Little magicians are accomplished by electrons. They appear to be in two places at the same time, and their behavior in chips is what powers the modern world. One of their most impressive tricks is simple. The electron seems to spin. It looks like an electron is doing tiny pirouettes as it makes its way through the world. The spinning doesn't seem to slow or speed up. Even if an electron is kicked or jostled, it always looks the same. A spinning object with electric charge should have a magnetic field. Physicists call this behavior Spin.
electrons don't spin They can't spin, that's a standard homework problem for any introductory quantum physics course. If electrons spun fast enough to account for all of the spinlike behavior they display, their surfaces would move faster than light. This seeming contradiction has just been written off by most physicists as a strange feature of the quantum world, nothing to lose sleep over.
Spin is crucial. Your chair would collapse if the electrons didn't spin. It would be the least of your problems if you collapsed as well. The periodic table of elements would come crashing down without spin. There wouldn't be a single molecule. Spin is one of the most important tricks that electrons pull. Any good magician will tell you how the trick is done. A new account of spin, one which shows how the magic works, may be on the horizon.
Spin has been hard to understand. The idea of spin was developed by the first people. In 1925, two young Dutch physicists, Samuel Goudsmit and George Uhlenbeck, were puzzling over the latest work from Wolfgang Pauli. According to Pauli, electrons have a "two-valuedness not describable classically." Pauli didn't say what physical property of the electron his new value was related to.
All they knew at the time was that Pauli was associated with a well-known property from classicalNewtonian physics. It's the tendency for a rotating thing to keep rotating. It keeps bikes upright. The shape and mass of the object are equally important as the speed of the object's rotation. A heavier object with more mass at its edges has more energy than a lighter object with less mass at its center.
The objects can have spin. The Earth going around the sun and a set of keys swinging around your finger are both examples of things revolving around something else. The source of Pauli's new number couldn't be determined by this type of momentum. The attraction between the negative electrical charge and positive pull of the protons in the nucleus appears to hold the electrons in place. They couldn't be Pauli's new number because of the angular momentum they have from this movement. Three numbers associated with the electron correspond to the three dimensions of space it can move in. The electron could move in four different ways. The two young physicists had only one option, and that was for the electron to be spinning as it traveled around the sun. If electrons could spin in either counterclockwise or clockwise, that would account for Pauli's two-valuedness.
After writing up their new idea, Goudsmit and Uhlenbeck showed it to their mentor. The idea was intriguing to a close friend of Einstein and a formidable physicist. He told the two young men to consult with the grand old man of Dutch physics who had anticipated much of the development of special relativity two decades earlier.
The idea of spin was not liked byLorentz. The electron was at least 3,000 times smaller than an atom and the atoms were a million times smaller than a sheet of paper. The electron was a billionth of a billionth of a gram in mass, and there was no way it could spin fast enough to account for the angular momentum Pauli was looking for. The surface of the electron would have to move 10 times faster than light to be possible.
Uhlenbeck went back to Ehrenfest to tell him the news after he was defeated. He was told that it was too late to scrap the paper because his mentor had already published it. The two of you are young enough to be able to pay for stupidity. He was correct. Spin was accepted as correct despite the fact that the electron couldn't be spinning. Physicists misinterpreted the finding to mean that the electron carried with it some inertia, even though it couldn't spin. The idea was still referred to as "spin" and was credited with being the progenitors of the idea.
The properties of matter were explained by spin. Theexclusion principle was suggested by Pauli in the paper where he had suggested his new two-valued number. If they were able to, every electron in an atom would fall to the lowest energy state, and virtually all elements would behave the same. There wouldn't be life. There wouldn't be water. The universe would be full of stars and gas, drifting through a boring and indifferent universe without seeing anything. Solid matter would not be stable. It was not clear why electrons couldn't share states. It is possible to understand the origin of Pauli's exclusion principle.
There was an answer to the puzzle that was spinning. Spin was found to be a fundamental property of all fundamental particles, and one with a connection to the behavior of those particles in groups. The connection between spin and group statistical behavior was proved by Pauli and Fierz in 1940. Pauli's exclusion principle was a special case of the spin-statistics Theorem. Physicist Michael Berry says that the theorem is a powerful fact about the world. It underlies chemistry and superconductivity. Spin was found to be useful in technology. Spin was harnessed to develop lasers, explain the behavior of superconductors, and point the way to building quantum computers in the second half of the 20th century.
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All of these discoveries, applications, and explanations leave the question of what is spin unanswered. If electrons can't be spinning, where does it come from? The standard answer is that this momentum is inherent to particles and doesn't correspond to a spinning idea.
This answer isn't satisfying to a lot of people. Charles Sebens, a philosopher of physics at the California Institute of Technology, doesn't like the account of spin that you got in a quantum mechanics class. You are introduced to it and you think it is odd. They act like they spin, but they don't. It's okay. I think I can work with that. It is strange.
He had an idea recently. He says that the electron is not rotating. quantum mechanics is not a good theory of nature. There is a deeper and more accurate theory called quantum field theory.
Einstein's discovery that matter can turn into energy and vice versa is one of the most famous equations in the world. The spin-statistics theorem can be traced back to quantum field theory. Existing particles can decay into something else if they interact with one another. This phenomenon is handled by quantum field theory, which describes particles as coming out of fields that are everywhere. The fields allow particles to appear and disappear in accordance with the laws of the quantum world.
The solution to the puzzle of spin may be found in these fields. He says that the electron is considered a particle. Every particle has a way of thinking about it as a field. The electron can be thought of as a spin in the Dirac field. The Dirac field has a rotation of energy. The region of the field carrying an electron's spin is much larger than the supposedly pointlike electron itself. According to Sebens, there isn't a spinning particle. Particles are formed by a spinning field.
Sebastian's idea has made ripples. Mark Srednicki is a physicist at the University of California, Santa Barbara. We are applying a concept that originated in the ordinary world to a place that doesn't really apply anymore. If you want to say the electron is spinning, it's just a matter of choice or definition. Hans Ohanian, a physicist at the University of Vermont who has done other work on electron spin, points out that the original idea doesn't work for antimatter
Physicists aren't always so negative. Sean Carroll is a physicist at the Santa Fe Institute. He is taking the field-ness of quantum field theory very seriously and he is very much on the right track. Physicists are pragmatists... The physicists are going to ask, what does that mean?
The University of Waterloo has a philosopher who echoes this point. She says she is open to the idea of having some sort of physical intuition in order to spin. You have a nice mathematical representation, but you want to take a physical picture with it. New theories or experiments that hadn't been done before might be led by a physical picture. I would like to know if this is a good idea.
It is too early to say if this kind of fruit will be found in his work. He wrote a paper about how to resolve Ohanian's concern about antimatter. There are many reasons to like the field idea. This is more of a challenge than an argument against it.
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