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Black Hole for Dummies


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#1    LucidElement

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Posted 02 November 2012 - 01:19 PM

haha, I had to title it this because I guess I truly never understood the defintion of a "black hole" in laymens terms... Ok, so the some part of space (universe) opens up and swallows everything around it? if something were to survive (not even sure if its possible) what would be on the other side?? I mean, isnt our universe infinite?? so it just makes me rather curious to understand what exactly would happen? i guess those who understand black holes, and string theories, could have fun with this one. But, i thought id make this topic for those people like me who have nooo clue what would happen and how itd work? hell, im still trying to figure out (after reading so much about it) what the hadron collider really does.... I was a history major.. space is completley over my head lol no pun intended.

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#2    WGH

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Posted 02 November 2012 - 02:32 PM

As I understand it, a black hole forms when an objects mass (which creates gravity) becomes so heavy that it "falls" through the fabric of space. Its called a black hole because the gravity is so strong that even light cant escape it.


#3    LucidElement

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Posted 02 November 2012 - 03:13 PM

so i wonderr what happens on the other side. I mean, is then what things get complicated and you have, supposedly, multi-deminsions and parrelel universes?

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#4    sepulchrave

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Posted 02 November 2012 - 04:26 PM

What a black hole ``is'' depends on what you think an accurate description of the Universe is. What a black hole ``does'' is not dependent on that.

Most people know there is a ``problem'' in physics: General Relativity and Quantum Mechanics don't work together. General Relativity, more or less, describes  space-time as a ``fabric''. General Relativity works extremely well for describing objects that are large and either moving extremely fast and/or have very large masses. Quantum mechanics works extremely well for describing objects that are very small.

Now for black holes:
You may be familiar with the concept of escape velocity; the speed you need to escape the gravitational pull of an object. If you are standing on the surface of the Earth, for example, you need to reach a speed of 11 200 m/s or more if you want to avoid being eventually pulled back by Earth's gravity.

Knowing about the escape velocity, one can easily calculate how massive and how large a spherical object needs to be before the surface escape velocity is equal to the speed of light; this is the Schwarzschild radius (and is easily found by setting ve = c in the escape velocity equation and rearranging to put r on the left-hand side).

EVERY object (including you) has a Schwarzschild radius. However black holes are the ONLY objects whose mass falls entirely within that Schwarzschild radius.

So far this is pretty simple. The real question about ``what'' a black hole is depends on what happens inside the Schwarzschild radius.

In General Relativity there is nothing to stop matter from being compressed infinitely, and it is impossible to exceed the speed of light. Therefore the large surface gravity of a black hole causes the matter making up that black hole to get squeezed down to a point.

In other words; once you have squeezed an object below its Schwarzschild radius (by a supernova explosion perhaps, or just an impossibly strong anvil press in your lab, or with your own superman hands, or whatever) that object will have sufficient surface gravity to squeeze itself smaller and smaller. (See the wiki on the Schwarzschild metric for a more technical description.)

General Relativity has no limits on how small an object can be squeezed, so eventually this black hole will be a true singularity - an infinitely small object with a finite mass.

For objects falling into the black hole the Schwarzschild radius acts as the ``boundary'' or the ``event horizon'' of the black hole; as long as you stay outside this boundary you can still (theoretically) escape.

In General Relativity, gravity is described as ``curvature of space''. In this description a singularity can be pictured as an infinitely deep ``dimple'' on the ``fabric of space-time''.

For a true Schwarzschild black hole, as described above, there is nothing ``one the other side''. There is no ``other side'' to go to. At the singularity all directions (not just those in space, but also those in time) are meaningless: it is kind of like trying to go ``North'' when you are already at the North pole.

In Quantum Mechanics a black hole cannot be properly described because Quantum Mechanics cannot describe gravity. However, Quantum Mechanics does have a lot of rules that prevent any kind of singularity from forming, so a black hole may have a finite size. Unfortunately a full Quantum description of what a black hole would look like is not possible at the present.

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One problem with talking about black holes is that we are unable to observe what happens inside the event horizon. There is good evidence that black holes exist; but we have no way of telling if these event horizons contain true gravitational singularities, or some sort of Quantum-balanced dark star. Without a Quantum theory of gravity we can speculate, but not rigourously define the limit where gravity beats the Pauli exclusion principle.

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In the context of General Relativity, it is also possible for the space-time ``dimple'' to be a space-time ``tunnel'' to somewhere else (another part of our Universe, or perhaps somewhere else entirely). A sufficiently narrow ``tunnel'' could still have an event horizon around the entrance, but not end in a true singularity.

There is no known mechanism for naturally forming this sort of black hole/wormhole however: a wormhole to a parallel Universe is theoretically possible according to General Relativity, but someone still has to build it -  a supernova remnant will not turn into a wormhole.

