# How do photons travel and what does the frequency of a photon mean?

I am pretty much confused about all this. I have researched a lot about this and many sites say that photons are particles, but this guy CuriousOne here doesn't even regard photons as particles and says that they do not travel. Is he correct? And what does frequency mean in E=mv? Is it the frequency of the photon? And how does it have a frequency when it does not oscillate?

Edit- I have one another question. Wave is a disturbance in particles. But in case of light in what particles is the disturbance caused?

And please keep it simple because I am just 10th grader.

Lets start with main stream physics. Photons are elementary particles in the standard model of particle physics and have to follow the rules of special relativity and quantum mechanics.

Elementary particles in the table are point particles, and have the masses and quantum numbers given in the table in the link. The photon has mass zero, spin + or -1 projected on its direction of motion and carries energy and momentum according to the special relativity rules, they are described by four vectors:

The energy momentum four vector has a "length" :

The length of this 4-vector is the rest energy of the particle. The invariance is associated with the fact that the rest mass is the same in any inertial frame of reference.

As the photon has zero mass, and it is always traveling with velocity $$c$$ ,it only has energy and momentum, which have to be conserved. Quantum mechanical studies have determined that the energy of the photon is equal to $$h.ν$$ where $$ν$$ is the frequency of a possible classical light beam made up of zillions of photons. This $$ν$$ is not seen as a waving photon, because the photon is a point particle.

BUT a photon is also a quantum mechanical entity, and the probability of finding a photon at an (x,y,z,t) point is given by a complex number wavefunction ( a solution of a wave equation) which is related to the classical wave that can be built up by a superposition of such photons.

It is the probability of detecting a photon that "waves" i.e. displays interference patterns.

Here is an experiment with single photons at a time

. Single-photon camera recording of photons from a double slit illuminated by very weak laser light. Left to right: single frame, superposition of 200, 1’000, and 500’000 frames.

when there are only few photons they look random dots, when they become thousands the classical interference pattern of light appears for the frequency $$ν$$ of the laser used in the experiment.

The mathematics of both the quantum for photons and the classical for light depend on the Maxwell equations in different ways, and the classical is a superposition of the quantum states so as to give a unified beautiful whole explanation which needs mathematics to be understood.

Wave is a disturbance in particles. But in case of light in what particles is the disturbance caused?

Wave is a solution of wave equations, and classical electromagnetic waves are described very well by Maxwell's wave equations without the need of a medium. When the underlying quantum nature of photons was discovered, one can show mathematically that classical electromagnetic waves emerge from the underlying quantum level, but the proof needs studies in mathematical physics.

The thread you are referring to is ultimately playing with terminology, and I strongly suspect the poster in question doesn't really understand that. Here is the key part of the exchange:

Photons don't travel at all. They are states of a quantum field and there is a certain probability to detect one of these states in a spacetime volume element. What "travels" is the wave (function) of the quantum field.

What (s)he's saying is that there is no object "in there" that moves from A to B. That is perfectly correct.

In our classical view when you see a pool ball move along a table you think of that thing as "really being there" from A to B. But at the quantum level that is no longer true, many things can happen between A and B and the "reality" of the pool ball is fuzzy indeed. But that is beyond the level of the question.

And where they go wrong is right here:

What "travels" is the wave (function) of the quantum field.

The definition of photon is "wave function of the quantum field". That is very important.

So they are saying photons don't actually travel, what's really happening is that photons travel.

The poster is guilty of precisely the problem they are accusing the other readers of. They are saying "there is no photon in there, you don't understand what is really going on" and failing to realize that the very term they are using actually refers to what they are saying is really going on.

'Tis a bit amusing.