# Are photons imaginary particles?

Since an electron generated a negative charge around itself and can push other electrons around itself, waves can travel through electrons. These are electromagnetic waves. But quantum theory proposes that the pushes between electrons happen in discrete packets. Electromagnetic packets called photons. Are photons imaginary particles then?

bhobba
Mentor
Since an electron generated a negative charge around itself and can push other electrons around itself, waves can travel through electrons. These are electromagnetic waves. But quantum theory proposes that the pushes between electrons happen in discrete packets. Electromagnetic packets called photons. Are photons imaginary particles then?

That's not what QM says at all.

And photons are very real.

But what they are is explained by Quantum Field Theory.

At your level here is the book to get:
https://www.amazon.com/dp/0473179768/?tag=pfamazon01-20&tag=pfamazon01-20

Once you have digested that post here with any questions and/or recommendations for further reading.

Thanks
Bill

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Right, so they wouldn't be able to travel through a vacuum then. So they behave as a wave when they're passed between electrons and as rays otherwise? How big an electron cloud do you need to absorb a photon? Is it a cloud colliding with a cloud?

Thank you.

jfizzix
Gold Member
Since an electron generated a negative charge around itself and can push other electrons around itself, waves can travel through electrons. These are electromagnetic waves. But quantum theory proposes that the pushes between electrons happen in discrete packets. Electromagnetic packets called photons. Are photons imaginary particles then?

Quantum theory is a tool that we use to very accurately predict what we are and are not likely to measure. To that end, we need "photons", and "electrons" to accurately predict measurement results of optical experiments.

As far as the difference between photons and electromagnetic waves go:

Photons are what we use to describe electromagnetic waves at the quantum level.

To quantum mechanically describe an electromagnetic wave, we break up a wave as a sum of many basis waves, one for each frequency. The energy in each basis is some integer number (of $\hbar \omega$ up to a constant zero point) just as a consequence of solving Schrodinger's equation for the electromagnetic field.

We can use quantum optics (the quantum mechanics of light coming from these equations) to predict optical interactions at the atomic level. And an accurate description of these phenomena seems to require "photons", "electrons", and "atoms" for the time being.

In short, photons are no more or less real than electrons, as far as theory goes.

Experimentally, what counts as a single photon is a bit murky, but we can generate and detect single photons, which is good enough for me.

bhobba
Mentor
Right, so they wouldn't be able to travel through a vacuum then. So they behave as a wave when they're passed between electrons and as rays otherwise? How big an electron cloud do you need to absorb a photon? Is it a cloud colliding with a cloud?

What photons are is excitations in the quantum EM field. A field is something that resides in space rather than travels through space. They are not waves nor are they particles - they are quantum stuff - without detailing exactly what that is.

Thanks
Bill

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vanhees71