# Please explain "Electromagnetic force is mediated by light"

#### Burken

We have talked about light behaving as a wave and a particle. Having trouble understanding what 'mediated' means in this context.

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#### Wrichik Basu

Gold Member
2018 Award
As you know, light is quantized by photons. Photons also quantise all electromagnetic force in this universe. That's why your book said that EM force is mediated by light.

But it is always better to say that EM force is mediated by photons instead of light.

#### sophiecentaur

Gold Member
It's a good idea to consider the History of this. The first work on EM was all to do with static Magnetism and Electricity and was based around the Forces. The classical approach provides a perfectly good 'explanation' of the Energy transfer and the Force exerted by light on objects. Light pressure is a calculable force, using classical EM theory without any mention of Photons. (This was part of my EM course at University in the 60's and all EM theory text books discuss it.)

From a different direction, Photons were identified as having properties of Energy and Momentum.

The two ideas had to be brought together and the chosen word that was used for this was "mediated". This was a clever move, imo, to try to discourage people from assuming that a stream of 'little bullets' would travel between two charged objects when they get close. The photons which are involved in the common / everyday mechanical interactions between charged particles are very low Energy. The wavelength that you could assign to these photons would be vastly more than the distance between the two objects. I think this would apply for any separation. So the new word (mediation) was introduced and it also fits in nicely in descriptions of Gravity and the other Nuclear Forces.

Staff Emeritus
Can we please stop trying to guess what the OP means?

@Burken, can you please tell us where you say this?

#### sophiecentaur

Gold Member
Can we please stop trying to guess what the OP means?

@Burken, can you please tell us where you say this?
He does specifically ask for the meaning of "mediated" in this context. I didn't need to "guess' that.
Edit - I assumed his use of the word "We" referred to general discussion and we can't totally disagree with that can we?

#### Burken

I appreciate the responses to my question. The first two responses have been very helpful!
The phrase was part of a summation in a high school physics book about Maxwell's equations that unified the electric and magnetic forces. This is the phrase directly from the book: "It is now understood that those equations tell us that the electromagnetic force is actually mediated by light and that light is an electromagnetic wave". I do not understand the term "mediated" in this context. I am searching for a different word or phrase that would be more descriptive and provide a better understanding... Maybe a different way of stating it that can be understood by an average high school student. Thanks!

Staff Emeritus
So "light" in this context is not correct, and "electromagnetic wave" is only slightly less incorrect.

Perhaps the least wrong way to explain this is that if you want a consistent theory of electric attraction/repulsion between particles, that theory most also include a) magnetism and b) light. The same electromagnetic interaction responsible for (i.e. "mediating") the force between charged particles logically requires light (electromagnetic radiation) as a mathematical consequence.

#### cosmik debris

"It is now understood that those equations tell us that the electromagnetic force is actually mediated by light and that light is an electromagnetic wave". I do not understand the term "mediated" in this context.
Mediated just means "in the middle" i.e. carries or transports the force between charges.

Cheers

#### Burken

I learned more than I intended to learn about this topic. The response from the last poster provided what I was initially searching for. Thank you all for your assistance!

#### Philip Koeck

This is actually something I've been wondering about since my time at university. We were told that "virtual photons" are responsible for all electric and magnetic forces. I understand that photons are the energy parcels of all electromagnetic radiation and I don't think two charged objects send such radiation back and forth between them in order to attract each other. Is there some truth in this concept of virtual photons and, if so, is there some easy way of understanding what they actually are and how they differ from real photons?

#### cosmik debris

This is actually something I've been wondering about since my time at university. We were told that "virtual photons" are responsible for all electric and magnetic forces. I understand that photons are the energy parcels of all electromagnetic radiation and I don't think two charged objects send such radiation back and forth between them in order to attract each other. Is there some truth in this concept of virtual photons and, if so, is there some easy way of understanding what they actually are and how they differ from real photons?
There are plenty of explanations of virtual photons on this site, Arnold's FAQ has some good stuff.

https://www.mat.univie.ac.at/~neum/physfaq/physics-faq.html

Cheers

"Please explain "Electromagnetic force is mediated by light""

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