Black holes!

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Originally posted by galathaea [*] The black holes that Mick was alluding to...[/list]
Those are some options for discussion. I just don't know where to begin.

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Look what has science ever done for humanity??? There are people starving all over the world, think about the children??? Lets get rid of NASA, they haven't done a single thing for our children....GM crops, GM crops...why no I won't eat GM crops, even though I'm starving....ohh the humanity...the horror, science needs to go, go, go....you are cruel you are evil...where's my tree to hug???

/"I say we let him go!"
//Nobody expects the spanish inquisition!!!

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Originally posted by Mick
Look what has science ever done for humanity??? There are people starving all over the world, think about the children??? Lets get rid of NASA, they haven't done a single thing for our children....GM crops, GM crops...why no I won't eat GM crops, even though I'm starving....ohh the humanity...the horror, science needs to go, go, go....you are cruel you are evil...where's my tree to hug???

/"I say we let him go!"
//Nobody expects the spanish inquisition!!!

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I hope you are kidding. In the last sentence though, you are definitely right.

My favorite universe model is the hypercube, but maybe only because there's such a cool story about a hypercube.

(hypercubes)
("And He Built a Crooked House" - Rob't Heinlein)

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Originally posted by solarflare
I hope you are kidding. In the last sentence though, you are definitely right.

My favorite universe model is the hypercube, but maybe only because there's such a cool story about a hypercube.

(hypercubes)
("And He Built a Crooked House" - Rob't Heinlein)

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solar solar solar, when have I not been dripping with sarcasm???

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Originally posted by Mick
solar solar solar, when have I not been dripping with sarcasm???

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Oh, so you do want the yankees to win? I knew you'd come around eventually.

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Originally posted by galathaea
As Simon has pointed out, the universe may be topologically a 3-sphere (a sphere with a three dimensional surface)

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well dont we call it Space-Time and its not spherical at all :)

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Now, concerning black holes.

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the problem with BH is that they work against all the laws of physics. that means, they dont obey any of the laws of physics. would that mean that us, humans at earth, are missing some elementary law? once that law is found, the mystery of BH will be solved.

The question about their existence is rather groupable! that would mean, a group believes in their existence, others dont. but that's a debate. every thing was intially debated. even that the earth is round :)

so, there are several topics of discussions for those who believe in their existence. and simply share the thoughts and share new information.

for those who dont beleive in BH, I would recommend starting up with ....
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In a Black hole times ceases to exist...how is this possible? Because time is something that will always go on..

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In a Black hole times ceases to exist...how is this possible? Because time is something that will always go on..

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A black hole is the ultimate abyss. You can't escape and you can't die. :cool::cool::cool:

Oh, and look at my status, please, everyone. Yes, the text above my saintly avatar. :o:o:cool:

<<A black hole is the ultimate abyss. You can't escape and you can't die. :cool::cool::cool:>>

Oh yes you can, the gravity force near the regular size black holes would tear you right to pieces before you even notice any time dilatation effects.

I could have sworn Tom posted something here...

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Originally posted by andy_tacker
the problem with BH is that they work against all the laws of physics. that means, they dont obey any of the laws of physics. would that mean that us, humans at earth, are missing some elementary law? once that law is found, the mystery of BH will be solved.

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Well, I would make a distinction. The black hole itself was predicted using the laws of physics, explicitly

Gmn = 8 p Tmn

where G is the Einstein tensor (defined in terms of the Riemann curvature and the metric) and T is the stress-energy-momentum tensor for the matter field studied. However, it is often stated that at the singularity at the center of the black hole, the laws of physics break down. That's true if you consider things like quantum mechanics, but general relativity is not consistent with qauntum mechanics even outside the singularity. Otherwise, the laws of general relativity are consistent. The singularity presents problems with path continuity, but that is a problem with point collisions in general and even shows up in classical newtonian physics.

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Originally posted by voidspace
In a Black hole times ceases to exist...how is this possible? Because time is something that will always go on..

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Well, time does not cease to exist in a black hole. Its just that time has some peculiar properties, and black holes emphasise these peculiarities. The strange properties of time first appeared in special relativity, where it was shown that the time measured to have elapsed in objects depends on how the object is moving relative to the person measuring. This is coupled to a similar property of length, and is due to the fact that the concept of distance was generalised from the space-distances of classical physics to the larger notion of metric distances in spacetime. Transformation laws that preserve the special relativity metric distance (ds^2 = dt^2 - dx^2 - dy^2 - dz^2), do not generally preserve the individual space or time distances. In general relativity, the metric used to measure spacetime distances was changed to one which can vary at every point of spacetime, which allowed the physics to describe motion on curved spacetimes. This allowed Einstein to postulate his equation which described spacetime curvature as a consequence of the presence of matter, and it was shown that gravity could then be considered as something not exactly a force, but merely the natural way that things move in a curved spacetime.

