When heisenberg proposed his interpretation of quantum mechanics, it was met with some skepticism in the scientific community. the most outspoken critic was einstein. perhaps you have heard his quote "God does not play dice". specifically, he is asserting his dissent from the orthodox view of quantum mechanics, which claims that nature is inherently probabilistic, and small particles do not exist in particular states, but in many states at once, each state having a probability of being measured. In the early days, einstein used to devise elaborate gedanken experiments wherein it was possible to know a particles momentum and position exactly. the quantum physicists would have to show him how his experments would fail, and in general, it was very difficult. einstein was very elaborate in the construction of apparatus that could be used for measurement. eventually, all his arguments were defeated. the culmination was when bohr used einsteins own theory of general relativity to show that einsteins measurements changed the state of the particle just enough to satisfy the heisenberg uncertainty principle. at this point, einstein et al. adopted a weaker position. there could no longer be any doubt that quantum mechanics (and the uncertainty principle) were correct. but they believed that quantum mechanics was incomplete. that there was more information in the system, that was for some reason hidden. this position is sometimes known as "realism". the position described above is sometimes known as "the orthodox position". einstein, schrÃ¶dinger, bohm, et al. were realists. included in their number were many of the early fathers of quantum mechanics. let me quote schrödinger in his gedanken experiment to show the absurdity of the orthodox position. this is known as schrödinger s paradox. to summarise, we put a cat in a box, and tie his fate to a quantum event, which is governed by quantum indeterminacy. if we perform no measurements on the system, then the cat must be simultaneously dead and alive. schrödinger (and others) regarded this as patent nonsense. the cat must either be dead or alive, it doesn t check to see whether anyone is looking before it decides whether to live or die.