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Black Hole At Our Doorstep: Trapezium?

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#26 llanitedave

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Posted 12 November 2012 - 03:12 PM

The black hole as a possible (pathological) solution to strict GR, is real. The point is not if the solution is real - the point is that one is making an enormous assumption that GR holds exactly as written in the strongest regimes. Since it does not even have a conservation law of energy, unlike the entirety of the remainder of physics, and since it is completely - not partially, COMPLETELY - untested in strong field regimes, this assumption is almost surely wrong.

-drl


Wait a minute: You base your argument against black holes not on any evidence against them, not on any evidentiary hint that the equations of GR are actually wrong, but simply because you think that there must, somewhere, be some arbitrary limit to them that prevents black holes from occurring?

We know, obviously, that there are limits to GR because of the mismatch with predictions of quantum theory at the smallest scales. But as I understand it, the formation of a black hole from a collapsing star would occur, long, long before that quantum limit is reached. So you're arguing for still another, as yet unpredicted (except by you) limit?

#27 Ira

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Posted 12 November 2012 - 05:33 PM

:gotpopcorn: :gotpopcorn: :help: :gotpopcorn: :gotpopcorn:

#28 deSitter

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Posted 12 November 2012 - 06:05 PM


The black hole as a possible (pathological) solution to strict GR, is real. The point is not if the solution is real - the point is that one is making an enormous assumption that GR holds exactly as written in the strongest regimes. Since it does not even have a conservation law of energy, unlike the entirety of the remainder of physics, and since it is completely - not partially, COMPLETELY - untested in strong field regimes, this assumption is almost surely wrong.

-drl


Wait a minute: You base your argument against black holes not on any evidence against them, not on any evidentiary hint that the equations of GR are actually wrong, but simply because you think that there must, somewhere, be some arbitrary limit to them that prevents black holes from occurring?

We know, obviously, that there are limits to GR because of the mismatch with predictions of quantum theory at the smallest scales. But as I understand it, the formation of a black hole from a collapsing star would occur, long, long before that quantum limit is reached. So you're arguing for still another, as yet unpredicted (except by you) limit?


My main beef is that they are invoked in every conceivable situation without any real thought. Now we are supposed to believe there is one in the Orion nebula! It's lazy and unimaginative. No progress will ever be made this way.

But beyond that, I'm familiar with physics history in detail. When things are bollixed up as they are with GR in such a way that basic principles fight with each other and one gets stuck between bad alternatives, it always means a deeper more inclusive principle is trying to make itself manifest. I would cite for example the extremely wicked knots that emerged from the Lorentz electron theory - ether, Poincare stresses, deformable electrons, electromagnetic mass, it was a huge mess. Then along came relativity and all these problems vanished immediately (to be replaced by harder ones in some ways).

String theory was motivated mainly as a road to unification. When things are so intricate that something as unphysical as string theory is seen as progress, it means the theory you are attempting to extend is not fundamental to start with. GR is surely an approximate theory, and bears a relation to the coming theory of gravitation in which the pathology will be lifted, that say static electricity does to full electromagnetism (probably a crude analogy).

-drl

#29 EJN

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Posted 12 November 2012 - 06:58 PM

:gotpopcorn: :gotpopcorn: :help: :gotpopcorn: :gotpopcorn:

I use a black hole as an ashtray in my car. Never have to empty it.

Black holes are far out and outta sight. :rimshot:



#30 deSitter

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Posted 12 November 2012 - 07:43 PM

:gotpopcorn: :gotpopcorn: :help: :gotpopcorn: :gotpopcorn:

I use a black hole as an ashtray in my car. Never have to empty it.

Black holes are far out and outta sight. :rimshot:


Well SOMETHING is disposing of my socks...

-drl

#31 Jason H.

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Posted 12 November 2012 - 09:04 PM

Stars orbiting Milky Way SM black hole

I'm curious as to why this isn't evidence? And what substitution of concepts (that a layperson could understand, and I'm not saying that's possible :) ) provides an alternative explanation of these observations? (Just respectfully curious, not attacking.)

Jason W. Higley

Did I say they were a fantasy? I said there was no evidence of an actual black hole, and there is not...



#32 deSitter

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Posted 12 November 2012 - 09:47 PM

Stars orbiting Milky Way SM black hole

I'm curious as to why this isn't evidence? And what substitution of concepts (that a layperson could understand, and I'm not saying that's possible :) ) provides an alternative explanation of these observations? (Just respectfully curious, not attacking.)

Jason W. Higley

Did I say they were a fantasy? I said there was no evidence of an actual black hole, and there is not...


You cannot conclude simply from the probability of a dense object that it is in actual fact a horizon. It just means lots of concentrated mass. The manifold outside doesn't care, the effects beyond the horizon will be the same, but near where the horizon should be, that will be different!

