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JKoelman
professor emeritus


Reged: 05/16/11

Loc: Bangalore, India
Black Hole At Our Doorstep: Trapezium?
      #5506493 - 11/06/12 08:51 AM

Next time you aim your scope at Orion's nebula, consider the fact that you might be peeking into a black hole hundred times (or more) the mass of our sun:

http://phys.org/news/2012-11-international-massive-black-hole-sword.html

Scientific publication: http://arxiv.org/pdf/1209.2114.pdf



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deSitter
Still in Old School


Reged: 12/09/04

Re: Black Hole At Our Doorstep: Trapezium? new [Re: JKoelman]
      #5506516 - 11/06/12 09:13 AM



-drl


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EJN
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Re: Black Hole At Our Doorstep: Trapezium? new [Re: JKoelman]
      #5506871 - 11/06/12 01:04 PM

This seems to be based on a whole chain of assumptions, and if one of the assumptions
is wrong then the conclusion collapses like a house of cards.


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Jarad
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Re: Black Hole At Our Doorstep: Trapezium? new [Re: EJN]
      #5507067 - 11/06/12 03:21 PM

Well, I could accept that there could be some large stars hidden in the gas and dust that we can't see that could be providing the mass needed.

But it seems to me that if there were a large black hole embedded in the nebula, it would probably be accreting some of that gas and dust, and we would be seeing a strong X-ray source in there somewhere.

Not so sure about this one.

Jarad

Edited by Jarad (11/06/12 03:22 PM)


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PhilCo126
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Reged: 01/14/05

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Re: Black Hole At Our Doorstep: Trapezium? new [Re: EJN]
      #5511722 - 11/09/12 01:53 PM

Quote:

This seems to be based on a whole chain of assumptions, and if one of the assumptions
is wrong then the conclusion collapses like a house of cards.




Well most theories are based on assumptions which allow for certain parameters to be chosen in computer programs to run simulations (e.g. accretion theory of the solar system)


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Sean Cunneen
Let Me Think
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Re: Black Hole At Our Doorstep: Trapezium? new [Re: PhilCo126]
      #5511871 - 11/09/12 03:35 PM

I have a computer model of birds angrily launching themselves at pigs... Do I win?

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llanitedave
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Re: Black Hole At Our Doorstep: Trapezium? new [Re: Sean Cunneen]
      #5513038 - 11/10/12 11:17 AM

Quote:

I have a computer model of birds angrily launching themselves at pigs... Do I win?




As long as it's testable.

I saw a pack of ravens angrily launching themselves at a couple of coyotes yesterday. It was pretty cool to watch.


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BillFerris
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Re: Black Hole At Our Doorstep: Trapezium? new [Re: JKoelman]
      #5514017 - 11/11/12 06:16 AM

Quote:

Next time you aim your scope at Orion's nebula, consider the fact that you might be peeking into a black hole hundred times (or more) the mass of our sun:

http://phys.org/news/2012-11-international-massive-black-hole-sword.html

Scientific publication: http://arxiv.org/pdf/1209.2114.pdf






The ApJ article is an interesting read and, given both the close proximity and almost constant attention given the Orion Nebula cluster, I wouldn't be surprised if the kind of detailed kinematic study needed to confirm or refute the presence of a 150 solar mass black hole is already under way.

Bill in Flag


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JKoelman
professor emeritus


Reged: 05/16/11

Loc: Bangalore, India
Re: Black Hole At Our Doorstep: Trapezium? new [Re: BillFerris]
      #5514046 - 11/11/12 07:24 AM

Quote:

given both the close proximity and almost constant attention given the Orion Nebula cluster, I wouldn't be surprised if the kind of detailed kinematic study needed to confirm or refute the presence of a 150 solar mass black hole is already under way.




Indeed. No doubt a number of teams across the world are now busy analyzing existing data. We will soon know more.

The laws of physics tell us that stars are transient phenomena, and that black holes are the inevitable (classical) equilibrium configurations. Yet, people less familiar with General Relativity find it difficult to accept black holes. "How can one be so sure black holes exist if they remain per definition hidden from eyesight?"

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.


