## Physics Can Be Spooky!

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?

A quantum is a ‘package’, and

is a way of looking at, for instance, electromagnetic radiation, which can be

viewed as acting with the characteristic of both

waves and particles, for example a photon (that transmits light

and carries the electromagnetic force).

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.”