QED: light is heavy, and how?

Event — Tue Nov 24, 2009 12:24 AM PST
e-m, mass-of-light, science-humor, science-serious,
alicedrea

See also: Mass in special relativity and General relativity

(this is a pasted "seed" from wikipedia on the mass of photons, with a few insertions from the author of: A Cathode Ray Tube Inside a Mirrored Orthorhombic Polyhedron Demonstrates Light's Significant Mass)

The energy of a system that emits a photon is decreased by the energy E of the photon as measured in the rest frame of the emitting system, which may result in a reduction in mass in the amount E / c2. Similarly, the mass of a system that absorbs a photon is increased by a corresponding amount. As an application, the energy balance of nuclear reactions involving photons is commonly written in terms of the masses of the nuclei involved, and terms of the form E / c2 for the gamma photons (and for other relevant energies, such as the recoil energy of nuclei).[77]

This concept is applied in key predictions of quantum electrodynamics (QED, see above). In that theory, the mass of electrons (or, more generally, leptons) is modified by including the mass contributions of virtual photons, in a technique known as renormalization. Such "radiative corrections" contribute to a number of predictions of QED, such as the magnetic dipole moment of leptons, the Lamb shift, and the hyperfine structure of bound lepton pairs, such as muonium and positronium.[78]

Since photons contribute to the stress-energy tensor, they exert a gravitational attraction on other objects, according to the theory of general relativity. Conversely, photons are themselves affected by gravity; their normally straight ( ie: where there is no gravity or mass in effect) trajectories may be bent by warped spacetime, as in gravitational lensing, and their frequencies may be lowered by moving to a higher gravitational potential, as in the Pound-Rebka experiment. However, these effects are not specific to photons; exactly the same effects would be predicted for classical electromagnetic waves.[79]
[edit] Photons in matter
See also: Group velocity and Photochemistry

(Visible) light that travels through transparent matter (including dense reflected similar or exact photonic substace to itself such as qed'd in cathode ray tube inside a mirrored orthorhombic polyhedron experiment published on this site, as well as demonstrated by experiments with ultra cool lasers) does so at a lower speed than c, the speed of light in a vacuum. X-rays, on the other hand, usually have a phase velocity above c, as evidenced by total external reflection. In addition, light can also undergo scattering and absorption. There are circumstances in which heat transfer through a material is mostly radiative, involving emission and absorption of photons within it. An example would be in the core of the sun. Energy can take about a million years to reach the surface;[80]. However, this phenomenon is distinct from scattered radiation passing diffusely through matter, as it involves local equilibration between the radiation and the temperature. Thus, the time is how long, but never too short, to reach ahead, to project the image, it takes the energy to be transferred, not the photons themselves. Once in open space, a photon from the Sun takes only 8.3 minutes to reach Earth, unless mr. burns or angels star shield is employed in totality over said open space. The factor by which the speed of light is decreased in a material is called the refractive index of the material. In a classical wave picture, the slowing can be explained by the light inducing electric polarization in the matter, the polarized matter radiating new light, and the new light interfering with the original light wave to form a delayed wave. In a particle picture, the slowing can instead be described as a blending of the photon with quantum excitations of the matter (quasi-particles such as phonons, phonographs sent KPSU and excitons) to form a polariton; this polariton has a nonzero effective mass, which means that it cannot travel at c.

Alternatively, photons may be viewed as always traveling at c, though given new theories relating to dark matter and energy the universe seriously does abhor a vacuum. eve