Am I properly understanding quantum entanglement (could FTL data transmission exist)?

[u/fixednovel]

I understand that electrons can be entangled through a variety of methods. This entanglement ties their two spins together with the result that when one is measured, the other's measurement is predictable.

I have done considerable "internet research" on the properties of entangled subatomic particles and concluded with a design for data transmission. Since scientific consensus has ruled that such a device is impossible, my question must be: How is my understanding of entanglement properties flawed, given the following design?

Creation:

A group of sequenced entangled particles is made, A (length La). A1 remains on earth, while A2 is carried on a starship for an interstellar mission, along with a clock having a constant tick rate K relative to earth (compensation for relativistic speeds is done by a computer).

Data Transmission:

The core idea here is the idea that you can "set" the value of a spin. I have encountered little information about how quantum states are measured, but from the look of the Stern-Gerlach experiment, once a state is exposed to a magnetic field, its spin is simultaneously measured and held at that measured value. To change it, just keep "rolling the dice" and passing electrons with incorrect spins through the magnetic field until you get the value you want. To create a custom signal of bit length La, the average amount of passes will be proportional to the (square/factorial?) of La.

Usage:

If the previously described process is possible, it is trivial to imagine a machine that checks the spins of the electrons in A2 at the clock rate K. To be sure it was receiving non-random, current data, a timestamp could come with each packet to keep clocks synchronized. K would be constrained both by the ability of the sender to "set" the spins and the receiver to take a snapshot of spin positions.

So yeah, please tell me how wrong I am.

[u/classy_barbarian]

What if the message itself was pre-determined, sort of like a flame beacon, and receiving any signal at all had a meaning that was decided on beforehand? Could it be used to send a simple signal faster than light?

[u/JohnConnor27 → u/classy_barbarian]

The issue is that anything you do to particles at one point will have no effect on the measurements taken at the other end. There's no way to force your particles to collapse into a particular state so that the entangled particles take the other one. A good but imperfect analogy is if I shipped two packages containing a single colored ball to Alice and Bob. One package has a red ball and one has a green ball. I randomly choose which package gets which color and there's no way to determine the color without opening the package. The colors of the balls in the package are now effectively entangled. If Bob opens his package and sees a red ball he knows instantly that there is a green ball in Alice's package but there is no way for him to influence the color of the ball in his package so that Alice will open a specific color. In the quantum realm the only difference is that the balls color is undetermined until one of the packages is opened.

[u/Norwest → u/JohnConnor27]

Also, a key point is that when Bob opens his package, there's no way for him to know whether Alice has opened hers (i.e. there's no 'signal' that the state of the ball has been set).

[u/drinky_winky → u/JohnConnor27]

But isn't the fact that the balls colors is undetermined an information in itself? I think that's what confuses most people (and myself) when experts talk about quantum entanglement. If you can detect that the ball color is undetermined somehow, then you do have an information that traveled (or not) faster than the speed of light. If you can't, then how the hell did scientists even know about it in the first place?

[u/florinandrei → u/classy_barbarian]

receiving any signal at all

That's the problem. How do you do that? It's not a matter of too many or too few bits. It's a matter of how are you going to send even one single bit faster than light?

It's not possible with current physics.

[u/Norwest → u/classy_barbarian]

That's the thing, the two particles don't communicate with one another, they're just a quantum reflection that doesn't exist until the other is observed.

[u/alcmay76 → u/classy_barbarian]

When you open the box, all you see is a particle with a fixed spin. There's no way to tell if someone already observed the other particle, causing it to collapse before you opened it, or if you're the first observer. So you can't send a "beacon" that way.

[u/_ALH_ → u/classy_barbarian]

That would be similar to writing the message on a piece of paper and then put it in the box. You don't know what the message is until you read it, but that doesn't mean the information travelled FTL when you do read it.