Historical research guide · 0605 · 1992
Gravitational effects on the magnetic attenuation of superconductors
Ning Li · D. G. Torr
In one minute
Everyone learns two facts about a superconductor and learns them separately: it carries current without resistance, and it pushes magnetic field out of its interior. Ning Li and Douglas Torr, at the University of Alabama in Huntsville, show that the two are not separate at all once gravity is written into the equations. Working in Physical Review B, they build what they call a conductivity-permeability model and find that perfect conductivity and perfect diamagnetism — the two historical hallmarks of an ideal superconductor — are related to each other through the gravitational terms. The title names the quantity that carries the effect: magnetic attenuation, the way a magnetic field dies away as it enters the material. Their conclusion is stated modestly and is the reason the paper matters here. Gravitational effects may be important for understanding superconductivity itself. That is a two-way street, and it is the opening the whole superconductor road to gravity control is built on.
Connection
Chapter 11 needs a peer-reviewed reason to think a superconductor is a place where gravity and electromagnetism meet on a benchtop, and this is it: a Physical Review B result in which gravity is not an outside influence on the experiment but a term inside the material’s own description. Chapter 3 takes the same point the other way round — if gravity shapes how a superconductor screens a magnetic field, then gravity is behaving as a field among fields rather than as a fixed backdrop.
From the source
When gravitational effects are taken into account, the two historically independent hallmarks of an ideal superconductor — perfect conductivity and perfect diamagnetism, characterised by zero permeability — are actually related to each other.Abstract, first sentence
That relation is not an analogy but a calculation: the authors develop an explicit theoretical conductivity-permeability model in the paper and read the connection off it.Abstract, first sentence, closing clause; Phys. Rev. B 46, pages 5489 to 5495
The authors’ own conclusion from the result is that gravitational effects may be important in understanding superconductivity — gravity entering the description of the material itself, not only the laboratory around it.Abstract, final sentence
The quantity the effect is carried by is the magnetic attenuation of the superconductor: the rate at which a magnetic field dies away inside the material, which the model makes a gravitationally sensitive property rather than a fixed material constant.Title and abstract, taken together
This is the second step of a programme rather than a single result: the same two authors had already shown in Physical Review D in 1991 that a gravitomagnetic field is not completely expelled from a pure superconductor and that the internal magnetic and gravitomagnetic fields are tied together through the mass-to-charge ratio of the Cooper pairs — and the measurement that would settle the line is a large, correctly fabricated, electromagnetically driven disc run under the full specified conditions.Companion paper doi 10.1103/PhysRevD.43.457, on this site at /library/stm-674560a77b; the disc programme at /library/stm-01481a5522 and the replication attempt at /library/stm-a0e6ef9f2d
The way in
https://doi.org/10.1103/PhysRevB.46.5489How to cite it
Ning Li, D. G. Torr (1992) Gravitational effects on the magnetic attenuation of superconductors doi:10.1103/PhysRevB.46.5489