Problem
Electrons are sent one at a time through a double slit. On the screen, a single dot appears for each electron. Letting millions of electrons pass, an interference pattern emerges. Explain.
Solution
The dot: corpuscular aspect. Each electron is detected as a localised event, a single dot on the screen. At this instant it behaves like a particle: it arrives “all at one point”, not spread out.
The pattern: wave aspect. A single dot seems to land at a random position. But the position is not entirely free: the probability of arriving at a given point is governed by the amplitude of the de Broglie wave, which passes through both slits and interferes with itself. Where the interference is constructive the probability is high; where it is destructive it is zero.
Summary. Accumulating millions of electrons, the distribution of dots reconstructs the squared modulus of the wave, i.e. the interference fringes. The crucial point: the pattern appears even when sending one electron at a time, so each electron interferes with itself — it is not a collective effect of electrons colliding with each other.
Moral (complementarity). The electron is neither “wave” nor “particle”: it is a quantum object that shows a corpuscular aspect in detection (the dot) and a wave aspect in propagation and in the statistics of arrivals (the fringes). The wave function describes probabilities; measurement gives a point-like outcome.
Collegamenti
Argomenti: Quantum physics Concetti: Wave-particle duality · Interference