CPT theorem is at heart of modern physics, suggesting causality working in both time directions – what are the arguments that it can only work past -> future? (it is different from statistical 2nd law of thermodynamics)
What approaches for reversed causality were considered (like wormholes, John Cramer’s, CPT analogue of laser)?
Anyway, I believe it is stimulating thought experiment: imagine scenario that such retrocausality device is invented – how would you imagine the consequences?
Related: Novikov self-consistency principle - Wikipedia
Here is my approach and brief answer for the last question (last paragraph of updated Section IV.A of https://arxiv.org/pdf/0910.2724 ):
Assuming CPT remains valid for macroscopic physics, still construction of such time-loop computer would be technically extremely challenging, but it might be reachable - should be at least taken into considerations. Especially that it might allow to break currently used cryptography (if reaching sufficient delay and strength): with verifier checking if a given key leads to decoded file not being just a noise. Protection against such attacks might be done by adding computationally costly initialization: necessary before application of a new cryptographic key - to require much longer delays and stronger channels. Further improvements of such channels could allow to use verifier e.g. testing molecules for desired properties for drug design, testing possible algorithms/methodologies for desired outcomes, etc. Finally, being able to send information back for macroscopic time differences, could allow to prevent currently unpredictable unwanted events: there would be attempt to send such missing information - creating inconstancy, hence action optimization should modify the weakest links of this reason-result chain (e.g. in quantum measurement level) to get self-consistent time loop, e.g with satisfying outcome: not requiring to use such channel. In other words, just having access to such channel, we would enforce physics to make its best to prevent our bad choices, optimize randomness for outcomes preferred by us. While there would be many dangers on the way, if well balancing strengths of such channels worldwide, it might lead to a much more harmonic world based on trust, without various types of gambling, with choices made optimizing their actual future consequences.
What approaches for reversed causality were considered (like wormholes, John Cramer’s, CPT analogue of laser)?
Anyway, I believe it is stimulating thought experiment: imagine scenario that such retrocausality device is invented – how would you imagine the consequences?
Related: Novikov self-consistency principle - Wikipedia
Here is my approach and brief answer for the last question (last paragraph of updated Section IV.A of https://arxiv.org/pdf/0910.2724 ):
Assuming CPT remains valid for macroscopic physics, still construction of such time-loop computer would be technically extremely challenging, but it might be reachable - should be at least taken into considerations. Especially that it might allow to break currently used cryptography (if reaching sufficient delay and strength): with verifier checking if a given key leads to decoded file not being just a noise. Protection against such attacks might be done by adding computationally costly initialization: necessary before application of a new cryptographic key - to require much longer delays and stronger channels. Further improvements of such channels could allow to use verifier e.g. testing molecules for desired properties for drug design, testing possible algorithms/methodologies for desired outcomes, etc. Finally, being able to send information back for macroscopic time differences, could allow to prevent currently unpredictable unwanted events: there would be attempt to send such missing information - creating inconstancy, hence action optimization should modify the weakest links of this reason-result chain (e.g. in quantum measurement level) to get self-consistent time loop, e.g with satisfying outcome: not requiring to use such channel. In other words, just having access to such channel, we would enforce physics to make its best to prevent our bad choices, optimize randomness for outcomes preferred by us. While there would be many dangers on the way, if well balancing strengths of such channels worldwide, it might lead to a much more harmonic world based on trust, without various types of gambling, with choices made optimizing their actual future consequences.
