4 ms·

Can this "negative mass" be used to construct wormholes and FTL drives, or is it just a math trick?

by xpl 2y ago

keepamovin 2y ago
I don't know man. Have not read the paper. But I think it's materials science kind of stuff. Hopefully a knowledgeable physicist can explain a bit.
- majoe 2y ago
  OK, I give it a shot, though it's been a long time since I worked with polaritons. Let's start from the beginning. If you look at a single atom, you find distinctive energy states for an electron, but in solid state physics these distinctive energy states blur into continua of possible state, called bands. Usually you will find plots of such band structures in the momentum space and here the mass of the electrons come into play. Juggling a bit with formulas one can see, that the curvature (second derivation) of the band structure is the (effective) mass of that particle. So, is this a "real" mass? Well, who cares, but certainly the particles behave like they have this mass and that's also why polaritons are so interesting. If you bombard your electrons with photons, so that they absorb/emit with an high enough rate (strong coupling), they stop behaving like electrons and instead behave like a combination of photons and electrons. We call this quasiparticle a polariton. Now, to tie that all together, the photon has m=0 and since the polariton inherits some properties from it, it also has a drastically reduced effective mass. The guys from this paper seem to have found a configuration, where the effective mass is not only small, but negative, which is surprising.
  - keepamovin 2y ago
    Cool this is great thank you. Gonna give it a good read later. I think that’s a fantastic explanation. You should do more of this! I understood everything you said :)
  - gus_massa 2y ago
    Nice explanation. But I want to add that a common case is that in a semiconductor some "electrons" have negative (effective) mass and negative charge. It's easier to reason about them as "holes" that have positive (effective) mass and positive change. This is an algebraic trick, not hanwaving or just a methaphore. In particular it's useful in some cases becuse the band is almost full and has a lot of "electrons" but very few "holes". I'm not sure if the same trick can be aplied here, but in some areas quasi-particles with negative (effective) mass are quite common.
    - keepamovin 2y ago
      That's interesting too. So, you can kind of say in the case you describe negative mass is an artefact of the model? Seems neither of us is sure how it connects to the paper at hand, but this is interesting to know, thanks! haha :)
sp332 2y ago
It's not negative from an absolute sense, it's just lower than it started. It would be a lot easier to make wormholes if space weren't so empty to begin with. You could probably make something like a wormhole on a lab bench though.

Can this "negative mass" be used to construct wormholes and FTL drives, or is it just a math trick?

by xpl 2y ago

Can this "negative mass" be used to construct wormholes and FTL drives, or is it just a math trick?

I don't know man. Have not read the paper. But I think it's materials science kind of stuff. Hopefully a knowledgeable physicist can explain a bit.

majoe 2y ago
OK, I give it a shot, though it's been a long time since I worked with polaritons. Let's start from the beginning. If you look at a single atom, you find distinctive energy states for an electron, but in solid state physics these distinctive energy states blur into continua of possible state, called bands. Usually you will find plots of such band structures in the momentum space and here the mass of the electrons come into play. Juggling a bit with formulas one can see, that the curvature (second derivation) of the band structure is the (effective) mass of that particle. So, is this a "real" mass? Well, who cares, but certainly the particles behave like they have this mass and that's also why polaritons are so interesting. If you bombard your electrons with photons, so that they absorb/emit with an high enough rate (strong coupling), they stop behaving like electrons and instead behave like a combination of photons and electrons. We call this quasiparticle a polariton. Now, to tie that all together, the photon has m=0 and since the polariton inherits some properties from it, it also has a drastically reduced effective mass. The guys from this paper seem to have found a configuration, where the effective mass is not only small, but negative, which is surprising.
- keepamovin 2y ago
  Cool this is great thank you. Gonna give it a good read later. I think that’s a fantastic explanation. You should do more of this! I understood everything you said :)
- gus_massa 2y ago
  Nice explanation. But I want to add that a common case is that in a semiconductor some "electrons" have negative (effective) mass and negative charge. It's easier to reason about them as "holes" that have positive (effective) mass and positive change. This is an algebraic trick, not hanwaving or just a methaphore. In particular it's useful in some cases becuse the band is almost full and has a lot of "electrons" but very few "holes". I'm not sure if the same trick can be aplied here, but in some areas quasi-particles with negative (effective) mass are quite common.
  - keepamovin 2y ago
    That's interesting too. So, you can kind of say in the case you describe negative mass is an artefact of the model? Seems neither of us is sure how it connects to the paper at hand, but this is interesting to know, thanks! haha :)

sp332 2y ago

It's not negative from an absolute sense, it's just lower than it started. It would be a lot easier to make wormholes if space weren't so empty to begin with. You could probably make something like a wormhole on a lab bench though.