> It has been a while since I followed particle physics, so I will waste
A very erroneous description.
> Has physics predicted an anti-photon?
Photons are their own anti-particles. Same for all the mediating
bosons (gravitons, W, Z, gluons).
> If so, since light is energy (or at least
Well, everything is energy. Photons have energy, and momentum, but have no
rest mass.
> what is the result of a photon/anti-photon
Depends one the energy involved. Can be the creation of massive particles. If
the photons have different wavelengths then nothing, they simply carry on
regardless. I think, it's been a few years.
> > It has been a while since I followed particle physics, so I will
Indeed, electrons and photons are quite different things.
This confusion was most like caused by some sentence using the term 'Free
Elctron' in connection with photons. Most likely contexts: a) Light particles
(photons) can knock electrons free from atoms, e.g. off a metallic surface
b) A 'Free Electron Laser' (FEL) uses a beam of high-energy electrons to
produce a laser beam (of photons). An FEL beam is freely tunable in light
frequency and can reach very high frequencies (the record stands somewhere in
the gamma ray region, if I'm not mistaken).
> > Has physics predicted an anti-photon?
As Steve said above, that would be a photon-photon-collision
> Depends one the energy involved. Can be the creation of massive
Particle/anti-particle pairs. Conservation laws have to be observed
> If the photons have different wavelengths then nothing,
I think they don't have to be the same wavelength to scatter off each other
(but certainly they should be very high-energy to have a chance to
interact.
I think, it's been a few years ;-)
Greetings,
Karl Heinz
> Steve Pugh wrote:
> > It has been a while since I followed particle physics, so I will
Yep. Though I've heard that term used as well.
A photon is actually an electron/anti-electron pair.
> > Has physics predicted an anti-photon?
This gets tricky to answer since photons don't have an anti-photon
particle but since light is also a wave, a photon can have a wave form that is
opposite to that of another photon. Those to photons meeting each other would
cancel each other out.
> A photon is actually an electron/anti-electron pair.
Hmm, let's see. An electron has a mass of 9.1x10^-31 kg. Same for a
positron (proper name for an anti-electron). So the total energy of
the mass of an electron/positron pair is given by E=mc^2 and is
1.638x10^-13 J
Now, the energy of a photon is given by planck's constant x
frequency. Planck's constant is 6.626x10^-34. So the minimum energy a
frequency a photon could have to have the equivalent energy of an
electron/positron pair is 2.47x10^20 Hz. Which is well into the gamma
ray range.
So, how is it possible that all photons are electron/positron pairs
when photons typically have much lower energies than the minimum energy of
such a pair?
This also links into another part of this thread: photon-photon
collisions can create particle/anti-particle pairs. Two photons of
frequency 1.23x10^-20 Hz or greater have enough energy to create
electron/positron pairs.
Steve wrote
> > A photon is actually an electron/anti-electron pair.
> frequency a photon could have to have the equivalent energy of an
Because that is not really the case. Photons "are" distinct particles
and not e+e- pairs. However, high-energy-photons - as you calculated
above, I didn't check the numbers - can be converted into
electron-positron
pairs when interacting with matter or other photons.
Also note, that according to Quantum Mechanics and Heisenberg's uncertainty
principle, there are such things as 'Virtual Particles' which "exist" only for
minuscule moments of time before disappearing again. As they can not be
directly observed, they don't have to obey most conservation
laws and for example, a low-energy photon can give rise to a virtual
e+e- pair. Of course, it is a question for philosophers if virtual
particles "exist". But certainly, there are measurable effects that you can
get out of the Quantum calculations only if you include virtual particles.
> This also links into another part of this thread: photon-photon
> > > A photon is actually an electron/anti-electron pair.
[snip maths]
> > So, how is it possible that all photons are electron/positron pairs
I know that, I was proving that the previous statement was wrong.
> However, high-energy-photons - as you calculated
I didn't check the numbers either. But they seem right. Working with these
silly units is a drag. But I thought that using eV and so on might confuse
some people. If anyone is still reading this thread at
all ;-)
> KH.Ranitzsch@t-online.de wrote:
> Also note, that according to Quantum Mechanics and Heisenberg's
which
> "exist" only for minuscule moments of time before disappearing again.
As they
> can not be directly observed, they don't have to obey most
This is what I was thinking of. It's probably where the "free electron"
designation got put on photons by some of the non-scientific press.