The concept of interference is strong evidence for the wave nature of light, because interference is a behavior that only waves exhibit.
When two or more light waves meet at the same point, they combine through interference. Depending on how their peaks and troughs align, they can either:
- Add up (constructive interference), making a brighter light, or
- Cancel out (destructive interference), resulting in darkness.
This can only happen if light behaves like a wave, with crests and troughs that can overlap and combine.
One of the most famous demonstrations is the Young’s double-slit experiment:
- When light passes through two narrow slits, the emerging waves spread out and overlap.
- On a screen behind the slits, alternating bright and dark fringes appear.
- These fringes result from constructive and destructive interference of the light waves from the two slits.
If light were purely a particle, we would expect just two bright spots from the slits, not a pattern of fringes. Therefore, interference patterns confirm that light behaves like a wave, supporting the wave theory of light.