Quantum Mechanics does not allow for FTL transmission. Disallowing information flow is the same as disallowing transmission.
cynar@lemmy.world 5 months ago
The universe seems to be keyed to disallow time travel. The speed of light limit, in relativity, is sat exactly at the limit where time travel would become possible. Conversely, quantum mechanics does allow for FTP transmission. What it doesn’t allow is information to flow along those links. It’s hit with a 0.5 error rate, which completely blocks FTP communication.
General relativity does allow for a few time travel options. However, these are sat well off in the sticks, where quantum relativity would dominate. Since we don’t have such a theory yet, our predictions are likely wrong. Even within these theories, a time machine would require a “closed timelike curve”. These can, in theory be made using several rapidly rotating black holes. Any ship traversing it, would never be able to leave before the time machine was built.
Basically, time travel is almost certainly blocked by our laws of physics. Any loopholes would be limited to the lifetime of the “machine” and would require stellar level engineering for even a few seconds of travel.
SmoothOperator@lemmy.world 5 months ago
cynar@lemmy.world 5 months ago
It seems to allow it, in a sense. The errors are also left on the transmission end. By transmitting them normally, the 2 signals can be combined to recreate the data. Something is shared, at some point.
It’s definitely a “we’re not sure what’s actually going on” type situation though. Either both ends are drawing on some (otherwise) hidden data layer, or FTL transmission is allowed, so long as no information flows (information as defined by quantum mechanics). It just turns out that weird entanglement based systems are the only ones (we’ve found so far) able to send infomationless transmissions.
Both solutions would give deeper insights into reality, and its underpinnings. Unfortunately, we’ve not actually teased out which is happening.
My gut feeling is that the speed of light is a side effect of a fixed/stable causality across all rest frames. Hidden information seems to be a lot more cumbersome.
SmoothOperator@lemmy.world 5 months ago
I’m not sure what you mean. If something is “shared”, but this something contains no information, how can we know that it was shared? In what sense does this something even exist?
The perfect correlation of entangled particles is well established, and very cool, but perfect correlation does not require sharing of “something”. The perfect correlation is baked into the system from the start, from local interactions only.
wkk@lemmy.world 5 months ago
The 2022 nobel prize was given to experimentalists that observed the violation of Bell’s inequality.
en.m.wikipedia.org/wiki/Bell's_theorem en.m.wikipedia.org/wiki/Quantum_nonlocality
I’m genuinely not an expert but I get it to mean that there aren’t hidden variables created alongside the entangled particles.
Dasus@lemmy.world 5 months ago
Ephera@lemmy.ml 5 months ago
As I understand, the FTL “transmission” in quantum entanglement is equivalent to just ripping a photograph in half, sticking the halves into envelopes and sending one of them to Australia.
By measuring the envelope you kept, i.e. opening it and seeing which half is in it, you gain instant knowledge, what the other half in Australia is.
This is mostly useless for communication, though, because the person in Australia does not get this information instantly.
In the case of quantum entanglement, the photograph halves are a particle, which has decayed into two particles, each of which have kept a shared property, like a spin of -1 and +1 respectively.
breckenedge@lemmy.world 5 months ago
This is the hidden-variables hypothesis and specific tests were made to check for it. See en.m.wikipedia.org/wiki/Bell's_theorem