The Antiphoton

[Kyrisch]

Is there any evidence for the existence of an antiphoton? Or an antimatter version of any of the other force-carrier particles?

[Mr Skeptic]

Yes, a photon is its own antiphoton.

[Kyrisch]

Could you elaborate?

[Mr Skeptic]

A photon is an electromagnetic wave. Like sound and water waves, or any other wave, if you overlap two copies of the wave that are half a wavelength apart (so the troughs of one are aligned with the crests of the other), then the waves will cancel. This is called interference.

[Kyrisch]

Ah, that does make sense. However, they will not annihilate, per se. I have taken High School physics and I understand wave mechanics. Nothing can perturb a wave except perturbations in its medium; interference and subsequent superposition with other waves only affects them at the instant they are superimposed. So if you blast two speakers some distance d apart, an audible interference pattern will emerge with silent spots and loud spots. The wave doesn't vanish, though.

[timo]

A photon is an electromagnetic wave. Like sound and water waves, or any other wave, if you overlap two copies of the wave that are half a wavelength apart (so the troughs of one are aligned with the crests of the other), then the waves will cancel. This is called interference.

Shouldn't that argument work for electrons, too? Particularly in the sense of the conclusion that electrons were their own anti-particles?

[Mr Skeptic]

Shouldn't that argument work for electrons, too? Particularly in the sense of the conclusion that electrons were their own anti-particles?

 

Interesting question. The two slit experiment, and all the electron interference experiments that I know of, have the electron's wavefunction interfere with itself. I know of no experiments that have two different electrons interfere with each other. Also, all the electron interference experiments I saw only shift where the electron is found, not "how much" electron there is (which would violate conservation laws).

[Realitycheck]

In an antimatter universe, or even in just a theoretical antistar, where all of the charges were reversed - electrons, protons, reverse hydrogen atoms, etc. - the antistar's output would be antiphotons.

[Klaynos]

Interesting question. The two slit experiment, and all the electron interference experiments that I know of, have the electron's wavefunction interfere with itself. I know of no experiments that have two different electrons interfere with each other. Also, all the electron interference experiments I saw only shift where the electron is found, not "how much" electron there is (which would violate conservation laws).

 

You can do it with mutliple electrons interfereing with each other.

 

Why would electrons violate conservation laws but photons not?

 

Show an experiment where you get less photons out than you put in with them only interacting with each other...

 

Photons are indistinquishable from their antiparticles....

[Gilded]

In an antimatter universe, or even in just a theoretical antistar, where all of the charges were reversed - electrons, protons, reverse hydrogen atoms, etc. - the antistar's output would be antiphotons.

 

Indistinguishable from photons etc...

 

Also, that sounds like a misconception about antimatter.

[Kyrisch]

Show an experiment where you get less photons out than you put in with them only interacting with each other...

 

Photons are indistinquishable from their antiparticles....

 

Your first statement seems like a challenge with the goal to show that antiphotons do not exist, however your second statement contends that photons are "indistinguishable from their antiparticles", implying that the antiphoton does exist with identical properties. How can this be right?

[Realitycheck]

Indistinguishable from photons etc...

 

Also, that sounds like a misconception about antimatter.

 

Au contraire.

 

In particle physics and quantum chemistry, antimatter is the extension of the concept of the antiparticle to matter, where antimatter is composed of antiparticles in the same way that normal matter is composed of particles. For example, an antielectron (a positron, an electron with a positive charge) and an antiproton (a proton with a negative charge) could form an antihydrogen atom in the same way that an electron and a proton form a normal matter hydrogen atom. Furthermore, mixing matter and antimatter would lead to the annihilation of both in the same way that mixing antiparticles and particles does, thus giving rise to high-energy photons (gamma rays) or other particle–antiparticle pairs.

http://en.wikipedia.org/wiki/Antimatter

[Klaynos]

Your first statement seems like a challenge with the goal to show that antiphotons do not exist, however your second statement contends that photons are "indistinguishable from their antiparticles", implying that the antiphoton does exist with identical properties. How can this be right?

 

My first statement was a general statement it bears no relation as to whether photons or antiphotons exist. In interference experiments you always get out the same number of photons as you put in.

 

They are indistinguishable so it is just easier to pick one and say everything is that.

[Gilded]

http://en.wikipedia.org/wiki/Antimatter

 

Yes? There is nothing to imply that an antistar's photon output could be distinguished from a normal star's output.

[Realitycheck]

I'll give you that.

[swansont]

Shouldn't that argument work for electrons, too? Particularly in the sense of the conclusion that electrons were their own anti-particles?

 

Electrons are distinguishable from their antiparticles, since they are charged.

[Klaynos]

Electrons are distinguishable from their antiparticles, since they are charged.

 

I think he meant using the two slit experiment as proof that photons are their own antiparticle.

[Riogho]

You have to be careful in saying that just because the photon has no charge it doesn't have an anti-particle. Neutrino's and Antineutrino's both have zero electric charge, but when a neutrino interacts with a W-boson it produces a negative lepton, while an antineutrino performs the same interaction it produces a positive lepton.

 

The important thing to note is that their spins are different.

 

Though, once more spin isn't the tell-tale sign as well (electrons can be spin-up and spin-down)

[Mr Skeptic]

What Atheist said

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Edited October 29, 2008 by Mr Skeptic
me is stupid

[timo]

Most photons have spin 1, btw.

[Severian]

Most? Have you observed one of a different spin?

[Klaynos]

Most? Have you observed one of a different spin?

 

I was wondering this also...

[Mr Skeptic]

He was correcting me. I had somehow said that they have zero spin.

[tomgwyther]

I'm not a particle physisist, but I think I see the answer.

 

The Idea of anti-matter is reliant on the concept of matter, i.e matter and particles thereof are massive; they have mass.

As I understand it, a photon is mass-less, therefore the idea of an anti-photon is unintelegable.

[Gilded]

I'm not a particle physisist, but I think I see the answer.

 

The Idea of anti-matter is reliant on the concept of matter, i.e matter and particles thereof are massive; they have mass.

As I understand it, a photon is mass-less, therefore the idea of an anti-photon is unintelegable.

 

Antimatter is just an extension of sorts, from antiparticles, so that's not a very good reasoning.