One of my favorite scientific ideas is the Schrodinger's Cat theoretical experiment. This is an illustration of Erwin Schrodinger's 1935 proposition of the quantum (physics) theory of superposition. The way it works is that a living cat is placed into a closed steel chamber, along with a device containing a vial of a radioactive substance. If the radioactive substance decays during the test period, then a relay mechanism will trigger the device and kill the cat.
The observer cannot know whether this has happened, and whether the cat is dead or alive, until the container is opened. Since the fate of the cat is unknown, in quantum terms, the cat is neither dead nor alive, and is instead in a superposition of states, or alternatively a cloud of relative probabilities, until the box is opened, and the condition of the cat is observed, crystallizing one outcome or the other. Obviously the experiment sounds pretty tough on the cat, but it's well demonstrated that while things appear to work in a much more deterministic way in the world we see around us, this quantum uncertainty is the way a quantum particle behaves.
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