# Are Photons Real? New Study Challenges Assumptions

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• log0
In summary: He gave the definition of "real" he uses. Things that interact with other things are real. Photons do, so they are real.
log0
Recently I've stumbled across a preprint in which the author describes a photon is a wave packet and even suggests a transverse extent.

I find it strange, as my understanding so far has been that a photon (and the EM field as such) is a construct used to model certain observed interactions between particles of matter.

Yes, I am assuming matter to be real, as something that interacts with each other. While force fields are mathematical models of those interactions.

https://arxiv.org/ftp/arxiv/papers/1706/1706.04475.pdf

Why wouldn't light be real?

mattt and vanhees71
log0 said:
Yes, I am assuming matter to be real, as something that interacts with each other. While force fields are mathematical models of those interactions.

But matter also interact with the force fields (eg. Compton scattering).

vanhees71
Many fields are real, among them the electromagnetic one. For me "real" means it's an observable entity of Nature, and indeed electromagnetic fields are observable. E.g., light and thus literally all we see is just a manifestation of the electromagnetic field. Another manifestation are the forces on objects you observe due to the presence of electrostatically charged bodies or the force between a permanent magnet and the door of your fridge etc. etc. In fact according to the most precise theory ever, the Standard Model of particle physics, all matter is also the manifestation of various (quantum) fields, and since you can observe this matter also these fields are "real".

Are forces real? Or are they just a mathematical concept "invented" to model how we describe natural phenomena?

What does it mean to be real? That's the Philosophy Department, two doors down. How do we know anything is real? How do we know we're not just brains in vats?

This is not physics. In physics, "just a model" is all you get.

jtbell, russ_watters, Dale and 5 others
log0 said:
Recently I've stumbled across a preprint in which the author describes a photon is a wave packet and even suggests a transverse extent.

I find it strange, as my understanding so far has been that a photon (and the EM field as such) is a construct used to model certain observed interactions between particles of matter.

Yes, I am assuming matter to be real, as something that interacts with each other. While force fields are mathematical models of those interactions.

https://arxiv.org/ftp/arxiv/papers/1706/1706.04475.pdf
That paper looks very iffy.

What does it mean to be real? That's the Philosophy Department, two doors down. How do we know anything is real? How do we know we're not just brains in vats?

This is not physics. In physics, "just a model" is all you get.
Physics is an empirical science, and "real" in the sense of the natural sciences is what can be reproducibly and objectively observed. Models and theories are the way to organize the empirically found knowledge in an efficient way.

russ_watters and phinds
He gave the definition of "real" he uses. Things that interact with other things are real. Photons do, so they are real.

russ_watters and mattt
I don't think he did - he would seem to exclude a magnetic field as real. But in any event, this is not physics. It's just not something physics concerns itself with. Is a Lagrangian real? Are image charges real? Wavefunctions? This is a fast way to get tied up in knots. Unproductive knots.

phinds
I don't think he did - he would seem to exclude a magnetic field as real.
He would but he shouldn't. It is real.
But in any event, this is not physics.
No, it is not. But that doesn't mean in it doesn't matter for physics. Mathematics is not physics but is usually not dismissed.
It's just not something physics concerns itself with. Is a Lagrangian real? Are image charges real? Wavefunctions? This is a fast way to get tied up in knots. Unproductive knots.
These are not real. They are mathematical objects (dont know what the image charges are).

martinbn said:
He gave the definition of "real" he uses. Things that interact with other things are real. Photons do, so they are real.
What if the object with which they interact is not "real"? This is a fundamentally circular definition whose utility eludes me. I guess it proves self -consistency which I think was the extent of @vanhees71 argument

malawi_glenn
hutchphd said:
What if the object with which they interact is not "real"? This is a fundamentally circular definition whose utility eludes me. I guess it proves self -consistency which I think was the extent of @vanhees71 argument
By this definition it cannot be not real. If it interacts it is real. It is symmetric not circular.

martinbn said:
By this definition it cannot be not real. If it interacts it is real. It is symmetric not circular.
This is foundationalism instead of coherentism..... but remember
What does it mean to be real? That's the Philosophy Department, two doors down. How do we know anything is real? How do we know we're not just brains in vats?

This is not physics. In physics, "just a model" is all you get.
.

DrClaude said:
That paper looks very iffy.
When a not so old paper uses ##h## rather than ##\hbar##, it's usually wrong.

vanhees71, malawi_glenn, DrClaude and 1 other person
Don't forget M. Williams, The Velveteen Rabbit.

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