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Edd
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Joined: 27 Jul 2005
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 Posted: Sun Jun 29, 2008 8:38 pm Post subject: |
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| joshuas3521 wrote: | | A black hole causes a singularity. Once something is so massive that light cannot escape, literally nothing can escape. Therefore, within a black hole, time is undefined because predictions cannot be made based on its current state. It's similar to the universe before the big bang. |
There's no reason to think GR doesn't work for most of the space inside a black hole. Only at the singularity (or very close to it). There's an awful lot of space inside a black hole that should be well described by GR - if it's correct. And there's no reason to think it isn't correct in those regions. |
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GodWarrior98
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Joined: 22 Mar 2008
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| Posted: Sun Jun 29, 2008 10:06 pm Post subject: |
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| Edd wrote: | | joshuas3521 wrote: | | A black hole causes a singularity. Once something is so massive that light cannot escape, literally nothing can escape. Therefore, within a black hole, time is undefined because predictions cannot be made based on its current state. It's similar to the universe before the big bang. |
There's no reason to think GR doesn't work for most of the space inside a black hole. Only at the singularity (or very close to it). There's an awful lot of space inside a black hole that should be well described by GR - if it's correct. And there's no reason to think it isn't correct in those regions. |
Really, with the limited knowledge we have of black holes, one could argue GR breaks down at the event horizon. Any mass falling into it will be infinity close to light speed immediately before it reaches the event horizon. If mass somehow reached light speed inside the black hole, GR would break down, seeing as it is based off of SR, and something that violates one of SR's basic premises is happening.
Of course, that's extremely speculative.
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In science one tries to tell people, in such a way as to be understood by everyone, something that no one ever knew before. But in poetry, it's the exact opposite. -Paul Dirac
I am not a theist. The name is a lie. |
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eximius
Phantom Rasperry Blower
Joined: 30 Aug 2007
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| Posted: Sun Jun 29, 2008 10:26 pm Post subject: |
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I'm currently reading "Bang" which is surprisingly about the Big Bang. It's a brilliant read. It discuses numerous things from inflation, to red hyper giants and does so in a very easy to read manner. It includes history on how the discoveries such as how cosmic background radiation was found, Einsteins self-proclaimed "biggest blunder" etc. It covers the universe in general from the big bang up to now, at first it deals in planck time but later moves on to billions of years.
It might seem as if it's for the general public with little understanding of physics etc but far from it.
Plus it's got pretty pictures!
Plus Brian May co wrote it! Queen motherfuckers!
http://www.amazon.co.uk/Bang-Complete-History-Universe-Brian/dp/1844422313/ref=sr_1_1?ie=UTF8&s=books&qid=1214796150&sr=8-1
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joshuas3521
Nobody Expects the Spanish Inquisition!
Joined: 19 Dec 2007
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| Posted: Sun Jun 29, 2008 10:50 pm Post subject: |
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| GodWarrior98 wrote: | | Edd wrote: | | joshuas3521 wrote: | | A black hole causes a singularity. Once something is so massive that light cannot escape, literally nothing can escape. Therefore, within a black hole, time is undefined because predictions cannot be made based on its current state. It's similar to the universe before the big bang. |
There's no reason to think GR doesn't work for most of the space inside a black hole. Only at the singularity (or very close to it). There's an awful lot of space inside a black hole that should be well described by GR - if it's correct. And there's no reason to think it isn't correct in those regions. |
Really, with the limited knowledge we have of black holes, one could argue GR breaks down at the event horizon. Any mass falling into it will be infinity close to light speed immediately before it reaches the event horizon. If mass somehow reached light speed inside the black hole, GR would break down, seeing as it is based off of SR, and something that violates one of SR's basic premises is happening.
Of course, that's extremely speculative. |
Well, in order to achieve light speed, the matter would be of infinite mass. Isn't it already believed that black holes have infinite density?
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"What I'm saying is, if God wanted to send us a message, and ancient writings were the only way he could think of doing it, he could have done a better job." --Carl Sagan
"In the beginning the universe was created. This has made a lot of people very angry and has been widely regarded as a bad move." --Douglas Adams
In memory of George Carlin. May he rest in peace.