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deSitter
Still in Old School


Reged: 12/09/04

Re: Black Hole At Our Doorstep: Trapezium? new [Re: JKoelman]
      #5514057 - 11/11/12 07:49 AM

Quote:


The laws of physics tell us that stars are transient phenomena, and that black holes are the inevitable (classical) equilibrium configurations. Yet, people less familiar with General Relativity find it difficult to accept black holes. "How can one be so sure black holes exist if they remain per definition hidden from eyesight?"





This has nothing at all to do with black hole skepticism, which is based on this:

1) GR has not been tested in any way in dense matter conditions. The only tests are the accurate prediction of the orbits of test particles around a massive object (a satellite in earth orbit, a planet around the Sun..), the accurate prediction of gravitational redshift, and the accurate prediction of the rotation curves in spiral galaxies. The first two cases are extreme weak field tests (essentially the one-body problem) while the latter is simply weak field (non-linearity of equations respected). No strong field test of any sort exists. There is little reason to doubt that GR is correct as one enters the strong field regime, but a great deal of reason to doubt that it is correct in the extremely strong field regime. The main point is...

2) It is certain that gravitation and the other interactions have a common origin, in the sense that a theory must exist in which all play essential roles and all are accounted for by one over-arching principle. These relationships are certain to become manifest in extreme conditions, while they may be entirely missing in the weak field case. That is true for example of electromagnetism - the relationship of electricity and magnetism does not become entirely clear until one has high field densities, high (relativistic) velocities, etc. In the weakest regime they are entirely disconnected (static charge and simple magnets). The black hole religion fails entirely to account for this certainty that the other interactions manifest alongside gravity in extreme conditions, and takes GR to be literally correct down to the smallest levels. This however is impossible for a third, and deadly reason..

3) There is no conservation law for energy and momentum for gravitation. It is therefore impossible even to make naive arguments based on simple energy conservation unless very special circumstances are at hand, all of which preclude a strong-field condition.

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.

-drl


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Ira
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Re: Black Hole At Our Doorstep: Trapezium? new [Re: deSitter]
      #5514456 - 11/11/12 01:05 PM

So, are you saying black holes don't exist? They're a simple-minded mistake? Or that THIS black hole in M42 doesn't exist?

/Ira


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JKoelman
professor emeritus


Reged: 05/16/11

Loc: Bangalore, India
Re: Black Hole At Our Doorstep: Trapezium? new [Re: deSitter]
      #5514468 - 11/11/12 01:15 PM

Quote:

GR has not been tested in any way in dense matter conditions. The only tests are the accurate prediction of the orbits of test particles around a massive object (a satellite in earth orbit, a planet around the Sun..), the accurate prediction of gravitational redshift, and the accurate prediction of the rotation curves in spiral galaxies. The first two cases are extreme weak field tests (essentially the one-body problem) while the latter is simply weak field (non-linearity of equations respected). No strong field test of any sort exists. There is little reason to doubt that GR is correct as one enters the strong field regime, but a great deal of reason to doubt that it is correct in the extremely strong field regime.



This is incorrect. GR has been tested extensively in conditions that go well beyond the weak-field (the so called post-Newtonian approximation) limit. On top of that, the Hulse-Taylor system and PSR J0737-3039 provide superb strong field tests.

More importantly, the formation of black hole horizons doesn't require extreme gravity. This is something few people realize. Black holes are gravitational horizons: boundaries that define space-time regions causally disconnected from our universe. Such horizons form under mild gravity conditions.

One last point is that as higher-order gravity effects have been tested, there is absolutely no reason to doubt the strong field limit. The analogy with electromagnetism is instructive, but for reasons opposite to what you suspect:

Quote:

electromagnetism - the relationship of electricity and magnetism does not become entirely clear until one has high field densities, high (relativistic) velocities, etc. In the weakest regime they are entirely disconnected (static charge and simple magnets).



Any current no matter how small creates a magnetic field, and any change in a magnetic field no matter how small creates a current. It is absolutely untrue that the unification between electricity and magnetism was achieved only after stronger currents or higher magnetic fields were achieved.

It is correct that the full integration of electricity and magnetism was achieved only under Einstein's special theory of relativity, but this integration changed nothing whatsoever in the predictions of the theory.

