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Black Holes NOT Science?

by AdkinsJr
Tags: black, holes, science
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Chronos
#19
Oct23-09, 12:07 AM
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We do not understand how matter behaves at extreme density, and there is no known way to replicate it in a laboratory. As Chroot noted, we may be quite surprised by the answer. The gap between neutron star masses and imputed 'black holes' remains very puzzling to me.
Phrak
#20
Oct23-09, 12:34 AM
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Quote Quote by russ_watters View Post
No one answered the question, though....

Black holes are objects and they most certainly exist as they have been observed countless times.
I don't think so. It takes an infinite amount of time for matter to cross an event horizon. I think this quantifies the question "how long does it take a black hole to form?". I've had no informed responses on the this, so I can only make an ill-educated guess. Forever is a long time.

I would like to see the argument that a proto-black hole is measurably different than a black hole, and that observed objects touted as black holes in the pop-science press are measurably disinguishable.

Edit: I've jumped in without reading all the post, so forgive me if im not in sync.
Dmitry67
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Oct23-09, 02:33 AM
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Black holes are more than objects: they are timespace structures

When we ask 'Does X exist'? (existed, will exist) we assume some global 'NOW' in neutonian sense. It is not applicable to the BH.

To make it clear, formulate the question this way: Does the Blach Hole exist NOW?
Obviously, the question does not make any sense: SOME timeline trajectories from you WILL 'hit' the black hole (if you decide to fly there), others - will even never cross the lightcone from there.
russ_watters
#22
Oct23-09, 06:09 AM
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Quote Quote by chroot View Post
Russ,

I think your conviction is understandable, but also too strong.

As Chronos said, we have observed curious things in the universe -- immense sources of energy, jets, accretion discs, large gravitational effects on other objects, even gravitational lensing -- which can only be understood as the consequences of extremely massive (and dense) objects.

Currently, the only theoretical candidate that we have to explain these observations is the black hole, as described by the general theory of relativity.

If you take the definition of "black hole" as "super dense body," then yes, there is observational proof that black holes exist. If you take the definition of "black hole" to mean the narrower "body as described by general relativity," then their existence is, at best, plausible. The actual nature of these super dense bodies could be radically different than anything we think we know today.

- Warren
Warren, while you said my position is too strong, your description of the situation agrees exactly with what I said. I don't know quite what is going on here, but it seems like people are reading something in my posts that I didn't say.

Perhaps a more stark example of the same concept would help. The ancients observed many "planets" and gave them proper names like "Venus". They were woefully wrong about what, exactly they were viewing, nevertheless, they were viewing the same object we still call "Venus" and classify as a "planet" today.

So, fast forward 1000 years and assume turns out the exact body predicted by GR is woefully inadequate to describe what is being observed. All I am saying is that there is still an object SGR A - it's really there - and I even think that in 1000 years, they'll still call that object a "black hole". Whether they do or not, that doesn't change the fact that there really is an object there, just like regardless of what name and theory we use to describe Venus, it is still the same object the ancients were looking at.
Jonathan Scott
#23
Oct23-09, 07:26 AM
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Quote Quote by russ_watters View Post
All I am saying is that there is still an object SGR A - it's really there - and I even think that in 1000 years, they'll still call that object a "black hole". Whether they do or not, that doesn't change the fact that there really is an object there, just like regardless of what name and theory we use to describe Venus, it is still the same object the ancients were looking at.
So far, even the blackness is theoretical. These objects typically emit large amounts of energy at some wavelengths (for quasars, this amount is almost impossibly huge), but it is usually assumed on theoretical grounds that this emission is coming from accretion disks around a black hole (as we cannot yet resolve the central component separately). If theory proves wrong, and significant energy is being emitted by the central object too, then I don't think that such objects would continue to be called "black".
twofish-quant
#24
Oct23-09, 02:15 PM
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Quote Quote by Chronos View Post
Neutron stars with masses in excess of about 1.33 solar mass are virtually unobserved to date - far short of the ~ 3 solar masses necessary to form a black hole.
The 3 solar mass limit depends crucial on the equation of state for neutron star material which is unknown. If you assume that neutron star material is soft (which it may be), it's not hard to get a limit of 1.33 solar mass as the cutoff.

The smallest black hole detected to date weighs in at nearly 4 solar masses. This is quite a mystery, imo. Where are all the 'tweeners'?
It's not that much of a mystery. A neutron star has a surface and once material falls onto it, there are ways of getting the material off. Once material falls into a black hole it's going to stay there.
twofish-quant
#25
Oct23-09, 02:20 PM
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Quote Quote by Phrak View Post
I don't think so. It takes an infinite amount of time for matter to cross an event horizon.
No it doesn't. Material falling into a black hole will take a finite (and quite small) time to pass through the event horizon to the singularity at which point who knows what happens.

