5 ms·

> Hossenfelder's thoughts about FTL travel in her video from yesterday I didn't watch said video, but we have theories rooted in GR and Quantum Mechanics that

> Hossenfelder's thoughts about FTL travel in her video from yesterday I didn't watch said video, but we have theories rooted in GR and Quantum Mechanics that would allow for FTL travel already using negative energy/pressure. We know there exists mechanisms to create negative pressure, like the Casimir effect. We know the universe is non-local, as per the Nobel prize awarded last year. And we are beginning to see experiments violate local causality. Who's to say we might not be able to engineer FTL travel at some point?

throwaway290 3y ago
What experiments violate causality?
- likeabbas 3y ago
  https://phys.org/news/2017-04-physicists-violate-local-causality.html https://phys.org/news/2017-04-physicists-violate-local-causa... is one
  - throwaway290 3y ago
    It seems like a huge leap to use a violation of bilocal (not even local in general) causality as confirmation of even theoretical possibility of human FTL travel
  - GoblinSlayer 3y ago
    >If a Bell inequality is violated, then either locality or realism (or simply "local realism") has also been violated. In other words, it's a violation of classical realism, not a violation of locality.
    - aa-jv 3y ago
      Why not both? i.e. truly a violation.
      - GoblinSlayer 3y ago
        Locality is necessary for the special theory of relativity. That's why not both.
      - simonh 3y ago
        Violation of the Bell inequalities tells us certain things. Other things it doesn't tell us might also be true, but that's speculation not derivation unless we have some other evidence to work with.
simonh 3y ago
Just to nitpick, the Casimir effect only produces negative pressures relative to the vacuum energy. They're not truly negative. Just in case anyone reading that misunderstands. Also 'violates causality' is an awful lot to unpack, and is glossing over so much nuance that I don't think it's really a meaningful thing to say. For example violation of the Bell inequalities does not rule out superdeterminism, and that has a very solid account of causality. It's just not a conventional one.
- likeabbas 3y ago
  You left one portion out of the explanation of the Casimir effect > The Casimir effect shows that quantum field theory allows the energy density in certain regions of space to be negative relative to the ordinary vacuum energy, and it has been shown theoretically that quantum field theory allows states where the energy can be arbitrarily negative at a given point.[57] Many prominent physicists such as Stephen Hawking,[58] Kip Thorne,[59] and others[60][61][62] therefore argue that such effects might make it possible to stabilize a traversable wormhole. There’s also solutions to FTL travel that don’t have to violate causality. Space itself is expanding faster than light. My overall point is it’s weird for scientists to shut down the possibility of FTL travel when we have theories that don’t disprove it outright, especially when we don’t really know whether gravity is a bending in spacetime or is governed by the same rules as QFT. The ER=EPR conjecture really intrigues me, and I think following that path may help lead us to a better understanding of what’s possible.
  - mr_mitm 3y ago
    > There’s also solutions to FTL travel that don’t have to violate causality. Space itself is expanding faster than light. But you can't use expansion of space to move matter or to travel. You could even argue that distant galaxies aren't even moving at all, they just appear to do so because the distance between them and us increases. Comparing velocities of distant objects in curved spacetime is tricky in general.
    - likeabbas 3y ago

throwaway290 3y ago

What experiments violate causality?

likeabbas 3y ago
https://phys.org/news/2017-04-physicists-violate-local-causality.html https://phys.org/news/2017-04-physicists-violate-local-causa... is one
- throwaway290 3y ago
  It seems like a huge leap to use a violation of bilocal (not even local in general) causality as confirmation of even theoretical possibility of human FTL travel
- GoblinSlayer 3y ago
  >If a Bell inequality is violated, then either locality or realism (or simply "local realism") has also been violated. In other words, it's a violation of classical realism, not a violation of locality.
  - aa-jv 3y ago
    Why not both? i.e. truly a violation.
    - GoblinSlayer 3y ago
      Locality is necessary for the special theory of relativity. That's why not both.
    - simonh 3y ago
      Violation of the Bell inequalities tells us certain things. Other things it doesn't tell us might also be true, but that's speculation not derivation unless we have some other evidence to work with.

simonh 3y ago

Just to nitpick, the Casimir effect only produces negative pressures relative to the vacuum energy. They're not truly negative. Just in case anyone reading that misunderstands. Also 'violates causality' is an awful lot to unpack, and is glossing over so much nuance that I don't think it's really a meaningful thing to say. For example violation of the Bell inequalities does not rule out superdeterminism, and that has a very solid account of causality. It's just not a conventional one.

likeabbas 3y ago
You left one portion out of the explanation of the Casimir effect > The Casimir effect shows that quantum field theory allows the energy density in certain regions of space to be negative relative to the ordinary vacuum energy, and it has been shown theoretically that quantum field theory allows states where the energy can be arbitrarily negative at a given point.[57] Many prominent physicists such as Stephen Hawking,[58] Kip Thorne,[59] and others[60][61][62] therefore argue that such effects might make it possible to stabilize a traversable wormhole. There’s also solutions to FTL travel that don’t have to violate causality. Space itself is expanding faster than light. My overall point is it’s weird for scientists to shut down the possibility of FTL travel when we have theories that don’t disprove it outright, especially when we don’t really know whether gravity is a bending in spacetime or is governed by the same rules as QFT. The ER=EPR conjecture really intrigues me, and I think following that path may help lead us to a better understanding of what’s possible.
- mr_mitm 3y ago
  > There’s also solutions to FTL travel that don’t have to violate causality. Space itself is expanding faster than light. But you can't use expansion of space to move matter or to travel. You could even argue that distant galaxies aren't even moving at all, they just appear to do so because the distance between them and us increases. Comparing velocities of distant objects in curved spacetime is tricky in general.
  - likeabbas 3y ago