Quote:

There is no conservation law for energy and momentum for gravitation. It is therefore impossible even to make naive arguments based on simple energy conservation unless very special circumstances are at hand, all of which preclude a strong-field condition.



Local energy and momentum conservation are part and parcel of GR. What is highly nontrivial, however, is to translate this into global conservation laws. But this is in no way a demonstration of problems inherent to GR. It is just a manifestation of the complex implications of GR. It is almost a century since Einstein wrote down the equations for GR, yet working out all its implications is still continuing. Physicists struggled for decades with the Schwarzschild solution, and for many years they refused to accept the physical reality of black holes. Yet, with all the evidence building up over the years, there is no single scientist knowledgable in the area that continuous to doubt the reality of black holes.

The bottom line is: black hole skepticism is crackpottery, What exactly happens deep beyond black hole horizons is dependent on the integration of gravity with the other forces, but the physics up to and including black hole horizons is well understood and unanimously accepted by experts (who became experts thanks to their inquisitive mind and their skeptical nature).


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deSitter
Still in Old School


Reged: 12/09/04

Re: Black Hole At Our Doorstep: Trapezium? new [Re: JKoelman]
      #5515052 - 11/11/12 08:38 PM

Quote:


Local energy and momentum conservation are part and parcel of GR.





Show me. Well this is not fair, but I feel feisty. Give it your best shot. Write a local law of energy momentum conservation in GR right here. I don't care where you get it from, just write it down, or link it, or whatever. Point out to me this thing that is "part and parcel of GR". And when I show you that you are wrong, what then? What will you do? Will you learn? Or will you just become entrenched in what you have failed to understand?

-drl


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Neutrino?
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Re: Black Hole At Our Doorstep: Trapezium? new [Re: JKoelman]
      #5515099 - 11/11/12 09:14 PM

Quote:

It is absolutely untrue that the unification between electricity and magnetism was achieved only after stronger currents or higher magnetic fields were achieved.




I don't need to defend drl, as he can defend himself quite easily, but that is not what he said.

Quote:

It is correct that the full integration of electricity and magnetism was achieved only under Einstein's special theory of relativity, but this integration changed nothing whatsoever in the predictions of the theory.




Why would the predictions of the theory change? I am surprised this is even part of your argument, because we all know this and you missed the point. The classical equations by luck were already invariant under the Lorentz group. So of course formulating SR and finding these symmetries later had no change on the theory. It only let us better understand what was fundamentally happening. If the classical theory didn't adhere to these symmetries, it would have to be modified and then the predictions would have changed.

This could be happening with a bunch of things. That is what he is looking at.


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EJN
Carpal Tunnel
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Reged: 11/01/05

Loc: 53 miles west of Venus
Re: Black Hole At Our Doorstep: Trapezium? new [Re: Sean Cunneen]
      #5515111 - 11/11/12 09:28 PM

Quote:

Local energy and momentum conservation are part and parcel of GR.




Not true. Energy/momentum is conserved only in cases where the covariant
derivative of the energy-momentum tensor equals zero.


Quote:


I have a computer model of birds angrily launching themselves at pigs...Do I win?



I have a computer model of angry pterodactyls launching flying toasters at
flying monkeys.
I win.


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JKoelman
professor emeritus


Reged: 05/16/11

Loc: Bangalore, India
Re: Black Hole At Our Doorstep: Trapezium? new [Re: deSitter]
      #5515166 - 11/11/12 10:11 PM

You react to and dispute solely one of the many clarifications I have given you. I take it therefore that you have withdrawn all your objections against black holes, except for one. That is good. That means we are getting to the point of embracing black holes as inevitable consequences of the laws of physics.

Ok, your last remaining concern: energy-momentum conservation in General Relativity. You pose a rather trivial challenge:

Quote:

Write a local law of energy momentum conservation in GR right here. I don't care where you get it from, just write it down, or link it, or whatever. Point out to me this thing that is "part and parcel of GR".



You can open any textbook on General Relativity. Each of them will explain that locally energy-momentum conservation holds. This is trivial as soon as you realize that GR represents nothing more than a patchwork of Minkowskian space-times.

