Physics › Quantum
Quantum mechanics
At the smallest scale, particles behave like waves and probability replaces certainty. The strangest, best-tested physics we have.
Double-slit experiment
Look at the slit and the wave collapses to particles.
Unobserved: interference fringes (bright + dark bands). Observed: two bright bumps — particles, not waves.
Wave–particle duality
Fire single electrons one at a time at a barrier with two slits. Don't watch which slit each one goes through — you get an interference pattern, like a wave going through both. Watch which slit it picks — the pattern collapses to two bumps, like little bullets.
Heisenberg's uncertainty
Δx · Δp ≥ ℏ/2.Probability, not paths
A quantum particle doesn't have a definite trajectory — it has a wavefunction ψ that gives the probability of finding it at each location. Squaring the wavefunction gives the chance.
Quantised energy
An electron in an atom can only have certain energies — not anything in between. It jumps levels by absorbing or emitting a photon of just the right colour. That's why hot gases produce sharp emission lines.
Why you don't notice
A baseball is a quantum object too — but its wavelength is unimaginably small (about 10⁻³⁴ m). The wave nature only becomes visible at the scale of atoms and electrons.