Is Light a Wave or a Particle?
Light travels and spreads like a wave, but it is always detected in whole packets called photons. In 1905 Albert Einstein used Planck's packets, E = h × f, to explain the photoelectric effect: one photon knocks out one electron, and only if that photon carries enough energy. Brighter light means more photons, not bigger ones.
Why does this old argument matter for quantum computers?
Some quantum computers use single packets of light as their qubits. Every quantum computer uses light or microwaves to control its qubits and read them out. So we need to know what light really is.
For more than 200 years, scientists argued about it. Is light a stream of tiny bullets, or a wave like ripples on a pond? The honest answer surprised everyone. This chapter shows the two experiments that set up the puzzle.
- What made scientists sure that light is a wave?
- What is the photoelectric effect, and why did it break the wave idea?
- Worked example: which colors can free an electron?
- Who proved Einstein right?
- Run it: one photon meets a half-silvered mirrorINTERACTIVE
- Try this: a mirror that reflects only a quarterINTERACTIVE
- Try this: two photons, two mirrorsINTERACTIVE
- So which is it, a wave or a particle?
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