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Buckethead

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- TL;DR Summary
- Why do differing temporal points on the block universe time line appear to both be the "present moment".

Consider two observers, Alice and Bob, standing on the Earth together with synchronized clocks. Bob asks Alice, “Is this now?” to which Alice replies, “Yes, it is”. They are clearly both in the present moment. Bob climbs a mountain and some time later, due to the lower gravitational field, finds his clock has advanced and hour relative to Alice’s clock. He returns to lower ground where Alice is waiting for him, and he asks again “Is this now?” to which Alice replies, “Yes, it is”. However, as indicated by their clocks, Bob has moved through time faster, relative to Alice.

Since the block universe diagram represents a yardstick of time (as well as spatial location), Bob’s time is at a different temporal location than Alice. If we consider the moment when Bob returns from the mountain as being the present time and we mark this temporal point as the present on the block universe diagram, then Alice would be located one hour earlier in this diagram at a different temporal point, clearly not in the present moment. But when Bob and Alice meet up again, they agree they are both in the present moment. Where is the flaw in my thinking?

Since the block universe diagram represents a yardstick of time (as well as spatial location), Bob’s time is at a different temporal location than Alice. If we consider the moment when Bob returns from the mountain as being the present time and we mark this temporal point as the present on the block universe diagram, then Alice would be located one hour earlier in this diagram at a different temporal point, clearly not in the present moment. But when Bob and Alice meet up again, they agree they are both in the present moment. Where is the flaw in my thinking?