# Black-holes, space time and their bending [closed]

I have been watching some videos related to how space-time is bent because of the mass (just "visually", not mathematically), and then I watched some videos about black holes.

1. In the place where there is mass, there is no space. Space wraps mass (that's why space is bent). This is what represents the picture below. Lines are spacetime lines, which are bent because of the mass particle. "d" is like "the separation between spacetime lines" so I can draw it. Let's say that if I shoot light beams starting from a line, it will follow the line (so, follow the curvature).
2. (Now I open quotes because maybe this is stupid) "As space is bent, the force of space for recovering its initial form ("linear") is the gravity" (end of quotes). Looking at the picture above, we can imagine that those (spacetime) lines are making a force towards the mass, to recover the space the mass was ocupying.
3. If an object has finite density, it means that there is some space in between particles with mass, so space does not "completly wrap the object". As less dense, more space in between the object, so less gravity (picture below). As more dense, less space in between the object, so more gravity. However, if the density of the object is infinite, there is no space in between particles with mass, so space wraps completly the object (pictuve above).

Assuming that what I said is right, from the center of the object with mass to the outside, we have mass, then space.

Following the shape of spacetime produced by a black whole:

• Why a black-hole has that shape?
• Where is the mass located?
• What is the singularity? I mean, I have read what it is, but I do not understand it.
• If not even light can scape from it, it means that the space is bent so that at the end everything crashes with the mass of the black hole, or it means that spacetime is infinitely bent that light travels forever in an infinite space.
• Why a black hole is black if the spacetime wraps the black hole? So light goes around it, but not inside it right?

I am a little confused, and maybe all what I said is wrong, but I needed to ask. If you could post some references or videos I would be thankful.

Thank you.

## closed as too broad by Danu, John Rennie, ACuriousMind♦, user10851, HDE 226868Sep 5 '15 at 22:29

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

• "In the place where there is mass, there is no space." No. Please, try to refrain from relying on visualizations: There is no reason why something like this should be true. I think most of what follows is based on this false premise. – Danu Sep 4 '15 at 16:11
• Furthermore, the list of questions at the end seem to be only tangentially related, and much too broad (and to numerous) to be answered in one go. You should post separate questions for them, or better yet: Search the site for similar question, because some may have been asked before! – Danu Sep 4 '15 at 16:12

Mass doesn't exclude space. Mass allows two different types of curvature to line up. For instance the vacuum outside a star can be curved like a funnel. The vacuum inside a shell can be flat like a disk.

If you drop a penny into a funnel you'll see that the curvature changes from the curved funnel to the flat disk and that transition between the two types of curvature is what mass and energy and momentum and stress and pressure do. They allow different curvatures to line up and transition.

What is the singularity?

A singularitiy is a hypothetical thing that has never been seen. If you follow a curve and the curvature blows up in finite time or finite length then you call it a singularity. It is a sign your theory is broken. Even worse would be if people could see it and interact with it. Then your theory has serious problems.

If not even light can scape from it, it means that the space is bent so that at the end everything crashes with the mass of the black hole,

This is confusing many different things. There is an event horizon and that is what traps light. The singularity is (hopefully) inside the event horizon otherwise we would see it (a naked singularity). It is mathematically possible to have an event horizon without a singularity.

or it means that spacetime is infinitely bent that light travels forever in an infinite space.

No. It just means there is an inside and an outside. And you can't cross from the inside to the outside. There are many kinds of horizons. If somebody was accelerating away from you and had a head start you might not be able to reach them even if you chased at the speed of light. And of you chased them right after they left you would catch them. There is a boundary between the time-places that can catch them and the time-places where you can't catch them. That boundary is a horizon.

For a black hole the event horizon is also just a surface and the surface is moving outwards at the speed of light in an inertial frame (just like the surface for your accelerating friend was). When the event horizon crosses you you don't feel a thing. An event horizon could form right on top of you and start expanding at the speed of light right now. All it takes is some distant matter forming a shell around you with you at the center and then there is a last moment you could take off and get to the shell before it seals up. That last moment is the divide from being able to escape the shell around you and not being able to escape.

But since you can't locally feel a shell being placed around you, you don't feel anything. Of course after they seal the shell and it starts compressing everything as it falls that is a problem. But you still won't feel not until it starts to compress you. So it is lightyears in radius of will be years before you feel anything.

Why a black hole is black if the spacetime wraps the black hole?

It is black because things don't get out. More rightly it is dim and red to the people outside because they see dim and red images from what the outside looked like before the shell was sealed.

So light goes around it, but not inside it right?

People on the inside of the horizon see light go in. The people on the outside do not see any light go out. When people say space is curved they do not mean that it is lines in some space that are curved.

A good analogy is that you have a 4d block and you can measure time durations with clocks and space intervals with rulers. And that how the clocks and rulers measure depend on where you started and stopped and what path in 4d you took.

For instance you could imagine a a plane were your radial directions act like they are moving in or out of a funnel but direction orthogonal to that are like going around a funnel at a constant height. It is still a 2d space but it has the same kinda of lengths as an ant living on a funnel would notice. But time itself is also affected so it is more complicated.