Bonus: quantum physics
Learn the game · The physics of the game · Bonus: quantum physics
An introduction, not a course. Each card ends with a common mix-up.
Energy comes in packets
Around 1900 Max Planck explained the glow of hot objects by treating energy as exchanged in discrete amounts proportional to frequency (E = hf). In 1905 Einstein used light quanta to explain the photoelectric effect.
Mix-up: "quantum" just means a discrete amount. It does not mean mystical or tiny jump.
Waves and particles
Send electrons through two slits one at a time. Each lands as a single dot, but over time the dots build an interference pattern, like waves. The rules for where a particle can show up behave like waves; detections are localised events.
Mix-up: it is not "a little ball that is also a wave"; it is something that follows wave rules for probabilities.
Superposition
A quantum state can be a combination of possible states. Measuring gives one outcome, with probabilities set by the state (the Born rule).
Mix-up: Schrodinger's cat (1935) was a thought experiment about how odd it sounds to apply this to a cat. Real cats lose superposition almost instantly (see decoherence).
Uncertainty
Position and momentum cannot both be sharply defined: the spread in position times the spread in momentum is at least h-bar over 2.
Mix-up: it is not just clumsy measuring. It is a property of wave-like states.
Entanglement
Two parts can share one state so that their measurement results are correlated more strongly than any local hidden-variable theory allows (Bell, 1964). Experiments confirmed this, and Alain Aspect, John Clauser and Anton Zeilinger won the 2022 Nobel Prize in Physics for them.
Mix-up: you cannot send messages faster than light with it. Each side alone just sees random results.
Tunnelling
A particle can get through a barrier it does not have the energy to climb. It is essential for fusion in the Sun and is used in scanning tunnelling microscopes and flash memory.
Mix-up: it is not people walking through walls. The chance drops extremely fast with thickness and mass.
Decoherence
Interactions with the surroundings quickly wipe out the interference of big objects, which is why everyday things behave classically. It is a leading explanation of why we never see a cat in superposition.
Quantum Darwinism, the idea that the environment stores many copies of the information, is an active research proposal rather than settled fact.
Measurement is not about minds
In physics, a measurement is an interaction that leaves a record. It does not need a conscious observer.
Mix-up: "the observer creates reality" is a popular claim, not what the physics says.
Quantum computers
They use qubits and can, in theory, solve some problems (like factoring large numbers with Shor's algorithm) much faster than ordinary computers. Today's machines are small and noisy.
Mix-up: they do not try every answer at once and then pick the right one.