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  #21  
Old 27-04-2010, 02:28 AM
Karls48 (Karl)
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It should be relatively easy to prove/disprove effect of plasma on the photons by the experiment. If my memory serves me right there was some very energetic plasma created for experiments to create fusion. It could be possible to fire laser beam to graze this plasma and measure if any deviation from the straight path took place I do realise that power density of man made plasma is a small fraction of the power of plasma around the sun. But under laboratory conditions it could be possible to measure if any deflection took place.
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  #22  
Old 27-04-2010, 06:45 AM
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I am still following this discussion with great interest (despite being accused of placing irrelevant remarks..)..
While personally I can not contribute much - the lack of deeper understanding of the subject (mathematics - mine is on the engineering level, more than enough for what I do professionally but totally in-adequate for going deeper into GR) prevents me from making any statements apart from general ones (which I did earlier), I did some research among people who know the stuff and who-is-who (one friend of mine is in this subject up to his neck, if not deeper) and he confirmed for me that plasma effect on light bending WAS taken into account, during original experiment/measurement... That is why this discussion is pretty meaningless. As it is meaningless to take this author into account too seriously in general ("Only I understand and see what is going on here, all the others were stupid and blind..." which is what he is saying in essence, cherry-picking the experimental results while not describing in detail the methods used, which suggests to the average reader that measurement results were misinterpreted in haste to prove relativity.. which is very far from the truth..... and he is doing exactly the same, only to disprove it. In my book, this is not very scientifically credible approach.. )

Also, for the experimental confirmation of effects of gravity to EM, have a look here:
http://hyperphysics.phy-astr.gsu.edu...iv/gratim.html

In the meantime, I am trying to find gravitation simulator (Einstein's ring issue) on the web, which is based on relativity.. I stumbled on it quite some time ago, but I lost the link.
If this simulator is producing the same images as seen in reality (and as I remember it did, quite so), then we can forget about this guy, IMHO.


EDIT:
This is not quite the same website but it will do (simulator is very simple, it uses only one, pointlike mass.. the clusters of galaxies are - as we know - distributed, so the images they produce are much more complex than shown here in simulation):
http://www.astrophysicsspectator.com...sPointSim.html

also:
http://www.astrophysicsspectator.com...ldLensSim.html
http://en.wikipedia.org/wiki/Einstein_ring#A_simulation
http://www.photon.at/~werner/bh/gvsim.html

Last edited by bojan; 27-04-2010 at 08:41 AM.
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  #23  
Old 27-04-2010, 10:35 AM
Jarvamundo (Alex)
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Re SJ: Thanks will comment

Re Karl: Yes the author mentions experiments where GR and plasma predictions will differ. I have also seen some recent plans for experiments using radio waves.

Re: Bojan, you keep telling me about these guys you know? I don't care.
The first link you sent regarding experimental proof of EM and gravity makes no mention of lensing?

The next link, the lensing simulator you sent, is exactly where i am struggling... It uses 1 solar mass at 1 parsec.

With SagA i have 2.6 million solar masses at say 8,000 parsecs.

On one hand we herald the proof of g-lenses as:
http://en.wikipedia.org/wiki/Gravita..._lense#History
Quote:
According to general relativity, mass "warps" space-time to create gravitational fields and therefore bend light as a result. This theory was confirmed in 1919 during a solar eclipse, when Arthur Eddington observed the light from stars passing close to the sun was slightly bent, so that stars appeared slightly out of position.
But now SJ is saying i cannot use the same physics to predict and measure the lensing of an object with 2.6 Million solar masses.... the black hole at SagA*

I don't get how:
1) We can use eddington's measurements as confirmation of GR, by bending of light around the sun (1 solar mass)

but

2) I cannot use the absence of bending of light around a 2.7 Million solar mass body as disproof?

Which one is it?

I don't think this is cherry picking observations, this was a 10 year observational program using sophisticated equipment, it was simply not possible to take these measurements in the past... This data does not come around everyday.

I seriously doubt how eddington was able to achieve such a highly accurate confirmation of GR. (note this is still heralded as the proof!)

