(I am going to assume you have studied physics while answering this question)

This is a crucial distinction. Traditional wavefunction collapse implies a physical reduction of the quantum state to a single outcome upon measurement, but this interpretation has long faced philosophical and theoretical challenges. Decoherence, on the other hand, provides a more elegant mechanism, showing how quantum superpositions become unobservable due to entanglement with the environment.

In the double-slit experiment, the electron’s superposition includes all paths through the slits. As the electron interacts with the experimental apparatus or external environment, its quantum state entangles with these degrees of freedom. This entanglement effectively transfers the phase information (responsible for interference) to the environment. When you trace out these environmental variables, the reduced density matrix of the electron no longer shows coherence between the paths. This loss of coherence explains the absence of interference without invoking a physical collapse.

The critical insight is that the superposition doesn’t vanish, it becomes encoded in correlations with the environment, inaccessible to direct observation. Decoherence reframes what we call “collapse” as the emergence of classicality, grounded in the inaccessibility of the full quantum state to local measurements. It reveals that the quantum world isn’t replaced by classical reality but rather reshaped in how it manifests to us.