As Erwin Schrödinger cruises down the highway, a patrol officer pulls him over for a suspicious-looking car. The officer strolls up to Schrödinger’s open window and asks for his license and registration and whether the Nobel laureate will allow a search of his trunk. Schrödinger pops the trunk and the officer looks around. Approaching the window again he asks, “Are you aware you have a dead cat in your trunk?” Angrily, Schrödinger replies, “Well, I do now!”
This joke refers to the eminent physicist Erwin Schrödinger’s famous thought experiment involving a cat that exemplifies the oddity of quantum mechanics. In the thought experiment, a box contains a cat and a vial of poison that a radioactive atom will trigger upon decaying. Because the radioactive decay is a quantum event, after one hour the atom will be an equal mixture of a decayed state and an undecayed state. According to some interpretations of quantum mechanics, the cat also exists in a mixture of dead and alive states. The really interesting aspect comes in trying to determine the correct interpretation of quantum mechanics.
Some interpretations argue that the mathematical tools used to do quantum calculations, namely the wavefunction ψ, reflect the actual reality of the world and that the cat exists simultaneously in a mixture of disparate states. Others contend that the wavefunction represents our lack of knowledge; the cat is either dead or alive but we won’t know the proper state until we open the box. Even after 100 years of studying quantum mechanics, no experiments give a clear answer on the proper class of interpretations, although recent research tends to favor the “wavefunction-as-reality” models.
A third class of models offers a more radical solution based on the existence of a multiverse. These models propose that a repulsive force exists between particles in each of the clones in parallel universes. This repulsive force causes ripples to propagate through all the parallel universes, leading to the weird effects seen in quantum experiments. Computer simulations with 41 such universes reproduce many of these “quantum” effects, including those of the iconic double-slit experiment, and the level of agreement increases with the number of parallel worlds. This suggests the intriguing possibility that future research may determine the number of parallel worlds in the multiverse.1
At this point no one knows the final answer to the question, what is the ultimate nature of reality? Maybe things really exist simultaneously in different states or maybe not. Perhaps quantum effects simply result from interacting multiverses. The very nature of the question assumes an objective physical reality, governed by physical laws, that exhibits an intelligible regularity. Furthermore, this physical reality must not be divine (and thus an object of worship) but it must be good (and thus worthy of study). Finally, to question the ultimate nature of reality requires that the human mind can comprehend all these things. Only the Christian worldview anchors all these necessary requirements for asking questions about the nature of reality. The fact that scientists consider it important to ask such questions, and diligently seek answers, points to the existence of an Intelligence behind the universe.
- Zeeya Merali, “Quantum Physics: What Is Really Real?,” Nature 521 (May 2015): 278–80.