Noether theorem says that with symmetries come conservation laws, and so because of time, translation and rotation symmetry, EM field itself guards energy, momentum and angular momentum conservation. While atom deexcitation there clearly appears energy and angular momentum difference, so there should be created EM field configuration/wave "carrying this difference". Photon's angular momentum is usually imagined as only some abstract quantum property, but in fact it is a very real "mechanical" torque. For example Richard Beth in 1936 has measured the tiny reaction torque due to the change in polarization of light on passage through a quartz wave plate: http://prola.aps.org/abstract/PR/v50/i2/p115_1 Here is nice video of rotating macroscopic object using circularly polarized light - at about 20 second the polarization was switched to opposite one: Is optical photon something more than just EM wave carrying energy, momentum and angular momentum? If not - what more? Other than EM interactions? Some electric/magnetic moments? Is it just a "twist-like wave"? - like behind marine propeller, but this time in viscosity-free environment - and so does not dissipate: can travel undeformed for years (is soliton) from a concrete deexciting atom to be absorbed by anther one ... We say that because of spin conservation, it has also spin 1 - e.g. due to electron changing spin from -1/2 (down) to +1/2 (up) ... but isn't it just 180deg rotation - twist again? Especially that in opposite to other particles with spin, photon doesn't have magnetic dipole moment... Another question: why it has momentum? Is that just required for this kind of waves or maybe there is some momentum change required while atom deexcitation?