# Do anti-photons exist?

I know what anti-matter is and how when it collides with matter both are annihilated. However, what about anti-photons? Are there such things as anti-photons?

I initially thought the idea preposterous. However I am curious because, if anti-photons don't exist, then anti-matter could theoretically transfer its energy to normal matter - through the mechanism of light. Is it right?

• I thought only fermions need to have anti-particles, not bosons. Bosons are different from fermions and, for example, do not obey Pauli’s exclusion principle.
– user
Commented Aug 21 at 11:03

Well, they do and don't. Depends on your point of view. Here's the story.

Quantum field theory requires for consistency reasons that every charged particle has its antiparticle. It also tells you what properties will the anti-particle have: it will have the same characteristic from the point of view of space-time (i.e. Poincaré group) which means equal mass and spin. And it will have all charges of opposite sign than a matter particle.

If the particle is not charged then QFT doesn't impose any other constraint and so you don't need antiparticles for photons (since they are not charged). But you can still consider the same operation of keeping mass and spin and swapping charges and since this does nothing to photon, you can decide to identify it with an antiphoton. Your call.

• There are uncharged Antineutrons Commented Aug 17, 2011 at 10:21
• I would say that QFT requires that every particle has an antiparticle, but that some uncharged particles (like photons) can be their own antiparticles. Commented Aug 17, 2011 at 11:06
• @Helder: Antineutrons have baryon charge -1 (corresponding to a $U(1)$ baryon symmetry). One should understand charges here more generally than just electrical ones. After all, properties of arbitrary QFT (such as Yang-Mills SU(N)) surely can't depend on electromagnetism but will depend on the corresponding charges of the theory (for Y-M the color charges). Commented Aug 17, 2011 at 20:02
• More simply: Neutrons are made of quarks. An antineutron is made of antiquarks, which do have the opposite charge.
– user4552
Commented Aug 17, 2011 at 20:26
• @Michael: photons do annihilate themselves. Reactions like $\gamma + \gamma \to e^+ + e^-$ exists. Now it's true that you won't find a single vertex with 2 photons because a process involving a photon must be related to a flux (current in QFT jargon) of electric charges. With 2 (neutral) photons, such flux is impossible. Commented Jan 18, 2015 at 17:46

The short answer to "are there anti-photons" is "yes", but the disappointment here is that anti-photons and photons are the same particles. Some particles are their own antiparticles, notably the force carriers like photons, the Z boson, and gluons, which mediate the electromagnetic force, the weak nuclear force, and the strong force, respectively. Particles that are their own antiparticles must be electrically neutral, because an aniparticle has the opposite electrical charge as its partner particle. Other things must also be zero, like the number of quarks. A neutron cannot be its own antiparticle because it is made up of quarks and an antineutron is made up of antiquarks. A $\pi_0$ is made up of a quark and an antiquark and is in fact its own antiparticle also.

You can find lots out about particles at the particle adventure(http://particleadventure.orghttp://pdg.lbl.gov), part of the Particle Data Group's web site( ).

• what about the force carrier W bosons, they are not neutral. So the one (W-) is antiparticle of other (W+) ? Commented Sep 13, 2019 at 16:59
• This is by far the best of the three answers. It’s too bad Dale picked the other confusing answer. Commented Jul 28, 2021 at 17:02

Photons are simply their own antiparticles, but aren't called antphotons.

A subatomic particle that is its own antiparticle is called a "Truly neutral particle". It remains itself under the charge conjugation. All charges: electric, magnetic, color, flavor etc, must be zero.

Positronium, the bound state of an electron and a positron (e−, e+) is also truly neutral, so two photons colliding (two photon physics) can produce a positron and an electron. Or other composite particles that are truly neutral, like a proton antiproton, which requires a lot of energy. (I believe particle accelerators can't provide, but it happens in cosmic rays.)

Remember though that photons do not really collide (at least this is extremely rare). Pair production is a little more complicated than that and happens near a nucleus.

Although the photons behave almost as if real, they are technically virtual.

Physics question from University Illinois. Is that anti-photons and photons are the same particles. Some particles are their own antiparticles, notably the force carriers like photons, the Z boson, and gluons. As they have electrically neutral charge. Where as other characteristics like spin and such...

• I don't see anything right here. An antiparticle is a particle with the same mass, but different charge as a particle (hence the $e^-$ and $e^+$). Photons also don't have a charge (they're neutral), so it can't be charged as you suggest. Commented Feb 13, 2015 at 20:04