Does friction slow down the speed of light?

how fast does light travel I heard everything that travels is eventually slowed down by friction. If this is true is light slowed down by friction or does it always keep a constant speed?Why does it always travel the same speed?is there anyway to slow down light?could this possibly be a way for time travel?How... show more how fast does light travel I heard everything that travels is eventually slowed down by friction.
If this is true is light slowed down by friction or does it always keep a constant speed?Why does it always travel the same speed?is there anyway to slow down light?could this possibly be a way for time travel?How fast would light travel if there was friction affecting its speed?
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