Friday, April 24, 2015

A Particular Universe: Quantum Theory and Multiverses

While the existence of other universes appears to be a difficult idea to grasp, it can be surprising that the most important part in proving their existence involves studying the smallest particles that exist. Simply stated, the study of quantum physics is a crucial part of our understanding of multiverses.

Perhaps the first thing we must understand about in quantum physics is that we don’t truly understand anything at all. More accurately, the only certain thing we are sure about quantum mechanics is uncertainty, as represented in the Heisenberg Uncertainty Principle. According to this principle, given a particle with two physical properties, the more certain we are of the value of one property implies the less we know about the other. In this case, we are particularly interested in the relationship between the position and momentum of an electron. According to the uncertainty principle, the more we accurately pinpoint an electron’s location, the less we know about its momentum, and vice-versa.

This statement brings us to an important part of quantum physics: the wave function. The wave function is the mathematical formula used to describe quantum objects. Unlike traditional formulas, however, the wave function does not provide concrete information about an electron, but probabilities of where the electron may lie. A standard example to illustrate the wave function is the firing of an electron gun toward a phosphorescent screen. After the gun is fired, the probability of the electron being in any given spot is reduced as time passes. However, when the electron hits the phosphorescent screen, the exact position of the electron is known again; this reset is known as the collapse of the wave function.

The Copenhagen Interpretation of the wave function states that a quantum particle does not exist in one state or another, but exists in all states at the same time. It is only when the particle is observed that it is “forced” to choose a state, which is what becomes observed. The implications of the Copenhagen Interpretation are well described in the phenomenon of Schrodinger’s quantum cat. In this thought experiment, there exists a box, split in half, with a single electron as well as a cat. Along with this cat, there exists an explosive. If the electron is found on the same side as the cat, the explosive detonates and the cat dies. Otherwise, the cat stays alive. According to the Copenhagen Interpretation, as long as the box remains closed, the cat is both dead and alive at the same time, also known as a superposition of states. If the two halves of the box are separated, and placed at opposite ends of the world, this duality continues to exist. It is only when the box is opened, and the wave function collapses, that we can determine the state of the cat.

The Many Worlds Interpretation, proposed by physicist Hugh Everett, was first thought of by Everett when he was wondering what would happen if the wave function never collapsed, even upon opening the quantum box. According to his interpretation of the wave function, Everett states that when the box is opened, the universe splits into two separate universes: one where the cat is alive, and the other where it is dead. This philosophy can then be extended such that every time the universe is faced with a quantum decision, it is split such that a universe exists where that decision is made, and another where the decision is not made. Succinctly stated, this phenomenon implies that every possible state of the universe exists, leading us to modern propositions of multiverse theory.


Gribbin, John. In Search of the Multiverse. London: Allen Lane, 2009.
Kaku, Michio. Parallel Worlds: A Journey through Creation, Higher Dimensions, and the Future of the Cosmos. New York: Doubleday, 2005.
- Alex Du