In physics, wave function collapse, or collapse of the wave function, is the position held that all particles, electrons in particular, have a “wavelike” motion (Louis de Broglie, 1923), which can be mathematically quantified according to a “wave function” (Erwin Schrodinger, 1926), and that normally an electron will fill a certain volume of space, such as a box, in entirety, being found anywhere inside that volume, but that when we look into either side of the volume to find the location of the particle, the wave function will instantaneously collapse, thus form into a particle, and “decide” which location to be in. 
The mathematical formalism describing the collapse of the wave function was developed by John Neumann, based on the previous so-called “Copenhagen interpretation” work of Niels Bohr, Max Born, and Werner Heisenberg’s uncertainty principle.
The famous thought experiment of Schrodinger’s cat, i.e. a cat that is both dead and alive, is based on the absurdity of certain interpretations of the notion of a wave function collapse owing to observation.
Adjacent is a visual depiction, according to English physicist John Gribbin, of the notion of the wave function collapse, : (A) common sense dictates that an electron is in a definite location, even if we don’t know where it is; (B) the Copenhagen interpretation states that the electron exists as a wave filling the box, and could be anywhere inside; (C) at the moment we look for the electron, the wave function collapses at a certain location; (D) common sense says that if we slide a partition into the box, without looking, the electron must be on one half of the box; yet the Copenhagen interpretation states that as long as we don’t look, the electron will still occupy both halves, and that it only collapses on one side when “we look”; (E) as long as we don’t look, even if we move the two halves of the box far apart, the wave still fills both boxes; (F) if we then “look” into the two separated boxes (even if they are light years apart), the wave function will collapse, instantaneously, and the particle will “decide” which box it is in. 
In human physics, some have argued that wave function collapse explains things such as: consciousness, free will, and or the existence of God.
American physicist Robert Doyle, for example, argues, in his 2011 book Free Will, that the wave function collapse is one of the steps, along with entropy increase, involved in the “creation” of every material object in the universe, and that measurement of the wave function collapse produces new information, and that, in some way, this gives humans free will. 
● Double slit experiment
1. (a) Gribbin, John. (1998). Q is for Quantum: An Encyclopedia of Particle Physics (pgs. 87-89). Simon & Schuster.
(b) Thims, Libb. (2007). Human Chemistry (Volume One) (Molecular Orbitial Theory Timeline, pgs. 248-50)). Morrisville, NC: LuLu.
2. Doyle, Bob. (2011). Free Will: the Scandal in Philosophy (pg. 12). I-Phi Press.
● Wave function collapse – Wikipedia.