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I've been wondering about the "last parsec problem" ever since I read about it but this prompted me to look it up. Turns out the reason it's actually possible f

by taneq 5y ago

I've been wondering about the "last parsec problem" ever since I read about it but this prompted me to look it up. Turns out the reason it's actually possible for black holes to actually merge instead of just orbiting each other forever is "dynamical friction" (basically as a black hole moves through a bunch of stars or other masses, its gravity pulls them inwards so that the stars it's already passed tend to be more directly behind it than the stars in front of it, so the net force on the black hole is backwards.) The more you know.

dylan604 5y ago
>The more you know. The more questions you have ;-)
- blueprint 5y ago
  Not necessarily. Besides, if that were the case, you would lose the ability to say you've learned anything at all... which, sadly, is also a self-contradiction. Only someone who knows can make such statements, another self-contradiction, so they wouldn't say them either. If you look in practical cases, people who really master a subject don't seem to have many questions left at all. The real problem is humans have not mastered physics yet.
  - dylan604 5y ago
    That's like saying you took the first step up a ladder so there's no point in continuing to the next step. That just doesn't follow. Now, you just know you need to know more. The unknown unknowns become the known unknowns so you can learn to make the unknowns known.
    - blueprint 5y ago
      I am saying the precise opposite of that. Saying that you, at your supposed low level, know that you only get more questions the more you learn, is exactly such a statement as you are claiming I am making. From another perspective, the statement sounds like an excuse for not reaching a higher level of mastery that the person admits they don't know humans are capable of. It's a self-contradiction. Thanks for all the downvotes, y'all! Definitely didn't trigger anyone.
gizmo686 5y ago
That is part of it, but as the orbit shrinks, relativistic effects start to become the dominant source of orbit decay. The most striking demonstration of this effect is what happens around the photon sphere (3/2 the radius of the event horizon of a non-rotating black hole. The orbital velocity at this radius is the speed of light. Consider the two body problem, of a single mass interacting gravitationally with the black hole. If this mass crosses the photon sphere from the outside, it will inevitably spiral into the event horizon. If the mass crosses the photon sphere from the inside, it will either escape to infinity proceed to cross it again from the outside (and subsequently spiral into the event horizon). The more general phenomena is orbital decay that happens in any 2 body problem under general relativity. From a conservation of energy standpoint, the massive amounts of energy contained within gravitational waves come from the release of gravitational potential energy as the two orbiting objects fall towards each other.

by taneq 5y ago

dylan604 5y ago

>The more you know. The more questions you have ;-)

blueprint 5y ago
Not necessarily. Besides, if that were the case, you would lose the ability to say you've learned anything at all... which, sadly, is also a self-contradiction. Only someone who knows can make such statements, another self-contradiction, so they wouldn't say them either. If you look in practical cases, people who really master a subject don't seem to have many questions left at all. The real problem is humans have not mastered physics yet.
- dylan604 5y ago
  That's like saying you took the first step up a ladder so there's no point in continuing to the next step. That just doesn't follow. Now, you just know you need to know more. The unknown unknowns become the known unknowns so you can learn to make the unknowns known.
  - blueprint 5y ago
    I am saying the precise opposite of that. Saying that you, at your supposed low level, know that you only get more questions the more you learn, is exactly such a statement as you are claiming I am making. From another perspective, the statement sounds like an excuse for not reaching a higher level of mastery that the person admits they don't know humans are capable of. It's a self-contradiction. Thanks for all the downvotes, y'all! Definitely didn't trigger anyone.

gizmo686 5y ago

That is part of it, but as the orbit shrinks, relativistic effects start to become the dominant source of orbit decay. The most striking demonstration of this effect is what happens around the photon sphere (3/2 the radius of the event horizon of a non-rotating black hole. The orbital velocity at this radius is the speed of light. Consider the two body problem, of a single mass interacting gravitationally with the black hole. If this mass crosses the photon sphere from the outside, it will inevitably spiral into the event horizon. If the mass crosses the photon sphere from the inside, it will either escape to infinity proceed to cross it again from the outside (and subsequently spiral into the event horizon). The more general phenomena is orbital decay that happens in any 2 body problem under general relativity. From a conservation of energy standpoint, the massive amounts of energy contained within gravitational waves come from the release of gravitational potential energy as the two orbiting objects fall towards each other.