Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

Speciality Forums >> Science! Astronomy & Space Exploration, and Others

Pages: 1 | 2 | 3 | (show all)
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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
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


Post Extras: Print Post   Remind Me!   Notify Moderator  
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


Post Extras: Print Post   Remind Me!   Notify Moderator  
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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
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


Post Extras: Print Post   Remind Me!   Notify Moderator  
llanitedave
Humble Megalomaniac
*****

Reged: 09/26/05

Loc: Amargosa Valley, NV, USA
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?


Post Extras: Print Post   Remind Me!   Notify Moderator  
Ira
Carpal Tunnel
*****

Reged: 08/22/10

Loc: Mitzpe Ramon, Israel
Re: Black Hole At Our Doorstep: Trapezium? new [Re: llanitedave]
      #5516379 - 11/12/12 05:33 PM



Post Extras: Print Post   Remind Me!   Notify Moderator  
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


Post Extras: Print Post   Remind Me!   Notify Moderator  
EJN
Carpal Tunnel
*****

Reged: 11/01/05

Loc: 53 miles west of Venus
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.



Post Extras: Print Post   Remind Me!   Notify Moderator  
deSitter
Still in Old School


Reged: 12/09/04

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


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jason H.
Pooh-Bah


Reged: 11/23/07

Loc: Central Florida
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...





Post Extras: Print Post   Remind Me!   Notify Moderator  
deSitter
Still in Old School


Reged: 12/09/04

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


Post Extras: Print Post   Remind Me!   Notify Moderator  
JKoelman
professor emeritus


Reged: 05/16/11

Loc: Bangalore, India
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."

""


Post Extras: Print Post   Remind Me!   Notify Moderator  
Sean Cunneen
Let Me Think
*****

Reged: 08/01/07

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

Best. thread. ever.

Post Extras: Print Post   Remind Me!   Notify Moderator  
EJN
Carpal Tunnel
*****

Reged: 11/01/05

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


Post Extras: Print Post   Remind Me!   Notify Moderator  
stephen63
sage
*****

Reged: 05/19/10

Loc: Central Pa
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...


Post Extras: Print Post   Remind Me!   Notify Moderator  
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


Post Extras: Print Post   Remind Me!   Notify Moderator  
llanitedave
Humble Megalomaniac
*****

Reged: 09/26/05

Loc: Amargosa Valley, NV, USA
Re: Black Hole At Our Doorstep: Trapezium? [Re: deSitter]
      #5518752 - 11/13/12 09:43 PM

Hey, the hippies could do cosmic.

Post Extras: Print Post   Remind Me!   Notify Moderator  
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


Post Extras: Print Post   Remind Me!   Notify Moderator  
Mister T
Pooh-Bah


Reged: 02/01/08

Loc: Upstate NY
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! "



Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | (show all)


Extra information
2 registered and 4 anonymous users are browsing this forum.

Moderator:  LivingNDixie, FirstSight, JayinUT 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 2700

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics