Why the Meissner effect is not understood and how to understand it

The Meissner effect, the expulsion of magnetic field from the interior of a metal entering the superconducting state, raises fundamental questions that require answers, including: (1) How is the Meissner current generated in apparent violation of Lenz’s / Faraday’s law that oppose changes in magnetic flux? (2) How is the momentum of its carriers compensated so that momentum conservation is not violated? (3) In the reverse process, the superconductor to normal transition in a magnetic field, how does the supercurrent stop without development of Joule heat, which is forbidden by the reversibility of the process?  

Neither conventional BCS theory nor theories proposed to describe “unconventional superconductors” have addresed those questions.  

I will answer those questions [1]. Essential parts of the answers are: (i) Radial flow and counterflow of charge is required; (ii) normal carriers with negative effective mass are required; (iii) the electromagnetic field mediates the dissipationless momentum transfers; (iv) lowering of kinetic rather than potential energy drives superconductivity; (v) electron-hole asymmetry is key.

[1] J. E. Hirsch, ``The Meissner effect in superconductors: emergence versus reductionism’’, arXiv:2510.17805 (2025).