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I have a little bit of confusion: From my understanding (which could be totally wrong), photons are the same as electromagnetic waves but are called photons because their frequency is in the realm of what we can see.

Seems too simplistic. Can anyone enlighten me?


marked as duplicate by John Rennie, enumaris, Qmechanic Dec 3 '18 at 19:33

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It's probably most correct to add a layer of indirection. EM waves and photons both model the same thing. They just model it differently. This thing is what we informally call "light."

The different models are better at handling different sorts of situations where "light" behaves one way or another. Photons are effective at modeling what happens when light behaves in discrete ways, such as when it interacts with PV cells. Electromagnetic waves are effective at modeling light when it is behaving in continuous ways, such as diffracting through a small hole.

It's also worth noting that there's also more than one model which uses photons. "Classical" photons are wonderful little creatures which fly around like little billiard balls and have all the nice properties that makes classical mechanics fun. Quantum mechanics provides a more nuanced concept of the photon. In many cases they are compatible, but when you look at particularly funny experiments, such as the single-photon double-slit experiment, the classical model fails to describe what we really see, while the quantum model does a much better job of predicting the results.

  • $\begingroup$ ok, I think I get it: different models applied to the same phenomenon depending on the context at hand? $\endgroup$ – Thomas Dec 3 '18 at 19:17
  • $\begingroup$ @Thomas Bingo. The only thing that makes it hard is that we have a tendency to sell some of these models (such as EM waves) as "this is how it really works." It's then terribly hard to backpeddel and admit that really what we had was just a model, and the model stops working well when you push it into some corner cases. $\endgroup$ – Cort Ammon Dec 3 '18 at 19:20

are photons and electromagnetic waves the same thing?

Photons are quantum mechanical entities, a particle in the standard model of particle physics. Light is perfectly modeled as an electromagnetic wave with classical Maxwell equations , so they are not the same. They are related similar to the way bricks are related to a building.

Photons are spin one zero mass particles , described by a wavefunction from a quantized form of Maxwell's equations. The quantum mechanical superposition of the wavefunctions of zillions of photons builds up the total wavefunction of a light beam, and the connection with the values measure macroscpically and fitted with the classical Maxwell's equation comes through the probability distribution for the ensemble of photons. A quantum field theoretical analysis can be seen here.

Because of the same equation giving classical and quantum descriptions the frequency found in $E=hν$ of the photons is the same as the frequency $ν$ of the classical electromagnetic wave.

The visible is a very small part of the frequencies in the electromagnetic spectrum. All the light spectrum is described by the superposition of photons with a given frequency.


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