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GodWarrior98
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| Posted: Sun Jun 29, 2008 10:52 pm Post subject: |
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| joshuas3521 wrote: | | GodWarrior98 wrote: | | Edd wrote: | | joshuas3521 wrote: | | A black hole causes a singularity. Once something is so massive that light cannot escape, literally nothing can escape. Therefore, within a black hole, time is undefined because predictions cannot be made based on its current state. It's similar to the universe before the big bang. |
There's no reason to think GR doesn't work for most of the space inside a black hole. Only at the singularity (or very close to it). There's an awful lot of space inside a black hole that should be well described by GR - if it's correct. And there's no reason to think it isn't correct in those regions. |
Really, with the limited knowledge we have of black holes, one could argue GR breaks down at the event horizon. Any mass falling into it will be infinity close to light speed immediately before it reaches the event horizon. If mass somehow reached light speed inside the black hole, GR would break down, seeing as it is based off of SR, and something that violates one of SR's basic premises is happening.
Of course, that's extremely speculative. |
Well, in order to achieve light speed, the matter would be of infinite mass. Isn't it already believed that black holes have infinite density? |
Yes, most conventional theories (Read: Not string theory) say the singularity is of infinite density.
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In science one tries to tell people, in such a way as to be understood by everyone, something that no one ever knew before. But in poetry, it's the exact opposite. -Paul Dirac
I am not a theist. The name is a lie. |
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Edd
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| Posted: Mon Jun 30, 2008 3:15 am Post subject: |
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| joshuas3521 wrote: |
Well, in order to achieve light speed, the matter would be of infinite mass. Isn't it already believed that black holes have infinite density? |
The singularity is. The density averaged out to a sphere of the same size as a region enclosed by the event horizon can be surprisingly mundane. |
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GodWarrior98
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| Posted: Mon Jun 30, 2008 3:20 am Post subject: |
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| Edd wrote: | | joshuas3521 wrote: |
Well, in order to achieve light speed, the matter would be of infinite mass. Isn't it already believed that black holes have infinite density? |
The singularity is. The density averaged out to a sphere of the same size as a region enclosed by the event horizon can be surprisingly mundane. |
Unless I'm mistaken, GR's equations don't treat a perfect sphere and an infinitely dense point with the same mass the same.
_________________
In science one tries to tell people, in such a way as to be understood by everyone, something that no one ever knew before. But in poetry, it's the exact opposite. -Paul Dirac
I am not a theist. The name is a lie. |
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Totalitarian Superstar
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| Posted: Mon Jun 30, 2008 3:36 am Post subject: |
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http://www.google.com/search?hl=en&q=black+holes+do+not+exist
Recent mathematical theories have postulated a black hole cannot exist. Instead, it is now thought a black hole is actually a dark energy star, called "black stars".
This news is actually a year old. I'm surprised no one here is aware.
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joshuas3521
Nobody Expects the Spanish Inquisition!
Joined: 19 Dec 2007
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| Posted: Mon Jun 30, 2008 3:40 am Post subject: |
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To show that black holes do not exist, you would have to prove that light is not effected by gravity. Good luck disproving general relativity 
_________________
"What I'm saying is, if God wanted to send us a message, and ancient writings were the only way he could think of doing it, he could have done a better job." --Carl Sagan
"In the beginning the universe was created. This has made a lot of people very angry and has been widely regarded as a bad move." --Douglas Adams
In memory of George Carlin. May he rest in peace.
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Edd
Forum Plebian
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| Posted: Mon Jun 30, 2008 3:44 am Post subject: |
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| joshuas3521 wrote: | | To show that black holes do not exist, you would have to prove that light is not effected by gravity. Good luck disproving general relativity |
You can pretty much already show light is affected by gravity. This doesn't prove in itself that black holes do exist. All you'd need is a mechanism for preventing enough mass gathering in a sufficiently small volume to prevent them from forming. |
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joshuas3521
Nobody Expects the Spanish Inquisition!
