4 ms·

Can someone ELI5 if the video with the magnet levitating is supposed prove something? Is this visual result only possible with superconductors? If so, why?

svachalek 3y ago
Magnets can also levitate over other magnets, so it's not only possible with superconductors. But it does happen with superconductors. The magnet will induce a current in the superconductor, which creates a magnetic field, which repels the magnet.
- eesmith 3y ago
  > Magnets can also levitate over other magnets Earnshaw's theorem describes why a free-floating (paramagnetic) magnet cannot levitate over another such magnet. There must be at least one stable axis which is not from a magnet. See https://en.wikipedia.org/wiki/Earnshaw%27s_theorem https://en.wikipedia.org/wiki/Earnshaw%27s_theorem > The magnet will induce a current in the superconductor That's a different sort of levitation. See https://en.wikipedia.org/wiki/Electrodynamic_suspension https://en.wikipedia.org/wiki/Electrodynamic_suspension . We know it's not the same because you can see a magnet floating above a superconductor even though there's no motion. The relevant reason is https://en.wikipedia.org/wiki/Superdiamagnetism https://en.wikipedia.org/wiki/Superdiamagnetism . ] Superconducting magnetic levitation is due to superdiamagnetism, which repels a permanent magnet which approaches the superconductor, and flux pinning, which prevents the magnet floating away. ] Superdiamagnetism is a feature of superconductivity.
  - it_citizen 3y ago
    So does that mean the video would exclude honest mistakes from the researchers? Either it is indeed a superconductor at room temperature or the makers of video actively faked the result.
    - eesmith 3y ago
      I'll quote from the linked-to page: > In both of these magnetic repulsion videos, keep in mind that magnetic repulsion and/or levitation are not, by themselves, probative of superconductivity: a diamagnetic material such as pyrolytic graphite [16], can be made to levitate [19] in a magnetic field without being superconductive. See https://en.wikipedia.org/wiki/Magnetic_levitation#Diamagnetic_levitation https://en.wikipedia.org/wiki/Magnetic_levitation#Diamagneti... .
mgsouth 3y ago
The levitation results from something called "diamagnetism" [1]. Diagmagnetism induces a magnetic field that opposes the original field; in this case it pushes the magnet away from the sample material. All superconductors are strongly (perfectly, actually) diamagnetic, and its a classic cool demonstation of their properties. However, not all strongly diamagnetic things are superconductors. In fact, diagmagnetism is present in all materials, but it is usually swamped by other magnetic effects (ferromagnetism and paramagnetism). [1] https://en.wikipedia.org/wiki/Diamagnetism https://en.wikipedia.org/wiki/Diamagnetism

svachalek 3y ago

Magnets can also levitate over other magnets, so it's not only possible with superconductors. But it does happen with superconductors. The magnet will induce a current in the superconductor, which creates a magnetic field, which repels the magnet.

eesmith 3y ago
> Magnets can also levitate over other magnets Earnshaw's theorem describes why a free-floating (paramagnetic) magnet cannot levitate over another such magnet. There must be at least one stable axis which is not from a magnet. See https://en.wikipedia.org/wiki/Earnshaw%27s_theorem https://en.wikipedia.org/wiki/Earnshaw%27s_theorem > The magnet will induce a current in the superconductor That's a different sort of levitation. See https://en.wikipedia.org/wiki/Electrodynamic_suspension https://en.wikipedia.org/wiki/Electrodynamic_suspension . We know it's not the same because you can see a magnet floating above a superconductor even though there's no motion. The relevant reason is https://en.wikipedia.org/wiki/Superdiamagnetism https://en.wikipedia.org/wiki/Superdiamagnetism . ] Superconducting magnetic levitation is due to superdiamagnetism, which repels a permanent magnet which approaches the superconductor, and flux pinning, which prevents the magnet floating away. ] Superdiamagnetism is a feature of superconductivity.
- it_citizen 3y ago
  So does that mean the video would exclude honest mistakes from the researchers? Either it is indeed a superconductor at room temperature or the makers of video actively faked the result.
  - eesmith 3y ago
    I'll quote from the linked-to page: > In both of these magnetic repulsion videos, keep in mind that magnetic repulsion and/or levitation are not, by themselves, probative of superconductivity: a diamagnetic material such as pyrolytic graphite [16], can be made to levitate [19] in a magnetic field without being superconductive. See https://en.wikipedia.org/wiki/Magnetic_levitation#Diamagnetic_levitation https://en.wikipedia.org/wiki/Magnetic_levitation#Diamagneti... .

mgsouth 3y ago

The levitation results from something called "diamagnetism" [1]. Diagmagnetism induces a magnetic field that opposes the original field; in this case it pushes the magnet away from the sample material. All superconductors are strongly (perfectly, actually) diamagnetic, and its a classic cool demonstation of their properties. However, not all strongly diamagnetic things are superconductors. In fact, diagmagnetism is present in all materials, but it is usually swamped by other magnetic effects (ferromagnetism and paramagnetism). [1] https://en.wikipedia.org/wiki/Diamagnetism https://en.wikipedia.org/wiki/Diamagnetism