3 ms·

Happens the other way too. In the 80s high-temperature superconductors were discovered, which were 'impossible' by previous understanding. The theory is still c

Happens the other way too. In the 80s high-temperature superconductors were discovered, which were 'impossible' by previous understanding. The theory is still catching up to that.

Steuard 11y ago
And even low-Tc superconductors looked "impossible" under the physics of their day. No question about it! Science thrives on surprises: it's the very best part of what we do. But maybe non-physicists don't have a sense of the range of meanings that "that isn't possible within current theory" can have. High-Tc might have been "impossible" under basic BCS superconductivity theory, but BCS theory itself taught us that it was possible to find novel theoretical mechanisms generating zero resistance, so needing a new one was surprising but not unprecedented. "Standard" low-Tc superconductivity appeared "impossible" under the usual models of materials' resistivity, but even that was merely a violation of a well-tested model when it was extended to a previously untested very-low-temperature regime. Resolving that apparent impossibility didn't require rewriting any fundamental principles, it just required very careful application of the existing theoretical framework. These speculative new propulsion theories appear to violate the conservation laws underlying all of our existing models of physics, and in an experimental regime of size/temperature/etc. where (I believe) they have been very well-tested in the past. Any calculation within the framework of quantum field theory or general relativity will inevitably result in momentum being (locally) conserved: it's unavoidably built in to the formalism. So as I said to begin with, although it's obviously not truly impossible that some entirely different framework could turn out to be correct, that is an enormously bigger jump than any stage of the discovery and explanation of superconductivity.
- gus_massa 11y ago
  I agree completely. I´ll try to explain this with a simpler example. A long time ago, people thought that the faster than sound planes were impossible, perhaps some wrote that formally. The materials didn't have enough strength, it would become too hot, the pressure at some point would be too high, ... To model a faster than sound plane you need to model a lot of complicated interactions between a lot of atoms, and then you need some simplifications, and with the simplifications used at that time it was impossible. The conservation of momentum is a very low level result, so you don't need to put a lot of simplifications to prove it or measure it. For example you can measure the conservation of momentum when a photon hits an electron almost directly: http://en.wikipedia.org/wiki/Compton_scattering http://en.wikipedia.org/wiki/Compton_scattering
MCRed 11y ago
I worked for the Texas Center for Superconductivity, where Paul Chu discovered superconductors that operated at liquid nitrogen temperatures, in the 1980s a year or so after his discovery. We spent a great deal of time trying to figure out how the mechanism worked, and about half the team were theoreticians who would try and posit theories, or evaluate theories posited by other teams, and the the other half of the team spent time either testing the new theories, or experimenting to try and improve the results of previous experiments. Y1B2C3O is not even a metal, but a ceramic crystal. This was kinda mind blowing at the time. It shouldn't even conduct. IIRC the best theory at the time was that it was superconducting because of particular errors in the formation of the crystal due to the production process. But I left the lab in the early 1990s.

Happens the other way too. In the 80s high-temperature superconductors were discovered, which were 'impossible' by previous understanding. The theory is still catching up to that.

Steuard 11y ago

And even low-Tc superconductors looked "impossible" under the physics of their day. No question about it! Science thrives on surprises: it's the very best part of what we do. But maybe non-physicists don't have a sense of the range of meanings that "that isn't possible within current theory" can have. High-Tc might have been "impossible" under basic BCS superconductivity theory, but BCS theory itself taught us that it was possible to find novel theoretical mechanisms generating zero resistance, so needing a new one was surprising but not unprecedented. "Standard" low-Tc superconductivity appeared "impossible" under the usual models of materials' resistivity, but even that was merely a violation of a well-tested model when it was extended to a previously untested very-low-temperature regime. Resolving that apparent impossibility didn't require rewriting any fundamental principles, it just required very careful application of the existing theoretical framework. These speculative new propulsion theories appear to violate the conservation laws underlying all of our existing models of physics, and in an experimental regime of size/temperature/etc. where (I believe) they have been very well-tested in the past. Any calculation within the framework of quantum field theory or general relativity will inevitably result in momentum being (locally) conserved: it's unavoidably built in to the formalism. So as I said to begin with, although it's obviously not truly impossible that some entirely different framework could turn out to be correct, that is an enormously bigger jump than any stage of the discovery and explanation of superconductivity.

gus_massa 11y ago
I agree completely. I´ll try to explain this with a simpler example. A long time ago, people thought that the faster than sound planes were impossible, perhaps some wrote that formally. The materials didn't have enough strength, it would become too hot, the pressure at some point would be too high, ... To model a faster than sound plane you need to model a lot of complicated interactions between a lot of atoms, and then you need some simplifications, and with the simplifications used at that time it was impossible. The conservation of momentum is a very low level result, so you don't need to put a lot of simplifications to prove it or measure it. For example you can measure the conservation of momentum when a photon hits an electron almost directly: http://en.wikipedia.org/wiki/Compton_scattering http://en.wikipedia.org/wiki/Compton_scattering

MCRed 11y ago

I worked for the Texas Center for Superconductivity, where Paul Chu discovered superconductors that operated at liquid nitrogen temperatures, in the 1980s a year or so after his discovery. We spent a great deal of time trying to figure out how the mechanism worked, and about half the team were theoreticians who would try and posit theories, or evaluate theories posited by other teams, and the the other half of the team spent time either testing the new theories, or experimenting to try and improve the results of previous experiments. Y1B2C3O is not even a metal, but a ceramic crystal. This was kinda mind blowing at the time. It shouldn't even conduct. IIRC the best theory at the time was that it was superconducting because of particular errors in the formation of the crystal due to the production process. But I left the lab in the early 1990s.