The discussion revolves around the theoretical possibility of trapping an antiproton inside a fullerene structure and the broader implications for storing neutral antihydrogen using magnetic fields. Participants explore concepts from quantum mechanics, electromagnetic theory, and experimental setups related to antimatter.
Participants generally agree that trapping an antiproton in a fullerene is not possible under current theoretical frameworks, but there is no consensus on alternative methods for storing antimatter or the implications of using neutral antihydrogen.
Limitations include the dependence on specific configurations and the unresolved nature of theoretical concepts for antimatter storage. The discussion reflects ongoing uncertainty in the field.
LastOneStanding said:I'm assuming you mean "put inside a fullerene in such a way that it would stay there" (i.e. trap it). This isn't possible, which can be argued without even doing a quantum calculation: Earnshaw's theorem (https://en.wikipedia.org/wiki/Earnshaw's_theorem) says that it is impossible for a charged particle to be held in a stable equilibrium by any configuration of charges—there is always a "leak" somewhere. The electric field of a neutral atom is naturally very weak (effectively zero over distances larger than the typical scale of molecular bonds), so for a best case scenario, imagine you replaced each carbon in the fullerene with a negatively charged particle. In this case, negative charges will be able to leak out through the center of each icosahedron face. So, if the antiproton were slightly displaced from the center (as its own thermal movements would do) it would be carried out by the electric field. Griffiths has a similar exercise for a charge inside a cube of point charges (ex. 3.2) which might be instructive for seeing how this works. So if you can't trap a classical negative charge with an icosahedral distribution of negative charges, you certainly won't be able to do it with neutral atoms whose electric field is much weaker—and if you can't do it for a classical negative charge, you certainly can't do it for a particle obeying quantum mechanics, where quantum tunneling allows even classically trapped particles to escape under the right circumstances.
mfb said:Even worse: The antiproton would not have to leave the cage - once it sees the electric field of a nucleus (at a radius comparable to the electron wave functions), it gets attracted by it and the antiproton can annihilate with a nucleon there.
There are some ways to avoid Earnshaw's theorem, but I think you need neutral antihydrogen for those.
The important result of Earnshaw: Geometry does not matter. You cannot store a charged particle with electric fields. You can store diamagnetic materials and moving (spinning) ferromagnets, but an antiproton is neither.vemvare said:What would happen if one instead tried to keep a charged particle between two charged plates, or in a torus?
Neutral antihydrogen is attracted my minima of the magnetic field strength, and those are possible. This is done at the ALPHA experiment at CERN.How? Are there any other theoretical concepts for storing antimatter? The Brillouin limit is brutalizing my sci-fi fantasies.