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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...right?

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Actually as per physics text books, photons are its own antiparticle. Have a look here this ought to be a comment but I don't have the privilege to comment .. :( Regards, –  Vineet Menon Aug 17 '11 at 7:04

3 Answers 3

up vote 26 down vote accepted

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.

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There are uncharged Antineutrons –  Helder Velez Aug 17 '11 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. –  Peter Shor Aug 17 '11 at 11:06
Doesn't the need for antiparticles also come from the CPT symmetry? I guess maybe that's the same thing you're saying, but from a mathematician's point of view. –  Peter Shor Aug 17 '11 at 11:25
@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). –  Marek Aug 17 '11 at 20:02
More simply: Neutrons are made of quarks. An antineutron is made of antiquarks, which do have the opposite charge. –  Ben Crowell Aug 17 '11 at 20:26

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.org, part of the Particle Data Group's web site( ).

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It is my understanding that antiparticles are the opposites of each other such as electron positron pair -- which means the positron is an electron flipped 180 degrees on its axis --same angular velocity, same size but PHOTONS are not particles, they are electromagnetic waves which rotate 360 deg for every wavelength so in effect are "positive" 50% of time and "negative" 50% of the time as they move forward so each "photon" impulse is its own anti"impulse" half the time

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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. –  Kyle Kanos Feb 13 at 20:04
Your claim about spin is wrong. Whether the particle is matter or antimatter does not affect its spin "direction." Also, photons are particles - they're the particle equivalent of electromagnetic waves. And elementary particles are point particles, so there's no point in comparing sizes. –  HDE 226868 Feb 13 at 20:14
"photons are not particles"... Don't tell that to the Standard Model... –  Sean Apr 7 at 11:54

protected by Qmechanic Feb 13 at 22:39

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