Introduction
Quantum mechanics sometimes rears its ugly head in the news, and while the stories are pretty amazing, they are often misleading or just plain wrong.
Let’s face it, quantum mechanics, at its core, is a pretty dry subject. It involves blackboards covered in mathematical equations, and words like superposition and decoherence. But as of late, the subject of quantum teleportation is the “Star Trek is now!” story du jour in science media. Especially with the awarding of the Nobel Prizes in physics to three men studying quantum entanglement and quantum teleportation.
The concept of quantum teleportation is very different from what most people probably think of as teleportation. It does not in any way involve “beaming” a person or thing from one location to another. It’s merely the transmission of data from one place to another. Sort of like the WiFi of tomorrow.
The term, quantum teleportation, was christened by a group of scientists in 1993 that had developed a process of communication derived from quantum entanglement. They originally called it quantum telepheresis, but one of them, Charles Bennett, thought telepheresis sounded pretty lame. So, he came up with an alternative with a little more pop, and the term quantum teleportation was born.
That said, quantum teleportation is pretty damn cool. It relies on a quality of quantum mechanics called quantum entanglement.
Quantum Entanglement
It’s been confusing physicists since the 1930s. Einstein derisively called it “spukhafte Fernwirkung.” Pretty harsh right? It’s German for “spooky action at a distance” and Einstein was having none of it. In fact, he thought that all of quantum mechanics was terribly flawed and wrote papers designed to disprove its theories. Interestingly enough, those same papers are often cited as major catalysts for further study in quantum mechanics. Physicists love irony.
So, what is quantum entanglement? You know all those tiny particles that make up reality, like electrons and photons? Under certain conditions, like when a particle decays into two new particles, the two new particles can share quantum state. That’s entanglement.
OK, we need to back up a little. What is quantum state you might ask. It’s just a measure of what a particle is doing right now. Physicists have observed several different particle states, but the one they love to talk about the most is spin. Particles called electrons have two spin states: spin up and spin down. Are these particles actually spinning round and round? No, spin is merely a confusing way to express the electromagnetic charge of a particle. It’s like if someone asked you, “what’s the state of that light switch, is it on or off?” and you responded, “it’s on.”
So, now we know that when two particles are entangled, it means that they share state. Did I mention that it’s inverse state? Let’s say we have two entangled particles. If particle A is measured to be spin down, then its entangled partner, particle B is guaranteed to be spin up. That’s it. By itself that’s not particularly amazing. But, you need to know two more things about quantum mechanics in order to understand why this entanglement thing is particularly weird and why Einstein didn’t like it.
First, particles do not even exhibit a quantum state like spin until the state is measured by someone like you or me. Particle A is just bopping around without a definitive state until Alice the physicist and her crew measure it. Then bang! “Hey this electron is spin up.” I know that sounds bizarre since nothing in our day to day world behaves like that. Imagine if a light switch was both on and off at the same time until someone looked at it, and then it suddenly picked a state. Weird right? Yet it’s a foundational principle of quantum mechanics. Don’t ask a physicist how or why that’s the case, they don’t know, or at best you will find yourself falling down a philosophical rabbit hole of multiple universes and dead cats.
The second thing you need to know is that the distance between entangled particles can be arbitrary, yet they remain entangled. Two microns or a million-billion-gazillion miles.
So what all this means is that when Alice in her lab in Singapore measures entangled particle A as being spin down, Bob in his lab in Canada with entangled particle B will know that his particle is spin up. It doesn’t make sense, does it? How are the particles communicating with each other?
These qualities have some crazy implications about the nature of reality. Einstein thought, sure, experiments seem to indicate all this weird stuff is happening, but it merely implies that we don’t understand what is really going on. There must be hidden variables at work behind the scenes and we need to figure them out and stop all this nonsense.
John Stewart Bell
In 1964, along came Dr. Bell, an Irish physicist who wanted to address Einstein’s concerns about quantum mechanics. He proposed that physicists had made a critical false assumption: that quantum mechanics is governed by the principle of locality.
Locality refers to our basic perception of reality as being a series of causes and effects. If you push a ball, it will roll. If you hold a magnet next to a steel disc, the steel disc will move. Basic stuff. It amounts to a thing traveling through space to cause another thing to happen. That is locality.
But quantum entanglement does not seem to have a cause moving through space, it only has an instantaneous effect, and that is really, really odd. Bell called it non-locality. If entangled particle A is measured to have spin up, then entangled particle B has spin down. How? They are not connected in any way, there is no field emanating from either particle, yet they seem to “know” what the other is doing immediately. This implies that the particles are not only communicating with each other, but they are doing so faster than light, which totally violates Einstein’s special theory of relatively. Nothing goes faster than light.
Like Einstein, Bell used thought experiments to find answers. He developed Bell’s Theorem in which he conjectured that either quantum mechanics is in fact not governed by the principle of locality, making Einstein wrong about everything, or Einstein was right, and we need to keep searching for those hidden variables.
Conclusion
There have been several scientific experiments designed to prove or disprove Bell’s Theorem, and each and every experiment has been inconclusive. The sticking points are what are called loopholes. Experiments have not been able to completely rule out the possibility of one theory or the other being correct with absolute certainty. Someone, somewhere always finds the potential for effects from those infamous hidden variables in the experiment, invalidating its results. It is, after all, very hard to design a foolproof experiment, especially when it involves the quantum world. To this day, and even considering the Nobel Prize winners, no one understands the true nature of quantum entanglement, nor in fact the whole of quantum mechanics.
