Another perspective of the Schrödinger’s Cat Experiment
Why do we attach the quantum event probability to a macroscopic object like a cat?
Even if you are from a non-science background, you must have come across the term “Schrödinger’s Cat” at some point of time. This thought experiment served as a challenge to the problem seen in Copenhagen’s interpretation of quantum mechanics. Let’s define the thought experiment once again:
Inside a steel chamber, there is a Geiger counter that has a tiny amount of radioactive substance such that it decays in about one hour. With an equal probability, the atom may not decay too. If the discharge happens, it releases a hammer through the relay and smashes the small beaker containing hydrocyanic acid. If the entire system is left for one hour, the cat can either be alive or dead depending on whether the atom has decayed or not.
Let’s assume that our experiment is free of the Zeno effect for simplicity. In this thought experiment, we only think about whether the cat is alive or dead based on the radioactive material inside it. But why is the existence of the cat being decided as a quantum event, when it itself is a macroscopic entity? Macroscopic items follow Newtonian mechanics. So, why is quantum behavior attached to the existence of the cat?
Well, everything in the world is made of atoms. Taking the example of a human, we can think of this phenomenon as quantum behavior being exhibited at an atomic level, while our body as a whole (or any part conceived as non-microscopic) exhibits Newtonian behavior. However, we are yet to answer the question at the beginning, i.e. why do we attach quantum behavior to the existence of the cat.
In quantum mechanics, we have a phenomenon called quantum entanglement, which means that wave functions can interact with each other, or get “entangled” to result in a new wave function. Since, cats are also atoms at the microscopic level, so, the radioactive substance gets entangled with the atoms of the cat. Hence, the quantum behavior of radioactive substance gets entangled with the hammer, then with the hydrocyanic acid and then finally the cat. Due to this entanglement, we attach quantum probability to the existence of the cat.
An interesting fact about quantum mechanics is that we follow two different equations for two different instances for defining the quantum state of an atom:
- When we are not observing, the wave functions evolve under the Schrödinger’s equation:
2. When we are observing an instance of the wave function, we just square the complex amplitude of the wave function to determine the probability of finding that particle in that region:
This proved that the world is no longer deterministic, but rather probabilistic. This didn’t go down well with many notable scientists. It was in response to this that Albert Einstein famously said:
“God does not play dice with the Universe.”
However, maybe we have got it all wrong. Maybe, the Schrödinger’s equation paints a complete picture of the universe, while the measurement at any instance is just a tiny fraction of it, the part where we become entangled with, resulting in quantum superposition. This view now makes the universe deterministic again because “our original version” only experiences the instance that we get to experience, while the parallel worlds will see the other instances and it will be as real for them, as it is for us. One common argument about this explanation is violation of energy conservation. As per quantum mechanics, the energy is 100% conserved in each world, but, the way it is perceived in each world changes. The fabric of reality is different in different quantum version of you.
Now, coming back to the thought experiment, why does the quantum event end once we open the box to see whether the cat is alive or dead? Well, going by theory of multi-worlds, we can interpret this as the cat being alive or dead depends on “which version of us” sees the cat state. At every instance, our atoms entangle with other atoms around us. These result in the creation of new wave functions every time. When the wave functions come in contact with the environment, it is known as environmental decoherence. Since humans are also made up of atoms, we can imagine that multiple versions of us are created every instant with varying quantum probabilities (proportional to A²) due to decoherence, and these versions of us see different versions of the cat.
So, while your conscious copy may see the cat as alive, one of your quantum copies might be seeing it as dead. And remember, these quantum copies aren’t aware of each other’s existence and don’t interact with each other, another strong reason why we haven’t been able to find parallel universes. All these copies are said to exist in the real plane, which otherwise would be thought of as imaginary, as a common misconception. Sadly, there’s no answer to how many quantum copies of us exist because it increases every time a quantum superposition happens due to quantum entanglement.
Probably, one of my many quantum copies is reading this blog right now while I am writing this. I just want to say to my quantum copy, Hi!
P.S.: Everything mentioned in this article is as per my interpretations of the Theory of Many-Worlds. I have tried to put it in my own way for simpler understanding. If you liked reading this, please leave a clap!
