LET THERE BE LIGHT

Expanding our understanding of LIGHT (it has so many properties)

• We see with it.
• It is self-perpetuating and propagates through empty space.
• By its presence, it fills space so it is not really empty.
• It is itself the stuff that causes electric and magnetic fields, and is the fundamental cause of forces among charged particles.
• It is made up of particles (photons) that have a specific position, velocity, direction, spin, energy, momentum, angular momentum (but no mass).
• These particles possess an intrinsic periodicity with a frequency and a wavelength.
• They also possess coherent group properties, and all tend to do the same thing at the same time (in contrast to electrons, where no two do the same thing at the same time).

RELATIVITY

• The fact that photons move with a finite speed distorts our perceptions.
• Visual perceptions (& electromagnetic forces) depend on our relative distances from, and our motion relative to, the objects that we see with this light.
• Thus we tend to underestimate distances and overestimate times and masses.
• Since electric fields are a game-of-catch between charged particles, moving charges cause photons to emanate from a place where the charge now isn't, which give rise to the magnetic field.

LIGHT FROM SOLIDS vs LIGHT FROM GASES

• Light from a heated solid comes in a continuous distribution of colors indicating only the temperature and not the composition.
• Light from a heated gas contains only certain colors, indicative of the elemental constituency.