Schrödinger’s cat is one of the well-known thought experiments to explain the Copenhagen interpretation of quantum mechanics. In the extreme microscopic scale, we can no longer observe things in the manner that Newtonian physics works.
Observing things in the quantum level, what we see would be no longer distinctive between particles and waves. As commonly known, when and if we see them, they act like particles; at the same time, when and if we don’t, they act like waves. With this duality, we would face the uncertain probability of indeterminacy — whether these fundamental elements are waves or particles. Einstein said as follows:
It seems as though we must use sometimes the one theory and sometimes the other, while at times we may use either. We are faced with a new kind of difficulty. We have two contradictory pictures of reality; separately neither of them fully explains the phenomena of light, but together they do.
Physicists call them the wave-particle duality, which is typically from the result of the famous double-slit (actual) experiment, which eventually entailed Schrödinger’s thought experiment.
In the double-slit experiment, one fires electrons from one side. These electrons go through the double-slit partition and finally reach the screen on the other side. When one observes the electrons passing through the double slit, they act as particles. The result on the screen, however, showed that they worked as waves.
When we observe them, they are particles. When we don’t, they are waves. The result implies the unavoidable interference of our observing action per se.
Our act of observation is, after all, perceiving a set of electrons and other particles interacting with the objects we observe. As such, we can’t be completely objective. Because of such inter-subjective nature of our observation, anything we see is inevitably the particles; at the same time, this experiment also teaches us anything we see could be the waves as well. Without our observation, however, the quantum elements must be simultaneously the particles and the waves, which is called quantum superposition.
(It could also be part of the observer effect discussions in which some physicists point out category errors. But we don’t go to these technical details here.)
Indeed, spacetime in the universe consists of the full continuum of such quantum elements, which are in the probability of wave-particle duality. And the act of our observation itself is also part of this continuum. We can never stand outside of this quantum spacetime. Thus, we are inevitably at the prison of a tautology, saying what we can see is what we can see; what we can’t is what we can’t.
Aside from this double-split experiment, what we know well is Schrödinger’s cat.
Like Einstein, Schrödinger himself didn’t agree with this wave-particle duality. His intention for this thought experiment was to show how this duality sounds contradictory, ambiguous, even nonsense.
It goes this way:
There are a cat, a flask of poison, and a radioactive source are in a sealed box. If a set of Geiger counter detects radioactivity (a single atom decaying as a particle), the flask breaks and releases the poison, which kills the cat. If the Copenhagen interpretation is right, this cat must be simultaneously alive and dead unless and until one looks in the box to check the cat is either alive or dead, not both alive and dead. It poses the question of when and how quantum superposition ends and reality collapses into one possibility or the other.
Just like other cosmological theories from the Big Bang to Singularity to black holes and more, describing such a thing as quantum mechanics with our everyday items would sound paradoxical, even nonsense.
Like Einstein did not accept the expansion of the universe, Schrödinger himself tried to demostrate his disagreement of the quantum superposition by introducing this thought experiment. Einstein also welcomed it. Quantum physics was still so uncommon in the 1930s.
Contrary to his intention, however, Schrödinger’s cat positively caught many curious attentions, even cited among various pop cultural trends. Artists and philosophers loved it.
Despite the risks of various misuses and category errors, its implication of this thought experiment was so impactful, which could lead us even to the realm of contemplation. After all, the thought experiment of theoretical physics and cosmology could be quite similar to the contemplative reflections.
The ultimate reality would inevitably rest in such superposition.
Does God exist or not?
He is in the superposition of the Cloud of Unknowing. It is so uncertain and probable. Once we try to see Him, some would say He exists, and others would say He doesn’t. It is up to how we try to see Him. Just like Schrödinger’s cat, it is up to us if He is alive or dead.
Image by Gerd Altmann