at random, and other small gaps remained. In 2015 separate teams in Delft, Vienna and Boulder closed the main loopholes together in single experiments. Aspect, Clauser and Anton Zeilinger shared the 2022 Nobel Prize in Physics.

One thing entanglement cannot do is send a message. Each side’s results look perfectly random on their own. The correlation only appears when the two lists are brought together and compared, which takes an ordinary signal.

Try it: the cat stop asks whether you open the box. The Bell stop gives you Bob’s two dials and asks you to beat the 75% line. The hint is ±22.5°.

Quantum at work: 1947–today

The transistor. On 16 December 1947 at Bell Labs, John Bardeen and Walter Brattain demonstrated the first transistor, a small germanium device with gold contacts that could amplify a signal. It works because electrons in a solid can only occupy certain bands of energy, which is quantum mechanics at the scale of a crystal. Transistors went on to fill every radio, computer and phone. Lasers, LEDs and MRI scanners rest on the same physics, and so does the timekeeping in the atomic clocks that make GPS work.

QED. The quantum theory of light and electrons, quantum electrodynamics, kept producing infinite answers when anyone tried to calculate beyond a first approximation. In the late 1940s Feynman, Schwinger and Tomonaga found ways to tame them. Feynman’s version used little diagrams, each one a way an event can happen; add up the contributions from every possible way and you get the answer. Feynman and Schwinger both presented their methods at the Pocono conference in Pennsylvania in 1948. Tomonaga had worked out his in wartime Japan and wasn’t there. The three shared the 1965 Nobel Prize. The theory predicts the electron’s magnetism, a quantity known as g/2, and a 2023 measurement found 1.00115965218059, agreeing with theory to better than one part in a billion.

Qubits. In 1981 Feynman pointed out that simulating nature would be much easier with a computer that itself followed quantum rules. An ordinary bit is 0 or 1. A qubit holds a wave spread over both values, and like the electron waves at the double slit, those waves can reinforce or cancel. A quantum algorithm is a careful arrangement of that interference, so that wrong answers cancel out and the right one builds up. In 1994 Peter Shor showed that a large enough quantum computer could factor huge numbers quickly, which would break encryption that protects much of the internet. That’s why, in August 2024, the US National Institute of Standards and Technology published its first three standards for encryption designed to resist quantum computers. Today’s machines are still small and error-prone, and taming those errors is where most of the work is.

Try it: the last stop gives you a single qubit. Press H and measure a hundred times to get roughly half zeros and half ones. Press H twice and every measurement comes back 0, because the two paths to 1 cancel.

A myth worth dropping

The story often opens with physicists in 1900 believing their subject was finished. That’s largely a myth. The line “there is nothing new to be discovered in physics now” is widely credited to Lord Kelvin, but no one has found a source for it. What Kelvin actually told the Royal Institution in April 1900 was that two dark clouds hung over physics. One cleared into relativity and the other into quantum mechanics. Historians describe the years around 1900 as a period of excitement and unease, with radioactivity, X-rays and the electron all newly discovered. The animation keeps the “nearly finished” mood as a hint of that folklore and moves straight on to the clouds.

Where the History Comes From

The script was checked against the sources below. Dates in datelines follow the event each front page reports, so some are approximate: Bohr’s paper came out in July 1913, and “Göttingen, 1925” stands for work done across Helgoland, Göttingen and Arosa.