Black holes

[Stiganator]

In the beginning, all matter was condensed into a single point and it exploded.


Now we have matter all over over the place with nothing in between, but we there are black holes all over the place.

A black hole condenses matter to a singularity too, but there are more than one of them, so how does that work? Will they attract each other? Which one will get sucked into the other, when they are close enough?

Also, how is the area of effect of a black hole limited if they all have infinite mass? Wouldn't they all have the same gravity field, being of infinite value? Which leads me to.....

Is the earth slowly being pulled towards a black hole? Or can we assume there are an infinite number of black holes and the net attraction is zero, but that doesn't really seem to make sense since we know (we do know, right?) that matter too close to black holes get pulled into singularity and presumably our chunk of rock is no different from any other out there.

How long does it take to go from any given point in space to the singularity?

 

[BrownTown]

Well for one thing they don't have infinite mass or infinite gravitational fields.

 

[degibson]

Originally posted by: Stiganator
In the beginning, all matter was condensed into a single point and it exploded.

So says the big bang theory. Could be true.

Now we have matter all over over the place with nothing in between, but we there are black holes all over the place.

A black hole condenses matter to a singularity too, but there are more than one of them, so how does that work? Will they attract each other?

Yes, of course. They will attract each other with force directly proportional to the produce of their masses, and inversely proportional to the square of the distance between the black holes.

Which one will get sucked into the other, when they are close enough?

Yes. More specifically, they will suck eachother into eachother, and combine to form one big black hole. I believe there is a theory suggesting this is how quasars are eventually formed, but I could be wrong.

Also, how is the area of effect of a black hole limited if they all have infinite mass? Wouldn't they all have the same gravity field, being of infinite value? Which leads me to.....

As BrownTown pointed out, their mass is large but finite.

Is the earth slowly being pulled towards a black hole? Or can we assume there are an infinite number of black holes and the net attraction is zero, but that doesn't really seem to make sense since we know (we do know, right?) that matter too close to black holes get pulled into singularity and presumably our chunk of rock is no different from any other out there.

How long does it take to go from any given point in space to the singularity?

The Earth is being pulled towards a black hole -- in fact, towards many black holes. So is all the rest of the matter in the universe. This boils down to the classic end-of-the-universe question: is the total matter in the universe sufficient to eventually reverse the big bang into the big crunch? Or, is the universe lightweight enough (hehe) to continue expanding forever, in spite of mutual gravitation (aka the big cool). Since nobody knows the mass of the universe, nobody knows the answer...

But, given that stars are still red-shifted (they're flying away from us right now), even if there is enough mass in the universe to eventually yield the big crunch, then we're not even halfway done with the universe yet.

Of course, Earth could get titanically unlucky and run into a previously-unknown black hole at random. I'm pretty sure we'd have a couple million years warning, though.

 

[KIAman]

Misconception 1: Black holes have infinite mass

Black holes have infinite density but only because of math. Density is mass/volume. The center of a black hole is a single point called the singularity which has no volume dimension. So dividing by zero, we get infinite. Notice mass does not have to be infinite for this to be true.

Misconception 2: Everything will get sucked into black holes

Although the gravity potential of a black hole is terrifying and powerful, the force of gravity falls off at an inverse square function. What does that mean? The further unit of distance you get, you feel a lot less gravity. If you wieghed 1 Unit at 1 Distance, you would weight 1/4 Units at 2 Distance and 1/9 Units at 3 Distance and 1/16 Units at 4 Distance, etc. etc. As Compared to other forces, gravity is very, very, very weak.

Misconception 3: The Earth is being sucked into a black hole

The majority of space junk, including Earth, will never have the pleasure of being sucked into a black hole. The expansion of the universe far overpower any pull a black hole might have.

Question: How long does it take to go from a point in space to the singularity?

Answer: Depends. If you are an outside observer, nothing ever touches the singularity. Time will slow to a standstill in the outsider's point of view as soon as anything reaches the event horizon.

If you are the one going from space to the singularity, your body will be obliterated long before you ever reach the singularity. At one point, you will stretch as your parts that are closer to the singularity is feeling a much stronger force that your parts that are further. Then, as you look at the universe, the entire life of the universe will pass by in a flash. Then you will turn into subatomic particles and merge into the singularity near the speed of light.

 

[Modelworks]

There is something in between.
http://en.wikipedia.org/wiki/Dark_matter
http://en.wikipedia.org/wiki/Dark_Energy

Science about black holes is constantly changing.
One such video that raises a lot of questions:
http://video.google.com/videop...d=-1575663918436440352

 

[PlasmaBomb]

Originally posted by: KIAman

Question: How long does it take to go from a point in space to the singularity?

