Simple, but adequate.
Definition from Wikipedia:
A thought experiment considers some hypothesis, theory, or principle for the purpose of thinking through its consequences. Given the structure of the experiment, it may or may not be possible to actually perform it, and, in the case that it is possible for it to be performed, there need be no intention of any kind to actually perform the experiment in question. The common goal of a thought experiment is to explore the potential consequences of the principle in question.
Thought experiments are one of my favorite thinking tools and I have found that they often help to illustrate points that are hard to put your finger on, or take much longer to explain on their own.
Enough background explanation. I am going to do a series of posts on some of my favorite thought experiments and then discuss what they are meant to illustrate. Let’s dive into number 1!
Schrödinger’s Cat:
(Lot’s of links and help from Wikipedia)
Background: Schrödinger’s cat is a thought experiment, usually described as a paradox, [although, I think it's just an apparent paradox] devised by Austrian physicist Erwin Schrödinger in 1935. It illustrates what he saw as the problem of the Copenhagen interpretation of quantum mechanicsapplied to everyday objects. The scenario presents a cat that might be alive or dead, depending on an earlier random event. Although the original “experiment” was imaginary, similar principles have been researched and used in practical applications.
The Experiment: A cat, along with a flask containing a poison and a radioactive source, is placed in a sealed box shielded against environmentally induced quantum decoherence. If an internal Geiger counter detects radiation, the flask is shattered, releasing the poison that kills the cat. The Copenhagen interpretation of quantum mechanics implies that after a while, the cat is simultaneously alive and dead. Yet, when we look in the box, we see the cat either alive or dead, not both alive and dead. Until the box is opened, we must act as if the cat is both dead and alive.
The Point: This thought experiment is designed to illustrate the counter-intuitive nature of quantum mechanics. The point is that, when dealing with certain types of sub-atomic events it is a fundamentally impossible to predict exactly when something is going to happen. All we can get are probability distributions. As it turns out, the universe of the very small is quite different from anything we can imagine. Quite honestly, I don’t know enough about quantum mechanics to explain this one much further. The one thing I can say is that if someone who isn’t a physicist tries to make defend an outlandish claim by invoking quantum mechanics (Deepak Chopra), they are almost certainly trying to pull one over on you.
If this post gets good reviews, I’ll do more like this. I’ve got a lot of favorite thought experiments that I can talk more about on my own without so much reliance on Wiki links. Cheers!
Steve, you covered the basics and are correct. Key is scale, at which very small things operate according to their wave function, which is expressed as a probability that the thing will be in a certain state at any given time. If unobserved, that function remains a range of possibilities (alive, dead) until observation forces the wave function to collapse into a discrete state.
That’s what I thought. Almost all of my knowledge of quantum physics comes from reading a few Stephen Hawking books. The world of the very small is incomprehensible to me. I can memorize a few facts and what not, but I don’t understand it. One of my goals is to learn enough physics to have a better understanding of the very small universe.
Read Brian Greene’s three books. He’s fun to read, and Hawking is always good too.
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