My question is: What is the contribution of Quantum Physics to the discovery, of the transistor? In Adam Becker's book What is real? I read that, "the discovery of quantum physics in the early twentieth century led directly to the [discovery] of silicon transistors..." He implies that, the observation that atoms can be in two places at once, as formulated in QM led to the discovery of the transistor. I read in Wikipedia that "Quantum mechanics differs from classical physics in that energy, momentum, angular momentum and other quantities of a bound system are restricted to discrete values (quantization); objects have characteristics of both particles and waves (wave-particle duality); and there are limits to the precision with which quantities can be measured (uncertainty principle)." So which of these fundamental principles of QM "led directly to discovery of silicon transistors?" There is a clue in Wikipedia History of Transistor page: " John Bardeen eventually developed a new branch of quantum mechanics known as surface physics to account for the "odd" behavior they saw..." But does not explain what these "odd behavior" are. And it is not clear if Quantum mechanical concepts were used to discover the transistor, or if, on the contrary, John Bardeen developed a branch of QM from what he observed. The two are different.