The preferred reference ("the bible of general relativists") is Wald's textbook "General Relativity" (ISBN 0-226-87033-2). Wald discusses energy-momentum conservation on p.69-70. It suffices to quote a single sentence:

Quote:

Thus equation (4.3.6) may be interpreted as a local conservation of material energy over small regions of spacetime.




The equation Wald refers to is Nabla(sup,a) T(sub,a,b) = 0. The quantity T is the energy-momentum pseudotensor. Wikipedia has the following to say about this pseudotensor:

Quote:

In the theory of general relativity, a stress–energy–momentum pseudotensor, such as the Landau–Lifshitz pseudotensor, is an extension of the non-gravitational stress–energy tensor which incorporates the energy-momentum of gravity. It allows the energy-momentum of a system of gravitating matter to be defined. In particular it allows the total of matter plus the gravitating energy-momentum to form a conserved current within the framework of general relativity, so that the total energy-momentum crossing the hypersurface (3-dimensional boundary) of any compact space-time hypervolume (4-dimensional submanifold) vanishes.




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JKoelman
professor emeritus


Reged: 05/16/11

Loc: Bangalore, India
Re: Black Hole At Our Doorstep: Trapezium? new [Re: EJN]
      #5515217 - 11/11/12 10:33 PM

Quote:

Quote:

Local energy and momentum conservation are part and parcel of GR.




Not true. Energy is conserved only in cases where the covariant derivative of the energy-momentum tensor equals zero.




Yes, this covariant derivative has to be zero. And it is zero. See my response above to DeSitter referring to equatiion 4.3.6 in Wald's book.


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EJN
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Reged: 11/01/05

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Re: Black Hole At Our Doorstep: Trapezium? new [Re: JKoelman]
      #5515233 - 11/11/12 10:45 PM

Quote:



Yes, this covariant derivative has to be zero. And it is zero. See my response above to DeSitter referring to equatiion 4.3.6 in Wald's book.



The covariant derivative is only equal to zero under special conditions,
with static spacetimes and asymptotically flat spacetimes. Also, using a psuedotensor
makes the result dependent on the coordinate system which is used, which is
not the case with "true" tensors.

Gravitational collapse satisfies neither of the above conditions. Neither does
the FRW metric of the expanding universe. The covariant derivative of the
energy-monentum tensor cannot be zero when the spacetime background is dynamic.

See:
http://math.ucr.edu/home/baez/physics/Relativity/GR/energy_gr.html

"The Schwarzschild metric describes spacetime around a massive object,
if the object is spherically symmetrical, uncharged, and 'alone in the universe'."

"For these reasons, most physicists who work in general relativity do not
believe the pseudo-tensors give a good local definition of energy density, although
their integrals are sometimes useful as a measure of total energy."


Quote:

The preferred reference ("the bible of general relativists") is Wald's textbook "General Relativity"



"Gravitation" by Thorne, Misner, & Wheeler is considered the true "bible" of GR.


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JKoelman
professor emeritus


Reged: 05/16/11

Loc: Bangalore, India
Re: Black Hole At Our Doorstep: Trapezium? new [Re: EJN]
      #5515292 - 11/11/12 11:32 PM

Quote:

Quote:

The equation Wald refers to is Nabla(sup,a) T(sub,a,b) = 0. The quantity T is the energy-momentum pseudotensor.



The covariant derivative is only equal to zero under special conditions, with static spacetimes and asymptotically flat spacetimes. Using a psuedotensor makes the result dependent on the coordinate system which is used, which is not the case with true tensors.

Gravitational collapse satisfies neither of those conditions. Neither does the FRW metric
of the expanding universe. The covariant derivative of the energy-monentum tensor cannot be zero
when the spacetime background is dynamic.

See:
http://math.ucr.edu/home/baez/physics/Relativity/GR/energy_gr.html

"The Schwarzschild metric describes spacetime around a massive object, if the object
is spherically symmetrical, uncharged, and 'alone in the universe'
."

"For these reasons, most physicists who work in general relativity do not believe the
pseudo-tensors give a good local definition of energy density, although their integrals
are sometimes useful as a measure of total energy."




