Black Hole... what is it?

Discussion of theories involving time as a dimension, time travel, relativity, branes, and so on, usually applying to the "real" universe which we live in.

Black Hole... what is it?

Postby brasileiro » Sun May 08, 2005 4:10 am

I suppose that if you are christian and/or believe in God and the creation, that you may know that Time and space are uncomprehendably old... therefore, you may not ever reach the center of the black hole... if there is one. That, or the black holes are really just entry-way's to wormholes...

You see, we don't know whether or not they all are, because nobody has ever reached one to find out... and even if they have, we have lost communication before they did reach it. My question is... is the Black hole a mass or a vacuum? Since, according to theory, no true black holes in space, or anywhere at that, then it has to be a mass. But, if it's a mass, then that means it can "travel" faster than the speed of light, right? Now, since nothing, to our knowledge and comprehension, travels that fast, that should bring us back to being a vacuum. And since you can't see it, unless it is sucking something up, it's practically invisible to the naked eye otherwise, then that also means it has very little, if not, microscopic mass. Then again, it has HUGE surface area because it has such a gravitational pull that it can even trap light, the fastest moving "thing" in the universe, so that it doesn't escape...
So somebody, please tell me what you think... is the Black hole a Body, or a vacuum... or just an entry-way to another dimension?
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Postby jinydu » Sun May 08, 2005 6:03 am

From the viewpoint of General Relativity, a black hole is a region where the spacetime curvature is so large that not even light can escape it. You seem to be claiming, if I understood correctly, that since a black hole has mass (and it certainly does, generally speaking a lot of mass!), it can travel faster than light. Exactly the opposite is true. According to relativity, objects with mass must travel slower than light, objects with no mass travel at the speed of light.
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Postby brasileiro » Sun May 08, 2005 7:38 am

once again, I apologize for coming across as saying they "travel", which I'm not saying they don't, but more like "travel at the speed of light". The matter which is being sucked up is though...
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Postby viralplatipuss » Sun Jun 26, 2005 1:51 pm

i thought black holes where just large pieces of mass that form when a star has exploded and leaves behind a small village sized mass block that has incredible mass which is compressed immensly. Allowing it to have such gravitational pull on even light!

I didn't believe it had anything to do with dimensions or worm-holes.

:?
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Postby wendy » Sun Jun 26, 2005 11:03 pm

A model of space exists where gravity is derived from curvature of space. Instead of having the space like a flat billard ball, large masses tend to "sink in" to the table and bend space around it.

For normal masses the effects of the bending is not very great. The sun is a gas, but denser than water, because of gravity. It is heat and assorted pressures that fight gravity.

When one gets a black hole, the sorts of pressures that keep the sun big are less than gravity, and the whole is ground into a very tiny but super dense point. It still has mass etc, but it lives inside a point.

The stretching of space caused by a point weighing 6 solar masses, in the order of say, 10,000 miles, is considerably noticable. As one gets closer, say 20 miles, there is quite a strain on space, and the gravitational tension of space itself is powerful enough to rip molecules apart.

This is why a number of black holes are surrounded by accreation-disks and a pair of powerful jet-like radiators from their poles, each in its beam, brighter than whole galaxies: these are quasars.

Because there is a curvature of space, some folk need to deal with curvature in something (hence a fourth dimension: not time).

The idea of wormholes is that the shape of the curvature looks like a funnel. Conceiveably, one could have two funnels back to back, and travel through these funnels and come out somewhere else: a wormhole.

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Postby timespace » Mon Jun 27, 2005 4:43 am

also, theoretically if someone had entered the pull of a black hole, even if we didnt lose contact they would be ripped apart. If your feet were to enter the hole's pull first, it would have more mass than your upper body, and it would travel at a greater speed than your upper body, and you can form your own images (correct me if im wrong)
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Postby jinydu » Mon Jun 27, 2005 6:20 am

Several inaccuracies.

timespace wrote:also, theoretically if someone had entered the pull of a black hole, even if we didnt lose contact they would be ripped apart.


It depends. If you were sufficiently far away from a black hole, you would be able to orbit it, just as you would orbit any other massive object. In fact, the current consensus is that we're orbiting a black hole right now; the supermassive black hole at the center of the Milky Way. And of course, if you were really far away, you wouldn't notice the black hole at all (which we didn't, until the last century or so).

Now, what you probably have in mind is what happens when an observer falls into a black hole. In that case, people on Earth (or any other place a safe distance from the black hole) would eventually lose contact with the observer when the observer crossed the event horizon, since no communications could escape the event horizon.

