The double-slit or two-slit experiment was originally performed by Thomas Young in 1801, but it has become one of the key experiments illustrating the probabilistic nature of quantum mechanics, which do not follow Newtonian physics. It defines how light can display characteristics of waves and particles at the same time, or where electrons seem to have appeared at two separate positions at the same time. In relation to momentum and position in this experiment, Richard Feynman has written that in relation to the uncertainty principle of Werner Heisenberg, he “recognized that if it were possible to measure the momentum and the position simultaneously with a greater accuracy, the quantum mechanics would collapse” (Feynman 2011).