Answer: Depends. If you are an outside observer, nothing ever touches the singularity. Time will slow to a standstill in the outsider's point of view as soon as anything reaches the event horizon.

If you are the one going from space to the singularity, your body will be obliterated long before you ever reach the singularity. At one point, you will stretch as your parts that are closer to the singularity is feeling a much stronger force that your parts that are further. Then, as you look at the universe, the entire life of the universe will pass by in a flash. Then you will turn into subatomic particles and merge into the singularity near the speed of light.

I don't think that's quite right. From an outside point of view, a person falling into a black hole will simply vanish once they cross the event horizon.

The stretching is spot on, as the tidal forces on your feet are vastly different to those on your head (assuming you fell in either head or feet first).

 

[QuantumPion]

Originally posted by: PlasmaBomb

Originally posted by: KIAman

Question: How long does it take to go from a point in space to the singularity?

Answer: Depends. If you are an outside observer, nothing ever touches the singularity. Time will slow to a standstill in the outsider's point of view as soon as anything reaches the event horizon.

If you are the one going from space to the singularity, your body will be obliterated long before you ever reach the singularity. At one point, you will stretch as your parts that are closer to the singularity is feeling a much stronger force that your parts that are further. Then, as you look at the universe, the entire life of the universe will pass by in a flash. Then you will turn into subatomic particles and merge into the singularity near the speed of light.

I don't think that's quite right. From an outside point of view, a person falling into a black hole will simply vanish once they cross the event horizon.

The stretching is spot on, as the tidal forces on your feet are vastly different to those on your head (assuming you fell in either head or feet first).

No, KIAman was correct. For an outside observer, an object will never cross the event horizon. It will become more and more redshifted until it stops completely at the boundary.

If you were going into an event horizon, (and if it was a big one so that the tidal forces were insignificant), you would see the outside world becoming increasingly blueshifted as time would seem to speed up.

 

[Biftheunderstudy]

The outside observer part is bang on, as well as the tidal forces. Now if you look at supermassive blackholes like the ones which reside in the centers of galaxies the tidal forces there are uncomfortable but in fact survivable. Now when you have something like this, the event horizon is nothing special to the person falling into the black hole. Your perspective of time or anything else for that matter does not change since the event horizon is a mathematical asymptote not a physical one. Also by nothing special I mean that the effects of relativity are normal.

To the OP, it is incorrect to think of black holes as mini Big Bangs. Black holes are singularities of mass while the Big Bang was a singularity of Space-time.

 

[dorion]

Ok I just want to make sure what I've been taught is right.

Yes black holes have extremely large masses and a great amount of gravitational pull, but only because they have the large amount of mass. The pull of the supposed black hole in the middle of our galaxy on our planet has the same amount of gravitational pull as a large star with the same amount of mass taking it same position. Black holes sucking power reaches the "oh shit" phase at and beyond the event horizon. So we really dont have as much to worry about falling into a black hole because we'll have a better chance suffering some catastrophic solar system collision.

Right?

 

[CycloWizard]

Originally posted by: Biftheunderstudy
The outside observer part is bang on, as well as the tidal forces. Now if you look at supermassive blackholes like the ones which reside in the centers of galaxies the tidal forces there are uncomfortable but in fact survivable. Now when you have something like this, the event horizon is nothing special to the person falling into the black hole. Your perspective of time or anything else for that matter does not change since the event horizon is a mathematical asymptote not a physical one. Also by nothing special I mean that the effects of relativity are normal.

The mathematical asymptote describes a physical one. Things inside the event horizon cannot escape because the escape velocity is greater than the speed of light. If I were an astronaut getting pulled towards a black hole, I would get ripped to shreds due to differential acceleration on different parts of my body. The part of the body closest to the black hole would experience a much higher force than would the part furthest away. Hawking goes into this in painstaking detail in "A Brief History of Time."

 

[Biftheunderstudy]

Yes the event horizon describes a physical point in space. The point I was trying to make however, is that to the astronaut, aside from the body ripping tidal forces passing the event horizon is nothing special. From infinity to r/2s to r=0 there is no discontinuity in the frame of the astronaut. You can prove that r/2s is mathematical by switching coordinates to get rid of the singularity, as it turns out switching the variables for time and space gives a solution to Einstein's equation for inside the event horizon. With this in hand you can plot the position versus time of the astronaut and it is a classic accelerating mass the whole way in. As I mentioned before, the supermassive galactic black holes have such a large event horizon that you wouldn't even he ripped to shreds by tidal forces approaching it, you might even accidentally cross it if you were a galactic traveller and really stupid.

This is all assuming a nonrotating chargeless black hole.