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Location: Birmingham, Alabama
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| Posted: Mon Jun 30, 2008 3:53 am Post subject: |
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| Edd wrote: | | joshuas3521 wrote: | | To show that black holes do not exist, you would have to prove that light is not effected by gravity. Good luck disproving general relativity |
You can pretty much already show light is affected by gravity. This doesn't prove in itself that black holes do exist. All you'd need is a mechanism for preventing enough mass gathering in a sufficiently small volume to prevent them from forming. |
To be honest, that would simplify quite a bit if it were true. Thank you for showing me my oversimplification of the problem
_________________
"What I'm saying is, if God wanted to send us a message, and ancient writings were the only way he could think of doing it, he could have done a better job." --Carl Sagan
"In the beginning the universe was created. This has made a lot of people very angry and has been widely regarded as a bad move." --Douglas Adams
In memory of George Carlin. May he rest in peace.
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Totalitarian Superstar
Intern
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| Posted: Mon Jun 30, 2008 4:06 am Post subject: |
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| joshuas3521 wrote: | | To show that black holes do not exist, you would have to prove that light is not effected by gravity. Good luck disproving general relativity |
It's not that black holes do not exist, my fellow anti-KnoB comrade. The current scientific consensus is that a black star is what a black hole is. However, it cannot reach the point of collapse into a black hole, and it remains a black star. I don't fully understand it because I am not a degree-holding scientist; are you?
Here's the article I found, enjoy it.
| http://space.newscientist.com/article/dn12089-do-black-holes-really-exist.html wrote: |
Black holes might not exist – or at least not as scientists have imagined, cloaked by an impenetrable "event horizon". A controversial new calculation could abolish the horizon, and so solve a troubling paradox in physics.
The event horizon is supposed to mark a boundary beyond which nothing can escape a black hole's gravity. According to the general theory of relativity, even light is trapped inside the horizon, and no information about what fell into the hole can ever escape. Information seems to have fallen out of the universe.
That contradicts the equations of quantum mechanics, which always preserve information. How to resolve this conflict?
One possibility researchers have proposed in the past is that the information does leak back out again slowly. It may be encoded in a hypothetical flow of particles called Hawking radiation, which is thought to result from the black holes' event horizons messing with the quantum froth that is ever-present in space.
But other researchers argue the information may never have been cut off in the first place. Tanmay Vachaspati and his colleagues at Case Western Reserve University in Cleveland, Ohio, US, have tried to calculate what happens as a black hole is forming. Using an unusual mathematical approach called the functional Schrodinger equation, they follow a sphere of stuff as it collapses inwards, and predict what a distant observer would see.
They find that the gravity of the collapsing mass starts to disrupt the quantum vacuum, generating what they call "pre-Hawking" radiation. Losing that radiation reduces the total mass-energy of the object – so that it never gets dense enough to form an event horizon and a true black hole. "There are no such things", Vachaspati told New Scientist. "There are only stars going toward being a black hole but not getting there."
Dark and denseThese so-called "black stars" would look very much like black holes, says Vachaswati. From the point of view of a distant observer, gravity distorts the apparent flow of time so that matter falling inwards slows down. As it gets close to where the horizon would be, the matter fades, its light stretched to such long wavelengths by the dark object's gravity that it would be nearly impossible to detect.
But because the pre-Hawking radiation prevents the formation of a black hole with a true event horizon, the matter never quite fades entirely. As nothing is cut off from the rest of the universe, there is no information paradox.
The idea faces firm opposition from other theoretical physicists, however. "I strongly disagree," says Nobel laureate Gerard 't Hooft of Utrecht University in the Netherlands. "The process he describes can in no way produce enough radiation to make a black hole disappear as quickly as he is suggesting." The horizon forms long before the hole can evaporate, 't Hooft told New Scientist.
Lab testSteve Giddings of the University of California in Santa Barbara, US, is also sceptical. "Well-understood findings apparently conflict with their picture," he told New Scientist. "To my knowledge, there hasn't been an attempt to understand how they are getting results that differ from these calculations, which would be an important step to understanding if this is a solid result."
