About quantization of light

Question

We all know that light is absorbed and emitted in discrete packets called quanta(or photons) not continuously. I am little bit confused that if it happens like that, then is it because the source is not oscillating continuously? OR even a continuously oscillating source is not capable of producing a continuous wave.

Answer 1

We all know that light is absorbed and emitted in discrete packets called quanta(or photons) not continuously.

Yes, one of the experimental reasons quantum mechanics had to be invented was the photoelectric effect.

I am little bit confused that if it happens like that, then is it because the source is not oscillating continuously? OR even a continuously oscillating source is not capable of producing a continuous wave.

Lets clear up, that although light is composed out of the superposition of the wavefunctions (quantum mechanical) of zillions of photons, photons are not light, in the same way that tarmac makes a road, but a road is not tarmac, and tarmac is not a road.

Once one found experimentally that the underlying nature is quantum mechanical one can no longer rely on the classical electrodynamics to describe photons. Quantum electrodynamics has to be used for the microcosm of atoms and particles, and photons are particles.

See this entry for how individual photons that just have energy and spin + or minus to their direction of motion build up a polarized beam.

So there are two ways of getting photons when seen at the micro level. By accelerating a charged particle, same as in classical electrodynamics, except that they come out in quanta, but could have any energy, so can give a continuous spectrum all together and be seen as light. And by atomic and molecular transitions of electrons in atoms, which give up photons as seen in the spectra of atoms, another reason quantum mechanics was invented. When there are many atoms and molecules these blend into light, as we see in incandescent lamps.

So it is not oscillating sources at the quantum level, of the simple type. The two mathematical description in the region of overlap can be shown to be consistent. The emmision of electromagnetic waves from an antenna can be understood both classically and quantum mechanically, it needs different mathematics. When discussing photons one needs quantum electrodynamics, of how the photons emitted by the imposed oscillation add up to the electromagnetic wave, one has to study quantum field theory.