3 common misconceptions about quantum mechanics
Any scientific breakthrough or paradigm revolution is followed by at least two things, progress and confusion. Progress, as the momentum of the breakthrough leads to unprecedented leaps in understanding and technology. Confusion, because the novelty of the discovery will also give rise to misinterpretations, misconceptions and sometimes malicious use of new and trending terminology.
Quantum mechanics is no different. Not only did its discovery constitute a complete flip of the way we understand the world, it is also very counterintuitive. It is riddled with hard concepts and experimental results which are difficult to interpret. Not surprisingly, an enormous number of misconceptions followed. Taking into account the fact that physicists still don’t fully understand the true meaning of quantum mechanics, this shouldn’t be a surprise.
In this article we will try to clarify three of the most common misconceptions of quantum mechanics. These misconceptions refer to some of the deepest concepts of the theory, hence clarifying them is a good step towards beginning to get a grasp of quantum mechanics.
Particles can be in more than one place at the same time
Classical and quantum physics have something in common: they aim to understand physical systems in terms of states. A state is just the information you need to describe the system. This particular misconception arises from a subtle difference between how classical and quantum physics describe states.
Coins make for a good explanation of the concept of state. Imagine you have a coin in your hand. It has two states: heads up or heads down. According to classical physics the coin must either be in one state or the other. This is what everyday life tells us. If we consider a “quantum coin”, things are different though. The quantum version of the coin can also be found heads up and tails up, but also in any mixture in between. For example, it can be in a superposition of 50% heads up and 50% heads down. This doesn’t mean you will see two coins where there was only one though. By a process called wavefunction collapse, which we still do not understand well, only one of the states is there upon observation. Which state you may ask? Nature randomly selects one upon measurement, with the chance of getting one result or the other being determined by how much of the two ordinary states is present in the superposition (this principle is key quantum computing, and for Quantum1Net’s quantum encryption key generator).
One can also describe the state of a system in terms of positions, i.e where the system is allowed to be. Does this mean that a quantum system in a superposition can be in more than one place at a time? If the system is a ball on a staircase, does that mean that the same ball could be sitting on multiple steps at the same time?
We have included this item in the misconceptions because people tend to say either yes or no, quite stringently. The truth is though that the superposition principle is an enormous causes of headaches for physicists. Experiments tell us that the possibility of a particle being in more than one place at the same time, or in a superposition of states, has real effects on the evolution of a physical system. But every time we try to see the superposition, collapse kicks in and we get the particle in one of its states. It is still open to interpretation whether the particle is in both states, whether it is potentially in both states, or whether it exists or not until measurement.
The Heisenberg Uncertainty principle is due to technological limitations.
First year undergraduate labs is one of the most important modules in a science degree. Not because of the experiments you will perform but because it is where you are first introduced to errors and uncertainties. In a nutshell, you learn that experiments are not perfect and that for a variety of reasons there is always a limitation to the accuracy of your measurements (limitations of the device, human error, statistical errors… and many more). More importantly, you learn how to quantify these uncertainties and take them into account in your results.
Of course, as technology improves and we learn more about the Universe, our ability to control these uncertainties improves. Before the advent of quantum mechanics it could have been be envisioned that one day we would be able to perform certain measurements with perfect accuracy. Once again, quantum theory changed our perspective of the Universe.
The Heisenberg Uncertainty Principle, first formulated in the 1920s and developed during the following decades, establishes a very strict limit on how accurately one can simultaneously measure the position and velocity of a particle. At first it was understood as stemming from the the fact that to measure where something is, you must disturb it in some way, for example by shining light on it. Following that line of thinking, with a very sophisticated light source one should be able to disturb the particle very little, thus being able to overcome the Uncertainty Principle.
As the years passed it became clear that this is not the case. As sophisticated of a measuring device you may use, you can never make a measurement with more accuracy that permitted by the Uncertainty Principle: you can never exactly know where a particle nor how fast it is moving. To add to that, the better measurement you have of one, the worse your measurement of the other will be.
The Uncertainty principle is not due to technological limitations, it is actually a very deep principle of physics. Without going into detail, it is related to one of the sources of quantum weirdness: in quantum mechanics, the concepts of a “position” or “velocity” aren’t valid as we would usually understand them. Particles are never really in a single place, or at least not how to the concept of position is currently understood (don’t worry, this is very hard to grasp, hopefully it will make you feel like investigating the topic a little more).
Everything can happen, because “quantum physics”
This is perhaps the biggest misconception of them all and one of the largest sources of cons, tricks and lies to ever be related to quantum mechanics. It is essentially due to the fact that there are many strange phenomena which arise as a consequence of superposition and the probabilistic nature of quantum theory.
Quantum mechanics allows things to happen which are classically impossible. For example, superfluid helium can flow through a solid container. In the Sun, atomic nuclei can penetrate high potential wells, allowing fusion and powering our star. This is kind of like kicking a football at a solid wall and it passing straight through (without making a hole). These sort of events are permitted because due to quantum effects, there is a non-zero probability of them occurring. And if we can make a statement about the Universe, as bold as it may sound, it is this: if something can happen, eventually it will, as long as it is compatible with the laws of physics.
The problem here is that many, by accident or on purpose, misinterpret this as anything can happen and will happen, allowing crackpots, cheats and supposed experts to justify ridiculous claims or assert the existence of impossible physical situations, on the basis of quantum mechanics. They forget about the physically possible tag. So while, according to Michio Kaku, quantum mechanics gives a non-zero probability of every single atom in your body materializing on Mars within the next 20 minutes (don’t worry, the probability of this is very small!), it cannot justify magic, witchcraft or most of the things you will see and hear in B-class sci-fi movies, as much fun as they are.
Quantum mechanics is great, but hard
Of course, misconceptions aside, there are still many aspects of quantum mechanics which scientists do not fully grasp. In fact, the general consensus is that nobody, not even the greatest physicists in the world, understand quantum mechanics. We have evolved in a world which we perceive as described by classical physics. The weirdness of quantum mechanics (superposition, interference, entanglement, collapse) is foreign to our minds. Luckily though, we are capable of performing experiments and developing theories which help us learn about and exploit the properties of the microscopic world. But remember, the next time you hear someone using the term “quantum” lightly, be a little sceptical.
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