I guess my question is, if we haven't measured it, how do we know that it was neither Spin Up nor Spin Down? That wasn't addressed in the show. It seems to me that something unmeasured may be uncertain from our point of view, but in the grand scheme of things it either is or isn't, and is just waiting for us to find out.

Two people, say Alice and Bob, want to comunicate so they take a pair of electrons and entangle them. Alice takes one and Bob the other.
Now Alice takes a third electron and encodes her information on in (for example, making its spin "up" or "down" with the convention that "up" means "0" and "down" means "1") This is usually called a qubit
Next Alice makes her two electrons interact (so we have 3 entangled electrons) and then measure them both thus instantly "acting at a distance" on Bob's electron.
Now here's the catch. Because of the probabilistic nature of quantum mechanics, Alice can get 1 out of 4 different possibilities and Bob doesn't necesarily have the qubit that Alice wanted to send. To complete te process Alice has to tell Bob (by phone for example) which one of the outcomes she got and then Bob cleverly manipulates his qubit to obtain the desired one.

But, because Alice and Bob have to communicate using classical means there's no faster than light speed communication.

This seems like too much trouble for transmiting one simple "1" or "0" with no gain in speed however there's this thing called "superdense coding" which allows to transmit 2 classical bits with just just one qubit.

One of the amazing aspects of quantum communication is that any observation collapses the wavefunction of the system so, no one can eavesdrop without collapsing the wafeunction and making itself visible. There are some people already selling "100% secure communication" using this phenomena (www.smartquantum.com) although the "100% secure" part is still a matter of debate.

Best regards

Andrés

P.S. I hope I'm being fairly clear in my explanation but please feel free to send me a mail with wathever question about this subject. I totally love quantum computers (almost as much as this show XD )

ags3006@gmail.com

When the wave forms of both particles are collapsed by measuring the spin of one of them, the particles remain entangled. You can flip the spin on one particle to send a bit of information, and the other particle flips too because they are still entangled, and the person on the other end can detect the flip thus receiving the information.

The previous paragraph is all assumptions I am making, and not statements of what I believe to be true. If that is all true, and only if that is all true, the limit of the rate of data transmission would be the slower of how fast you can flip the particle or how fast the other person can detect the flip.