Hoping for that loophole and free lunch…

If rotating one entangled particle here causes the other particle on the far side of the solar system to rotate…

This simply isn’t the case, that isn’t what entanglement means… though certainly many a sci-fi story has claimed otherwise.

We know of no way to transmit data faster than the speed of light, and there are good reasons to say that is impossible… could there be a loophole we haven’t discovered? I guess its possible, but it would require a lot of rewriting of the foundations of physics, and would throw causality out the window.

A small subset of these down-converted photons will consist of entangled photon pairs. The polarizations of each of the 2 photons will be perpendicular – if you measure one of them to be vertically polarized, then you know the other one of the entangled pair will be polarized horizontally.

Until you measure one of the polarizations the polarization state of the photons is in a superposition. Each photon is polarized in a superposition of the two polarizations.

If you let the 2 photons travel in opposite directions for a year, and then measure one to have vertical polarization, you know that the other photon 2 light years away must be polarized horizontally; the moment you measure one photon, the wavefunction of the pair collapses- the distance doesn’t matter . It may _seem_ like the photons have communicated to each-other faster than the speed of light… but YOU have NOT sent any information faster than the speed of light. Some other grad student receiving the other photon and seeing it is horizontally polarized knows nothing about what is happening with you 2 light years away.

You do not have any way of manipulating your photon to somehow send information to the other. You simply do a measurement and the photon tells YOU how its polarized.

If you put an optic in the path of your photon that will rotate its polarization, you are NOT rotating the polarization of the other entangled photon. Additionally, the act of interacting with your particle to rotate its polarization may be enough to cause the wavefunction to collapse and destroy the entanglement.

similarly, the example of the two particles with opposite spin (first of all, ‘spin’ refers to the direction of the angular momentum vector, and while objects that are spinning have angular momentum, you should not think of the particles as little balls that are actually spinning… they simply have a set inherent quanta of angular momentum- yeah, it weird). For instance all electrons are ‘spin 1/2′ particles- fermions. The orientation of the angular momentum vector between 2 particles can be entangled so that the angular momentum vectors are different by 180 degrees. If you measure one to be spin up, then the other must be spin down. If you do something to change the direction of one particle’s spin, then that may destroy the entanglement but it WON’T change the direction of the spin vector in the other.

I hope I have explained this clearly- its greatly simplified, but the bottom line is that there is no known way to use entanglement to transmit information, in fact if there WAS a way to do so, it would lead to a break down of causality, and would contradict Special Relativity.

TANSTAAFL

Do you get what I’m saying? Entangle a particle here on earth, put it on the next Pluto Express type space craft, have an AI on the probe that can rotate the entangled particle back and forth super fast, and we read the coded message back here on earth in real time.

If you can do something to that particle here (spin it up) and it is does something to that entangled particle there (spins it down), what is causing that to happen? And why can’t whatever that is be used to send or receive information back and forth? Already SOME kind of information (the spinning up and spinning down) is passing from one particle to the other over that vast distance in real time. If some other type of information could be stored on the particle couldn’t it share it with the distant entangled particle?

The particles wavefunctions are viewed as collapsing at the same time no mater the distance between them, but that is no help in transmitting information faster than the speed of light.

If you create an entangled pair of particles such that one must be ‘spin-up’ and the other must be ‘spin down’, and you transport them (at sub light speed) so they are 1 light-year apart, and you measure your particle to be spin-up, you know instantly that the particle a light year away is spin-down… but that in no way helps you to transmit data faster than the speed of light…

(I actually have a fun alternate interpretation of what happens that makes for fun sci-fi, maybe I will get into that another time…)

I was kind of hoping you would weigh in on this:

“…if we can develop quantum communication through entanglement, why couldn’t that lead to instant communication with spacecraft on the far end of the solar system and beyond?”

So I will see if I can find original paper, but that article is garbage…

https://dailygalaxy.com/2024/11/scientists-measure-quantum-entanglement-speed-groundbreaking-experiment/

If this result is confirmed, it suggests FTL travel and/or communication would be instantaneous, regardless of the distance involved. Well, maybe not instantaneous, but limited to 2.32 x 10^-16 s.

Newton and Einstein must be spinning in their graves.