-drl

#33 JKoelman

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Posted 13 November 2012 - 01:38 AM

"the earth is roughly spherical in shape"

"you have no proof for that"

"our laws of gravity tell us objects as heavy as earth have to attain a spherical shape"

"your laws for gravity are bollixed up. You apparently are unaware of three fundamental problems. Firstly, your theory has not been tested when gravity is extreme. Secondly, you need a quantum theory of gravity before you can conclude anything about the shape of earth. And thirdly, your theory violates energy conservation."

"None of the points you raise are valid objections against a round earth. Firstly, our theory of gravity has been tested under extreme gravity conditions. But that is not even relevant here. Earth mass objects collapse into spherical shape under very mild gravity conditions, with the gravitational acceleration at surface staying at very low values. Secondly, quantum effects are completely irrelevant in the description of earth mass objects collapsing into spherical shape. And finally, your point on energy conservation brings to surface a subtlety in our theory of gravity. The theory of gravity tells us energy conservation is not an issue, every local experiment you do will demonstrate energy conservation. However, if you look at faraway phenomena, it becomes less clear how energy conservation should be accounted for. This is no different from the fact that concepts like simultaneity break down when trying to apply these to distant phenomena. None of these subtleties lead to any inconsistencies in the theory. The theory is sound."

"Show me energy is locally conserved. Give it your best shot. Give a local law of energy momentum conservation right here. I don't care where you get it from, just tell me or write it down, or whatever"

"You focus on energy conservation only. I take it that means I have convinced you on the other two points you raised? Anyway, your request is easy to fulfill. Any textbook on general relativity will clarify the point. Let's take the textbook by Wald that is used all over the world in postgrad courses. Equation 4.3.6 on page 70 expresses local energy and momentum conservation."

"You miss the point. If you take a large volume, energy is not conserved. Baez has a web page that says so. Oh, and by the way, Wald sucks."

"I already told you that at large distances things work out in a more complex way. We were discussing local conservation laws. Maybe you actually should read Baez, he is very explicit on local energy conservation. And by the way: haven't you spotted that Baez refers to Wald?"

"I didn't say Baez gave a correct argument, just a better one than Wald. There is no conservation law of any kind, local or global, without additional assumptions, and they preclude the strong field regime. There is no evidence for a spherical earth!"

"I thought we had closed that part of the discussion. You have not reacted to my statement that the collapse of large objects into spherical shape does not require a strong gravitational field. You classify earth being round as a fantasy. Fine with me. I am done discussing."

"Did I say it is a fantasy? I said there was no evidence of an actual spherical earth, and there is not."

"What is your alternative?" What shape do you assign to earth, and what theory of gravity supports such a shape? Can you give me references that support your claims"

"Listen. I know all about it. Don't be fooled, there is no evidence for a spherical earth."

":foreheadslap:"

#34 Sean Cunneen

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Posted 13 November 2012 - 10:57 AM

Best. thread. ever.

#35 EJN

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Posted 13 November 2012 - 11:32 AM

Best. thread. ever.

Needs more cowbell

#36 stephen63

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Posted 13 November 2012 - 03:50 PM

Out of curiosity, I went looking and found this. Indication of a black hole near the trapezium. 1972.
http://articles.adsa...ournal=Ap+SS...

#37 deSitter

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Posted 13 November 2012 - 08:35 PM

Hippies!

-drl

#38 llanitedave

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Posted 13 November 2012 - 09:43 PM

Hey, the hippies could do cosmic.

#39 skyguy88

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Posted 29 November 2012 - 04:19 PM


It would be wonderful if Theta Orionis is confirmed to contain a black hole. I imagine amateur astronomy public outreaches in which the view of the Giant Orion Nebula is accompanied by an explanation of the dance of the trapezium stars around a dark massive object. This would bring 20th century science very close to direct experience. [/quote]

There is a nice animation from the UCLA Galaxy Center Group that works well for outreach. http://www.astro.ucl...bitsMovie.shtml I use it as an opening act before it's dark enough to find Polaris and start my video observing programs. The animation provides a good opportunity to introduce discussion of gravity, black holes, orbits and more.

Bill

#40 Mister T

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Posted 29 November 2012 - 06:43 PM

"S0-16, which comes a mere 90 astronomical units from the black hole."

"Fasten your safety belts, clench your buttocks! It's going be a bumpy ride! "

:help:

#41 Pess

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Posted 11 December 2012 - 01:27 PM


Black hole skepticism has nothing at all to do with something so naive as "I can't see it, it must not exist". It has to do with understanding how the rest of physics works, how it emerged historically, and what is the ground common to all physical theories. The black hole option is invoked in every conceivable circumstance because it is, for one thing untestable and therefore irrefutable, and for another, amounts to an automatic publication-generation algorithm. Thinking hard takes time and effort and both are in short supply.