Here is an interesting read on the modern interpretations of the history:
http://www.newtonphysics.on.ca/eclipse/index.html
Quote:
According to Einstein's general theory of relativity published in 1916, light coming from a star far away from the Earth and passing near the Sun will be deflected by the Sun’s gravitational field by an amount that is inversely proportional to the star’s radial distance from the Sun (1.745'' at the Sun's limb). This amount (dubbed the full deflection) is twice the one predicted by Einstein in 1908(16) and in 1911(17) using Newton's gravitational law (half deflection). In 1911, Einstein wrote: A ray of light going past the Sun would accordingly undergo deflexion to an amount of 4´ 10-6 = 0.83 seconds of arc. Let us note that Einstein did not clearly explain which fundamental principle of physics used in the 1911 paper and giving the erroneous deflection of 0.83 seconds of arc was wrong, so that he had to change his mind and predict a deflection twice as large in 1916.
In order to test which theory is right (if any), an expedition led by Eddington was sent to Sobral and Principe for the eclipse of May 29, 1919(18). The purpose was to determine whether or not there is a deflection of light by the Sun's gravitational field and if there is, which of the two theories mentioned above it follows. The expedition was claimed to be successful in proving Einstein's full deflection(18,19). This test was crucial to the general approval that Einstein's general theory of relativity enjoys nowadays.
However, this experimental result is not in accordance with mass-energy conservation(14) . This was not a real problem in those years, as we will show that the deflection was certainly not measurable. We will see that the effect of the atmospheric turbulence was much larger than the full deflection, just like the Airy disk. We will also see how the instruments could not possibly give such a precise measurement and how the stars distribution was not good enough for such a measurement to be convincing or even measurable. Finally, we will discuss how Eddington's influence worked for Einstein's full displacement and against any other possible result.
Any layman should be able to understand a good theory. That simulator is a good example, but when i hold it up to the sky it just don't work.

Which is what i'm trying to explore here with SJ... still struggling with it.

I don't get how a distributed cluster of galaxies can form a spherical lense, but a concentrated super massive BH at 2.7 million solar masses cannot, when the proof we have used to confirm GR is 1 solar mass.

I hope you see the logical contradictions here.

What would be really interesting is a similar paper on the SAME observational data using the interpretation SJ is familiar with. SJ if you have this i'm all ears.

It seems as far as SJ is concerned that 1 solar mass simulator is trash?

Best
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  #24  
Old 27-04-2010, 10:54 AM
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Quote:
Originally Posted by Jarvamundo View Post
Re: Bojan, you keep telling me about these guys you know? I don't care..
Well, you do not have to.

Quote:
Originally Posted by Jarvamundo View Post
Re: Bojan, you keep telling me about these guys you know? I don't care.
The first link you sent regarding experimental proof of EM and gravity makes no mention of lensing?
It mentions the gravity and effects on EM.
The result of this experiment must be taken into account when considering lensing as well - meaning, this guy's interpenetration must explain it as well.

Quote:
Originally Posted by Jarvamundo View Post
I don't think this is cherry picking observations, this was a 10 year observational program using sophisticated equipment, it was simply not possible to take these measurements in the past... This data does not come around everyday.
I think it is exactly this (based on all I know and what my mates are telling me.. and I tend to believe them, and not you and this Don Quixote de la Goddard space flight center)...

Did you do those measurements yourself?

Last edited by bojan; 27-04-2010 at 11:11 AM.
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  #25  
Old 27-04-2010, 11:13 AM
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Quote:
On one hand we herald the proof of g-lenses as:
http://en.wikipedia.org/wiki/Gravita..._lense#History

Quote:
According to general relativity, mass "warps" space-time to create gravitational fields and therefore bend light as a result. This theory was confirmed in 1919 during a solar eclipse, when Arthur Eddington observed the light from stars passing close to the sun was slightly bent, so that stars appeared slightly out of position.
But now SJ is saying i cannot use the same physics to predict and measure the lensing of an object with 2.6 Million solar masses.... the black hole at SagA*
Hold your horses. The Sun does not have an external event horizon so you cannot equate the Eddington experiment to black holes.

Black holes are very effective at bending light if their event horizons are close to their centres or singulariites. A one solar mass black hole will bend light far more noticeably than our Sun or a one million solar mass black hole.

The radius of the event horizon (Schwarzchild radius R) is

R= 2MG/c^2.

So as you increase mass M the event horizon radius R increases. The radius of a one million solar mass BH is one million times larger than the radius of a one solar mass BH. The larger the radius the less space time curves at the horizon.

Regards

Steven
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  #26  
Old 27-04-2010, 11:14 AM
Jarvamundo (Alex)
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Re: Bojan

I do not question your personal affinity with your mates. I certainly make no claim to any personal connection with this papers author.

but again we are straying from the science.

I still don't see how eddington has proved GR with 1 solar mass, when i can't use 2,700,000 solar masses to find a significant result?

But then we can use a cluster of irregularly shaped galaxy cluster to produce a spherically lensed image?

Eddington says a 1 sun did it
SJ says a 2,700,000 sun BH wont do it
Apparantly a group of BHs can combine powers

I do not care (in a sincerely respectful way) about the personal relationships you continue to invoke, the logic does not line up for me.
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  #27  
Old 27-04-2010, 12:02 PM
Jarvamundo (Alex)
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Quote:
Originally Posted by sjastro View Post
Hold your horses. The Sun does not have an external event horizon so you cannot equate the Eddington experiment to black holes.

