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So it is said that particles are excitations of fields. We are given examples like photons for electromagnetic field, gravitons for gravity, etc. We are also told that normal matter is an excitation. However the former are all virtual particles that can never be detected. So how are particles like protons that can be detected on the same footing?

Qmechanic
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user43470
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You are confused because of the difference between static EM fields and EM radiation.

An electromagnetic field (also EM field) is a classical (i.e. non-quantum) field produced by moving electric charges.[1] It is the field described by classical electrodynamics and is the classical counterpart to the quantized electromagnetic field tensor in quantum electrodynamics.

https://en.wikipedia.org/wiki/Electromagnetic_field

Now in your example, the magnets' static EM fields are what are represented by these virtual photons. These virtual photons are not real, they are just a mathematical description of a phenomenon called the static EM field. In reality we do not really know how these static fields affect each other (or other particles), we just see that they do in experiments. We describe this with virtual particles.

In physics, electromagnetic radiation (EM radiation or EMR) refers to the waves (or their quanta, photons) of the electromagnetic field, propagating (radiating) through space, carrying electromagnetic radiant energy.[1] It includes radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays.[2]

https://en.wikipedia.org/wiki/Electromagnetic_radiation

Now EM waves are what are made up (QFT) of real photons, the very quanta of light. These photons can be detected in experiments.

Árpád Szendrei
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