Mariposa – A programming language with time-travel • Hacker News Board

Re: Mariposa – A programming language with time-travel

#61

Post by lrschaeffer » Thu, Jan 11, 2024, 4:14 PM UTC

eigenket wrote: post #58

lrschaeffer wrote: post #54

Earlier quoted context omitted.

Maybe in general, but this is in the context of "time loop logic". Ordinarily, you can have entangled states where measuring both parts will produce the same (random) outcome. Unfortunately the outcome cannot be influenced by either party, so it's useless for communication, as you say. Now suppose that the first party resolves to go back in time and kill his grandfather unless the bits he measures are precisely the m…

Ah I guess I misunderstood what was being claimed. I thought the claim was "you can use entanglement to instantly send messages", but it's actually "you can use entanglement and this model of how time travel might work to send messages instantly". Obviously these are rather different. In fact I feel like the entanglement doesn't even help in the time-travel protocol. If you want to send messages instantly and you can…

Assuming what I wrote above is correct (I don't actually know anything about closed time-like curves), it's actually weirder than just going back in time and mailing a letter early so it arrives when you want. Specifically, once you set up the entangled state, no other communication between the parties is necessary.

Re: Mariposa – A programming language with time-travel

#62

Post by rkagerer » Thu, Jan 11, 2024, 5:57 PM UTC

Terr_ wrote: post #60

rkagerer wrote: post #50

Earlier quoted context omitted.

The salient bit from _Marak_'s article: Time-loop logic does not violate causality. We are able to retrieve the answer instantly because we have committed to spending sixty seconds in the future calculating the answer and sending it back. Maybe quantum superposition is just the universe compiling.

The blog-post asserts causality is not violated, but the author contradicts it elsewhere by claiming the hypothetical system would grant other benefits like "zero latency" gaming, which in turn means arbitrary data (e.g. human decisions) can somehow travel back-and-forth faster than light. Then FTL communication opens up an enormous can of causality-worms.

That's a point, and I let them expand their definition of causality to include a chain of events flowing in a reversed arrow of time. I think they hand-wave away all those worms with the precept that any attempt to cause a paradox or other inconsistency would fail in practice. But I'd love to hear some examples that come to mind of problems that crutch doesn't fix.

Re: Mariposa – A programming language with time-travel

#63

Post by eigenket » Thu, Jan 11, 2024, 8:45 PM UTC

lrschaeffer wrote: post #61

eigenket wrote: post #58

Earlier quoted context omitted.

Ah I guess I misunderstood what was being claimed. I thought the claim was "you can use entanglement to instantly send messages", but it's actually "you can use entanglement and this model of how time travel might work to send messages instantly". Obviously these are rather different. In fact I feel like the entanglement doesn't even help in the time-travel protocol. If you want to send messages instantly and you can…

Assuming what I wrote above is correct (I don't actually know anything about closed time-like curves), it's actually weirder than just going back in time and mailing a letter early so it arrives when you want. Specifically, once you set up the entangled state, no other communication between the parties is necessary.

Yeah I understand the proposed protocol using entanglement. I'm just saying that if you're assuming we have access to the ability to send messages back in time there are much simpler protocols to achieve instant communication /without/ having to do anything involving entanglement.