A modern physical theory which is vital to describing extremely small objects, like electrons around an atom. Though this theory also applies to larger objects, its effects become very similar to those of Newton's theory — which is typically much easier to use and understand. One of the most important ideas in Quantum Mechanics is the Uncertainty Principle.
Now, here, you see, it takes all the running you can do, to keep in the same place. If you want to get somewhere else, you must run twice as fast as that.
The Red Queen in Lewis Carroll's Through the Looking Glass