Stern-Gerlach Device for Measuring Quantum Spin скачать в хорошем качестве

Stern-Gerlach Device for Measuring Quantum Spin

This video shows a schematic of a device used in an experiment that found that atoms have “quantized spin.” The device is called a “Stern-Gerlach device” (SG), after its German inventors, Otto Stern and Walter Gerlach. Their famous experiment of 1922 has since been repeated many times with a variety of quantum particles. It should be noted that, as explained in the footnote, the video is more metaphorical than realistic in its depiction. However, it is useful for demonstrating basic concepts. Stern and Gerlach used silver atoms because they have magnetic poles and, so, are affected by magnetism. The physicists shot the atoms through the magnetic field of the device. The strength of the field varies in different locations. This varying field is due to the top magnet having a point, thus creating a stronger magnetic field than the bottom magnet. Of course, all magnets have both north and south poles, but the SG device is constructed to bring only a single north and south pole together in close proximity. The atoms are deflected up or down depending on their “spin.” Spin has a rather circular definition—it’s the property of atoms and subatomic particles which generates a magnetic field around the particle. Spin gives each particle a north and south magnetic pole. The property of atoms and other small particles which generates their magnetism was called “spin” due to an erroneous assumption. At first, physicists assumed that the particles were acting like an ordinary object. When everyday objects with an electrical charge, spin, they develop a magnetic north and south pole and a magnetic field. Physicists thought the silver atoms must be spinning on their axes. Later, mathematical calculations found that if electrons, for example, were spinning, they would have to do so faster than the speed of light—not possible. But regardless of the source of the magnetic field, the atoms that were sent through the SG device, showed that they did have magnetic fields. Were the atoms that entered the device similar to classical objects, their magnetic poles would be aligned in random directions – with their north poles pointing in all conceivable angles in three dimensions. So, one might expect that the atoms would be deflected in any and all directions. After exiting the device, they would form a vertical line on the detection screen. Atoms with their north poles pointing straight up would be at the top of the line (most attracted to the stronger upper, south, magnet), and particles with their south poles pointing straight up would be at the bottom of the line (most repelled by the stronger upper, south magnet). In between, on the vertical line, would be all the other atoms, due to their poles being pointed in less extreme positions. The actual result of the experiment, however, is different. The atoms arrive at the detection screen in two clumps. The clump at the top is considered to have “spin up.” And the clump at the bottom is considered to have “spin down.” It appears that their north poles must point either straight up or straight down, with nothing in between. The directions of their poles have only two discrete values; they are “quantized” in direction. Physicists call this “quantized spin.” As a note, while this video shows the pointed magnet at the top of the device being the south pole, in the original Stern-Gerlach experiment, it was the north pole. In reality, classical magnets are not measured with the Stern-Gerlach device. The stronger (south) magnetism at the top of the device would twist each atom so that after traveling through the device, every one of them would have their north poles pointing up. In other words, little classical magnets, after traveling through a Stern-Gerlach device, would not display the range of pole orientations shown in this video. In contrast, a quantum particle seems to have inertia which resists such twisting, similar to how a little spinning gyroscope would. Such inertia would explain why quantum particles, apparently, retain the orientation of their magnetic poles as they travel through the SG device rather than being twisted into a single orientation by the stronger south magnet. This behavior, again, points to the idea that the particle is physically spinning, despite physicists’ calculations showing that this would violate Special Relativity (namely, the speed of light). The Transactional Interpretation of quantum mechanics proposes that quantum particles operate in a sublevel of reality. This interpretation may be helpful in visualizing what the particle is really doing.