Doubts about GR (split from Exclusive: Grave doubts over LIGO’s discovery of gravitational waves)

[Q-reeus]

11 hours ago, swansont said:

... Electromagnetic waves do not need a physical medium in order to propagate. Why would gravitational waves? ...

Well within GR paradigm GW's are nothing other than purely spacetime ripples. The better analogy then is one between sound waves and GW's. Both are distortions of a medium, and not something else propagating on top of or through the medium. Anyway there is a logical issue with GR's take on GW's as pure transverse spacetime distortions.
Given GW's carry away energy and momentum, they should also self-gravitate like all other forms of energy-momentum-stress do within GR.
But by definition, the vacuum gravitational field - both static and dynamic i.e. GW's, is NOT a source of further gravity in GR. Hence a self-consistency issue exists - there is an overall loss of gravitating mass when a binary BH or NS merger sheds GW's. That portion converted to GW's no longer gravitates.

In some other gravity theories, there is no such dilemma. For instance, Svidzinsky's Vector Theory of Gravity posits GW's are comprised of quanta - gravitons. Propagating on a notionally flat background metric. In that scenario gravitons self-gravitate similar to photons do.

[beecee]

1 hour ago, Q-reeus said:

Well within GR paradigm GW's are nothing other than purely spacetime ripples. The better analogy then is one between sound waves and GW's. Both are distortions of a medium, and not something else propagating on top of or through the medium.

Perhaps he [the person Swansont was replying to] is referring to what could be called a "physical medium" or ether...Spacetime as real as I believe it is, is certainly not physical and certainly gravitational radiation is simply ripples in that same spacetime. 

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Anyway there is a logical issue with GR's take on GW's as pure transverse spacetime distortions.
Given GW's carry away energy and momentum, they should also self-gravitate like all other forms of energy-momentum-stress do within GR.
But by definition, the vacuum gravitational field - both static and dynamic i.e. GW's, is NOT a source of further gravity in GR. Hence a self-consistency issue exists - there is an overall loss of gravitating mass when a binary BH or NS merger sheds GW's. That portion converted to GW's no longer gravitates.

Gravitational waves are spacetime....gravity is geometry...why would geometry of spacetime need to create more geometry?  Doesn't make sense to me. Plus of course this gravitational wave/radiation that emenates from a particular mass, will affect all other masses that it passes through.eg: the aLIGO arms responsible for the discovery. Not sure any real issue exists within GR.

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In some other gravity theories, there is no such dilemma. For instance, Svidzinsky's Vector Theory of Gravity posits GW's are comprised of quanta - gravitons. Propagating on a notionally flat background metric. In that scenario gravitons self-gravitate similar to photons do.

As mentioned previously, that issue is already being looked at by the professionals in that arena, both associated with aLIGO and separated from them, and looked at I would add  impartially and fairly. I mean with all the young up and comers in the discipline, who would not like to improve and/or extend on the great man's theory and be in line for a Nobel. Gravitons of course are still only hypothetical, so I'm not sure how it can be raised to support any alternate gravity hypothetical.

 

Edited November 28, 2018 by beecee

[Q-reeus]

30 minutes ago, beecee said:

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Perhaps he is referring to what could be called a "physical medium"...Spacetime as real as I believe it is, is certainly not physical and certainly is ripples in that same spacetime.

?? Perhaps reword that bit as it makes no coherent sense.

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Gravitational waves are spacetime....gravity is geometry...why would geometry of spacetime need to create more geometry. Doesn't make sense to me.

Either you understand my earlier point re lack of universality within GR of stress-energy-momentum as source of gravitation, and it's consequences, or you don't.

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Doesn't make sense to me.

Doesn't have to. Some folks here do understand that there is a supposedly universally valid continuity law within GR, div T_μν = 0. Well that law certainly fails outside of its differential form when GW emissions enter the picture. As per that pointed out earlier.

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 Plus of course this gravitational wave/radiation that emenates from a particular mass, will affect all other masses that it passes through.eg: the aLIGO arms responsible for the discovery.

And? A moot point not relevant to above.

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As mentioned previously, that issue is already being looked at by the professionals in that arena, both associated with aLIGO and separated from them, and looked at I would add  impartially and fairly. I mean with all the young up and comers in the discipline, who would not like to improve and/or extend on the great man's theory and be in line for a Nobel.

I sure hope it's without any fear or favour. And, once again, I don't have all my eggs in one basket. I consider at this stage Vector Gravity has many points favouring it over GR, but make no firm endorsement of it. Similarly re Yilmaz gravity. The final decider will be Nature. Once all the expected many challenges and criticisms are resolved. How long that will take is anybody's guess.

