4 ms·

The phrase "warp drive" is based on the idea of warping the structure of space-time around the ship such that it is now there when it was here. But in some sens

by btilly 3y ago

The phrase "warp drive" is based on the idea of warping the structure of space-time around the ship such that it is now there when it was here. But in some sense it did not move. https://en.wikipedia.org/wiki/Alcubierre_drive https://en.wikipedia.org/wiki/Alcubierre_drive shows that this is, in principle, not a violation of general relativity. But that drive depends on finding something with negative mass. Most physicists don't think that that can be done. (But the phenomena of extracting zero point energy with the Casimir effect holds out a slender ray of hope for cranks who think that they have done it.) So it isn't that I didn't notice that something was moving fast. It is that I know that the idea is to get from here to there by doing something other than moving.

SideburnsOfDoom 3y ago
> So it isn't that I didn't notice that something was moving fast. It is that I know that the idea is to get from here to there by doing something other than moving. I think that this is a semantic distinction without any practical difference whatever. It would get you there before light would: you are outside of your light-cone, the end, game over. Word-games won't help with that.
- btilly 3y ago
  I think that this is a semantic distinction without any practical difference whatever. What you think doesn't matter. General Relativity says that the Alcubierre drive would work if you could find a source of negative mass. It can get a vehicle from here to there, outside of its light cone. And yet that's not game over. That's not a word game. That's mathematics applied to our best model of how space-time works. If you want to imagine it, imagine ants crawling on a balloon. Motion is their crawling. But now start blowing up the balloon as it crawls. Distances are changing, and it isn't the ant doing it! Think this is unrealistic? The current model of the Big Bang says that things we see from 13.7 billion year old light are now 47 billion light years away from us. Our naive ideas of motion can't explain that. But general relativity does, and it is exactly parallel to the ants on a balloon image. Now imagine coming along, pinching the balloon, having the ant walk over the fold, then unpinching the balloon. The ant got from here to there faster than it could possibly walk! That's the idea of a warp drive. Is it possible? Probably not. But we know of nothing that forbids it other than the fact that we can't figure out how to do it.
  - SideburnsOfDoom 3y ago
    It you want to be true doesn't matter either. > It can get a vehicle from here to there, outside of its light cone. And yet that's not game over. It's time travel, so game over for causality. You're fixated on the details of how you get there, and it is irreverent. > if you could find a source of negative mass. It Word games with imaginary numbers.
    - btilly 3y ago
      It's time travel, so game over for causality. You're fixated on the details of how you get there, and it is irreverent. No, it isn't necessarily time travel. See https://news.ycombinator.com/item?id=37013305 https://news.ycombinator.com/item?id=37013305 for my presentation of the standard argument that FTL leads to causality violations. Note that you need it to be FTL in more than one reference frame to do it. That's why, as I pointed out in https://news.ycombinator.com/item?id=37012594 https://news.ycombinator.com/item?id=37012594, FTL only in the fixed reference frame of the distant stars does NOT lead to causality violations. Again, we have no reason to believe that this is possible. But if it were possible, the standard objections would not apply. Word games with imaginary numbers. No, that's tachyons. This one was just negative numbers.

by btilly 3y ago

SideburnsOfDoom 3y ago

> So it isn't that I didn't notice that something was moving fast. It is that I know that the idea is to get from here to there by doing something other than moving. I think that this is a semantic distinction without any practical difference whatever. It would get you there before light would: you are outside of your light-cone, the end, game over. Word-games won't help with that.

btilly 3y ago
I think that this is a semantic distinction without any practical difference whatever. What you think doesn't matter. General Relativity says that the Alcubierre drive would work if you could find a source of negative mass. It can get a vehicle from here to there, outside of its light cone. And yet that's not game over. That's not a word game. That's mathematics applied to our best model of how space-time works. If you want to imagine it, imagine ants crawling on a balloon. Motion is their crawling. But now start blowing up the balloon as it crawls. Distances are changing, and it isn't the ant doing it! Think this is unrealistic? The current model of the Big Bang says that things we see from 13.7 billion year old light are now 47 billion light years away from us. Our naive ideas of motion can't explain that. But general relativity does, and it is exactly parallel to the ants on a balloon image. Now imagine coming along, pinching the balloon, having the ant walk over the fold, then unpinching the balloon. The ant got from here to there faster than it could possibly walk! That's the idea of a warp drive. Is it possible? Probably not. But we know of nothing that forbids it other than the fact that we can't figure out how to do it.
- SideburnsOfDoom 3y ago
  It you want to be true doesn't matter either. > It can get a vehicle from here to there, outside of its light cone. And yet that's not game over. It's time travel, so game over for causality. You're fixated on the details of how you get there, and it is irreverent. > if you could find a source of negative mass. It Word games with imaginary numbers.
  - btilly 3y ago
    It's time travel, so game over for causality. You're fixated on the details of how you get there, and it is irreverent. No, it isn't necessarily time travel. See https://news.ycombinator.com/item?id=37013305 https://news.ycombinator.com/item?id=37013305 for my presentation of the standard argument that FTL leads to causality violations. Note that you need it to be FTL in more than one reference frame to do it. That's why, as I pointed out in https://news.ycombinator.com/item?id=37012594 https://news.ycombinator.com/item?id=37012594, FTL only in the fixed reference frame of the distant stars does NOT lead to causality violations. Again, we have no reason to believe that this is possible. But if it were possible, the standard objections would not apply. Word games with imaginary numbers. No, that's tachyons. This one was just negative numbers.