I have read somewhere that Loop Quantum Gravity predicts a variable speed of light. According to the theory, high energy photons travel ever so faster than low energy photons. I wonder, how big is the variability according to the theory? Is it sensitive enough to be measured with today's technology, and if so, has it been measured?
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$\begingroup$ en.wikipedia.org/wiki/Variable_speed_of_light $\endgroup$Lagrangiann– Lagrangiann2024-08-08 09:37:26 +00:00Commented Aug 8, 2024 at 9:37
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$\begingroup$ If I remember correctly I saw a conference of David Elbaz, where he said that a cosmic event where it was known that two photons (one with high energy and the other with low energy) were emitted simultaneously, was observed on Earth and no difference in velocity was observed. I think it has ruled out some approaches to Loop Quantum Cosmology, but not LQG as a whole. Maybe someone will remember the name of this event... $\endgroup$Jeanbaptiste Roux– Jeanbaptiste Roux2024-08-08 09:48:33 +00:00Commented Aug 8, 2024 at 9:48
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$\begingroup$ The speed of light has nothing to do with light to begin with. It's the speed of causality. If LQG were to make a prediction about the dispersion of the electromagnetic field, that means that it would have to be reducible to an effective quantum field theory in the low energy limit. I am not aware that that's actually possible, at least not yet. $\endgroup$FlatterMann– FlatterMann2024-08-08 12:18:35 +00:00Commented Aug 8, 2024 at 12:18
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