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What would happen to light at absolute zero? Any change of a property? Or to say it in different words, what would happen to photons at absolute zero?

  • I have read that to slow down light, nearly to stop it,a cloud of nearly motionless atoms, at absolute zero, work. A physics professor in Harvard states so. But how is it possible, since light is not a matter but pure energy? I thought nothing would happen to light at absolute zero. I am confused.
QuantumCasanova
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  • Light is made up of photons, photons are not light, in the similar way that buildings are made out of bricks, but bricks are not buildings. When one has more than one photon and considers the sum of their four vectors, they have an invariant mass, even though each individual photon has mass zero. Example, the pi0 decays to to photons but has a mass of 140 MeV and can sit still in the center of mass. Slowing down light when examined at the photon level, means that the photons are manipulated so that the center of mass of the beam can slow down . – anna v Mar 22 '18 at 10:13
  • Refraction as explained in the duplicate, is a slowing down of light, even though the individual photons composing the light still travel with constant velocity c. They just travel longer paths .It is all in the mathematics :) of the four vectors describing photons and how they superimposed to form the classical em wave. Mass and energy are interchangeable in special relativity – anna v Mar 22 '18 at 10:16
  • @anna v How come light beam has a center of mass? – QuantumCasanova Mar 22 '18 at 10:26
  • One would have to define a specific plane ,find the four vectors of the photons composing it and the sum of four vectors has a length, which is the invariant mass of that bundle of photons. There is the energy of light, connected with the poynting vector see https://www.brown.edu/research/labs/mittleman/sites/brown.edu.research.labs.mittleman/files/uploads/lecture04.pdf . – anna v Mar 22 '18 at 11:04

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