>The problem is that if something arrives at B before B sees it leave A, then there is a way to arrange for a message to be sent from B to A, and a response back from A to B, such that the response arrives before the message was sent.
No, you're changing your terms in that sentence. If something arrives at B before B sees it leave A, it doesn't imply it hasn't left A. B could send a response that similarly goes faster than B sees, and the whole system could end up with A receiving a response from B before A sees B receive the original message. B still sent the message after A sent theirs.
That's not a paradox, that's just faster communication than sight. Similar to how two people can jog towards each other, and receive a response before they reach the other person, much less reach each other's starting points.
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As I have in another reply in this main thread, I understand that this is what special relativity says. But I also thought special relativity says it's impossible to travel faster than light, so is anything outside what it claims is possible even within its rule-set? How does special relativity apply to the apparently-contradictory world of quantum behavior? Even Einstein didn't think quantum mechanics was correct and didn't fit with relativity, but we deal with quantum behavior on a daily basis, so it's very definitely real.
edit: perhaps more clearly:
Special relativity claims that anything faster than c goes back in time. (I think/thought) it also claims anything faster than c is impossible. But it's an easy thought-exercise to cause instantaneous transmission without causing a paradox, an easy solution being things happening faster than sound not causing paradoxes. Just because you haven't heard it doesn't imply it hasn't happened yet.
Comments
>The problem is that if something arrives at B before B sees it leave A, then there is a way to arrange for a message to be sent from B to A, and a response back from A to B, such that the response arrives before the message was sent.
No, you're changing your terms in that sentence. If something arrives at B before B sees it leave A, it doesn't imply it hasn't left A. B could send a response that similarly goes faster than B sees, and the whole system could end up with A receiving a response from B before A sees B receive the original message. B still sent the message after A sent theirs.
That's not a paradox, that's just faster communication than sight. Similar to how two people can jog towards each other, and receive a response before they reach the other person, much less reach each other's starting points.
---
As I have in another reply in this main thread, I understand that this is what special relativity says. But I also thought special relativity says it's impossible to travel faster than light, so is anything outside what it claims is possible even within its rule-set? How does special relativity apply to the apparently-contradictory world of quantum behavior? Even Einstein didn't think quantum mechanics was correct and didn't fit with relativity, but we deal with quantum behavior on a daily basis, so it's very definitely real.
edit: perhaps more clearly:
Special relativity claims that anything faster than c goes back in time. (I think/thought) it also claims anything faster than c is impossible. But it's an easy thought-exercise to cause instantaneous transmission without causing a paradox, an easy solution being things happening faster than sound not causing paradoxes. Just because you haven't heard it doesn't imply it hasn't happened yet.