And yes, at some point, the observer would get torn apart by tidal forces. But I'll get to that later.

timespace wrote:If your feet were to enter the hole's pull first, it would have more mass than your upper body


No. Your feet would be closer to the singularity; therefore the gravitational force on your feet would be greater than the gravitational force on your upper body.

timespace wrote:and it would travel at a greater speed than your upper body


A greater speed? Speed with respect to what? The correct statement is that your feet's acceleration towards the singularity would be greater than the acceleration of your upper body. For small accelerations, your body can counterract this net acceleration, but eventually, the net acceleration would exceed the tensile strength of your body, tearing you apart.

But note that this effect is not caused by the strength of the gravitational field, but rather the difference in strength between the gravitational field at your feet and at your head.

Also note that we expect the gravitational field to be continuous, the smaller you are, the longer you will survive.

timespace wrote:and you can form your own images (correct me if im wrong)


:? I don't really know what you're trying to say here.
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Postby Gilles » Thu Aug 11, 2005 3:57 pm

Mass and vacuum are present everywhere.

In a black hole, everything is just proportially different then here. It is just another universe, which exchanges energy with ours, as do you and me right now.
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True, but....

Postby Neo Alucard » Mon Aug 15, 2005 3:34 am

I believe, through all the science textbooks I've read, a black hole is mass in itself. Space IS vacuum, so vacuum can't exist without containment (in space). Think of it this way: The actual black hole is a "basketball" in the middle of a football field. The surrounding stadium is actually a vortex, caused by the star exploding within itself. Therefore, my theory (not an original one) is that once all black holes eat up everything, the black holes will eat each other, then the massive black hole will either: A) just be a black hole forever OR B) "Blow Up" and create a new universe. But rest easy everyone....that won't happen for millions upon billions of years. And about timespaces "images" idea, I think he means that if you waved your hands in a vortex, the bending would cause you to see many "hands at once", hence "creating images". Of couse, this is seconds before your body is ripped apart at the mercy of this pinpoint of mass.
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Postby PWrong » Mon Aug 15, 2005 9:58 am

I thought of something today and it's been troubling me a bit.

Gravitons, like photons, don't have any mass, but they are still affected by gravity somehow. If that's the case, and if a photon can't escape from a black hole, then how can a graviton escape?

It seems like a paradox to me, but maybe I'm missing something.
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Postby houserichichi » Mon Aug 15, 2005 3:00 pm

It's a valid question, what you're asking - I did the same thing once and luckily for both of us there is a proper answer. Turns out that gravity (and electromagnetism) are mediated by respective bosons, the gravitons (and the photon). What's interesting, and what you'd come across later in your studies is that these particles are actually virtual. As such they are allowed to violate such things as superluminal velocities and other cuddly properties of the universe we're used to. That's how your gravitons "get out" of the black hole and that's how we see them. They travel superluminally out, "die" very quickly (otherwise they wouldn't be virtual), and transfer their properties outside.

Of course I'm sure you know that no gravitons have ever been detected so this is all in theory...but it is necessary if the theory is to be correct.
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Postby wendy » Mon Aug 15, 2005 11:10 pm

The other model of gravity is that space is curved less in the direction of heavy objects.

Here is a simple model of how curved space works.

From any point, we can construct a circle, and divide it into 360 degrees. We then draw a circle, and measure each degree. For our circle, we suppose the length is 1 mm.

When space is positively curved, then the degrees have less than 1 mm of circle: one sees this by drawing a circle on a sphere. When space is negatively curved, the degree has more than 1 mm, eg 1.001 mm. This is what hyperbolic geometry is.

Now if space is in tension, then the tension arises from the length of chord, not the length of degrees. So if some quadrant is 90.01 mm long, and another is 89.99 mm long, then the nature of stable rest is to move to where the 90.01 quadrant is: ie gravity can be represented as a tension in space.

We also see that "straight" bisects the chord, not the angle. So a photon that travels in a straight line travels so that there is as much length-of-curvature on one side as there is on the other.

Travelling through the above circle could "deflect" the thing by 0.01 degrees.

Note the nature of curvature is such that not all circles need 360 mm of tension. In a region of strong curvature, one might have 400 mm of tension, but only 360 degrees.

Tension is transmitted locally: there is no need for a radiant particle to be sent through the infinities of space. Also, the nature of tension is that the space has a measure of elasticity, so waves travel at a finite speed.

