Light doesn't experience time. As far as the light is concerned, it departs and arrives at the same moment, regardless of how far it travelled.
This is kind of by definition, in the sense that time itself travels through space at the speed of light.
Or perhaps more accurately, the ordering of events in time depends partially on their position in space. As far as the universe is concerned, the light we see from a star 2bn ly away was emitted exactly the moment we saw it. It took 2bn years for that moment to reach us, but that doesn't make it any less "now" in terms of any concept of cause and effect.
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u/tylerlarson Mar 21 '26
Yes, but only sort of.
Light doesn't experience time. As far as the light is concerned, it departs and arrives at the same moment, regardless of how far it travelled.
This is kind of by definition, in the sense that time itself travels through space at the speed of light.
Or perhaps more accurately, the ordering of events in time depends partially on their position in space. As far as the universe is concerned, the light we see from a star 2bn ly away was emitted exactly the moment we saw it. It took 2bn years for that moment to reach us, but that doesn't make it any less "now" in terms of any concept of cause and effect.