Here’s a multiverse question I received the other day.

I would like to know how parallel universe advocates use the double slit experiment of firing photons through the slits results in validation of a parallel universe model. Could you explain and elaborate?

Answering the question requires a working knowledge of the double slit experiment. Rather than reinvent the wheel, the following video explains the relevant aspects of the experiment well.

The pertinent points are:

1. As an electron propagates from the gun to the slit, it exists in a superposition of different states (going through one slit, the other slit, neither slit, or both slits). The interference pattern on the wall confirms this indeterminate state.

2. Researchers measure which slit the electron passed through, which then causes the electron to exist in a definite state (passing through either one slit or the other, but not both).

Mathematically, physicists describe the initial superposition of states with a wave function. Yet any specific measurement of the system results in a definite state. Furthermore, mathematical operations on the wave function correctly determine the probability of each of the possible outcomes.

The slit experiment’s results are well established—the question is how tointerpret those results. An increasingly popular interpretation of the experiment results argues that measurements cause an irreversible interaction with the system that leads to the definite result. Rather than the wave function collapsing, it “decoheres” like a single strand of hair disentangling from a large knot. And this is where the experiment becomes relevant to the multiverse discussion. Physicist Hugh Everett used this quantum decoherence to develop the many-worlds interpretation of quantum mechanics. This interpretation posits that reality is a many-branched tree consisting of every possible quantum outcome rather than being a single unfolding history. This interpretation leads directly to Level III multiverse ideas.

Historically, the most popular interpretation, the Copenhagen interpretation, argued that the measurement forced the superposition of states defined by the wave function to “collapse” to the specified value that was measured. In other words, the act of measuring took the indeterminate state and forced it into a determined state. The quantum “weirdness” arises because the value of the determined state can only be calculated in terms of probabilities, and the probability of any given result is usually less than one.

It remains to be seen which quantum interpretation will prevail. However, the evidence to date argues that a multiverse strengthens rather than threatens the Christian faith.

If you would like to see a question about the multiverse addressed in this forum, send it to multiverse@reasons.org.