Schrodinger's Cat

Up to this point, I've covered mostly topics involving geology and light. To shake things up a bit, this post will cover something a bit different - quantum mechanics. Generally speaking, quantum things are too small to photograph without a powerful microscope. However, there is a good macroscopic analogy for one of the most important quantum processes. The Schrodinger's cat paradox was originally used by Erwin Schrodinger to show how silly quantum mechanics seemed when applied to the macroscopic world in which we live. In contrast, his cat paradox has turned into one of the most widely used analogies for explaining the quantum phenomenon of superposition.

If you're not familiar with the Schrodinger's cat paradox, here's how it goes:
(Note: Do NOT try this at home. This is a thought experiment only, not something actually carried out. Please do not needlessly harm animals.)

Start with a solid box. Inside the box is a vial of poison attached to a special device that contains an unstable atom. This unstable atom has a 50% chance of decaying within an hour. If the atom decays, the device will trigger a hammer to smash the vial of poison. Let's now place a cat inside the box and then close the box. If we wait an hour, there is a 50% chance that the device was trigger and the vial smashed. If that happened, we would expect to see a dead cat upon opening the box. However, there is also a 50% chance that nothing happened and the cat is still alive. So, without opening the box, is the cat dead or alive after an hour of waiting?

As long as we don't observe the cat by opening the bow and looking at it, we can say that it is in a state of being both dead and alive. Now, this doesn't make much sense. Obviously, an animal can only be dead or alive, not both. This is why it is a paradox and why Mr. Schrodinger used this as an example of how ridiculous the quantum theory of superposition seemed. Now, what exactly is superposition and why is it important?

From the cat paradox, you may have figured out what superposition is. In simple terms, superposition means that a quantum particle, such as an electron, can be in multiple states at the same time. There is one catch though - if you try to measure or observe the particle, it will assume only one of the states. Going back to the cat paradox, once you open the box and check to see what happened, the cat will be either alive or dead. You can no longer say that it exists in both states.

One consequence of this is that the act of measuring a system can affect how the system is behaving. This is something that rarely happens in the macroscopic world. If you use a ruler to measure the length of a pencil, the act of measuring will not change the length of the pencil. Its length will be exactly the same before and after you measure it. In the quantum world, however, things are different. Because particles are so small, even light can easily affect the properties of a particle. For example, when light collides with an electron, it can pass momentum to the electron and change its speed and/or path of motion. This consequence becomes significant when trying to do things on a quantum level, such as building a quantum computer. These computers use the fact that an atom can simultaneously be in multiple states to speed computations by doing more than one at the same time. However, to get the computation results you would need to interact with the atoms. This causes them to lose all but one of their current states and breaks the multiple-state basis of the computer.

There are experiments that modern day scientists can use to test the theory of superposition. Even though it was questioned back in the 1930s when the cat paradox was first introduced, it is now a well accepted theory. That said, from Mr. Schrodinger's days until now, one thing remains the same - the quantum world remains a very strange one that few people can even begin to fully understand.


Further Reading
Schrodinger's Cat Comes into View - By physicsworld.com
No. 347: Schrodinger's Cat - By John Lienhard at the University of Houston
Another step toward quantum computers: Using photons for memory - By Eric Gershon, phys.org
What Is Quantum Superposition? - By the Science Channel