3 ms·

this is also my experience with simulated gravity and galaxy systems. i guess newton physics alone would be enough to make a body flung out if it comes close en

by z3t4 10y ago

this is also my experience with simulated gravity and galaxy systems. i guess newton physics alone would be enough to make a body flung out if it comes close enough. and i guess a merge is close enough. i was working on a space mmo and after leaving the server running for weeks some body would always be flyng away with crazy speed.

strainer 10y ago
The newtonian model itself doesn't produce this behaviour as it is continuous, so however much bodies accelerate towards each other they can decelerate just as much once they have passed. In n-body simulation the continuous model is 'squeezed' into time-slices, where bodies can accelerate towards each other in one time-slice and in the next be too far past each other to slow each other down again. Seemingly in the real astrophysical world, blackholes will free-fall towards each other by their masses 'dragging' on spacetime, causing deep perturbations in spacetime (as gravity waves). Eventually there is a 'merge' as you called it, an operation during which the resulting merged body can get a directed kick from the persisting spacetime perturbations, one powerful enough to eject it from a galaxy. In the real world, overall it is expected energy and momentum is not defied during this merge operation, it seems remarkable considering how exceptional and energetic these events appear. edit ...on second thoughts, this 'merge event' produces GRAVITATIONAL PROPULSION - sorry for the caps but I think they might be justified.
- kristianp 10y ago
  Finally we have reactionless space travel! All we have to do is merge two black holes!
  - AnimalMuppet 10y ago
    It's not reactionless. It's essentially a "gravitational wave rocket".
- grigjd3 10y ago
  General relativity is a continuous theory as well.
abecedarius 10y ago
In Newtonian gravity you need at least three bodies to arrange an ejection: two of them start orbiting more tightly, to counterbalance the third one flying out to infinity. (IIRC this happens a lot in globular clusters, and simulations like yours.) With just two bodies you get only Newton's solutions, the conic sections.

by z3t4 10y ago

strainer 10y ago

The newtonian model itself doesn't produce this behaviour as it is continuous, so however much bodies accelerate towards each other they can decelerate just as much once they have passed. In n-body simulation the continuous model is 'squeezed' into time-slices, where bodies can accelerate towards each other in one time-slice and in the next be too far past each other to slow each other down again. Seemingly in the real astrophysical world, blackholes will free-fall towards each other by their masses 'dragging' on spacetime, causing deep perturbations in spacetime (as gravity waves). Eventually there is a 'merge' as you called it, an operation during which the resulting merged body can get a directed kick from the persisting spacetime perturbations, one powerful enough to eject it from a galaxy. In the real world, overall it is expected energy and momentum is not defied during this merge operation, it seems remarkable considering how exceptional and energetic these events appear. edit ...on second thoughts, this 'merge event' produces GRAVITATIONAL PROPULSION - sorry for the caps but I think they might be justified.

kristianp 10y ago
Finally we have reactionless space travel! All we have to do is merge two black holes!
- AnimalMuppet 10y ago
  It's not reactionless. It's essentially a "gravitational wave rocket".
grigjd3 10y ago
General relativity is a continuous theory as well.

abecedarius 10y ago

In Newtonian gravity you need at least three bodies to arrange an ejection: two of them start orbiting more tightly, to counterbalance the third one flying out to infinity. (IIRC this happens a lot in globular clusters, and simulations like yours.) With just two bodies you get only Newton's solutions, the conic sections.