Black holes are very effective at bending light if their event horizons are close to their centres or singulariites. A one solar mass black hole will bend light far more noticeably than our Sun or a one million solar mass black hole.

The radius of the event horizon (Schwarzchild radius R) is

R= 2MG/c^2.

So as you increase mass M the event horizon radius R increases. The radius of a one million solar mass BH is one million times larger than the radius of a one solar mass BH. The larger the radius the less space time curves at the horizon.

Regards

Steven
Thanks SJ, I'm starting to piece together the illogical geometric picture a Schwardschild Black Hole Lense creates... This is not what the gravitational lense simulators show.

To me it seems to be violating all geometry i am familiar with in all aspects of empirics... generally the inverse square root law, which is apparent is nearly all nature .... hmm...

I think we are starting to get somewhere atleast with trying to describe Schwartschld characteristics.

What we are saying is that a Schwardschild black hole lense IS NOT the same as a gravitational lense?

So the bigger a black hole gets, the sharper the gradient of lensing?

From this:

1) Should we not see these stars disappearing as they pass behind SagA*? As they are 'blocked out' by the sharp event horizon.

This would be the only way to directly confirm a black hole exists?

2) Gaussian curvature of light for a large Schwartzchild black hole is not as applicable, as that of as the gaussian curve of a large gravitational body.

a Schwartzchild Geometrical Curvature picture:
small black hole: ````\__/````
large black hole: ```|_____|```

It seems the r in the Schwartzchild solution is not the same as the r in the GR gravitational lense solutions? Although it's used when considering gravitational effects of orbiting stars...

On one hand we use r to determine curvature of spacetime and the orbits of stars
Then on the other we can't use r to determine the curvature that would effect light

It seems Schwartzchild BH's get their own special set of rules.
puzzling

Why on one hand do we use the gravitation field of the black hole to explain the orbits of those stars.
But on the other... the spacetime curvature is non existent beyond a SMBH horizon, and does not lense.

It's like it's the curvature exists for determining orbits, but does not exist for lensing.... its a contradiction.

Last edited by Jarvamundo; 27-04-2010 at 01:30 PM.
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  #28  
Old 27-04-2010, 03:24 PM
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Quote:
Originally Posted by Jarvamundo View Post
Thanks SJ, I'm starting to piece together the illogical geometric picture a Schwardschild Black Hole Lense creates... This is not what the gravitational lense simulators show.

To me it seems to be violating all geometry i am familiar with in all aspects of empirics... generally the inverse square root law, which is apparent is nearly all nature .... hmm...

I think we are starting to get somewhere atleast with trying to describe Schwartschld characteristics.

What we are saying is that a Schwardschild black hole lense IS NOT the same as a gravitational lense?
The same principles apply. The only difference is that we can observe the bending of light as close as the limb of a star or galaxy(s). For BHs this is the event horizon. Bending of light occurs inside the horizon, unfortunately we cannot observe it.

Quote:
So the bigger a black hole gets, the sharper the gradient of lensing?

From this:

1) Should we not see these stars disappearing as they pass behind SagA*? As they are 'blocked out' by the sharp event horizon.

This would be the only way to directly confirm a black hole exists?
The BH's mass is confirmed by the Keplerian orbits of nearby stars. If the orbiting stars are in the same plane as the accretion disk of the BH then probably we would not be able define a sharp horizon. If the orbits are not in the same plane the event horizon would "eclipse" the stars relative to our frame of reference.

Quote:
2) Gaussian curvature of light for a large Schwartzchild black hole is not as applicable, as that of as the gaussian curve of a large gravitational body.

a Schwartzchild Geometrical Curvature picture:
small black hole: ````\__/````
large black hole: ```|_____|```
The Gaussian curvature is dependant on the density of an object rather than its mass.
Hence the curvature around a one solar mass star is nearly flat where as the curvature around a one solar mass BH is extreme. The curvature of a supermassive BH is also extreme as we get closer to the centre. We can't observe the effects however due to the event horizon.

Quote:
It seems the r in the Schwartzchild solution is not the same as the r in the GR gravitational lense solutions? Although it's used when considering gravitational effects of orbiting stars...

On one hand we use r to determine curvature of spacetime and the orbits of stars
Then on the other we can't use r to determine the curvature that would effect light

It seems Schwartzchild BH's get their own special set of rules.
puzzling
Nothing unusual at all.
The GR equation for the bending the light has the R value equal to the radius of the star, for BHs R is the event horizon radius.

I'm taking a break from this thread.

Regards

Steven
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  #29  
Old 27-04-2010, 04:57 PM
Jarvamundo (Alex)
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I'm still seeing contradictions, will explore Schwartzchild solutions... How an event horizon can pop into existence and change spacetime in a different way to GR mass puzzles me no end.

cheers mate, thanks for your input...
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