There could be a way to test the new theory. The Large Hadron Collider being constructed at CERN in Geneva might just be capable of making microscopic black holes – or, if Vachaspati is right, black stars. Unlike the large, long-lived black holes in space, these microscopic objects would evaporate fast. The spread of energies in their radiation might reveal whether or not an event horizon forms.
Alternatively, colliding black stars in space might reveal themselves, as Vachaspati says they would churn out not only gravitational waves (like colliding black holes) but also gamma rays. He suggests that they could be responsible for some of the gamma-ray bursts seen by astronomers.
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josephpalazzo
Illusion Master
Joined: 30 Aug 2006
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| Posted: Mon Jun 30, 2008 4:49 am Post subject: Re: Blackholes |
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| xena wrote: | Has it been decided yet about black holes? I just watched a documentary which has confused me even more. One minute it says that blackholes destroy everything around them, the next it says they are the reason for the creation of life and then it says, andromeda and the milkyway could clash at at anytime and destroy life as we know it. I'm not too good on concentrating. Have they come to a conclusion yet or is it still not known?
New to this science stuff.
Anyone got any links I could read or watch? |
Black holes are not holes, the name confuses people. They are objects like our sun, but much more dense, so dense that light cannot escape its gravity, hence to an observer they would appear as black. Because of this extraordinary mass, and the resulting gravity they deploy, black holes would "swallow" anything within a certain radius, which is called the event horizon. They are traced only by indirect observation -- if gases for example are being swallow in a given region of space. Could they swallow matter forever? Hawking and Bekenstein postulated in the 1970's, using relativity and thermodynamics, that at a certain mass, they would start to radiate electromagnetic waves.
Because of their great mystery, they have been used extensively in science fiction, and many theories proposed in the last twenty years are highly speculative. They are like the flavor of the month. So I wouldn't pay too much attention to these far out ideas. One thing seem to be valid tho', which is that at the center of every galaxy, it seems to be a hotbed for black holes.
Until we developed a quantun theory of gravity, nothing much can be learned about black holes. String theory is the only theory so far on the market that can produced a particle with spin 2, the graviton, which is needed to put gravity on the same level field as the other fundamental forces ( electromagnetic, weak and strong nuclear forces). That theory has its hurdles to overcome (see http://www.atheistforums.com/what-is-the-buzz-with-string-theory-t3249.html). |
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Edd
Forum Plebian
Joined: 27 Jul 2005
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| Posted: Mon Jun 30, 2008 6:30 am Post subject: Re: Blackholes |
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| josephpalazzo wrote: | Could they swallow matter forever? Hawking and Bekenstein postulated in the 1970's, using relativity and thermodynamics, that at a certain mass, they would start to radiate electromagnetic waves.
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I think mentioning (Bekenstein-)Hawking radiation straight after that question is misleading.
Hawking radiation intensity is much higher for very small holes than for large ones. For astrophysically sized black holes, the Hawking radiation is incredibly small, and in no way limits the ability of a black hole to consume matter.
Nothing prevents any non-microscopic black hole from continuing to consume matter. They're most likely limited in the speed at which they can consume, but larger holes can eat faster than a small hole, and nothing prevents a hole continuing to consume matter indefinitely other than the supply of that matter. |
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Dawkadoodle
Forum Master
Joined: 03 Feb 2008
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| Posted: Mon Jun 30, 2008 1:28 pm Post subject: |
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| Totalitarian Superstar wrote: | http://www.google.com/search?hl=en&q=black+holes+do+not+exist
Recent mathematical theories have postulated a black hole cannot exist. Instead, it is now thought a black hole is actually a dark energy star, called "black stars".
This news is actually a year old. I'm surprised no one here is aware. |
Dark Star Theories haven been around for 250 so years, the latest being the dark matter stars. Dark stars were the previous names of what are now commonly called black holes, until a distinction between "Black Holes" and "Dark Stars" was made along with the new term "Black Star" popping up to represent yet another theory. |
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