Schrödinger And His Cat


If you want to see fear in eyes of an quantum physicist, just mention the measurement problem. Basically the problem is how does a wave function collapse. When microscopic particles are not observed their wave function happily obey Schrödinger wave equation. But when we observe the microscopic particle, its wave function collapses. But this contradicts Schrödinger wave equation as it does not allow wave function to collapse*.

Here is what Schrödinger’s cat paradox is:

We take a box and we place in it an unopened container of cyanide.

Connect it to a radiation detector of some radioactive material.

Now when the radioactive substance decay, its decayed material is detected by radiation detector. This caused cyanide to evaporate in environment and anything living (the cat in this case) inside the box will instantly die if it inhales the vapours.

Next we place a cat in the box, and quantum mechanics takes over instantly we close the lid of the box.

When we close the lid, the inside of the box becomes dark. Since we are not observing the atoms of the radioactive material inside, it has a choice; whether to decay or not decay, whether to release cyanide and if cat is dead or not. So until and unless we open the lid and make a conscious measurement, cat is both dead and alive at the same time, which is really a paradox.

Albert Einstein, who was impressed by the ability of the thought experiment to highlight these issues**. In a letter to Schrödinger dated 1950, he wrote:

You are the only contemporary physicist, besides Laue, who sees that one cannot get around the assumption of reality, if only one is honest. Most of them simply do not see what sort of risky game they are playing with reality—reality as something independent of what is experimentally established. Their interpretation is, however, refuted most elegantly by your system of radioactive atom + amplifier + charge of gunpowder + cat in a box, in which the psi-function of the system contains both the cat alive and blown to bits. Nobody really doubts that the presence or absence of the cat is something independent of the act of observation.

It is mysterious fog which prevails in the quantum world. A hundred years and we still need many questions to answer.

Here are some links to know more on Quantum nature.

* Davisson–Germer Experiment

** EPR Paradox

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One thought on “Schrödinger And His Cat

  1. The same kind of paradoxes apply to things like an actuate (verses a potential) infinite. For example, if I were to read an actual infinite number of 100-page books, and my friend read only the first page of every other book that I read, we would both have read the exact same number of pages.

    What this shows is that via reductio ad absurdum, actual infinites don’t exist. The same applies to certain assertions in quantum mechanics. Observation does not establish reality, but rather the other way around. And this is what the cat thought experiment demonstrates.

    But then you will have people that will say ‘you’re laws of logic are classical, mine are quantum’ as if to impress you with their novel idea. Let me illustrate with a story: a man believes he is dead. His wife tries to convince him otherwise but he still believes he is dead. She calls the doctor who explains to him that dead men don’t bleed. Just to prove it to him, they go to a morgue and the doctor pricks one of the cadavers and it doesn’t bleed. Then the doctor says ‘see, dead men don’t bleed. Now if you’re dead you shouldn’t bleed either.’ The doctor then pricked the man’s finger and it started to bleed. As soon as the man saw the blood dripping off of his finger he exclaimed ‘what do you know, dead men do bleed after all’.

    The point is that presuppositions (and everyone has them) will determine what you accept as valid evidence and proof and what you don’t. They determine how you try and rework all of your experimental data to fit your preconceived conclusions. And this is what many quantum physicists do with their concepts of uncausality, superposition, and monism.

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