5 ms·

"Small" Dyson sphere is relative. The tidal forces at 50km from an earth-mass black hole would still be pretty significant, so it probably couldn't be smaller t

"Small" Dyson sphere is relative. The tidal forces at 50km from an earth-mass black hole would still be pretty significant, so it probably couldn't be smaller than that. E.g. to pick something on the scale of a human, the difference in gravitational acceleration (being GM/(r^2)) between two points at 50000 and 50002 meters from such a black hole would be about 1.6 G.

pas 6y ago
What does that do? I mean you can walk in 1G just fine, so probably we could go there, take a walk/sit there in 1.6G, and leave, right? That means that if we put a 100km wide structure around it, we can service it easily(?) even without robots.
- wcoenen 6y ago
  You can't "walk" in this 1.6G. You'd experience it while floating freely in space. And the stress on your body would be tension instead of compression. I guess it would feel like hanging upside down, except that your blood rushes to both your feet and your head.
  - deleted 6y ago
    [deleted]
- juped 6y ago
  The difference in gravitational acceleration between two points, not the gravitational acceleration at the points.
- lmilcin 6y ago
  I can't imagine we will be building things like that manually. By the time a swarm of robots will process blueprints and take raw materials and construct the structure semi-autonomously or even completely autonomously. The structure would most certainly not admit human presence. It only has to redirect radiation to where it is useful (maybe send a starship on a laser beam, for example).
  - Recurecur 6y ago
    Maybe ships will need laser power . It remains to be seen if near-C travel is at all feasible, due to radiation/erosion from impacting interstellar material. If not, a ship can easily carry its own fuel, it will just be a generation/hibernation ship. Or, perhaps our extropian descendants won't care about travel time. ;-) OR, maybe the black hole could power a hyperspace portal or something equally exotic... Regardless, having a compact object nearby to play with would be fun!
    - dogma1138 6y ago
      One thing will have to change if we ever can travel at relativistic speeds or have function cryogenics (or anything similar) will be markets and investments, just think of putting even a relatively small amount into a yielding investment even an index fund and going to “sleep” for 200 years not only would you get immediately to benefit from 200 years of advancement but you’ll also get to benefit form 200 years of what effectively is compound interest. I really wonder what will the societal implications of such a path being possible are going to be. There are plenty of people that will be willing to push a pause button right now to be able to wake up in a world where you could buy a ticket to mars, add to that the quite likely possibility of becoming a millionaire if not a billionaire if you put enough money into any inflation beating investment and you get quite the incentives package. Sure you might never wake up because the world is going to end in a nuclear holocaust or your icebox will experience a kernel panic 17 years into your suspended animation but overall this quite likely be a much lower possibility than dying prematurely today.
      - deleted 6y ago
        [deleted]
- Recurecur 6y ago
  It's not that, it's the difference in the gravity field between two points. On Earth, the gravity field is very close to uniform. Near a small black hole, the field changes rapidly and is very strong. It's a "pull" effect, meaning that if you were oriented with your feet towards the object as described by the GP, and 2m tall, your feet would experience 1.6 G more "gravity" than your head. It's a tidal force, literally working to pull you apart (same effect causes tides on Earth). If you were to fall into the black hole, at some point you'd be "stringified" as that force stretched you into spaghetti shape.
  - Recurecur 6y ago
    BTW, regarding "standing" in this gravity field... If there were a structure to stand on, rather than you being in orbit, the force of gravity would be about 160 billion times the force of gravity on Earth (~1,594,000,000,000 m/s^2). That's for a 10,000,000 Earth mass black hole at 50 km.
    - lovemenot 6y ago
      If Planet 9 were indeed a black hole its significance would surely be that prevalence of lower mass black holes is orders of magnitude more common than currently known. This particular one may not be practical for energy generation, but it would be obviously worth looking for others of more useable mass.
      - sliken 6y ago
        Why not? There's various approaches to extracting energy from a black hole of any size, and being smaller generally makes things easier.
  - Recurecur 6y ago
    So, I just calculated the orbital speed at 50 km. It came out to 282,378 km/s. The speed of light is 299,792.5 km/s, so we're way into relativistic territory. Good luck having enough energy to build a structure around it! ha

pas 6y ago

What does that do? I mean you can walk in 1G just fine, so probably we could go there, take a walk/sit there in 1.6G, and leave, right? That means that if we put a 100km wide structure around it, we can service it easily(?) even without robots.

