B Cosmic expansion and shock waves

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Galaxies that surpass the speed of light during cosmic expansion do not emit radiation waves akin to a sonic boom. The concept of absolute motion does not apply as space expands, meaning local light emission remains unaffected. Cosmic inflation occurred before the formation of stars and galaxies, complicating the notion of "speed" in curved spacetime. While particles exceeding light speed in a medium produce Cerenkov radiation, this phenomenon does not relate to galaxies in the context of cosmic expansion. Therefore, the analogy to sonic booms is not applicable in this scenario.
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TL;DR
Do galaxies that have surpassed the speed of light during the cosmic inflation process emit radiation waves comparable to the sonic boom when an aeroplane breaches the sound barrier?
Do galaxies that have surpassed the speed of light during the cosmic expansion emit radiation waves comparable to the sonic boom when an aeroplane breaches the sound barrier?
 
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Adel Makram said:
TL;DR Summary: Do galaxies that have surpassed the speed of light during the cosmic inflation process emit radiation waves comparable to the sonic boom when an aeroplane breaches the sound barrier?
No. When space expands, there is no sense in which a galaxy has absolute motion. Locally, stars will emit light independent of the expansion of space. There's nothing happening locally to affect the emission of light.

Note that cosmic inflation took place in the very early universe when there were no stars of galaxies.
 
"Speed" is a slightly more slippery concept in curved spacetime than flat spacetime, and those galaxies aren't moving faster than light in the relevant sense.

Particles that exceed the speed of light in a medium emit Cerenkov radiation as they slow down.
 

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