Black Hole Formation: Does it Start at the Center or Simultaneously?

  • Thread starter Thread starter nitsuj
  • Start date Start date
  • Tags Tags
    Blackhole Form
nitsuj
Messages
1,388
Reaction score
98
Saw somewhere that the force of gravity "cancels out" in that if in the approx. centre of the Earth you would feel no gravity (net zero).

Does a black hole "start" forming from a particular point? (ie where gravity is strongest) Or "start" to form from the centre out? Or does it all just happen simultaneously?

Last would the centre of a black hole have the same net zero gravity area as Earth?
 
Physics news on Phys.org
I believe there is not "in" or "out" in a black hole. You see, the reason that you feel less gravity as you move toward the center of the Earth is because gravity is determined by how much mass is "inside a sphere" between you and the Earth's center. As the 'sphere' inside you shrinks, so does the gravitational pull.

Now, with a black hole all the mass is concentrated as a very, very tiny center. So there is no way for you to have some of the mass "outside" of you, because of the way it exists. But someone else will surely clarify this, I hope!
 
schaefera said:
I believe there is not "in" or "out" in a black hole. You see, the reason that you feel less gravity as you move toward the center of the Earth is because gravity is determined by how much mass is "inside a sphere" between you and the Earth's center. As the 'sphere' inside you shrinks, so does the gravitational pull.

Now, with a black hole all the mass is concentrated as a very, very tiny center. So there is no way for you to have some of the mass "outside" of you, because of the way it exists. But someone else will surely clarify this, I hope!

I can help clarify my question.
I get there is no going into a black hole. But it does have a measurable size so Id guess math can figure out the "centre" and math models for the distrabution of gravity.

I guess to ask it differently does the direction of acceleration of Earth gravity all focus to some point in the centre of the earth?
 
Force and Mass are proportional, so, when you are at the center of the Earth, all the mass is (for the sake of ease we'll assume is distributed evenly) evenly around you, which is to say, you are being pulled from every direction equally, which causes the situation where you are experiencing all the acceleration canceling itself out.

Edit: ...you are experiencing... acceleration in every direction equally.
 
Last edited:
OK, so this has bugged me for a while about the equivalence principle and the black hole information paradox. If black holes "evaporate" via Hawking radiation, then they cannot exist forever. So, from my external perspective, watching the person fall in, they slow down, freeze, and redshift to "nothing," but never cross the event horizon. Does the equivalence principle say my perspective is valid? If it does, is it possible that that person really never crossed the event horizon? The...
In this video I can see a person walking around lines of curvature on a sphere with an arrow strapped to his waist. His task is to keep the arrow pointed in the same direction How does he do this ? Does he use a reference point like the stars? (that only move very slowly) If that is how he keeps the arrow pointing in the same direction, is that equivalent to saying that he orients the arrow wrt the 3d space that the sphere is embedded in? So ,although one refers to intrinsic curvature...
So, to calculate a proper time of a worldline in SR using an inertial frame is quite easy. But I struggled a bit using a "rotating frame metric" and now I'm not sure whether I'll do it right. Couls someone point me in the right direction? "What have you tried?" Well, trying to help truly absolute layppl with some variation of a "Circular Twin Paradox" not using an inertial frame of reference for whatevere reason. I thought it would be a bit of a challenge so I made a derivation or...
Back
Top