6 ms·

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 i

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.

alde 2y ago
How would you compare two infinities? E.g. speed of light inside a moving train vs speed of light outside of it.
- MattPalmer1086 2y ago
  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.
gavmor 2y ago
Here's a great video explaining how, due to relativity, FTL travel can cause grandfather paradoxes: https://youtu.be/an0M-wcHw5A?si=RYFGOmQOlaC2t0bM 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.
- MattPalmer1086 2y ago
  Nice video, thanks for posting.
- david-gpu 2y ago
  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.
  - gavmor 2y ago
    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.
  - MattPalmer1086 2y ago
    Right. The speed limit itself is arbitrary.
  - coldtea 2y ago
    Mainly in the sense that you can create an amp that goes to 11.
  - layer8 2y ago
    With respect to what, though? One light-second would still be one light-second. The sizes of atoms and elementary particles probably also are a function of that. (We don’t know that, but it seems plausible.)
  - simonh 2y ago
    You'd be able to use an FTL laser to shoot your own grandfather as a baby. Plus you'd be able to receive an FTL broadcast of what's going to happen tomorrow.
andsoitis 2y ago
> 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). If everything happens instantaneously then there is no real cause and effect, and the universe would be over before it really got started.
- SoftTalker 2y ago
  This is the experience of a photon.
- amelius 2y ago
  No speed limit does not mean that everything goes infinitely fast.
  - lazide 2y ago
    If the speed limit is infinite, what else would you expect to happen?
    - amelius 2y ago
      Light traveling at infinite speeds, atoms and such not.
      - andsoitis 2y ago
        If effects were instantaneous then atoms would not exist.
        amelius 2y ago
        There can be many types of effects in a hypothetical universe. Imagine a universe like Conway's way of life, where only neighboring cells can be affected in one timestep. Now add to it a rule that all blocks have a color, and the color of all blocks are changed when one block changes color. Now you have a universe with both immediate and non-immediate effects.
mistermann 2y ago
> How could an effect precede a cause I can't think of anything purely in the physical plane, though there's this: https://en.m.wikipedia.org/wiki/Retrocausality https://en.m.wikipedia.org/wiki/Retrocausality But if one includes metaphysics, one example (there are others) is an individual's anticipation of another individual doing something in the future could cause them to act in the present. This is quite the stretch on its own, but if you include this (which exists, as much as people don't like to admit it depending on the context): https://en.m.wikipedia.org/wiki/Consensus_reality https://en.m.wikipedia.org/wiki/Consensus_reality ...it is possible, in that it comes down to the question of is it true that the effect proceeded the cause, and if enough people believe something is true, it is true. And if you disagree, observe human behavior for a while and see for yourself - people will tell you it is true with absolute sincerity, and they often will act in the physical plane based upon that "truth". Wars are started over "not true" "truths", perhaps even all of them. And if that's not enough, another route is perhaps people really can see the future. People with absolute sincerity tell me they can constantly. Perhaps they are hallucinating (they swear to me they are not), but perhaps they are not, maybe it is yet another thing that science has yet to discover, or cannot discover due to non-determinism, non-falsifiability, consensus reality (a theory cannot be(!) true unless there is consensus agreement that it is true), etc. Please don't shoot the messenger.

alde 2y ago

How would you compare two infinities? E.g. speed of light inside a moving train vs speed of light outside of it.

MattPalmer1086 2y ago
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.

gavmor 2y ago

Here's a great video explaining how, due to relativity, FTL travel can cause grandfather paradoxes: https://youtu.be/an0M-wcHw5A?si=RYFGOmQOlaC2t0bM 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.

MattPalmer1086 2y ago
Nice video, thanks for posting.
david-gpu 2y ago
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.
- gavmor 2y ago
  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.
- MattPalmer1086 2y ago
  Right. The speed limit itself is arbitrary.
- coldtea 2y ago
  Mainly in the sense that you can create an amp that goes to 11.
- layer8 2y ago
  With respect to what, though? One light-second would still be one light-second. The sizes of atoms and elementary particles probably also are a function of that. (We don’t know that, but it seems plausible.)
- simonh 2y ago
  You'd be able to use an FTL laser to shoot your own grandfather as a baby. Plus you'd be able to receive an FTL broadcast of what's going to happen tomorrow.

andsoitis 2y ago

> 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). If everything happens instantaneously then there is no real cause and effect, and the universe would be over before it really got started.

SoftTalker 2y ago
This is the experience of a photon.
amelius 2y ago
No speed limit does not mean that everything goes infinitely fast.
- lazide 2y ago
  If the speed limit is infinite, what else would you expect to happen?
  - amelius 2y ago
    Light traveling at infinite speeds, atoms and such not.
    - andsoitis 2y ago
      If effects were instantaneous then atoms would not exist.
      - amelius 2y ago
        There can be many types of effects in a hypothetical universe. Imagine a universe like Conway's way of life, where only neighboring cells can be affected in one timestep. Now add to it a rule that all blocks have a color, and the color of all blocks are changed when one block changes color. Now you have a universe with both immediate and non-immediate effects.

mistermann 2y ago

> How could an effect precede a cause I can't think of anything purely in the physical plane, though there's this: https://en.m.wikipedia.org/wiki/Retrocausality https://en.m.wikipedia.org/wiki/Retrocausality But if one includes metaphysics, one example (there are others) is an individual's anticipation of another individual doing something in the future could cause them to act in the present. This is quite the stretch on its own, but if you include this (which exists, as much as people don't like to admit it depending on the context): https://en.m.wikipedia.org/wiki/Consensus_reality https://en.m.wikipedia.org/wiki/Consensus_reality ...it is possible, in that it comes down to the question of is it true that the effect proceeded the cause, and if enough people believe something is true, it is true. And if you disagree, observe human behavior for a while and see for yourself - people will tell you it is true with absolute sincerity, and they often will act in the physical plane based upon that "truth". Wars are started over "not true" "truths", perhaps even all of them. And if that's not enough, another route is perhaps people really can see the future. People with absolute sincerity tell me they can constantly. Perhaps they are hallucinating (they swear to me they are not), but perhaps they are not, maybe it is yet another thing that science has yet to discover, or cannot discover due to non-determinism, non-falsifiability, consensus reality (a theory cannot be(!) true unless there is consensus agreement that it is true), etc. Please don't shoot the messenger.