Or, if you'll pardon me for translating into laymans terms.... GR works in the macroscopic world where we can test it.

However, with no realistic theory of gravity all that can be done is extrapolate down to the dense field structures and hope everything in GR holds as we expect.

But until we can incorporate some theory that combines gravity & GR (and whatever else) into some sort of unified field theory.. that thought that black holes form as we expect them to is just a wild asz theory.

Is that about right?

Pesse (Obviously without a full understanding of gravity we are attempting to assemble a big puzzle with 25% of the pieces missing) Mist

#42 deSitter

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Posted 11 December 2012 - 09:47 PM

That's it. The important study here is the analysis of the "broad line region" in Seyfert nuclei. That makes clear that resolution of the actual horizon is a completely forlorn hope, and so there is utterly no possibility of confirming that a BH in fact exists when the only actual evidence is for dense matter in whatever state it may be found.

-drl

#43 Pess

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Posted 12 December 2012 - 10:10 AM

Well some predictions seem pretty fundamental. We know light is influenced by gravity. If you collect enough mass together it makes sense that gravity will increase to the point where the escape velocity of light is exceeded and you have your basic black hole.

Obviously the mass is still there since the gravitational field is maintained.

I think the question is, "Does the mass compress down to a singularity or is there some dimension to the ball of mass where some unknown force kicks in to thwart further compression?

Of course, if this counter force were sufficiently strong enough then the radius of the compressed center may not be sufficient density (small enough radius) to generate a gravitational field which requires an escape velocity greater than light speed.

For our Sun, it is easy to compute the smallest size of the center mass to form a Schwarzschild radius:

RS = (1.486*10−30)*(1.988*1030) km = 2.954 km

So a star with the mass of our Sun would only need to be compressed to a radius of 2.954km or less to become 'black'.

This is certainly not a singularity and not an unreasonable size for compression of mass under physics as we understand it.

Of course, this unknown repulsive effect 'may' kick in before this density is reached.

Forgive all this layman talk, but what are you suggesting happens when matter approaches these densities?

I think observations have shown that these mass densities do come close to observed gravitational influences? Correct me if I am wrong.

Of course, mine and your definitions of what constitutes a Black Hole may differ. For the sake of this discussion I call any lump of mass with sufficient density to form a Schwarzschild radius a BH.

Pesse (Just curious.) Mist

#44 deSitter

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Posted 12 December 2012 - 12:17 PM

The question is how light and gravity are actually related. Electromagnetic energy in GR generates gravity but not directly vice--versa. This is analogous to the situation in electromagnetism before Maxwell added the displacement current term in the equation for curl B - a changing magnetic field generated an electric field through Faraday's law, but there was no reciprocal relationship involving a changing electric field. Ampere's law was a static phenomenon. Symmetrizing these two laws via the displacement current effectively united electricity and magnetism as a single phenomenon, and carried with it an explanation of light itself as a consequence. A proper theory of gravitation and light and charge will involve exactly this sort of reciprocal relationship, and gravitational fields will directly generate electromagnetic fields. In that case all naive bets on light horizons are off.

In fact we can say more. The ordinary 4-d geometry of spacetime is not rich enough to allow a geometric unification of gravitation and electromagnetism. Thus any realization of the above scenario will automatically involve a richer geometry and an escape, if you will, from the bounds of strict Lorentz invariance. In that case the entire idea of bent-over light cones and non-escaping light becomes meaningless - the geometry will be so changed that this analysis will be moot.

-drl

#45 Pess

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Posted 12 December 2012 - 01:23 PM

So Danny, if I follow correctly this conversion would mean that instead of forming 'Black Holes' these hyperdense structures would radiate as 'White Holes'. And then wouldn't this conversion of gravitational fields into electromagnetic fields cause a fairly rapid evaporation of mass from the WH?

Pesse (And should we be able to detect these giant flashlights?) Mist

#46 JohnMurphyRN

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Posted 12 December 2012 - 01:40 PM

I did some reading on wikipedia on the topics of neutron degeneracy, collapsars, Chandrasekhar's limit, the Tolman–Oppenheimer–Volkoff limit, stellar remnants, and other compact objects. Pess and others reading this thread may find the topics interesting.

#47 deSitter

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Posted 12 December 2012 - 02:20 PM

So Danny, if I follow correctly this conversion would mean that instead of forming 'Black Holes' these hyperdense structures would radiate as 'White Holes'. And then wouldn't this conversion of gravitational fields into electromagnetic fields cause a fairly rapid evaporation of mass from the WH?

Pesse (And should we be able to detect these giant flashlights?) Mist


Well all you can really say without some equations and their solutions is that it would not just be a simple horizon. The denser things got, the more intricately intermixed would be ambient electromagnetic phenomena (e.g. radiation from the accretion disk) and intrinsic electromagnetic phenomena, coming from changes in local geometry (gravitational in origin).

-drl






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