4 ms·

What about building a circular ship around a micro black hole? Or is that just real gravity and not anti-gravity?

Cthulhu_ 3y ago
Note: armchair reply, I don't know enough astro whatnots to substantiate this take: That implies that you can actually move the black hole; a black hole producing 1G requires it to be as heavy (or, to have as much attraction) as the earth itself. It would be a lot more compact - a black hole as heavy as the earth is about the size of a ping pong ball - but if my intuition is correct, would require as much force to move as it would to move the earth.
- db48x 3y ago
  Yep, F=ma. For a given force, if mass is big then the acceleration must be small. Also, I feel compelled to mention that to get an Earth–like gravitational field near the event horizon of a non–spinning black hole, it needs to mass more than the whole galaxy. It would be about a light–year across, iirc, and if you built a shell around it (which would not be easy) then the surface area would be so large as to beggar description. Small black holes are not very earth–like because of the extreme tidal forces. Trying to stand on that ping–pong ball would be extremely uncomfortable.
  - User23 3y ago
    If it’s an antimatter black hole you can dump normal matter into it to release energy, assuming some way exists to turn that into useful acceleration.
    - nyssos 3y ago
      An "antimatter black hole" is just a black hole. There might still be something behind the event horizon to annihilate with, there might not, the question might be meaningless, but in any case you're not getting anything back out again.
      - User23 3y ago
        Don’t have to get anything out just need to accelerate the singularity.
        ben_w 3y ago
        It doesn't, at least not within currently understood physics: https://www.youtube.com/watch?v=cFslUSyfZPc https://www.youtube.com/watch?v=cFslUSyfZPc You'll push the black hole with precisely the same momentum (in the opposite direction) as you yourself got from whatever device was pushing the matter towards the black hole.
      - User23 3y ago
        What happens when an antimatter black hole collides with an equal mass matter black hole? Does the total mass convert to energy? If so what happens to the gravitational effects?
        nyssos 3y ago
        No, an antimatter black hole is literally just a black hole. They're the same thing. > Does the total mass convert to energy? If so what happens to the gravitational effects? Energy density and mass density are the same thing too. A kilogram of hydrogen next to a kilogram of antihydrogen gravitates in exactly the same way as ~10^17 joules of equivalently distributed photons. The only difference is that the photons won't stay equivalently distributed for long.
        User23 3y ago
        I asked my particle physicist buddy about this and he pointed me here[1]. It sounds like you're giving the "classical" answer, but it's an area of open discussion. He thinks it could conceivably emit energy as gravitational waves. [1] https://physics.stackexchange.com/questions/7290/no-hair-theorem-for-black-holes-and-the-baryon-number https://physics.stackexchange.com/questions/7290/no-hair-the...
        3y ago

Note: armchair reply, I don't know enough astro whatnots to substantiate this take: That implies that you can actually move the black hole; a black hole producing 1G requires it to be as heavy (or, to have as much attraction) as the earth itself. It would be a lot more compact - a black hole as heavy as the earth is about the size of a ping pong ball - but if my intuition is correct, would require as much force to move as it would to move the earth.

db48x 3y ago
Yep, F=ma. For a given force, if mass is big then the acceleration must be small. Also, I feel compelled to mention that to get an Earth–like gravitational field near the event horizon of a non–spinning black hole, it needs to mass more than the whole galaxy. It would be about a light–year across, iirc, and if you built a shell around it (which would not be easy) then the surface area would be so large as to beggar description. Small black holes are not very earth–like because of the extreme tidal forces. Trying to stand on that ping–pong ball would be extremely uncomfortable.
- User23 3y ago
  If it’s an antimatter black hole you can dump normal matter into it to release energy, assuming some way exists to turn that into useful acceleration.
  - nyssos 3y ago
    An "antimatter black hole" is just a black hole. There might still be something behind the event horizon to annihilate with, there might not, the question might be meaningless, but in any case you're not getting anything back out again.
    - User23 3y ago
      Don’t have to get anything out just need to accelerate the singularity.
      - ben_w 3y ago
        It doesn't, at least not within currently understood physics: https://www.youtube.com/watch?v=cFslUSyfZPc https://www.youtube.com/watch?v=cFslUSyfZPc You'll push the black hole with precisely the same momentum (in the opposite direction) as you yourself got from whatever device was pushing the matter towards the black hole.
    - User23 3y ago
      What happens when an antimatter black hole collides with an equal mass matter black hole? Does the total mass convert to energy? If so what happens to the gravitational effects?
      - nyssos 3y ago
        No, an antimatter black hole is literally just a black hole. They're the same thing. > Does the total mass convert to energy? If so what happens to the gravitational effects? Energy density and mass density are the same thing too. A kilogram of hydrogen next to a kilogram of antihydrogen gravitates in exactly the same way as ~10^17 joules of equivalently distributed photons. The only difference is that the photons won't stay equivalently distributed for long.
        User23 3y ago
        I asked my particle physicist buddy about this and he pointed me here[1]. It sounds like you're giving the "classical" answer, but it's an area of open discussion. He thinks it could conceivably emit energy as gravitational waves. [1] https://physics.stackexchange.com/questions/7290/no-hair-theorem-for-black-holes-and-the-baryon-number https://physics.stackexchange.com/questions/7290/no-hair-the...
        3y ago