Physics is the science of motion. To experience its fascination, here is a selection of videos.
The belt trick as proof of the spin-statistics theorem: spin 1/2 particles are fermions
First video: belts with buckles have spin 1/2
This beautiful animation is copyright and courtesy of Antonio Martos. Assume that the belt cannot be observed, but the square object can, and that it represents a particle. The animation then shows that such a particle (the square object) can return to the starting position after rotation by 4 pi (and not after 2 pi). Such a `belted' particle thus fulfills the defining property of a spin 1/2 particle: rotating it by 4 pi is equivalent to no rotation at all. (The belt thus represents the spinor wave function; for example, a 2 pi rotation leads to a twist; this means a change of the sign of the wave function. A 4 pi rotation has no influence on the wave function.) You can repeat the trick at home, with a paper strip. The equivalence is shown here with two attached belts, but the trick works with any positive number of belts! Can you find a proof for this? By the way, such belted buckles - together with equivalent constructs made of ropes or tubes - are the only possible systems that show the spin 1/2 property.
Second video: belts with buckles are fermions
This unique animation is copyright and courtesy of Antonio Martos. Assume that the belts cannot be observed, but the square objects can, and that they represent particles. The animation shows that two particles (the two square objects) that are connected to infinity by belts return to the original situation if they are switched in position twice (but not once). Such particles thus fulfill the defining property of fermions. (For the opposite case, that of bosons, a simple exchange would already lead to the identical situation.) You can repeat the trick at home, using paper strips. The trick is shown here with two belts per particle, but the untangling works with any number of belts. Together, the two animations are the essential parts of the proof that spin 1/2 particles are fermions. This result is called the spin-statistics theorem.
Here is a reduced version of the films for download:
Flying around the Earth
More details here.
More details here.
The wave properties of matter
Stars orbiting "our" black hole
The flickering of stars at night
The pdf files also feature embedded films of moving electrons made visible in liquid helium, of the astonishing solitons in water, of the elementary particles inside atoms, about the motion of cilia that determine that our heart grows on the left side of our body, and much more. Just download the pdf files to see the videos; they run inside Adobe Reader.
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