speed of light

Genesis

This might be a bit off-topic, but... Is light a particle or a wave?

mormonator_rm

If you leave light alone it acts very clearly as a wave, as in diffraction and interference experiments. But as soon as you do something to detect or deflect it, it makes a decided choice on its quantum state, and acts like a particle. This is clearly demonstrated in diffraction experiments where the photons passing through a grating trigger a detector; resulting in the total breakdown of the diffraction pattern (as if it were no longer a wave).

Adrian Baker

Your example is a good one, but the wording quoted above is a little imprecise. For example, the Photoelectric effect can ONLY be explained by considering light as a particle. It does not need to be 'left alone' to do this.
It is perhaps best to say that light can ACT like a particle, or like a wave but is neither.

Benzun_1999 - if this leaves you asking, "How is it possible to visualise this?" then join the queue with the rest of us.......

mormonator_rm

"Detected or deflected". If a photon is deflected, then it is clearly NOT left alone (though the experimenter has done nothing directly, an interaction has). "Deflected" includes the Photoelectric effect. If a photon strikes something, such as an electron on the surface of a metal, then it is forced to chose a quantum state, and hence act as a particle. Until it strikes the object, though, it is still in wonderful wavefunction limbo-land.