How are photons actually created?

Question

(Searched and although this has been asked before I still can’t find an answer that makes much sense to me)

So how does a photon come into existence, and how can it instantly be travelling at C? I turn on a light bulb and photons are instantly created and travelling at C…but created from what, exactly? The light bulb filament is in a vacuum, but every time I turn on the light bulb new photons are simply created out of nothing (with no “fuel” to draw from)?

I guess I’m struggling to understand how heating the filament results in billions (?) of photons in a constant stream travelling at C, when a millisecond earlier there was just an inert metal thread in a vacuum.

In: Physics

Answer 1

So if you’re familiar with the whole mass/energy equivalence thing (E=mc^2 etc) then you can start to see how energy can be converted to matter (setting aside that photons are massless; the principle still holds). Generally when you get photon emission, it is caused by some particle (say an electron) transitioning from a higher-energy state to a lower-energy state. That difference in energy must be liberated somehow, and photon emission is often the result. Conversely, absorption of photons can promote particles up to higher energy states – this is the basic principle of the photoelectric effect.

In an incandescent light bulb, what you are actually seeing is a conversion from thermal energy to electromagnetic energy; so in some sense the vibrational energy of the particles in the filament is converted (in some fraction) to photons of a range of energies.