You are confusing global energy conservation with local energy conservation. As I said in my first post: translating local energy conservation into a corresponding equation for global energy conservation is highly non-trivial. Static spacetimes and asymptotically flat spacetimes are examples where global energy conservation can easily be derived from local energy conservation.

Baez, in the text you linked to, is careful to distinghuish the two. He choses the following words when describing local energy conservation:

Quote:

The differential form says, loosely speaking, that no energy is created in any infinitesimal piece of spacetime. The integral form says the same for a finite-sized piece.




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deSitter
Still in Old School


Reged: 12/09/04

Re: Black Hole At Our Doorstep: Trapezium? new [Re: JKoelman]
      #5515496 - 11/12/12 04:26 AM

You are missing the point completely.

To have a conservation law, you must be able to convert a integral throughout a volume into one on the surface of that volume via Stoke's theorem. There is nothing at all complicated about this. It does not depend on "interpretation". It is just a simple fact. In order for the amount of a conserved quantity contained within a volume to change, it has to go through the surface that bounds the volume.

But you cannot apply Stoke's theorem in GR unless a special condition is met - namely, you must be able to convert a covariant derivative into an ordinary derivative. This is always possible for a vector field;

Ja;n = (1/sqrt g) d/dxn (Ja sqrt g)

where g is the determinant of the metric tensor. This extra term that shows up may be thought of as the correction that appears from the changing volume element within the manifold. In general this rearrangement of terms by bringing in the volume element is always possible for a totally antisymmetric tensor of any rank. But the energy tensor is symmetric. It is not in general possible to convert the covariant derivative of the energy tensor into an ordinary divergence so that Stoke's theorem may be applied.

GR has the form

Rmn - 1/2 gmn R = 8 pi Tmn

The covariant divergence of the left side is identically zero (Bianchi identity). Thus

Tmn; n = 0

and since this is a covariant divergence of a symmetric tensor, it does not represent a conservation law. There is no conservation of energy and momentum in general relativity.

By the way, I own Wald and it's an awful book.

-drl


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JKoelman
professor emeritus


Reged: 05/16/11

Loc: Bangalore, India
Re: Black Hole At Our Doorstep: Trapezium? new [Re: deSitter]
      #5515548 - 11/12/12 07:02 AM

You asked for references or links, and I gave you both.

You are not responding to this evidence. Instead you change the goalpost by restating a point that I made at the start of this discussion (translating the local energy-momentum conversation in GR into a global conservation law is not possible in any straightforward way) and presenting this as if it is a new point you bring up. Also you call the standard graduate text on relativity written by an eminent scientist on the subject "an awful book".

You probably persist in your belief that black holes are a fantasy resulting from a conspiracy among thousands of scientists. That's all fine with me, but don't expect me to further waste my time here.

You might find a few people here who really believe your science credentials are better than Wald's, and some might even believe you have deeper insights than the whole global community of theoretical physicists together. Others might scratch their heads. It doesn't matter. I wish you lots of fun here.


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deSitter
Still in Old School


Reged: 12/09/04

Re: Black Hole At Our Doorstep: Trapezium? new [Re: JKoelman]
      #5515558 - 11/12/12 07:22 AM

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

And I did not invent the agument presented her, Einstein did. But I refuse to engage in "argumentum ad verecundiam".

I have owned, in my life, Wald, MTW, Adler, Eddington, Weyl, Einstein, Tolman, Cooperstock, and several more that slip my memory. Wald is by far the worst of the lot. The best is by Weinberg.

-drl


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deSitter
Still in Old School


Reged: 12/09/04

Re: Black Hole At Our Doorstep: Trapezium? new [Re: JKoelman]
      #5515935 - 11/12/12 12:38 PM

Quote:

You react to and dispute solely one of the many clarifications I have given you. I take it therefore that you have withdrawn all your objections against black holes, except for one. That is good. That means we are getting to the point of embracing black holes as inevitable consequences of the laws of physics.

Ok, your last remaining concern: energy-momentum conservation in General Relativity. You pose a rather trivial challenge:

Quote:

Write a local law of energy momentum conservation in GR right here. I don't care where you get it from, just write it down, or link it, or whatever. Point out to me this thing that is "part and parcel of GR".



