Mo' Quantum Mech.

Quantum mechanics – dynamics of the miniature- the theory of the interaction between quanta (energy) and matter; the effects of quantum mechanics become observable at the submicroscopic distance scales of atomic and particle physics, but macroscopic (large) quantum effects can be seen in the phenomenon of quantum entanglement (see below).

Quantum entanglement – spooky action at a distance – Consider for a moment an orange thrown skyward. As the orange moves, it undergoes changes in its position, spin, and velocity (which in turn affects its acceleration). Similar properties are used to explain the ‘state’ of electrons (particles with mass) and photons (mass-less particles), and other elementary particles.


The state of a particle is also called its quantum mechanical description. Some of the properties used to describe a particles’ state are position, momentum, spin, and polarization.

Now imagine that this orange has a friend, which is also an orange. The orange friends are identical in every aspect, and even behave in exactly the same way. When one orange spins left, the other spins left, and these changes occur instantly for both oranges, as if they were in perfect sync. These instant changes occur no matter the distance between the oranges. One might be so brave to state that these oranges are quantum entangled!

Measurements on systems of entangled particles reveal that it is possible, no matter the distance, to change two things at once. This idea defies intuition, and sits very uneasily with most people who might ask questions such as

How can one account for something that was at one point indefinite with regard to its spin (or whatever is in this case the subject of investigation) suddenly becoming definite in that regard even though no physical interaction with the second object occurred, and, if the two objects are sufficiently far separated, could not even have had the time needed for such an interaction to proceed from the first to the second object?

Quantum field theory - (QFT) – the modern relativistic version of quantum mechanics used to describe the physics of elementary particles; it can also be used in non-relativistic fieldlike systems in condensed matter physics.