[Joe L. Ogan (OP)]

Does light have substance.  The only subsstance that I know I know about is that it is composed of electrons.  I find it interesting that it responds to the pull of gravity.  Thanks for comments.  Joe L. Ogan

[chris]

Hi Joe

Light is an electromagnetic (em) wave; put simply, this means that it comprises a changing magnetic field which in turn produces a changing electrical field, which in turn produces a changing magnetic field again, and so on. The resulting wave propagates at what we call the speed of light.

Various experiments support regarding light as wave, including the elicitation of what are called "interference" patterns such as that exemplified by passing light through two narrow slits in, say, a piece of card. Behind the card, a pattern or light and dark regions appear, consistent with light waves interacting to cancel out (dark) or add together (making a bright spot).

But, in other situations, it is convenient to consider light to be a particle, or packet of light energy, dubbed a "photon". Einstein got the Nobel prize for his solution to the photoelectric effect showing that light of different wavelengths has correspondingly more or less energy; this can only be explained by considering light in a particle form with shorter wavelengths consisting of more energetic particles than others.

[evan_au]

Light itself is not made of electrons.

However, the electric and magnetic fields (that light is made of) will interact with charged particles like electrons, protons, mesons, etc.

• An electron in an atom can drop into an orbit which is closer to the nucleus; the extra energy is released in the form of light.
• Visible light of the right frequency can kick an electron into an orbit further from the nucleus, and the light energy is absorbed in this process.
• Protons are more massive, and are bound together by the strong nuclear force. It takes far more energy to make an impact on protons - this light needs to be in the Gamma-Ray range.

In the 1800s, some people thought of light as a wave like an ocean wave or earthquake wave, which needs some substance to pass through (eg water or rock, respectively); some people called this hypothetical material "the aether". However, the Michelson-Morley experiment showed that there was no such substance, and paved the way for the theory of relativity, which allows photons to propagate through a vacuum (see http://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment).

[Even before this experiment, the aether had some challenging problems: To allow waves to propagate at the speed of light, it had to be incredibly stiff, and yet the planets could orbit through it without obstruction.]