Ok, so electrons can only be at set energy levels and there’s no way to get them to say, energy level 1 and a half. But what about light? Are photons restricted in this manner as well? Are there only (a very large amount of) limited wavelengths that lightwaves can assume? Are there a finite number of colours to the visible spectrum?
Photon energy is only quantized when it’s bouncing around inside a resonance cavity (i.e. standing wave). If a photon is just flying along freely, its wavelength is not quantized.
When we say light is quantized, we mean a light beam is made up of multiple photons. That’s all. There’s no restriction on the energy of each photon.
Light isn’t quantised in that manner. It forms a continuous spectrum.
Electrons are quantised because they need to exist at a wavelength that allows for a whole number of peaks and troughs each ‘orbit’. If you imagine an electron moving around a nucleus it can’t do so if the ‘orbit’ consists of, say, 3.5 wavelengths. That would cause the waveform to cancel itself out. So if the electron can’t maintain level 4 it has to drop all the way back down to 3 and emit the extra energy.
Photons don’t have any such restriction of course. They can never cancel themselves out because by definition they travel in straight lines. They can exist at any energy level at all.
Free electrons aren’t quantized, either. An electron not in an orbit can have any value at all.
Photons can’t be trapped in orbits by nuclei like electrons can (unaffected directly by gravity or other forces), but you can make an analogy to a laser resonator, in which only photons of certain discrete wavelengths can exist in the laser cavity, just as only electrons of a certain energy/wavelength can exist in stable orbits. But outside of that resonator photons can have any energy/wavelength, just like free electrons.
Free Electron Lasers are used, by the way, to generate light of any needed wavelength. The electrons are “trapped” by magnetic fields, which can be varied to propvide electron energy levels at the desired energies.
SCR, I know you’re the best source for me to ask: I thought (a) photons don’t really exist; it is a simple way to explain the particle-like behavior of light. Or, (b) if you say they do exist, aren’t they in fact produced by excited electrons jumping orbitals (or shells)? Also, when you speak of a “photon just flying along freely”, isn’t it quantized in the sense that you cannot have half a photon? Or, do I have too rudimentary a definition of the meaning behind “quantized”?
You’ve always been right on the money before, so I am not arguing - just trying to gain a better understanding of my misconceptions here…
Thanks, - Jinx
Well, if loop quantum gravity is right(PDF), everything is quantized. Of course, there’s doubt on that(PDF).
Jinx, let me take a shot:
You’re right, photons are quantized, in that you can’t have half of a photon. And the wavelength of the light determines the energy of the photon. So at a given wavelength, you can only emit specific amounts of energy (multiples of the energy of one photon).
However, any wavelength of light is possible; the wavelengths are not quantized in general. With the right kind of tunable apparatus, you could emit whatever wavelength of light you want.
There are many situations where either the wavelength is fixed by the physical arrangement (resonator in a laser) or the energy is fixed (electron changing between two specific orbits), but this is only because of the particular physical arrangement; a different arrangement could have any other wavelength.
As for whether photons ‘exist’, there’s no real answer in physics. Electromagnetic radiation is indeed quantized, so in that sense, yes they exist. But these quantized bursts of radiation do not act like an idealized simple point particle, so in that sense maybe photons don’t really exist.
And maybe nothing really ‘exists’, but that’s for philosophers to argue about, not physicists.