You can open any textbook on General Relativity. Each of them will explain that locally energy-momentum conservation holds. This is trivial as soon as you realize that GR represents nothing more than a patchwork of Minkowskian space-times.

The preferred reference ("the bible of general relativists") is Wald's textbook "General Relativity" (ISBN 0-226-87033-2). Wald discusses energy-momentum conservation on p.69-70. It suffices to quote a single sentence:

Quote:

Thus equation (4.3.6) may be interpreted as a local conservation of material energy over small regions of spacetime.




The equation Wald refers to is Nabla(sup,a) T(sub,a,b) = 0. The quantity T is the energy-momentum pseudotensor. Wikipedia has the following to say about this pseudotensor:

Quote:

In the theory of general relativity, a stress–energy–momentum pseudotensor, such as the Landau–Lifshitz pseudotensor, is an extension of the non-gravitational stress–energy tensor which incorporates the energy-momentum of gravity. It allows the energy-momentum of a system of gravitating matter to be defined. In particular it allows the total of matter plus the gravitating energy-momentum to form a conserved current within the framework of general relativity, so that the total energy-momentum crossing the hypersurface (3-dimensional boundary) of any compact space-time hypervolume (4-dimensional submanifold) vanishes.







Thanks, of course I know this argument. It's wrong. Here's a better one:

http://math.ucr.edu/home/baez/physics/Relativity/GR/energy_gr.html

It always amazes me that this wrong argument is perpetuated from book to book over the years. You can write

Tmn;n = 0

as

d/dxn (Tmn + tmn) = 0

This is now the ordinary divergence of a quantity, such as is required to apply Stoke's theorem. But the quantity is not a tensor and so depends on the coordinate system used. Thus it is not a conservation law of any kind.

I've never been able to understand why people don't just face facts. GR does not have a conservation law of energy. This is an enormous problem and colors everything you say about it and impacts every potential application, from condensed matter to gravitational wave propagation to the entire universe as a whole.

-drl


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JKoelman
professor emeritus


Reged: 05/16/11

Loc: Bangalore, India
Re: Black Hole At Our Doorstep: Trapezium? new [Re: deSitter]
      #5516110 - 11/12/12 02:25 PM

Quote:

Wald is by far the worst of the lot. [..] Here's a better one:

http://math.ucr.edu/home/baez/physics/Relativity/GR/energy_gr.html





LOL. Did you notice your "better one" (Baez) refers to Wald?

You not only prove yourself wrong, you also again fail to bring anything new into the discussion. We already discussed Baez above. As stated, Baez confirms local energy-momentum conservation with the following words:

Quote:

The differential form says, loosely speaking, that no energy is created in any infinitesimal piece of spacetime. The integral form says the same for a finite-sized piece.




Going back to the heart of the discussion, the same Baez that you quote tells us black holes are real. Black holes and a spherical earth are both direct consequences of the laws of gravity. You and I can't observe either of these directly, but there is plenty of indirect evidence for both phenomena.


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deSitter
Still in Old School


Reged: 12/09/04

Re: Black Hole At Our Doorstep: Trapezium? new [Re: JKoelman]
      #5516126 - 11/12/12 02:35 PM

I didn't say he gave a correct argument, just a better one in that at least he admits there is a problem! The differential form says nothing of the kind - there is no conservation law of any kind, local or global, without additional assumptions, and they preclude the strong field regime.

Mathematicians seem to like Wald because he dresses everything up in pretentious language which is both a distraction and a curse - a curse because the student might be persuaded he has understood something when in fact the teacher himself is confused. However you can't hide from facts with language. Weinberg, "Gravitation and Cosmology", is an infinitely better book because he sticks to simple physics language.

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


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llanitedave
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Re: Black Hole At Our Doorstep: Trapezium? new [Re: deSitter]
      #5516180 - 11/12/12 03:12 PM

Quote:


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?


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Ira
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Re: Black Hole At Our Doorstep: Trapezium? new [Re: llanitedave]
      #5516379 - 11/12/12 05:33 PM



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deSitter
Still in Old School


Reged: 12/09/04

Re: Black Hole At Our Doorstep: Trapezium? new [Re: llanitedave]
      #5516426 - 11/12/12 06:05 PM

Quote:

Quote:


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


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EJN
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Re: Black Hole At Our Doorstep: Trapezium? new [Re: Ira]
      #5516529 - 11/12/12 06:58 PM

Quote:





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

Black holes are far out and outta sight.



