I'd like to write this article, which appeared in the Argentine newspaper Página 12 the July 10 . The author is Claudio H. Sanchez, whom the newspaper's Web site gives no further details.
says:
Misunderstandings of quantum mechanics
By Claudia H. Sanchez
These misunderstandings are encouraged, in part, by some New Age literature (mainly, the book The Tao of Physics, Fritjof Capra, and the movie What do you know?). But also due to an inadequate choice of metaphors by scientists, educators and communicators. Every metaphor has a certain distance from the phenomenon that aims to illustrate. In the case of quantum mechanics, this gap is particularly large.
WHAT IS QUANTUM MECHANICS?
Quantum mechanics is the physics of the very young, the branch of physics that explains what happens in the microscopic world. For example, what happens inside the atom or what happens to the particles in the interior of the atom when they go out and interact.
Why quantum mechanics? Why the laws of the microscopic world are different from the everyday world?
Because the behavior of nature is not the same when changing the scale, changing the size of the objects involved. For example, if we drop a wooden board makes a certain noise. If you approach a match, burns with relative difficulty. If the same wood we reduce it to sawdust and let it fall, it does so slowly and hangs in the air for several seconds. If you approach a match burn quickly. This means that the properties of wood depend on its size. Likewise, the properties and behavior of a piece of iron are different from those of an atom of this metal.
atomic models
The existence of atoms was assumed by Democritus in the fourth century BC But signs were not certain of their existence and their properties until the early nineteenth century with the work of the Englishman John Dalton. Physicists began to suspect that atoms really existed and were the building blocks of matter: everything was made of atoms.
What we did not know was how were the atoms, what was its structure internal. In the late nineteenth century JJ Thomson (another Englishman) found that within the atoms had a negative electrically charged particles, we now call electrons. Since, as far as he knew, were electrically neutral atoms, these negative charges had to be offset by an equal amount of positive electric charge. Thomson imagined the atom as a mass positively charged with electrons (negative) embedded in it like raisins in a pudding. It was precisely the model of the pudding. Later
New Zealander Rutherford found that the positive charges (which we call protons) were concentrated in a region small within the atom, the nucleus and the electrons spinning around them like planets around the sun. It was called the planetary model.
This planetary model was very comfortable. Had the attraction of the effective metaphor: to something unknown (the atom) in relation to something known (Solar System). However, the model was doomed from birth. Physicists knew that could not be completely true because the electromagnetic theory predicted (and experience had confirmed) that emit electrical charges when they rotate. Therefore the atoms, with electrons revolving around it, should also issue power continuously. And not only was not observed (except in the case of radioactive substances) but, if so, at some point the energy is depleted and the electron would fall within the core. What is also happening. However
planetary model was so comfortable and stylish persisted. Even today the image that we all have the atom is the planetary model. Nuclear research institutes and nuclear technology companies use the planetary model as an emblem. And when, in 1967, Greece has issued a new 100-drachma banknote with the portrait of Democritus, also included a picture of a lithium atom, as planet.
To save the planetary model, physicists have attempted to show that "somehow", "under certain conditions, the electrons could revolve in stable orbits without emitting energy, against which indicated the experience and electromagnetic theory, but nobody knew how this could be possible.
THE DOUBLE SLIT EXPERIMENT
What we know today is that the electrons are "spin particles" but "waves that vibrate." It is unclear what vibrates. But this wave model avoids the contradictions of the global model for a vibration can be maintained in without losing energy, like a pendulum swinging in a vacuum without internal friction.
The problem with the wave model is that it is contrary to experience. But an experience that arises from the observation of nature (no one was directly an electron) but from observation of the books are so used to seeing the electrons represented as particles that we find it very difficult to consider waves.
to be convinced that electrons are waves and particles they can not refer to a now classic experiment: the double-slit experiment or two holes.
