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Feb. 19, 2006 In the Feb. 18 issue of Useless-Knowledge e-zine, I wrote about the "spooky" tunnel effect that scientists and engineers use to make "smart" credit cards. It's hard to believe, but it does successfully predict the behavior of subatomic particles, so I (somewhat reluctantly) do believe in it. But here's another one from the science of "quantum mechanics," which is even harder to believe: "entanglement." If you think I'm going crazy when you read my stuff below, you can look up that word in advanced physics books. But it would be hard to understand the whole thing, unless you've already studied a lot of math and physics, so I'm going to try and explain it in simpler terms. (By the way, so you don't think in advance that I'm slinging the bull here, you might quickly look up the word "entanglement" in www.wikipedia.org. Also, the words "double-slit," and "electron diffraction.") Let's say that you've got a mirror that has only a very thin layer of silver on the glass, so half of the light reflects, but the other half goes through. You could see through it if you are in a dark area, looking at something that is brightly lit, but somebody in the brightly lit area could not see you. Therefore this is sometimes called a "one-way" mirror. Now, if you shine a flashlight at the thinly silvered mirror, some of the "photons" of light (similar to the "electrons" of electricity) will go through, and some will reflect. Now, instead of a flashlight, let's use a laser. That can be weakened, by only putting a little bit of electricity into it, so that only one photon at a time comes out, separated from the next photons by a few seconds or minutes of time. The first photon (the smallest possible unit of light energy) might either go through or not. An important principle of "quantum mechanics," called the "Heisenberg uncertainty principle," tells us we are not allowed by the laws of nature to know in advance, which thing will happen, the photon going through or reflecting. If you shoot lots of photons at the mirror, about half will go through on the average, but we can't say which will be which. (Why not? Nobody knows why not. It simply is that way, because of the laws of nature, "uncertain" until afterwards.) OK, you have two photographic films, unexposed, and one is placed in each exit path. After a while, there will be developable spots growing on each one. So far, everything seems reasonable. Now, instead of a laser, let's use an electron beam, such as the one that's inside your TV tube. With a weak current, we can have one electron going at a time. Instead of a thin-silvered mirror, let's use "diffraction" from a thin quartz crystal. (If you want to, look up "electron diffraction" in wikipedia.) We'll get two or more separated beams of electrons coming out of the thin crystal, so let's just look at the two strongest exit beams. We can put two photo films in the exit paths, and two black spots could be developed, about half of the time, at random, just like with a laser. So far, it's all OK, right? Then we'll just send a single electron going into this thing. On which side will it exit? Well, we are not allowed to predict that, according to Heisenberg. Oh yeah? I'll fool nature! I'll make a big experimental set-up, so there is enough time to have some expensive equipment do some carefully timed things. (This has actually been done, slightly different from what I am describing, but following the same ideas.) OK. Gang, let's wait until a microsecond (or maybe a nanosecond) after (AFTER!) the electron has gone through the crystal, but before it hits either film. Then we'll suddenly push a magnetic sensor alongside one possible electron path. If the electron has chosen that path, the sensor will detect a slight magnetic field that the moving electron generates, and it will tell us "Hey, this is the film that's going to be hit --- ha, ha, I found out in advance, before it hits the film!" Oh yeah? You're going to fool nature? Well, nature is smarter than you are, and also a lot more powerful! The electron will ALWAYS choose that detectable path, and never the other one. You have violated the uncertainty principle by determining which path was chosen. Wait a minute! Do I mean that AFTER the electron has gone through the crystal, I have gone backwards in time and changed the properties of that crystal, so it always diffracted one particular way? Physicists have argued about this for many years (even though you might not have heard about it). Mainly what they say now is that both possible paths were being followed, but they were "entangled." After the electron hits one photo film or the other, the path not followed becomes "collapsed" (destroyed, in effect). And if anyone like you "observes" what's happening in advance, it also collapses the alternate path. Suppose a trained monkey or trained dog is used to squeal or bark when the magnetometer shows a signal, instead of a person. Will it work the same way? Is there something very special about human observers? We don't know --- that experiment hasn't been done, as far as I've heard. And a lot of other variations have not been done, unless they are just being "classified" secret by the U.S. Government. Lots of secret research is being done on this stuff. The useful idea would be that a secret message could be sent via a single electron or single photon, and if a spy observed it, the act of observing would warn us that there was a wire tap. If you want to read more about this, see the book "Where Did The Weirdness Go?" by David Lindley (1996). I think this might have a lot of philosophical implication, although I don't pretend to be clear about it myself. Mainly, I would just say, "There's lots that we can not know --- nature won't allow it." Black Holes, and Big Bangs and many such other things are included in that statement. We're just poor little dumb animals in this confusing universe. Does this tell us that there is a God running the whole show? Is what I've called "nature" really "God?" I don't pretend to know, because I can't see how it has to be a deity, or can't be a deity. You can believe whichever side you like, or so it seems to me. Whether you believe in God is a whole 'nother matter, in my humble opinion. One thing, though, it's all very humbling to this plain old scientist/engineer. ------------ About the author: Dan Shanefield is a retired engineering prof, who worked at Bell Labs and then at Rutgers University. He wrote the book "Industrial Electronics for Engineers, Chemists, and Technicians". Visit his website or email: shanefield@ieee.org Comment on this article here! ------------ All articles are EXCLUSIVE to Useless-Knowledge.com and are not allowed to be posted on other websites. ARTICLE THIEVES WILL BE PROSECUTED! |
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