Why does looking at something collapse its wave function?

Answer 1

It's a measurement. Measurements are represented by operators in quantum mechanics.

Every measurement forces the wave function to collapse to an eigenvector of the operator, the eigenvalue is your measured result.

Different operators have different sets of eigenvectors. This is not necessary, but non commutating operators like position x and momentum p have different sets of eigenvectors. So, if the wave function was in a well defined momentum state, this state is destroyed when you measure the position, and after the measurement the wave function is an position eigenfunction and the well defined momentum it had before the measurement is lost, in terms of momentum eigenfunctions the wave function is now in a superposition of many eigenfunctions.

Answer 2

Unless something is observed, any number of equally "real" possibilities exist.

A classic example of this is the "Schroedinger's cat" thought experiment.
In this, hypothetical, example....a cat is placed inside a totally sealed box with beaker of acid suspended above it. A radio active isotope is also placed within the box along with an apparatus which will detect any decay of the isotope which will then smash the beaker, releasing the acid and killing the cat.
Since the decay of a radioactive atom is a completely random and unpredictable occurrence, unless one looks into the box to check for sure...the cat is both alive AND dead at the same time.
Only by looking within the box to see if the atom has decayed (and thus killed the cat) can one know for sure. By looking inside [observing], one collapses the wave function into one single possibility....the cat is either alive or dead, not both.

Answer 3

because youre blocking the waves, baby.