It has a plate with two holes. If on this board a jet fires sand, some grains will pass through the hole on the left, others go through the hole on the right and if beyond the plate has a screen to collect the grains will form two piles of sand, one at each hole. And if the holes are very close together it is possible that the two piles overlap, there is a common area where falling grains of both holes. That is what one expects to happen with particles, and that's what actually happens.
If instead of a sandblaster that shoots over the holes is a bundle of waves (as sound, radio waves or waves in water), the result is quite different. As before, the beam is divided to pass holes. One part goes through the hole on the left and the other by the hole on the right. A suitable screen to record the arrival of the two beams show the buildup of waves in two areas, one in front of each hole. But in the central part where both beams overlap think of something special: it may be that at some point where the beam reaches the right vibrating "there" is the vibrating beam left "here." As a result the two vibrations are canceled and the screen will not register any vibration at that point. Is that waves do something that the particles can not do: interfere. At the point of the screen where you can find a grain of sand necessarily from each hole will have two granite. But the two beams meet, the result can be no beam.
If you do experience with an electron beam, the result is the same as with the waves: there are areas where the two beams interfere. This is not theoretical speculation, the experiment was done and the electron beam pattern was the same as that of a wave.
One might ask whether the electron really is a cool "or just" behaves like a wave. " But physics does not say "why" things are but "how" they are. It is a fact that the electron (and subatomic particles in general) behave as waves. And that explains at least one of the paradoxes of quantum mechanics: a particle can be in two places at once. One can imagine the particle duplicate, each in a different position, as two twins, one in the room and the other in the dining room. If we accept that the electron is a wave we can imagine it extended over all positions. It's like a person (only one) standing in the doorway separating the two rooms is at the same time in the living room and dining room. What is nothing paradoxical.
probability waves
When physicists began to accept that electrons were waves the problem arose investigate the nature of these waves. What was more or less obvious was that the intensity of these waves could be related to the probability of locating the electron in a certain place in space. In the double slit experiment, at the point of the screen where it accumulated more electrons, the wave intensity was high and, therefore, was also high probability of finding an electron. Arrived there where no electron waves interfere, the intensity became zero or near zero and was zero or near zero probability of finding an electron.
According to this criterion, the wave was not something "real" (as sound or radio waves) but a kind of mathematical entity associated with the particle, the particle was on one side and associated with it, the "wave of probability." Somehow, it was to keep the electron as a particle. But how a particle could interfere with another?
One answer is that the wave was not associated with individual particles but a bundle of many of them. After all, probability is a concept that applies to sets of elements and not to individual elements: if we see that the probability of getting face to tossing a coin is 50% we have to flip the coin several times. In the case of the double slit experiment electrons passing through could hit a hole that went through the other and distributed on the screen "as if" interfere.
But the double slit experiment can be done shooting electrons one by one with the same results. How can an electron interfere with the above, that already happened? Or, worse, with the following, which has not happened. The answer is, of course, that each electron is a wave in itself and, while crossing the plate, passing through the two holes at the same time. A particle can not. A wave, yes.
To better understand this behavior have been proposed variations to the double slit experiment. Detectors can be installed in board to "see" the electron is divided into two as it passes through each hole. But here comes another problem: the electron can not be seen directly, make it interact with something else (a magnetic field, for example). And that interaction changes the experiment and its result is not the same as no detector. You can also try alternately opening and closing holes to force the electron to pass through only one of them. In this case, the results still would not be changed because the experiment of the "double slit.
The results of these experiments can not be understood if we consider the electron as a particle. Richard Feynman (Nobel Prize Physics in 1965) said in this connection that "nobody understands quantum mechanics." In fact, what is not understood is how a particle can interfere with another. It is not a particle is a wave.
the electron changes its behavior depending on the experiment led to another misunderstanding: the belief that the electron is well suited to our intentions, or that "knows" if you are watching. Everything becomes clear when we understand that each experiment involving an interaction which must necessarily affect the electron. To say that an electron know they are watching because it changes its behavior is like saying that a lighted candle knows that are blowing it off.
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