Now, black holes have a strange metric (which for a non-spinning, non-charged black hole is described by the Schwarzschild solution). This metric predicts that there exists this place in space around a very dense object known as the event horizon, inside of which all equations of motions move towards the center (or singularity) of the black hole. This means that even light itself would always travel on paths that do not escape the event horizon. This metric also predicts that someone far away from a black hole would observe something freely falling into the black hole as approaching the event horizon slower and slower, and that it would take an infinite amount of time to for that object to cross the event horizon. However the amount of time needed to cross the event horizon as measured by something actually falling in is finite, and they even would reach the singularity in a finite amount of time in their view. Space-time still exists in the black hole, its just that it is not observable to anyone who does not fall inside in any finite time.

Which brings me to a topic I mentioned in my list, and one that might be of interest to computer scientists, namely the Church-Turing thesis. One can imagine a situation where an object falling into a black hole is able to destroy the black hole (perhaps by firing an amount of antimatter equivalent in mass to that of the black hole into the singularity) just as they cross the event horizon. In this way, it is possible for one observer to have passed an infinite amount of time with respect to a distant observer while still having travelled for only a finite time in its own reference frame. Now, if that distant observer were to run a program that was to send a signal to the object falling in if it finishes its calculation, and otherwise remain quiet, the object falling in would know in a finite time if that program ever finished. This is the computational problem known as the halting problem, and it has been shown that the halting problem is not Turing-computable. However, this setup shows that there exists a solution to the halting problem, and thus not all "effectively computable" problems are equivalent to Turing-computable problems (which was the postulate of Church and Turing). Its a weird solution and not at all practical, but it does show that black holes give some very interesting mathematical results when applied to areas that would seem not even remotely related.

And just a note:

I am in no way stating that I "believe" in general relativity or the solutions I am stating. I am only stating that the mathematical models have been shown to be consistent with the observations we are currently able to make and have even predicted results that no previous models were able to (such as the example of the precession of Mercury's perihelion given in most introductions to general relativity).

However, I try to follow as many alternate theories as I can find. That was even one of my concentrations when I was studying philosophy in college (which was a dual major of mine). For example, I absolutely love Bohmian mechanics, and have even recently begun to "bohminise" various string theories and other modern quantum theories (I have a thread I posted recently on sci.physics.research on just this topic -- which unfortunately has garnered no responses). I have even visited the site on Yilmaz's theory which Simon posted, and am currently trying to discern what predictions the model makes and how they may be supported / falsified. However, right now one problem I see is that the matter-creation-through-expansion concept seems to be just a version of the Brans-Dicke cosmology proposed in the 50s, which has faced alot of experimental problems due to the lack of detection of such signatures. Its still not completely resolved in the general case, but the revisions needed seem to so far face mathematical problems in invalidating other predictions, and I have yet to see a mathematical model that can maintain consistency to all observations. However, I do want to check out whether the Yilmaz theory accomplishes some of these consistency requirements.

In fact, I thinks it pretty clear that the current frameworks of general relativity and quantum mechanics do not work together consistently, and that new physics is required. With experiments showing the possible existence of dark matter and dark energy not currently predicted by any model, physics is not yet (and I would say, nowhere near) reveling the naked body of "truth" yet. It remains to be seen whether black holes will survive the necessary modifications, but I think that the observational evidence of objects that behave very much like black holes and their existence not very close to the realm where we believe the physical models to be incorrect (except at the singularity -- which does not require the modification of the notion of an event horizon), I think they are currently about as likely as the neitrino having mass. Even superstrings and M-Theory (which do unite quantum mechanics and general relativity in a consistent fashion), predict black holes and even give some new mathematical models for describing them.

good post great read galathaea!
But my knowledge on the subject is little but my facination is more ..:rolleyes:

Anyways all this seem to boil down to proving that time can be controlled ... has anybody proved this ..

Like move time forward or backward at will (except in those hollywood movies back to the future and Time Machine)

The last time heard about it (controlling time) was when someone did an experiment using very long tubes ..ahhh can't remember after that :(

Black holes are gravity wells, therefore, slow time. Black holes are the ultimate gravity wells, therefore, no time.

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Originally posted by Saint Xeon
Oh, and look at my status, please, everyone. Yes, the text above my saintly avatar.

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What the...??? How in the...???

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Originally posted by Simon666
Oh yes you can, the gravity force near the regular size black holes would tear you right to pieces before you even notice any time dilatation effects.

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How can you notice time-dilation effects unless you're looking in from the outside?

If the time is somewhat STOPPED in BH, can we be saying that travelling through BH (given you stay alive and dont get DEFORMED :) cos of Gravity) where will it lead?

How true is the fact that they might be a gateway to other worlds?

and if the gravity is so big out there, then if we found one in our Milky way, would we be able to travel to other universes using this gravity as a possible way to gain speed for human made satallites?

<<How can you notice time-dilation effects unless you're looking in from the outside?>>

If you look at outside stars and notice a fase shift towards blue. And you should also notice the stars are "moving" toward a position that is opposite to the direction you're falling. Or if you notice an observer not falling in the black hole who seems to age/move more rapidly...