Quantum Week - Day 3

The equation for the Uncertainty Principle rivals Einstein's E = mc2 in both importance and simplicity.

∆x is the change (the standard deviation of the probability distribution) in position
∆p is the change in momentum
h is Planck's constant, which is (about) 6.626 * 10 -34 joule/sec
h-bar (h/2∏) is reduced Planck's constant, which is (about) 1.054 * 10 -34 joule/sec

So, in general, the combination of (the error in position) * (the error in momentum) must be greater or equal to planck's constant. Since Planck's constant is so small, the principle can be ignored for all but the smallest and fastest particles. Given a million years (or some decent amount of time), a cue ball at rest, i.e. we know its exact momentum (∆p = 0), will change its position by the width of an electron. It's a poor excuse for missing a pool shot. Likewise, a baseball will never go fast enough for an outfielder to blame missing the ball's position on the Uncertainty Principle.

If you are having a hard time reconciling this newly discovered behavior of nature with classical physics, you can imagine how the top classical physicists felt. And Einstein, along with Newton, was the greatest classical physicist of all time. Einstein helped develop quantum physics with his work on the photoelectric effect. He won a Nobel prize in 1921 for his work on quantum physics, not relativity. He understood it as well as any physicist at the time, but he was strongly opposed to the quantum mechanics developed by Heisenberg and Schroedinger and the Copenhagen interpretation. His famous quote is "God doesn't throw dice." To which Niels Bohr, his good friend, apocryphally responded, "Don't tell God what to do."

Einstein, along with Podolsky and Rosen, developed the EPR thought experiment to disprove the Uncertainty Principle.





You may also be interested in another feature of quantum physics and the Uncertainty Principle called quantum tunneling. The video was made by a science teacher.



We know through a hundred years of experience that quantum physics is how nature behaves. It is experimental fact. There is no controversy. Like evolution, all scientists believe it. The controversy stems from scientists' interpretation of what quantum physics means.

I'm not going to directly comment on the various interpretations although some of these videos may have assumed the Copenhagen interpretation which is the most popular one. It's not that the interpretations aren't interesting or important, but it would take at least another week to address that subject.

Wikipedia may not be the best place to learn about this, but to get a feel for some of the interpretations you can look here.
Here's another listing that is a bit more humorous and readable.