Albert Einstein once said, ‘God does not play dice with the universe’, to which Niels Bohr replied, ‘Einstein, stop telling God what to do!’ Einstein did not believe in quantum theory because of the mind boggling ideas quantum mechanics predicted. Einstein thought that classical mechanics was the true explanation of reality. In classical mechanics, if the properties of a system are given to you at one instant, you can find the behavior of the system at a different instant. However, it does not happen in quantum mechanics. Quantum world is a world of probability where nothing is certain. Subatomic particles behave very differently than anything big. Do electrons act like waves? No, they do not exactly. Do they act like particles? No they do not exactly.
“Schrodinger’s cat is a thought experiment which explains the strangeness of such quantum aspects.”
Physicists are conservative revolutionaries in the sense that they have to be open for all sort of bizarre phenomena. Schrodinger’s cat is a thought experiment which explains the strangeness of such quantum aspects.
Erwin Schrodinger was among the pioneers of quantum mechanics. He designed this strange thought-experiment. Imagine a cat placed in a box. In addition to cat, there is a
radioactive source, a flask of poison and a Geiger counter. If the radioactive source decays, the mechanical system associated with it operates and breaks the flask. As a result, the cat dies. If the source does not emit radiations, cat stays alive. This is a very simple experiment and a very simple explanation.
However, it is not that simple. Radioactivity is a probabilistic quantum phenomenon. Source may or may not decay and give off radiations. Before the box is opened and its contents are revealed, just as the radioactive source has equal chances of being decayed or not, the cat would have equal chances of being poisoned or spared.
The real question is whether the cat is dead or alive. Quantum mechanics suggests that cat is neither dead nor alive but in the superposition of both the states. Well, at that point, one says that this is preposterous. How can you be both dead and alive? But this is true according to quantum mechanics. The combined states representing both the radioactivity and the cat’s state would be in a strange juxtaposition- half decayed, half not; half dead, half alive. Once someone opens the box, the combined states collapse into one of the two possibilities.
Another quantum physicist, Eugene Wigner, took this experiment one step further. He believed that this experiment could teach us something different about the working of universe, that ‘consciousness controls everything’. Wigner said that if he looked at the cat, his consciousness would determine the existence of the cat. At that point, Einstein went ballistic and said ‘What! You said that you are a conscious being, that’s why you determine that cat is alive or dead?’ The answer is yes.
Wigner made one more step. He asked how he would know that he was alive. According to him, he and cat were part of the same universe. He may be dead at the same time. Who will determine that he is alive? However, Wigner’s friend looks at him and then at the cat, so they exist. Now, who will determine that Wigner’s friend is alive? Someone else looks at him. As a result, an infinite chain of conscious beings starts. But the question is who is watching the last person in the chain? It was called the cosmic conscious: a consciousness that envelopes the whole universe. Wigner believed that nothing really happens in the universe unless a conscious mind observes it.
Another interpretation of this experiment is called ‘many-worlds interpretation’ or multiverse theory. According to this theory, as soon as you open the box, the universe splits into two universes. In one universe, the observer finds a dead cat in the box; and in the other universe, the cat is spotted alive. Multiverse theory proposes infinite number of worlds. There can be as many types of worlds as anybody can think of which may be slightly different from one another.
Quantum mechanics is full of such ideas which are hard to grasp and impossible to imagine. Schrodinger’s cat explains the weirdness of quantum theory. Deep underlying principles of reality are so subtle that they do not even make sense. Richard Feynman says that quantum mechanics describes nature as absurd from the point of view of common sense. And yet, it fully agrees with experiment. So, I hope you can accept nature as she is – absurd.