The Quantum Quandary: What the Hell does it Mean?

Prerequisite: Quantum Physics For Dummies: What Is It?

The study of quantum mechanics is a lot like the study of human memory. Neuroscientists have identified a solid set of consistent facts about our memory. For example, it is known that the more times you see an object the better you are able to remember it, and that the farther in time you move away from an event the more difficult it is to remember. Furthermore, neuroscientists can make accurate predictions about someone's ability to remember something based upon equations they have developed that describe the memory process. However, neuroscientists lack a full understanding of how the memory process works; the actual biological mechanisms that allow the brain to store and later retrieve information are still being worked out. It is very similar to how Isaac Newton developed an equation that described the action of gravity with pretty decent accuracy, but still did not understand how gravity actually worked or where it came from. It was not until several centuries later that Einstein came forth with a proposal for how gravity worked (that it was a result of the warping and curvature of physical space caused by massive objects). Right now, all that memory neuroscientists have is theories. And there are many, each with different interpretations and implications. This is where quantum mechanics is right now too.

The equations of quantum mechanics make extremely accurate statements about our reality. It is in fact considered to be one of the strongest mathematical descriptions of our reality ever formulated, and has thus far not made one incorrect prediction. Nevertheless, physicists have little to no understanding of how it works and what it implies about our reality, and this in turn explains why laypeople are also confused and constantly hear and read contradicting interpretations of quantum mechanics. It is because there is no single accepted interpretation - in fact there are at least ten and probably more.

The demon that has plagued our understanding of quantum mechanics is the "wave function". First let's very briefly summarize what a wave function is. Quantum mechanics says that just like energy has a wave-like motion (light waves, sound waves, etc.) so too does matter (electrons have wave-like properties; even humans do but it is too small to detect). The mathematical equation that describes a particle (its energy, momentum, position, etc.) is called its wave function. It is important to note that the wave function is an abstract, non-real, mathematical description, and not something that is physical. In other words, it does not imply that a particle actually moves in a wave-like motion, but rather that it has wave-like properties that can be described in the form of a wave equation.

One of the most important characteristics of the wave function is that it provides a probability distribution for the properties of the particle it describes, as opposed to exact properties. This does not reflect a shortcoming of the wave function, but rather reflects something fundamental about nature. For example, the wave function can tell you the probability that a particle is in a certain location, but it cannot tell you its exact location. The crux of the confusion comes from trying to decipher what this actually means. The double-slit experiment with one electron indicated that the electron somehow passed through both slits at the same time, but what is the underlying mechanism that allowed this to happen? And how can we reconcile this with the fact that when we view an object, it always is in one place? Does the act of observation randomly collapse the wave function of a particle from an infinite array of possible locations to a single location? What does this say about determinism? We only have theories. The following is a description of two of the more mainstream theories of the interpretation of quantum mechanics and their implications:

Copenhagen Interpretation:
This was one of the first widely accepted interpretations of quantum mechanics and is probably the one most are familiar with. It was formulated in 1927 by two of the trailblazers of early quantum theory, Neils Bohr and Werner Heisenberg, who collaborated in Copenhagen. Their theory was that the act of observation causes wave function collapse, in which the probability distribution describing all of the properties of a particle decays into a single reality that is defined by the measurement. In essence, it would mean that we as conscious observers of the world actually create reality - that we pick one reality out of a possibly infinite set of potential realities and give it a physical, definable form.

Many-Worlds Interpretation:
This relatively newer interpretation of quantum mechanics denies the phenomenon of wave function collapse. Instead, it views all possibilities dictated by the wave function to be equally real, and says that every possibility plays out in its own unique universe that is part of a grand multiverse. Thus, our universe represents one branch of outcomes out of all the possible outcomes that defines the multiverse. For example, when you roll a die, within the totality of the multiverse every number is rolled simultaneously in a different universe; in your universe, you may roll a 3, but at the same time in another universe, a copy of you may roll a 2. The Many-Worlds Interpretation claims that it provides an explanation for how random, non-deterministic events such as the nuclear decay of atoms can be described by the deterministic equations of quantum mechanics.

Whatever theory turns out to be correct (assuming that an answer can be ascertained, which is not a definite) one thing that is certain is that we are ignorant of some enormous details about our reality which carry huge implications.