Light made of particles?

Question

does the photoelectric effect prove that light is made of particles? do inference experiments prove that light is composed of waves?(is there a distinction between what something is and how it behaves)

Answer 1

Light is (and behaves) both as a wave and a particle.

Evidence which supports the notion of light as a wave is, of course, diffraction.
Light waves carry energy in the form of a self-propagating electromagnetic wave.

Evidence for light’s particle nature is the photoelectric effect (amongst other things, like Compton scattering).
The energy of light is said to be ‘quantized’, meaning that the energy exists in discrete packets called photons, not as a continuous wave.

The two natures are not mutually exclusive. Light is not either a wave or a particle, light is a wave and a particle. Depending on how one observes it determines its nature, but one cannot detect both nature’s at the same time.
The fact that light will diffract does not nullify the experimentally known phenomenon which support light’s particle nature.

Actually, even things we would ordinarily consider as only being a particle can have a duel nature too.
Electrons, for instance, have an associated wavelength (de Broglie wavelength) with them due to their momentum. λ = h / p, where p is the momentum and h is Planck’s constant (6.63 E-34 J s). Electrons have such a little mass that their wavelengths become measurable. Although it is true for more massive things too, things like baseball’s have far too large of a momentum (even traveling at slow speeds) to have a measurable momentum, so we do not observe ‘baseball-diffraction’.

Answer 2

No, no, and yes. In that order.

Light is neither a particle *nor* a wave, but it has some of the characteristics of each.


Doug

Answer 3

From http://www.adras.com/Plastic-Light.t9163-90-5.html

As I understand it, however, light can be demonstrated to have
momentum using a rather simple device: an evacuated bulb with
four vanes, each painted black on one side, white on the other,
and pivoted. (The evacuation must be very good otherwise the
hot side -- black -- will negate the desired effect, causing the
device to spin the other way.)

http://www.pa.msu.edu/courses/2000spring/PHY232/lectures/quantum/photons.html

Answer 4

light is radiation and is the out universal speed limit
http://en.wikipedia.org/wiki/Light