Quantum Does What Quatum Does

It is a proven scientific fact that objects at a sub atomic level act do not behave as expected ......

Be A Quantum Mechanic

.... every spookiness (as Einstein described this), from quantum entanglement, which is when two particles apparently remain connected, even when they are not in direct contact (proved for the first in 1969), to objects acting as a wave, when expected to be particles is weird.

This latter was found, with the classic double slit experiment, so beloved of science teachers at school. This, for those who school memories are a bit closer to Tom Browns School Days, than they care to think about, is where a single light source passes through some card with just two slits in it and is diffracted on to a screen. 

Double Slit Experiment

This suggests that light travels as a wave, like sound waves do, so, so far so good and as expected. However experiments found that when one single photon of light is fired at the two slits, then instead of the one photon going through one slit or the other, it also travels through both slits and diffracts ..... now that's spooky!!

This means that the one particle is still travelling as a wave ..... which tells experimenters that when a particle of light, i.e. a photon is observed, the act of observation cause the collapse of the wave function and it acts as a particle (known as the Copenhagen Interpretation). But when not being observed the photon is in a strange probabilistic state of being in more than one place and travels as a wave.

Einstein famously found this conclusion to be unacceptable. He understood the physics and indeed it was he who actually proposed that light could act as a particle, which he called a light quantum (now known as a photon), but Einstein eventually came to reject quantum mechanics, believing that it lacked a useful basis for physics. He thought that reality required firm predictions and direct observations.

But alternative explanations as to what is happening to that photon, when observed acting as a particle, but acting as a wave when unobserved, are also proposed. One, which has some supporters, is the Many Worlds Interpretation (MWI) of 1957 by Hugh Everett III. This essentially is an early Multiverse theory (which we have discussed in another post).

In the Everett version, whenever an observation is made, such as in the Schrodingers Cat conundrum (whereby the cat is both alive or dead in the box until its opened, at which point the cat is either alive or dead, but not in both states anymore),  then the universe splits into two: in one the cat is alive, in the other, the cat is dead. This neatly sidesteps the problem of how the universe decides the quantum event of whether the cat is alive or dead, but then introduces the concept of an infinite number of universes created by every quantum event, in every universe. So not an entirely satisfactory explanation either.

Whatever the explanation, some of this Quantum mechanics being tried in both:

•  Computers (using qubits in which a qubit can be or, or an arbitrary complex linear combination of states and called the quantum superposition) but with the restriction that Quantum computers will be practical and useful for only a limited type of problems only, typically problems with high complexity.
• And military communications via quantum cryptography (quantum communication creates secure channels for communication protected from eavesdropping by using quantum entanglement, quantum uncertainty, and the no-cloning theory which states that quantum information cannot be copied, to ensure a message hasn't been opened).  
  

Personally I think I'm with Einstein on this subject ....