Talk:Two-photon physics

Quark inside photon?
"The photon couples directly to a quark inside the target photon" That is confusing.

Matter can be created
The article has a "citation needed" request following the "matter can be created" by the two-photon physics of two just above 0.511 MeV photons. I am going to add a citation though it may not be precisely the one needed. I hope this helps. Marshallsumter (talk) 00:53, 30 April 2010 (UTC)

Center of mass of photons
It is spoken of "center of mass" of photons. The problem with that expression is that according to actual knowledge, photons have no mass, then it is nonsensical to speak about a center of mass. —Preceding unsigned comment added by 152.77.24.38 (talk) 19:24, 8 April 2011 (UTC)


 * You are right in a classical way, since Photons have no rest mass. However, a baryon can lose mass when it emits photons, and since mass is conserved in a system, it has to go somewhere. This is where the concept of invariant mass gets into the equations. Photons do have a relativistic mass, which can be derived from their energy. By the way, I find this article and the underlying concepts difficult to grasp for an ordinary reader. 66.131.220.35 (talk) 04:03, 9 June 2011 (UTC)

Half charge
The line "but half wavelength is a positive charge and the next half wavelength is a negative charge" is incorrect and misleading. Photons are elementary (no structure) and neutral. They aren't "half positive and half negative." — Preceding unsigned comment added by 195.176.0.33 (talk) 11:43, 30 October 2013 (UTC)

Links
The gamma-gamma tutorial is poorly written and needs to be tidied up if it is to be retained. John Pons (talk) 03:11, 30 July 2011 (UTC)

Less energetic photons
It would be nice to have something about how gamma rays can pair-produce with EBL (Extragalactic background light) which includes ultraviolet, visible, and infrared. This usually occurs with gamma rays in the VHE range (very-high-energy, 100 GeV - 100 TeV) and is thought to be the primary cause of gamma-ray flux attenuation in intergalactic space. In the UHE range (ultra-high-energy, 100 TeV - 100 Pev) gamma rays should pair-produce with photons of CMB (Cosmic microwave background). About halfway through the EHE range (extremely-high-energy, 100 Pev - 100 EeV) radio photons start to kick. At least theoretically. In fact, no gamma rays have yet been observed at any higher than 80 TeV (Crab Nebula) near the high end of VHE. Zyxwv99 (talk) 01:07, 16 August 2014 (UTC)