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Time is a dimension, but not like space

(bigthink.com)
171 points belter | 1 comments | 17 Oct 24 15:29 UTC | HN request time: 0.202s | source
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heed ◴[20 Oct 24 05:48 UTC] No.41893173[source]▶
Also consider the speed of light is also the speed of causality. If there was no such limit it means it would be possible for effects to precede causes which would lead to a very different kind of universe!
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MattPalmer1086 ◴[20 Oct 24 09:18 UTC] No.41894129[source]▶
How could an effect precede a cause if there were no speed limit to causality?

No matter how fast an effect propogates, it is always after the cause (with an infinite speed, I guess effects happen instantaneously, but not before).

Of course, this doesn't fit with a universe described by general relativity, where time can be different for different observers. But you wouldn't have a universe described by general relativity without that constraint in the first place.

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alde ◴[20 Oct 24 11:51 UTC] No.41894744[source]▶
How would you compare two infinities? E.g. speed of light inside a moving train vs speed of light outside of it.
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1. MattPalmer1086 ◴[20 Oct 24 14:21 UTC] No.41895543[source]▶
An infinite speed implies instantaneous effect. So it wouldn't matter how you were moving. If two people launched something that travelled with infinite speed, one on the train travelling at 100mph, and one on the ground beside it, it would take zero time for both of them to reach their destination.

At least, that's what I surmise. I'm not a physicist.