# Photon splitting?

#### Glynis

Hello,
My Name is Glynis and I am very interested in physics. I hope to learn from and have fun on this forum.
At the moment I am trying ascertain whether the photon has been split or not. If it has been split, is my idea too simple in thinking that is has been split into its solid and non-material properties. If this isnt the case, is it possible?
Thank you,
Glynis

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#### marlon

##### nereida gallardo
Hello,
My Name is Glynis and I am very interested in physics. I hope to learn from and have fun on this forum.
At the moment I am trying ascertain whether the photon has been split or not. If it has been split, is my idea too simple in thinking that is has been split into its solid and non-material properties. If this isnt the case, is it possible?
Thank you,
Glynis
A photon is a dicrete chunk of energy, as described in QM and QED. This energy value cannot be split up because a photons is entire defined upon this energy value. Like electrons, photons are elemetary particles meaning that they do NOT have any internal structure. Also, a photon is not really a particle in the sense of "a physical entity with finite spatial boundaries" because it is defined as a piece of energy.

marlon

#### Severian

Although the photon is a point particle, its electromagnetic interation allows it to change into electron-positron pairs, or quark-antiquark pairs (among others) so if you probe it closely enough you will see this 'structure' within.

See for example (a very limited sample of a large literature):

http://www.slac.stanford.edu/spires/find/hep/www?j=APPOA,B37,677 [Broken]
http://www.slac.stanford.edu/spires/find/hep/www?eprint=hep-ph/0601056 [Broken]
http://www.slac.stanford.edu/spires/find/hep/www?key=6383343 [Broken]
http://www.slac.stanford.edu/spires/find/hep/www?eprint=hep-ex/0311025 [Broken]

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#### marlon

##### nereida gallardo
Although the photon is a point particle, its electromagnetic interation allows it to change into electron-positron pairs, or quark-antiquark pairs (among others) so if you probe it closely enough you will see this 'structure' within.
The processes you describe are correct but i dont' understand how the conversion to positron electron pairs, for example, allows you to probe the "internal" structure. We must be careful not to degenerate into a semantics discussion here but "internal structure" would imply there is something inside the photon, right ? This is obviously not the case and that is why i don't understand your post.

greets
marlon

#### marlon

##### nereida gallardo
Photon splitting can be achieved e.g. through parametric down conversion:
http://en.wikipedia.org/wiki/Spontaneous_parametric_down_conversion

(Although your idea of photon splitting is, as you suspected, not correct.)
Yeah, ok, but like you said yourself coverting one high energy photon into two lower energy photons is not what the OP meant by photon splitting.

I'd say this is a conversion, not a splitting

greets
marlon

#### Severian

The processes you describe are correct but i dont' understand how the conversion to positron electron pairs, for example, allows you to probe the "internal" structure. We must be careful not to degenerate into a semantics discussion here but "internal structure" would imply there is something inside the photon, right ? This is obviously not the case and that is why i don't understand your post.

greets
marlon
Once again this is a semantic issue. What does one mean by 'internal structure'? This is the phrasology which is used in the subject, but of course, it does not mean structure actually 'inside' (whatever that means!) a point particle like a photon.

The point here is that the particles have interactions which have some characteristic range, and 'internal structure' is simply probing them within that range. In the case of the proton, for example, the characteristic range is very easy to see, because beyond the proton radius, separate quarks will hadronize. So the characteristic range is the proton radius (or in terms of energy, about 1GeV). For the photon it is more problematic, since the electromagnetism has an infinite range, but one can still examine the interactions close it it by making some arbirary definition of 'near'. This is useful (essential) because when you do scattering experiments with a photon you want to make sure that it really is a photon and not a particle-antiparticle pair that the photon has changed into temporarily.

#### humanino

We must be careful not to degenerate into a semantics discussion here but "internal structure" would imply there is something inside the photon, right ?
Hey Marlon,

I very much agree. One must be careful not to take hadronic and photon structure functions on the same footing. Photon structure functions can be considered more or less like "dressed propagators" in hadronic vacuum/near hadronic systems... In particular, electron and quark contents are different depending on how you look at them, they evolve differently with renormalization scale etc...

On the contrary, we believe more strongly into the reality of hadronic structure functions. This is because, in that case, we know there is a valence core surrounded by a transition region to the external vacuum. We know hadrons have a finite size, but we still think of the photon as point-like.

Take for instance a look at this http://www-dapnia.cea.fr/Sphn/Plaquette01/Nucl/nucl5.pdf [Broken], to see how the photon content depends on how it is probed.

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#### jack467

If you consider a photon as a paired mass as others have theorized
then splitting does not seem too far fetched. The question becomes
if the free half particles will mate with another in free space and what
is the resultant frequency shift?

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