I was having a debate with my friend the other day (I'm the computer guy, he's a virologist), and he's insisting that quantum mechanics isn't one of the most complete and accurate scientific theories that exist, implying that there's "something more" out there. I threw out the trope of "If quantum mechanics weren't real, than [picks up cellphone] wouldn't exist", but he rebutted that statement by claiming that plain materials engineering is sufficient to make functional chips.
I dispute that claim. To what degree are quantum mechanical principles used in a practical fashion in the production of semiconductor devices? Bonus points if you can name additional applications which utilize quantum mechanics!