Sometimes real science can be just plain weird or even genuinely spooky.

Take the phenomenon of quantum entanglement. Albert Einstein famously derided it as “spooky action at a distance” or “spukhafte Fernwirkung” in his original German.

So, what’s it all about?

Sometimes, when quanta interact with one another, they can form their own entangled system. Thus, when a pair or group of particles can no longer be said to be acting as a group of systems but can only be described in terms of a single system, the particles are said to be ‘entangled’.

An example of entanglement occurs when a subatomic particle decays into a pair of further particles. These decay events obey the various conservation laws; as a result, the measurement outcomes of one daughter particle must be highly correlated with the measurement outcomes of the other (so that total momenta, angular momenta, energy, etc remain roughly the same before and after this process).

Why is this important? Because there are a number of practical applications, especially in the IT area. Scientists are hoping quantum computing will enable us to build faster and more powerful computers.

And, if we can eventually make quantum computing work, how about quantum commuting? What’s the likelihood that we can beam ourselves into work and miss the traffic queues? Well, don’t hold your breath; however, so-called quantum teleportation may yet prove to be a useful, secure way to transmit encrypted information.

In 2012, the journal *Nature* published work by scientists
at the Institute for Quantum Optics and Quantum Information in Vienna. The team
succeeded in ‘teleporting’ photons 89 miles between the two Canary
Islands of La Palma and Tenerife. Later that year, *Nature* also published a Chinese team's work, which involved ‘teleporting’
photons 60 miles away.

Quantum teleportation is not actually what we see going on in *Star Trek*. Really, it’s a form of communication, the process by
which quantum information (eg the exact state of a particle) can be transmitted
from one location to another. Because it also depends on classical communication,
which can never work faster than light speed, it can’t be used for superluminal transport or communication.

There has been heated debate amongst the scientific community about quantum entanglement and whether some ‘classical’ (ie non-quantum mechanical) physical mechanism could eventually explain entanglement. The original research was initiated by a 1935 paper from Albert Einstein, Boris Podolsky and Nathan Rosen describing their EPR paradox (Einstein, Podolsky, Rosen) followed shortly afterwards by several papers from Erwin Schrödinger.

Although these renowned scientists were skeptical of certain counterintuitive properties of entanglement, many years later John Bell showed with his theorem that we can tell whether ‘spooky action at a distance’ is real or not. Eventually entanglement was verified experimentally using Bell’s theorem and recognized as a valid, fundamental feature of quantum mechanics. Nevertheless, the debate continues today.

Heisenberg's
uncertainty principle

This tells us we can never predict the momentum of a particle exactly,
or even the total momentum of two entangled particles. Thus, we can't ever know
exactly what the momentum of a particle will be before we measure it, but we do
know that the total momentum of the two particles put together doesn't change
when the particles act on each other (conservation of momentum).

Austrian physicist Erwin Schrödinger conducted his famous thought experiment in 1935.

Known as ‘Schrödinger’s cat’, this hypothetical experiment places a cat in a sealed box along with a radioactive source, a Geiger counter and a bottle of poison. Under the rules of this experiment, if the Geiger counter detects radiation, it triggers a mechanism that smashes the bottle of poison so the cat would die.

Thus, over a period of an hour, say, there is a certain statistical probability that the source will have released some radiation – goodbye cat! However, there’s also a probability that it won’t have. Thus, the only way to know whether the cat remains alive at the end of the experiment is to open the box and check it.

Schrödinger designed the experiment to illustrate flaws in the so-called ‘Copenhagen interpretation’ of quantum mechanics. This states that a particle exists in all states at once until observed; similarly, therefore, as long as the box remains closed, the cat is deemed to be simultaneously both dead and alive. Common sense clearly indicates that the cat cannot be both dead and alive (regardless of whether it is being observed) illustrating the problems of interpreting quantum physics in classical terms.

In Schrödinger’s own words, his thinking “prevents us from naively accepting as valid a ‘blurred model’ for representing reality.”

## Comments

You can follow this conversation by subscribing to the comment feed for this post.