From a distance, it appears that material will take an infinite amount of time to fall in, but that's something of an optical illusion.
Ivan Seeking
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Oct23-09, 03:00 PM
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Quote Quote by twofish-quant View Post
but that's something of an optical illusion.
Uh, no.
Dmitry67
#27
Oct23-09, 03:06 PM
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'optical' is not the right word
But I would not call the infitite time dilation for the fallign object real

Here is a best explanation of the BH I have ever seen
http://www.valdostamuseum.org/hamsmith/DFblackIn.gif
Bob_for_short
#28
Oct23-09, 03:19 PM
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Quote Quote by Dmitry67 View Post
'optical' is not the right word
But I would not call the infitite time dilation for the fallign object real

Here is a best explanation of the BH I have ever seen
http://www.valdostamuseum.org/hamsmith/DFblackIn.gif
No, the plot is wrong. A black hole is as a spherical black body, that's it.
Phrak
#29
Oct23-09, 06:32 PM
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Quote Quote by twofish-quant View Post
No it doesn't. Material falling into a black hole will take a finite (and quite small) time to pass through the event horizon to the singularity at which point who knows what happens.
hmm. Matter will take an infinite amount of time to cross an event horizon.

There is no event horizon that is crossed for this in-falling frame of reference.

There is no clock that will record a local and finite elapsed time to cross an event horizon. You have to confuzzle coordinate systems to get this to work using the distant observer's coordinate singularity (the horizon) and the in-falling observer's clock.

From a distance, it appears that material will take an infinite amount of time to fall in, but that's something of an optical illusion.
Without this optical illusion there is no Hawking radiation.
twofish-quant
#30
Oct24-09, 01:31 AM
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Quote Quote by Phrak View Post
hmm. Matter will take an infinite amount of time to cross an event horizon.
Incorrect. See

http://antwrp.gsfc.nasa.gov/htmltest...h_pub_faq.html

Also it references Misner, Thorne, and Wheeler.
Dmitry67
#31
Oct24-09, 01:35 AM
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Quote Quote by Bob_for_short View Post
No, the plot is wrong. A black hole is as a spherical black body, that's it.
Look at the diagram. It is spherical.
sweetsimple
#32
Oct24-09, 06:45 AM
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A black hole is defined as a dead star, whose escape velocity is greater than that of the speed of light.
Phrak
#33
Oct24-09, 10:58 AM
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Quote Quote by Phrak View Post
hmm. Matter will take an infinite amount of time to cross an event horizon.
Quote Quote by twofish-quant View Post
Incorrect. See

http://antwrp.gsfc.nasa.gov/htmltest...h_pub_faq.html

Also it references Misner, Thorne, and Wheeler.
If you are going to throw things out like this you should provide a quote.

Matt talks about some "useful sense". I have no idea what is supposed to be useful about falling into a black hole. Apparently this doesn't mean a "physical sense".
George Jones
#34
Oct24-09, 12:09 PM
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Quote Quote by Phrak View Post
Matt talks about some "useful sense". I have no idea what is supposed to be useful about falling into a black hole. Apparently this doesn't mean a "physical sense".
What in the world do you mean? I agree with twofish-quant.
Quote Quote by Phrak View Post
hmm. Matter will take an infinite amount of time to cross an event horizon.
This is wrong.
Quote Quote by Phrak View Post
There is no event horizon that is crossed for this in-falling frame of reference.
And this is wrong.
Quote Quote by Phrak View Post
There is no clock that will record a local and finite elapsed time to cross an event horizon. You have to confuzzle coordinate systems to get this to work using the distant observer's coordinate singularity (the horizon) and the in-falling observer's clock.
And this is wrong. Nothing has to be confuzzled. The in-falling observer's clock works just fine by itself.
Phrak
#35
Oct24-09, 06:46 PM
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Quote Quote by George Jones View Post
What in the world do you mean? I agree with twofish-quant.

This is wrong.

And this is wrong.

And this is wrong. Nothing has to be confuzzled. The in-falling observer's clock works just fine by itself.
I keep getting these one liners as if this solves everything.

Please provide a world line that Contains a coordinate singularity.
twofish-quant
#36
Oct25-09, 12:00 AM
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Quote Quote by chroot View Post
As Chronos said, we have observed curious things in the universe -- immense sources of energy, jets, accretion discs, large gravitational effects on other objects, even gravitational lensing -- which can only be understood as the consequences of extremely massive (and dense) objects.
In the case of accretion disks they can only currently be understood in terms of massive and dense objects that seem to behave according to how black holes should behave under the rules of GR. For some of the accretion disks, it's not merely a massive and dense object, but a massive and dense object with no apparent surface.

The actual nature of these super dense bodies could be radically different than anything we think we know today.
Possible but not likely. The thing about accretion disks is that a lot of them have been studied enough to reduce the likelihood of "weird physics." If there is something radically different than what we think we know then we have to explain why all that radical stuff only seems to affect the core object and not anything else.

Personally, I think that the observational evidence for black holes is roughly equal to that of exoplanets, and a finding that "black holes don't exist" would be as shocking as "exoplanets don't exist."


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