Quantum ‘Mystics’
This blog was written by Shaeema Zaman, during her PhD at Aarhus University, Denmark with the ScienceAtHome research group.
The ‘mystical’ properties of quantum physics have often been found in science fiction and popular culture. It is a difficult concept to understand but holds a fascination for many of us. So, what are the ‘mystical’ properties of quantum mechanics? Quantum mechanics is a mathematical description of the microscopic world. It is a world, where particles can exist in multiple places at once, spread themselves out like spooky waves, tunnel through impenetrable barriers and are also connected across vast distances.
Despite these bizarre properties, quantum mechanics rule everything around us. It’s present in the sun, USB memory sticks, touchscreens, electric chips on our phones and even in the cells of our body! You might ask why do we call it mystical if it's everywhere around us? It is because quantum mechanics runs against our everyday intuition about how the world works. The famous Schrödinger equation doesn’t dictate the rules we use to describe everyday motion. For that, we use Newton’s laws of motion. These are learned in high-school to investigate a vast majority of the phenomenon. We got used to investigating phenomena which obey the rules of classical mechanics and define our intuition of how things ‘should’ behave. Quantum mechanics challenges our intuition, so it seems weird and mystical. But it is just counter-intuitive!
The next question is whether classical mechanics and quantum mechanics ever meet. Yes, they do! A more appropriate answer would be that there is not a real difference between the rules that apply to the macroscopic and the rules that apply to the microscopic scale. The universe is quantum on every scale. The classical physics that we see is just the result of quantum physics when applied to really big things. If we look at the behavior of a single electron in an atom, it exhibits the quantum behavior where the energy will jump only to discrete levels. However, when we talk about a whole lot of the macroscopic number of electrons in a conductor, we don’t talk about the discrete levels. Once a voltage is applied across the conductor, the electrons move in a seemingly classical way. The average velocity seems to increase smoothly without any discontinuous jumps. Actually, the individual electrons in the conductor are still jumping between discrete states of energy. However, the states become more distinct as we add more electrons and the energy difference between states becomes smaller. There comes a stage where all the energy states become so close and classical, that we call them energy bands in solids. They're not really continuous energy bands. But when we’re working at the coarse scale that defines everyday life, they blur together so thoroughly that we call them continuous energy bands. It’s like saying that the quantum behavior gets blurred. It still exists but it’s so blurry that we can’t use it to describe the phenomenon. However, it is still widely unexplored where and how the transition between the quantum and classical world appears.
Given that quantum physics governs everything around us, it is interesting to step back and reflect on why we call it weird or mystical. We’re surprised by quantum physics because it is counter-intuitive!