What is the definition of a "measurement" in quantum physics? The usual example used is bouncing a photon off an electron in order to measure the electron's position or momentum. However, do photons not bounce of electrons naturally without measurements being made by a conscious observer? Do these physical interactions cause the collapse of the wavefunction or does there have to be an observer present? Furthermore, measurements can be made in a more indirect manner, for example the tides allow us to infer the existence of the moon. Everything in existence is contingent upon everything else in existence, so in measuring one property of one particle are indirectly measuring many other things. Do the wavefunctions of all these things collapse?