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A thought experiment is an experiment which is carried out in the realm of the imagination, rather than in a laboratory. Thought experiments are designed to test ideas, theories, and hypotheses which cannot physically be tested, at least with current scientific equipment. In addition to being used in some branches of the theoretical sciences, thought experiments also crop up in fields like philosophy, where people often explore complex topics which cannot be empirically tested or observed.
The most famous thought experiment is probably that of Schrödinger's cat, which is used to illustrate a concept known as quantum indeterminacy. In this thought experiment, one is asked to imagine a cat in a box with a vial of poison and a single radioactive atom which has a 50% chance of decaying and triggering the vial, causing the cat to die. In this thought experiment, before the box is opened, the cat is considered to be both alive and dead, because one has no way of knowing what's inside the box.
While Schrödinger's cat is kind of a gruesome example of a thought experiment, it poses an interesting conundrum. Using the current laws of physics as they are understood, something cannot be alive and dead at the same time. However, in this thought experiment, the possibility of such a state is clearly illustrated, thereby opening the door to an entirely new consideration of physics.
Thought experiments have been widely conducted since the 1800s, although researchers and philosophers in prior centuries laid the groundwork. A thought experiment can be used to challenge an accepted idea, to explore the outcome of a given hypothesis, to think about physics or other branches of the sciences in a new way, or to test the limits of a theoretical hypothesis. Many noted researchers have used thought experiments in their work, and thought experiments have led to very famous breakthroughs in the sciences, like Einstein's Theory of Relativity.
When someone performs a thought experiment, the boundaries of the mind and imagination are tested to their limits. It is often necessary to suspend disbelief, or to make intuitive leaps, two things which are normally not encouraged in the sciences. The ability to think outside the box by performing a thought experiment can be critical for people in the theoretical sciences, as it promotes unusual ways of thinking which can be used to power radical and sometimes extremely intriguing ideas.
@umbra21 - The Prisoners' Dilemma is a good one and we studied it at university when I was doing a paper in logic.
But, I have to say my favorite thought experiment of all time is the buttered cat.
It goes like this: If cats always land on their feet, and toast always lands buttered face down, what happens if you tie a piece of buttered toast, butter up onto the back of a cat?
I've heard people claim that, both sides being equal, this would cause the cat to defy gravity and hover in midair!
Of course, this one is just for fun, but it is a good way to introduce the idea of a thought experiment to your kids.
Schrödinger's cat is famous, but I would argue that the Prisoner's Dilemma is the most famous of all the thought experiment examples. We learned about this in high school and I've heard it many times since then. It can be used to teach math, philosophy, ethics and so on.
It goes like this. You have two people hauled in on the same charge, without a chance to talk to each other, and taken into separate interrogation rooms. If one narks and the other keeps silent, the nark goes free and the silent guy gets a year in prison. If neither narks, they each get a month. If both nark, they each get six months.
So, do you stay silent and
trust your partner to do the same? Or do you nark and risk the punishment for the potential gain? The best case scenario for both is for them to only get a month each, but that's not the best case scenario for them separately.
It's especially fun if you can act this out with kids before they have studied it.
I have heard science fiction called a "thought experiment".
Most fiction is a story and it might be a story you have already heard before, like a romance, or it might be a story that's trying to be original, like literary fiction. It might be a story exploring human emotion, or the consequences of certain actions or whatever.
But, science fiction is specifically exploring a "what if" question. For example "The Matrix" is exploring "what if the real world was actually just a computer simulation?"
This can be, in my opinion, one of the best kinds of thought experiment, because not only can you go through all the philosophical ramifications of a particular idea, you can also look at how it would effect reality as well.
Which is one of the reasons science fiction should be taken more seriously than it often is by mainstream readers.
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