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>>Put me firmly in the camp that believes the speed of light is a hard limit on the universe and I'll use Isaac Arthur dismissal of FTL travel as to why. I wou

>>Put me firmly in the camp that believes the speed of light is a hard limit on the universe and I'll use Isaac Arthur dismissal of FTL travel as to why. I would modify your sentence to say that the speed of light is a hard limit through space. Space on the other hand does not seem to have that limitation [1] [1] https://en.wikipedia.org/wiki/Alcubierre_drive https://en.wikipedia.org/wiki/Alcubierre_drive

ThrowawayR2 8y ago
The Alcubierre drive is a fantasy. It's the equivalent of saying "I can start a business selling unicorn rides if I have a unicorn." The unicorn in this case being "negative mass", there being no way to synthesize such a thing nor even a plausible path by which it might be possible.
- ben_w 8y ago
  And before anyone mentions Casimir cavities, I did a blog post in the style of a paper about that: https://kitsunesoftware.wordpress.com/2017/04/20/can-a-casimir-cavity-be-used-to-construct-true-negative-mass-metamaterials/ https://kitsunesoftware.wordpress.com/2017/04/20/can-a-casim...
  - magicalhippo 8y ago
    AFAIK the Casimir force is due to the van der Waals force between the plates, so doesn't that spoil the negative energy party from the get-go? https://arxiv.org/abs/1605.04143 https://arxiv.org/abs/1605.04143 https://arxiv.org/abs/hep-th/0503158 https://arxiv.org/abs/hep-th/0503158
    - sp332 8y ago
      I'm not an expert, but this paper makes a convincing argument that that's not a problem. https://arxiv.org/abs/1702.03291 https://arxiv.org/abs/1702.03291
      - magicalhippo 8y ago
        Ah, thanks, hadn't seen that follow-up paper.
- snowwrestler 8y ago
  We know for a fact that it is possible for space to expand because we have observed that space is expanding. Who knows why or how, or if it should be called “negative mass” or “dark energy,” but observing a phenomenon has always been the starting point for exploiting it. Radiation started out as a small unexplained observation too and look what we’ve done with that. I’m not claiming that the warp drive is around the corner, I’m just saying: we do not yet know enough to rule it out.
  - MrLeap 8y ago
    This is an interesting perspective! The frontier around dark energy / space accelerating in its expansion etc is interesting to me. A bit unrelated, my pet theory is that a dwindling of some quantity creates the things we're measuring as acceleration. My naive intuition is that celestial bodies aren't flying away from each other accelerated by some unseen energy so much as getting smaller. If two things shrink in place, the distance between them grows. Maybe there's some obvious reason why that couldn't be the case, i'd be interested to know!
    - Tepix 8y ago
      That wouldn't explain the redshift, would it?
      - ben_w 8y ago
        If we’re shrinking too, I think that we’d perceive a given photon getting longer and hence redder. (This leads to another problem: why don’t the photons shrink too?)
        snowwrestler 8y ago
        The amount of space for us to shrink into is absolutely miniscule compared to the space available to expand between us and distant galaxies. The metric expansion of space appears to be an extremely weak, small effect. It just adds up to something measurable in the vast gulfs between galaxies. Furthermore the amount of acceleration away from us is proportional to the distance from us (farther things are accelerating away faster). The shrinking hypothesis only makes sense of that data if it posits that we are the center of the universe.
cletus 8y ago
Isaac Arthur did and episode on this topic specifically [1]. It's one of his early ones. There are a whole lot of "ifs" here, just one of which is negative mass. [1]: https://www.youtube.com/watch?v=yCCsmxGjEV0 https://www.youtube.com/watch?v=yCCsmxGjEV0

ThrowawayR2 8y ago

The Alcubierre drive is a fantasy. It's the equivalent of saying "I can start a business selling unicorn rides if I have a unicorn." The unicorn in this case being "negative mass", there being no way to synthesize such a thing nor even a plausible path by which it might be possible.

ben_w 8y ago
And before anyone mentions Casimir cavities, I did a blog post in the style of a paper about that: https://kitsunesoftware.wordpress.com/2017/04/20/can-a-casimir-cavity-be-used-to-construct-true-negative-mass-metamaterials/ https://kitsunesoftware.wordpress.com/2017/04/20/can-a-casim...
- magicalhippo 8y ago
  AFAIK the Casimir force is due to the van der Waals force between the plates, so doesn't that spoil the negative energy party from the get-go? https://arxiv.org/abs/1605.04143 https://arxiv.org/abs/1605.04143 https://arxiv.org/abs/hep-th/0503158 https://arxiv.org/abs/hep-th/0503158
  - sp332 8y ago
    I'm not an expert, but this paper makes a convincing argument that that's not a problem. https://arxiv.org/abs/1702.03291 https://arxiv.org/abs/1702.03291
    - magicalhippo 8y ago
      Ah, thanks, hadn't seen that follow-up paper.
snowwrestler 8y ago
We know for a fact that it is possible for space to expand because we have observed that space is expanding. Who knows why or how, or if it should be called “negative mass” or “dark energy,” but observing a phenomenon has always been the starting point for exploiting it. Radiation started out as a small unexplained observation too and look what we’ve done with that. I’m not claiming that the warp drive is around the corner, I’m just saying: we do not yet know enough to rule it out.
- MrLeap 8y ago
  This is an interesting perspective! The frontier around dark energy / space accelerating in its expansion etc is interesting to me. A bit unrelated, my pet theory is that a dwindling of some quantity creates the things we're measuring as acceleration. My naive intuition is that celestial bodies aren't flying away from each other accelerated by some unseen energy so much as getting smaller. If two things shrink in place, the distance between them grows. Maybe there's some obvious reason why that couldn't be the case, i'd be interested to know!
  - Tepix 8y ago
    That wouldn't explain the redshift, would it?
    - ben_w 8y ago
      If we’re shrinking too, I think that we’d perceive a given photon getting longer and hence redder. (This leads to another problem: why don’t the photons shrink too?)
      - snowwrestler 8y ago
        The amount of space for us to shrink into is absolutely miniscule compared to the space available to expand between us and distant galaxies. The metric expansion of space appears to be an extremely weak, small effect. It just adds up to something measurable in the vast gulfs between galaxies. Furthermore the amount of acceleration away from us is proportional to the distance from us (farther things are accelerating away faster). The shrinking hypothesis only makes sense of that data if it posits that we are the center of the universe.

cletus 8y ago

Isaac Arthur did and episode on this topic specifically [1]. It's one of his early ones. There are a whole lot of "ifs" here, just one of which is negative mass. [1]: https://www.youtube.com/watch?v=yCCsmxGjEV0 https://www.youtube.com/watch?v=yCCsmxGjEV0