wcoenen 6y ago
You can't "walk" in this 1.6G. You'd experience it while floating freely in space. And the stress on your body would be tension instead of compression. I guess it would feel like hanging upside down, except that your blood rushes to both your feet and your head.
- deleted 6y ago
  [deleted]
juped 6y ago
The difference in gravitational acceleration between two points, not the gravitational acceleration at the points.
lmilcin 6y ago
I can't imagine we will be building things like that manually. By the time a swarm of robots will process blueprints and take raw materials and construct the structure semi-autonomously or even completely autonomously. The structure would most certainly not admit human presence. It only has to redirect radiation to where it is useful (maybe send a starship on a laser beam, for example).
- Recurecur 6y ago
  Maybe ships will need laser power . It remains to be seen if near-C travel is at all feasible, due to radiation/erosion from impacting interstellar material. If not, a ship can easily carry its own fuel, it will just be a generation/hibernation ship. Or, perhaps our extropian descendants won't care about travel time. ;-) OR, maybe the black hole could power a hyperspace portal or something equally exotic... Regardless, having a compact object nearby to play with would be fun!
  - dogma1138 6y ago
    One thing will have to change if we ever can travel at relativistic speeds or have function cryogenics (or anything similar) will be markets and investments, just think of putting even a relatively small amount into a yielding investment even an index fund and going to “sleep” for 200 years not only would you get immediately to benefit from 200 years of advancement but you’ll also get to benefit form 200 years of what effectively is compound interest. I really wonder what will the societal implications of such a path being possible are going to be. There are plenty of people that will be willing to push a pause button right now to be able to wake up in a world where you could buy a ticket to mars, add to that the quite likely possibility of becoming a millionaire if not a billionaire if you put enough money into any inflation beating investment and you get quite the incentives package. Sure you might never wake up because the world is going to end in a nuclear holocaust or your icebox will experience a kernel panic 17 years into your suspended animation but overall this quite likely be a much lower possibility than dying prematurely today.
    - deleted 6y ago
      [deleted]
Recurecur 6y ago
It's not that, it's the difference in the gravity field between two points. On Earth, the gravity field is very close to uniform. Near a small black hole, the field changes rapidly and is very strong. It's a "pull" effect, meaning that if you were oriented with your feet towards the object as described by the GP, and 2m tall, your feet would experience 1.6 G more "gravity" than your head. It's a tidal force, literally working to pull you apart (same effect causes tides on Earth). If you were to fall into the black hole, at some point you'd be "stringified" as that force stretched you into spaghetti shape.
- Recurecur 6y ago
  BTW, regarding "standing" in this gravity field... If there were a structure to stand on, rather than you being in orbit, the force of gravity would be about 160 billion times the force of gravity on Earth (~1,594,000,000,000 m/s^2). That's for a 10,000,000 Earth mass black hole at 50 km.
  - lovemenot 6y ago
    If Planet 9 were indeed a black hole its significance would surely be that prevalence of lower mass black holes is orders of magnitude more common than currently known. This particular one may not be practical for energy generation, but it would be obviously worth looking for others of more useable mass.
    - sliken 6y ago
      Why not? There's various approaches to extracting energy from a black hole of any size, and being smaller generally makes things easier.
- Recurecur 6y ago
  So, I just calculated the orbital speed at 50 km. It came out to 282,378 km/s. The speed of light is 299,792.5 km/s, so we're way into relativistic territory. Good luck having enough energy to build a structure around it! ha