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In my teacher's class notes, came across this definition of light today:

Light is an excitation of the electromagnetic field, with photons being the lowest energy excitation.

And the way in which it is phrased makes me think that more particles can be seen as excitations of the electromagnetic field, although I really don't know which, and the information I find about the different particles that constitute the standard model is kind of confusing.

Exactly which particles are described as excitations of the electromagnetic field?

Qmechanic
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Rye
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3 Answers3

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It fits with the long discussion we had on this question :

What is the connection between quantum optical photons and particle physics' photons?

and the answers and comments therein.

People working with quantum optics have a more general view of the term "excitations of the electromagnetic field". In the quantum field theory used in the standard model of particle physics, QED for electromagnetism, there is a single excitation of the electromagnetic field, called the photon field , which is the photon in the table. It is a zero mass, point particle with spin +/-1 and energy=hnu, where nu is the frequency of the classical electromagnetic wave built up by photons of this energy.

Quantum optics physicists use a generalized quantum field theory, which coincides with the particle QED when in vacuum. Classical light in matter has quantum behavior that can be described by a field theory, and they call the excitation of the field they use, photons.

This is what the sentence you quote:

Light is an excitation of the electromagnetic field, with photons being the lowest energy excitation.

implies. I would say the professor is a quantum optics physicist.

anna v
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Photons are excitations of electromagnetic field. These are part of the phenomenon that we call "light", so the phrasing in the book is misleading.

Closer to the matter: all particles can be though of as excitations of some field. When the field is electromagnetic, they are called photons.

In other words, the statement should be Photons are the excitations of the electromagnetic field rather than Photons are excitations of the electromagnetic field (I hope my English does not betray me.)

Roger V.
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You may be confused by the phrasing of the statement: particles as excitations of a field. This peculiar way of saying it comes from quantum field theory. A 19th-century physicist --before quantum field theory was established-- would probably say "light is the electromagnetic field moving through the vacuum" or "away from sources". It's photons that are excitations of the electromagnetic field. Photons are the so-called quanta of the field. In the same way, electrons are excitations of Dirac's electron field, etc.

joigus
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