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deSitter
Still in Old School


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Re: Black Hole At Our Doorstep: Trapezium? new [Re: EJN]
      #5516601 - 11/12/12 07:43 PM

Quote:

Quote:





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

Black holes are far out and outta sight.






Well SOMETHING is disposing of my socks...

-drl


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Jason H.
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Re: Black Hole At Our Doorstep: Trapezium? new [Re: deSitter]
      #5516751 - 11/12/12 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

Quote:

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





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deSitter
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Re: Black Hole At Our Doorstep: Trapezium? new [Re: Jason H.]
      #5516838 - 11/12/12 09:47 PM

Quote:

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

Quote:

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


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JKoelman
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Re: Black Hole At Our Doorstep: Trapezium? new [Re: deSitter]
      #5517182 - 11/13/12 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."

""


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Sean Cunneen
Let Me Think
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Reged: 08/01/07

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Re: Black Hole At Our Doorstep: Trapezium? new [Re: JKoelman]
      #5517668 - 11/13/12 10:57 AM

Best. thread. ever.

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EJN
Carpal Tunnel
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Loc: 53 miles west of Venus
Re: Black Hole At Our Doorstep: Trapezium? new [Re: Sean Cunneen]
      #5517734 - 11/13/12 11:32 AM

Quote:

Best. thread. ever.



Needs more cowbell


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stephen63
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Re: Black Hole At Our Doorstep: Trapezium? new [Re: EJN]
      #5518184 - 11/13/12 03:50 PM

Out of curiosity, I went looking and found this. Indication of a black hole near the trapezium. 1972.
http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?journal=Ap%2bSS...


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deSitter
Still in Old School


Reged: 12/09/04

Re: Black Hole At Our Doorstep: Trapezium? new [Re: stephen63]
      #5518655 - 11/13/12 08:35 PM

Hippies!

-drl


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llanitedave
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Re: Black Hole At Our Doorstep: Trapezium? new [Re: deSitter]
      #5518752 - 11/13/12 09:43 PM

Hey, the hippies could do cosmic.

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skyguy88
sage


Reged: 11/13/06

Loc: Prescott, AZ
Re: Black Hole At Our Doorstep: Trapezium? new [Re: JKoelman]
      #5545794 - 11/29/12 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.




There is a nice animation from the UCLA Galaxy Center Group that works well for outreach. http://www.astro.ucla.edu/~ghezgroup/gc/pictures/orbitsMovie.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


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Mister T
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Re: Black Hole At Our Doorstep: Trapezium? new [Re: skyguy88]
      #5546000 - 11/29/12 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! "



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Pess
(Title)
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Reged: 09/12/07

Loc: Toledo, Ohio
Re: Black Hole At Our Doorstep: Trapezium? new [Re: deSitter]
      #5565938 - 12/11/12 01:27 PM

Quote:



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


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deSitter
Still in Old School


Reged: 12/09/04

Re: Black Hole At Our Doorstep: Trapezium? new [Re: Pess]
      #5566626 - 12/11/12 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


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Pess
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Reged: 09/12/07

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Re: Black Hole At Our Doorstep: Trapezium? new [Re: deSitter]
      #5567268 - 12/12/12 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


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deSitter
Still in Old School


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Re: Black Hole At Our Doorstep: Trapezium? new [Re: Pess]
      #5567461 - 12/12/12 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


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Pess
(Title)
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Reged: 09/12/07

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Re: Black Hole At Our Doorstep: Trapezium? new [Re: deSitter]
      #5567577 - 12/12/12 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


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JohnMurphyRN
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Re: Black Hole At Our Doorstep: Trapezium? new [Re: Pess]
      #5567605 - 12/12/12 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.

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deSitter
Still in Old School


Reged: 12/09/04

Re: Black Hole At Our Doorstep: Trapezium? new [Re: Pess]
      #5567695 - 12/12/12 02:20 PM

Quote:

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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