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I would also like to stress a subject which I think is often misunderstood: outside of the Event Horizon black holes are normal, ``well behaved'' objects. If some super-villain somehow managed to spontaneously convert the Moon into a black hole we would not all be sucked to our doom. The black-hole Moon would still orbit the Earth like normal, the tides would still behave normally. Obviously we wouldn't be able to see the black-hole Moon anymore, and attempting to land on it would be extremely ill-advised, but other than that there would be no danger.


#5    LucidElement

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Posted 02 November 2012 - 10:39 PM

Thank you, still a little lost, but understand it better then I did.! so through black holes how you get the ideas of parrelel universes?

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#6    sepulchrave

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Posted 02 November 2012 - 11:12 PM

View PostLucidElement, on 02 November 2012 - 10:39 PM, said:

Thank you, still a little lost, but understand it better then I did.! so through black holes how you get the ideas of parrelel universes?
You don't.

If you believe in parallel Universes, black holes represent the most logical and scientifically justifiable way of ``getting there'' (although it is doubtful that if you dove into such a black hole you would come out the other side intact).

The mathematical formulation of General Relativity naturally lends to expressing the large-scale behaviour of the Universe as a consequence of shape, or topology (i.e. the Universe is a 3+1 dimensional shape embedded in an M+N dimensional framework). From this perspective, it is possible to conceive of other shapes ``along side'' (in some higher dimensional sense) our own Universe.

It is then possible to have narrow space-time ``tunnels'' occasionally (or constantly) connecting these different - and otherwise separate - Universes. In order for such a tunnel to exist it would naturally have to have significant space-time curvature, and therefore possibly look like a normal black hole (and if it were large enough, it might even be possible to travel through it without getting ripped apart, although you obviously couldn't come back out again).

But I would like to stress that this is more the realm of science fiction than fact. Having black holes (either only some special ones, or perhaps all of them) act as tunnels to somewhere else doesn't contradict any existing theory, but it is difficult to envision a scenario where this sort of thing would happen naturally (and obviously we haven't seen any evidence of some advanced alien race building these things either).

While it is possible to have space-time curve into all sorts of funky ``hyper-geometries'', all our observational evidence suggests our Universe is fairly ``flat''.

Similarly, while it is possible to have black holes connect to other otherwise unaccessible areas, there is no theory explaining how such a thing would occur. Normal gravitational collapse should just create a space-time ``valley'' that gets steeper and deeper until it eventually forms a singularity - an infinitely deep point in a valley. It is hard to explain why that ``valley'' should suddenly turn into a ``tunnel'' that goes somewhere else.

It could happen, but why is there some special point when it stops collapsing and starts tunnelling, and what determines what direction does the tunnel goes in, and what determines how far the tunnel will stretch?

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Of course while we may find it natural to think of the Universe as having some sort of shape embedded in a higher-dimensional ``super Universe'', it is not necessary to think that way.

You do not require extra dimensions to have curvature, and at the moment we have no way of knowing if the model of our Universe as a 3+1 dimensional shape in a higher dimensional framework (or, I guess if string theory is true, as a 9+1 or whatever dimensional shape) has any more meaning than just being a visual aid.

So at the moment there is no good reason to believe one way or the other whether parallel Universes exist, and even if they do there is no good reason to believe one way or the other whether there is an ``other side'' to some (or all) black holes.


#7    Pyridium

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Posted 08 November 2012 - 10:34 PM

Once you absorb all of the speculation and theories surrounding black holes you begin just how little we know about this subject.  The problem that Einstein had was his formula for a black hole resulted in infinity.  This meant that all of the mass consumed by the black hole ended up in a point of infinite smallness and infinite mass with infinite gravity.  Einstein just did not finish his formula correctly.

Only during a large enough super nova will a black hole form.  A black hole has all negative particles in the 'core'.  This core is "pushing" against each other trying to escape.  Around the core is the "solid" mass of the black hole, positive and neutral particles, that generates 90% of the gravity needed to prevent any light from escaping the "event horizon".  The size of a black hole is the total mass that it has consumed.  There is no information loss.  As more matter is consumed, the gravity gets stronger forcing the core to contract.  This heats up the core and it begins to expand back into balance.  Every black hole oscillates, like a heart beat.

We have solar systems and galaxies in our universe, there are solar black holes, galactic black holes and Universal sized black holes.  Our universe was just a collision of two massive ones.  This collision cracked one or both of the black holes and alowed some of the "core" to escape.  The impact allowed much of the positive and neutral particles to be captured by the escaping electrons and at a certain tempurature and density, our universe of hydrogen atoms were created, only hydrogen atoms.  It was the "spin" of the collision to give our universe the shape that it has, more like a tornado than a balloon expanding.  And yes, we are still expanding at a faster rate because the core that escaped the black hole that did not bond with positive matter, just became dark matter.  negative particles with negative energy, pushing everything away faster and faster.

I could go on for hours but thought you might enjoy one persons opinion.





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