Dead or Alive?

Imagine a black box. Inside is an atom of radioactive matter, a radiation detector, a flask filled with a toxic chemical and a cat. Once the box is closed, at some point, the radioactive atom will decay, emitting radiation, triggering the detector that is linked up to the flask, releasing the chemical and killing the cat. Being on the outside of this box means that you are not able to see if the cat is dead or alive. The only way to find out is to open the box.

This hypothetical experiment links the atomic world to the world that we know. A change in one leads to a change in the other. Or does it? 

The systems that govern the very small (atoms, electrons etc.) known as quantum systems, can exist in mixed states. Atoms and electrons can act as waves and as particles, inheriting the characteristics of both. At the human scale, we do not see mixed states. Have you seen a half-dead cat prowling around? We either see a dead cat or a live one, not a combination of the two scenarios. 

Finding a solution

One attempt at resolving this confusion is to suggest that the action of observing the cat by opening the box results in the known outcomes we observe in reality. This is known as the Copenhagen interpretation. An electron is not observed in a mixed state. Before being witnessed, the state of an electron is dependent on a probability in the same way that the flip of a coin could give you either heads or tails. It is only once the coin has been flipped and comes to a rest that you know the result is tails.

Unfortunately, the Copenhagen interpretation does not include an explanation for why these strange things happen. It is the same as asking someone to justify their answer and you get the reply “Because it just is”. After all, asking you to believe that a cat can be both dead and alive and then magically becomes one or the other is not a particularly robust argument. 

What if we use an iPhone to record the cat in the box? Well you can only see what the iPhone has filmed after you have opened the box. Before that, the iPhone is also in a mixed state: One iPhone features a recording of a live cat and the other features a recording of a dead one. 

What about the cat itself? Surely the cat can recognise that it is half-dead? Sadly, even consciousness can not help us. There would be a cat that experiences death and there would be another cat that would continue to experience life. 

Another universe? 

Each time there is a quantum possibility, which is represented here by the cat’s survival, we have a range of worlds, each representing one possible outcome. Now this is not the complete picture. When you think of a parallel universe you may think of those big decisions you have made during your life and how a different decision could have affected the rest of your life up until this point. 

However, while it may be possible for there to be another version of you, this relies on the assumption that a difference in quantum states is based upon the narrative of your life. But the laws of physics have little regard for your life story. The difference in outcomes between different universes can be as small as one electron in a different state. An alternative to a dead cat may not be a living cat. The cat could explode into glitter, it could become the prime minister, or it could survive the chemical altogether. In fact, the possibilities become endless. We can’t even describe all of the alternatives because we do not know the rules that govern these other universes. This makes the chance of there being another you negligible, so invest wisely in yourself.

“In fact, the mere act of opening the box will determine the state of the cat, although in this case there were three determinate states the cat could be in: these being Alive, Dead, and Bloody Furious.”

Terry Pratchett


Inspiration: Seventeen Equations that Changed the World by Ian Stewart

Image credit: Kitten Rain


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