Yes. And don’t do that, you could create a black hole!
Well, keep in mind that the fabric of space (really space-time) is 4 dimensional, not the 2-dimensional sheet it’s often depicted as. Probably its those same sheet-like depictions where you’ve seen a black hole drawn like a flat hole with a funnel coming down.
A black hole may on the inside be a point-like singularity, but the event horizon (the boundary of the black hole) is more like the surface of a ball (a somewhat flattened ball if the black hole is rotating). They aren’t flat in the sense I think you mean.
There is an idea that the information contained in the black hole is all contained in the fluctuations on its two-dimensional surface, but I don’t think that’s what you’re getting at. And in any case, we’re talking about the two dimensional surface of a ball (which encloses a 3-dimensional region of space), not a flat circle like you’re suggesting.
Please pardon the continued tangent, guys.
Okay, so if a black hole increases in mass as it continues to suck in matter, doesn’t its gravitational effect increase in proportion and, if so, does its event horizon continue to expand?
The size of a black hole’s event horizon depends only on its mass, and if the mass increases, so will the size of the horizon. It matters not whether it had that much mass at the time that it formed, or if it has gained mass later.
Meanwhile, as to dimensionality: The event horizon of a black hole is 2+1 dimensional, the region withing the event horizon is 3+1 dimensional, and the singularity predicted by current theories to be at the center of the hole is 0 dimensional. In this context, “3+1 dimensional” means 3 spacelike dimensions and 1 timelike dimension; the lack of the +1 on the singularity is intentional. Also note the “predicted by current theories” with regard to the singularity: We don’t yet have a theory of quantum gravity, but I don’t think anyone would be particularly surprised, once we get one, if it predicted something of finite extent in the center of a black hole instead of a singularity. But of course, one shouldn’t be surprised if it doesn’t say that, either.
Yes, as Buck Godot mentioned: m/r[sup]2[/sup]. So, the gravitational force (that being its Constant (Force = Mass1 x Mass2, inversely proportionate to the square of the distance) is related to how much mass is there (mass = m) inversely related to the body’s radius, squared (r[sup]2[/sup]).
Someone correct me if I’m wrong. Otherwise, hope that is clearer?
Also, the event horizon, is more of a “zone”* that demarcates the point at which matter or energy falling in would have to go beyond the speed of light to reach escape velocity.
If you had a clean view of a black hole, in theory, the sphere of the event horizon would be black, and the light from around and behind it would be warped, or lensed, around it in such a way that all the information from behind your field of view of the event horizon, would still be visible.
Let’s say you and I are in two different, waring spaceships. If you tried to hide “behind” a black hole by putting its event horizon between our respective fields of vision, it wouldn’t work, since the light reflected off your ship is completely bent around the horizon. I’d still be able to completely see you, but your image would looked warped, and especially smeared around the outline of the horizon itself, the closer that apparent feature crosses between my vision and the singularity itself (the very center of the black hole).
I thought that too cool not to mention.
*Which is why Chronos describes it as 2+1 in dimensionality. It has no thickness. Topologically, it’s a plane, but is manifest as a sphere in 3-D space.
You only use the body’s own radius if you’re interested in the gravitational force right at the surface of the body. In general, the “r” there is the distance from the center of the attracting body to the point you’re looking at, regardless of where that point is. If, for instance, you wanted to know the gravitational force of the Earth on the Moon, then r would be the distance from the Earth to the Moon, not the radius of the Earth. Replace the Earth with an Earth-massed black hole, and it doesn’t matter, since even though the attracting object is now the size of a grape, it’s still at the same distance from the Moon.
Thanks Chronos. Yeh, the more I thought about that, the more I realized it was the relation of the force of gravity on the surface of a massive body itself. And with a black hole, there is no surface.
A rotating singularity is a ring and not a point; I’m not sure what that means in terms of dimensionality.
As an aside, I was amused when looking this up to find out that “spaghettification” is apparently an acknowledged word for what happens if you fall in. Remind me of thagomizers.
I think that the singularity of a Kerr black hole (what Der Trihs was just referring to there) is 1+0 dimensional, but I’m a bit rusty on this, and singularities can be somewhat counterintuitive.
As for spaghettification, remember, scientists are human, too, and if there’s no better word, we’ll use the word we have. If it happens to be a fun word, so much the better.