The tension model of gravity aptly explains why weightless particles are affected by gravity: they really do travel straight (relative to the tension), and not straight (relative to the local angles). The bends we see are the result of the cumulative deflections of local angle.

It does not explain why gravity is a radiant field, adequately: one needs a more advanced device here.
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Postby Neo Alucard » Tue Aug 16, 2005 5:55 am

Gilles wrote:Mass and vacuum are present everywhere.

In a black hole, everything is just proportially different then here. It is just another universe, which exchanges energy with ours, as do you and me right now.


So, I suspect that you believe in "white holes" too?
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Postby KayaYautja » Wed Sep 21, 2005 1:09 am

So, a black hole is a star which has imploded and condensed to a point where is affects the curvature of space time so drastically that NOTHING can escape it's gravitational pull?

I don't have the smarts for this lol.
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Postby jinydu » Wed Sep 21, 2005 2:01 am

KayaYautja wrote:So, a black hole is a star which has imploded and condensed to a point where is affects the curvature of space time so drastically that NOTHING can escape it's gravitational pull?

I don't have the smarts for this lol.


Yes, essentially that's it. What's so difficult about that; it seems you already understood that point.

However, you should keep in mind that this is just a qualitative, English description. I often say to myself that in physics, you haven't really understood something until you can derive it mathematically, starting from the basic axioms of the theory.

Also, if you're 16 years old, you can't be that far behind (if you keep up with your school work). After all, I just turned 18 last month.
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Postby Batman3 » Wed Oct 05, 2005 4:02 pm

If photons are light and light moves at c, then photons move at c, at least on a scale beyond Quantum Mechanical atoms. Same for gravitons. If gravity proceedes at infinite speed the the diameter of the space surrounding the singularity at the enter of a black hole can be found by:

.5V^2=GM/r where V=c so r=2GM/c^2 where

G==Gravitationalconstant=6*10^-11 Newton-meters^2/kilogram, c==speed of light=3*10^8meters/second and M==the mass of the black hole.

r==the schwarstzfield radius or the farthest a photon emitted at the center can get away.

If gravity also moves at c, then wouldn't the gravitons be pulled in too, the black hole just droping out of our cosmos?
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Postby wendy » Wed Oct 05, 2005 10:51 pm

the schwarzwald diameter is GM/c². The radius is þen GM/2c².

The value for þe earth is 0.1746 inches. For the universe, it is typically the same order as the light-time * age, or somewhat less.
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Postby thigle » Thu Oct 06, 2005 10:51 am

and what about the following ?

to curve is to increase/decrease spatial density ?

so (mathematical continuity) = (infinite spatial density)

(-infinite curvature) ~ ( +infinite density)
(+infinite curvature) ~ ( -infinte density)

so if (m = infinite) then (spatial volume = 0) so (density = 0) ?

so space has gone singular ?
if so, then where/when would this be ?

in the einstein's classical assumption about the microworld, mass & spatial volume approach zero as a limit. so he presupposes that non-euclidean effects - inherent discontinuity, vanishes in the small.

[mostly quoted from memory, from Steve Rosen: Science, Paradox & the Mobius principle: evolution of transcultural approach to wholenedd, SUNY, 1994]
just checking...
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Postby houserichichi » Sat Oct 08, 2005 12:27 pm

If gravity also moves at c, then wouldn't the gravitons be pulled in too, the black hole just droping out of our cosmos?


No because the gravitons in question are virtual particles and can break the "speed barrier" of light.
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Postby papernuke » Tue Jul 11, 2006 5:47 pm

it is a body, because for an object to have a gravitational pull, it would need mass and a lot of it , its not a vaccum because a vaccum is nothing and no nothings (lol) can have a gravitational pull. its not a entrywway into another dimension because if you enter into a black hole, you just get streched a lot until you break and then youre parts are strectched until they break and so on until youre free flowing particles.
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Postby houserichichi » Wed Jul 12, 2006 2:46 am

...and where do these free flowing particles go?
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Postby Dimensional » Sat Oct 21, 2006 9:45 pm

A black hole is a region of space in which the fabric of space rips open. These are caused by huge stars exploding and causing so much weight to build up on one spot of space it rips open. Then the stardust materializes into a ball of solid matter with a gravitational pull so powerful it can bend light.
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Postby Myriaract » Thu Dec 13, 2007 11:44 pm

I don't think it's a rip in the fabric of space-time, I think it's merely a hole in our universe to the 4D one!
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