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The idea driving this conclusion is called the Relativity of Simultaneity - There is no absolute notion that two events happened "at the same time". You want to
by philipov 5d ago
The idea driving this conclusion is called the Relativity of Simultaneity - There is no absolute notion that two events happened "at the same time". You want to say that a distant event occurred at the same time as a nearby event that occurred 5 hours ago. However, a distant third party observing both events may not agree.
This becomes painfully apparent when dealing with black holes. Person A falling into a black hole passes through the event horizon normally and reaches the singularity in finite time. However, Person B observing from outside never sees Person A pass through the event horizon. From Person B's perspective, it doesn't make sense to ask what happens simultaneously with Person A reaching the singularity - it takes infinite time just to reach the event horizon. Even asking the question becomes nonsense.
https://en.wikipedia.org/wiki/Relativity_of_simultaneity https://en.wikipedia.org/wiki/Relativity_of_simultaneity