Sun 15 Nov 2009
“Any who says he understands quantum mechanics,” Niels Bohr once said, “doesn’t know the first thing about it.” Bohr, a Danish physicist who helped invent (discover?) quantum theory a century ago, presumably excluded himself from this dictum.
Quantum mechanics, which describes the behavior of electrons, neutrons, protons, photons and other tiny things, is arguably the most potent and precise of all scientific theories. The theory contributed to the development of nuclear power, computers, lasers and other technologies that underpin modern civilization.
And yet if the theory didn’t work so well, no one would believe it, because it makes absolutely no sense. It implies that an electron can act like a wave or a particle, depending on how you look at it, and it can be in two places at the same time. A cat can be both alive and dead at the same time, as long as you don’t look at it.
Einstein helped found quantum mechanics, but he never really embraced it, and he hoped that it would one day be superseded by a more sensible theory. Einstein was especially upset by a quantum phenomenon he called “spooky action at a distance.” Measure the spin of an electron over here, and you instantaneously determine the spin of another electron a mile or a million miles or a million light years away, through a mysterious linkage called entanglement.
Einstein refused to believe in “spooky action,” which he thought violated the prohibition of special relativity against faster-than-light communication. But all the nonsensical predictions of quantum theory, including “spooky action,” have been repeatedly confirmed by experiments. (Spooky action cannot be used for communication, however, so the ban on superluminal communication holds.)
If you’ve ever wondered about quantum mechanics—how it was discovered, by whom, how modern researchers are continuing to explore its mysteries, what it implies about our world—come to the next event of the Center for Science Writings, to be held at Stevens Wednesday, November 18, 4 p.m., in the Babbio Center, room 122. Our speaker will be the talented young science writer Louisa Gilder. author of a gripping new history of quantum mechanics called Age of Entanglement.
In a review in the New York Times, the Harvard philosopher of science Peter Galison praises Age of Entanglement as “a sparkling, original book,” which “beautifully evokes” the world of quantum explorers. A review in Nature hails Entanglement as a “welcome addition to the popular history of twentieth-century physics.” I can’t promise that by the end of Gilder’s talk you will understand quantum mechanics, because if Niels Bohr couldn’t, no one can. But you will come away with a better sense of just how wonderfully nonsensical the theory really is.
November 21st, 2009 at 4:29 am
The key to quantum mechanics is this: are all possible events in some sense real and at some future specified time do all of them truly possess a certain possibility of actually coming to pass?
For past events we establish an actuarial analysis which always verifies our favorite probalistic quantum theories. For future events predictions based on QM work exquisitely well also. All such calculations, however, only involve very simple systems in which quite elemental forms of matter and energy are interacting.
Once we start considering something as big as a cat which may or may not be alive depending on the state of a single atom, then we have to consider the Quantum Zeno effect, which hints to us that single atoms might be swayed in their behaviors by really big observers and their expectations (not to mention the vote the cat may have an an experimental outcome through its own psychic influence on the experiment.)
So, perhaps not every possible thing really did have a realizable potential. All of our statistics are really kind of a dead game, a summing over of outcomes that we have no way of knowing were ever truly realizable.
But we choose to think that we know these things, because it makes a lot of electronic technology possible. Whether we know anything at all beyond that primitive level of existence we should reserve judgment concerning.