Today folks, we’re going to talk about Quantum Entanglement, or what Einstein referred to as “…spooky action at a distance…”. The phenomenon of quantum entanglement in quantum physics at first glance seems to allow one to transmit information faster than the speed of light; however, one cannot transmit information in this way. Quantum entanglement is a property of the quantum mechanical state of a system containing two or more objects, where the objects that make up the system are linked in such a way that the quantum state of any of them cannot be adequately described without full mention of the others, even if the individual objects are spatially separated. Quantum entanglement is at the heart of the EPR paradox described by Albert Einstein, Boris Podolsky and Nathan Rosen in 1935, and was verified experimentally for the first time in 1972 by Stuart Freedman and John Clauser.
When particles decay into other particles, these decays must obey the various conservation laws. As a result, pairs of particles can be generated that are required to be in certain quantum states. For ease of understanding, consider the situation where a pair of these particles are created, having a two-state spin and one must be spin up and the other must be spin down. These two particles can now be called entangled since you cannot fully describe one particle without mentioning the other. This type of entangled pair where the particles always have opposite spin is known as the spin anti-correlated case, and if the probabilities for measuring each spin are equal, you have the singlet state.
Now that entangled particles have been created, imagine that we have two experimenters, Scary and Minx, and each one of them has one of the particles that form the entangled pair. Scary then measures the spin of her particle. For her, the measurement will be unpredictable, with a 50% probability of the spin being up or down. However, if she compares the spin she obtained with the spin Minx measured in his particle, she will see that they are always opposite, hence perfectly anti-correlated.
Note, however, that until now there’s nothing mysterious going on; the correlation seen in this experiment can be simulated classically. To see this, imagine that Scary and Minx have a coin, and they slice it along the circumference into two half-coins, in such a way that each half-coin is either “heads” or “tails”. They then put each half-coin in an envelope, one for Scary and the other for Minx, randomly. Scary then measures her half-coin, by opening her envelope. For her, the measurement will be unpredictable, with a 50% probability of her half-coin being “heads” or “tails”. However, if she compares the side of the coin she obtained with the side of the coin Minx measured in his half-coin, she will see that they are always opposite, hence perfectly anti-correlated.
While this phenomenon does NOT allow faster than light (FTL) communication between two experimenters, there is an argument that the particles themselves are communicating faster than light. There is a competing theory that the particles are actually connected, along with every other particle in the universe, and the information about when to change spin-state in an entangled pair is transmitted across this fabric at non- or near-FTL speeds, hence appearing to happen faster than light. My question to you is, what do you think? Is the spin-state information between two particles traveling faster than light or being transmitted across a collective whole?





