The Theory of Nothing

What the heck does 'Spooky action at a distance' mean?

What the heck does ‘Spooky action at a distance’ mean?

This phrase has been attributed to Albert Einstein. Supposedly, it’s what he defined Quantum entanglement to be. Einstein hated quantum physics even though he was partially responsible for its origin. He even wrote several journal articles connected with quantum entanglement.

To boil it down to a simple statement, quantum entanglement is what it implies: when a pair of particles is created it acts as if the particles (their physical states) are linked together no matter how far they are separated. If you think about this for a moment, you come to the conclusion that this could make for a very interesting means of communication.

How did they discover this totally unexpected phenomenon? Physicists found that when they measured the physical properties of entangled particles such as two positions, momentum, spin and what have you, these properties were correlated. In other words, they were the same despite being separated. You have to remember that taking a measurement on a quantum particle changes it. In this case one of the particle pair knows what measurement is being performed on its buddy and it conforms to the result. If this sounds crazy, believe me, it is. Hence, this is the reason Einstein termed it ‘spooky action’, implying in a subtle manner that its not what one would expect. That’s the way much of quantum physics is; it doesn’t make sense but experiments show that it’s true.

Most of these experiments involve a subatomic particle that decays into a pair of other particles. When a measurement is made on one of the decayed particles, the entire state of the entangled pair collapses instantaneously before the information about the measurement could reach the other particle, or so it seems. This paradox suggests that the information is transmitted to the other particle at faster than light. This doesn’t make sense, yet it happens.

There have been many attempts to explain this seemingly impossible phenomenon. One theory is that it’s a result of special relativity that says that time dilation (the slowing of time as one approaches the speed of light) causes the two particles to stand still as far as light is concerned. That’s crazy!

The math involving entanglement is very complicated. However, the method of accomplishing it is rather simple. One uses spontaneous parametric down-conversion using a nonlinear crystal in a quantum optic system to split photons into pairs that are phased-matched. See, that makes it simple, doesn’t it? Yeah, right!

As you might expect, this experiment is done with a laser beam, most of the photons of which pass through the crystal unchanged. An occasional photon undergoes what is known as spontaneous down-conversion with Type II polarization correlation. These photons split and make symmetrical beam cones at angles to the original laser entrance beam. These photon pairs are in sync as to polarization. In other words, their waves line up so that both are polarized perpendicular to each other. In other words they act like an old married couple. Just kidding!

This doesn’t sound all that fantastic, but it’s strong proof for quantum entanglement. The implications of this spooky behavior are many: long distance instantaneous faster-than-light communication--think of instant communication to astronauts a billion miles away from Earth; quantum computing--this may result in creating a true artificial intelligence.

However, there is much more experimentation to be done before we get to those future wonders.

Thanks for reading.