Problem

Interference requires that light waves maintain a constant phase relationship — the crests and troughs must stay locked together. Ordinary flashlights emit light from many independent atoms, each producing random bursts of waves with no fixed phase connection to the others. This incoherent light changes its relative phase faster than your eye can follow, so any interference pattern flickers in and out of existence. You'd need coherent sources — like a laser or light split from a single source — where the phase relationship stays stable long enough to create a visible, stationary pattern.

Interference requires that light waves maintain a constant phase relationship — the crests and troughs must stay locked together. Ordinary flashlights emit light from many independent atoms, each producing random bursts of waves with no fixed phase connection to the others. This incoherent light changes its relative phase faster than your eye can follow, so any interference pattern flickers in and out of existence. You'd need coherent sources — like a laser or light split from a single source — where the phase relationship stays stable long enough to create a visible, stationary pattern.