←back to thread

Time is a dimension, but not like space

(bigthink.com)
171 points belter | 1 comments | 17 Oct 24 15:29 UTC | HN request time: 0s | source
Show context
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!
replies(8): >>41893279 #>>41893283 #>>41893339 #>>41894129 #>>41895456 #>>41897144 #>>41897641 #>>41903045 #
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.

replies(4): >>41894744 #>>41895562 #>>41895599 #>>41903822 #
gavmor ◴[20 Oct 24 14:24 UTC] No.41895562[source]▶
Here's a great video explaining how, due to relativity, FTL travel can cause grandfather paradoxes: https://youtu.be/an0M-wcHw5A?si=RYFGOmQOlaC2t0bM

Edit: in short, not all reference frames can agree on the order of events, and FTL events propogate "backwards" between some reference frames.

replies(2): >>41896178 #>>41896640 #
david-gpu ◴[20 Oct 24 16:45 UTC] No.41896640[source]▶
That doesn't mean that light (causality) couldn't be faster, right? You could increase the speed of light (causality) as much as you want and wouldn't run into any paradox.
replies(5): >>41897026 #>>41897420 #>>41898803 #>>41899682 #>>41903643 #
1. gavmor ◴[20 Oct 24 17:33 UTC] No.41897026[source]▶
What does it mean to increase the speed of causality? This seems like asserting that we can add as many tick marks to the axis as we like, since the only universal unit of measurement is a velocity's percentage of C.

If we imagine something going faster than the speed of causality, we're simply misconcieving the properties of space.