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Gravitons of course are still only hypothetical, so I'm not sure how it can be raised to support any alternate gravity hypothetical.

You obviously fail to grasp the context of my earlier statement on that. Gravitons are a fundamental tenet of that theory, not a hypothesized modification as is the case in GR. Hence that gravitons propagating within a notionally fixed background will self-gravitate is a consistent and inherent feature of that theory. Got that?

 

 

Edited November 28, 2018 by Q-reeus

[beecee]

7 minutes ago, Q-reeus said:

?? Perhaps reword that bit as it makes no coherent sense.

?? It makes as much sense as saying a magnetic field is real..... 

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Either you understand my earlier point re lack of universality within GR of stress-energy-momentum as source of gravitation, and it's consequences, or you don't.

I understand enough to realise and understand that at this time GR GW's have been discovered 6...or is that now 7 times? And that is the accepted mainstream position at this time.

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I sure hope it's without any fear or favour. And, once again, I don't have all my eggs in one basket. I consider at this stage Vector Gravity has many points favouring it over GR, but make no firm endorsement of it. Similarly re Yilmaz gravity. The final decider will be Nature. Once all the expected many challenges and criticisms are resolved. How long that will take is anybody's guess

Without fear or favour, the final result will be as usual, observational science, and my money's still on GR for a while yet.

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You obviously fail to grasp the context of my earlier statement on that. Gravitons are a fundamental tenet of that theory, not a hypothesized modification as is the case in GR. Hence that gravitons propagating within a notionally fixed background will self-gravitate is a consistent and inherent feature of that theory. Got that?

I grasp enough to know that gravitons have yet to be verified and/or observed, and whether it is a tenet of that "theory" or not, that "theory" as yet is not the accepted mainstream position, and like the many theories of gravity, are somewhat at this time, more a novelty. But hey! If things change, I'll be the first to congratulate the scientists involved.

[beecee]

2 hours ago, Q-reeus said:

And? A moot point not relevant to above.

Of course its relevant...GW's are ripples in spacetime, and the troughs and crests in those ripples affect all mass that experiences it...as per the aLIGO arms.

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You obviously fail to grasp the context of my earlier statement on that. Gravitons are a fundamental tenet of that theory, not a hypothesized modification as is the case in GR. Hence that gravitons propagating within a notionally fixed background will self-gravitate is a consistent and inherent feature of that theory. Got that?

While already commenting on that, It's interesting to note that gravity/spacetime curvature is non linear, so gravity makes gravity so to speak. 

Edited November 28, 2018 by beecee

[Q-reeus]

31 minutes ago, beecee said:

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Of course its relevant...GW's are ripples in spacetime, and the troughs and crests in those ripples affect all mass that experiences it...as per the aLIGO arms.

No, still not relevant to what was at stake. Which is the issue of self-gravitation of GW's or rather lack thereof in GR.

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While already commenting on that, It's interesting to note that gravity/spacetime curvature is non linear, so gravity makes gravity so to speak.

'So to speak'? Umm...actually gravity does NOT make gravity within GR. There is nonlinear interactions but that is not synonymous with 'making more gravity'. Notwithstanding various online articles erroneously claiming otherwise. Here, check out this Wikipedia article re definition of what constitutes source terms in RHS of EFE's:
https://en.wikipedia.org/wiki/Stress–energy_tensor
First para there makes it clear only non-gravitational stress-energy-momentum is a source for gravitation. Later there, the notion of pseudo tensor formulations that claim to give GW's etc a sort of well defined source density are given some space. Fact is any attempt to circumvent the founding definition - that excludes gravitational curvature as source - is actually a sneaky reformulation of GR as something other than 'pure GR'. It's the kind of thing that is inevitable when sticking tenaciously to a theory that has inherent consistency issues.

 

[Strange]

6 hours ago, Q-reeus said:

But by definition, the vacuum gravitational field - both static and dynamic i.e. GW's, is NOT a source of further gravity in GR.

Are you sure? They have energy and so must be a source of gravitation. My understanding is that this self-gravitation is a cause of the non-linearity that makes GR so complex, mathematically. 

[beecee]

2 hours ago, Q-reeus said:

No, still not relevant to what was at stake. Which is the issue of self-gravitation of GW's or rather lack thereof in GR.

Of course it is, and you have yet to show it isn't, other then denial...

https://en.wikipedia.org/wiki/Self-gravitation"Self-gravity is the gravitational force exerted on a body, or a group of bodies, by the body(ies) that allows it/them to be held together".

Again gravitational radiation is simply ripples in spacetime and any effect that we feel as gravity is just geometrical spacetime that is curved, warped in the presence of mass/energy, or anything other then flat. So again, the troughs and crests that gravitational radiation exhibits in those ripples, which are caused by astronomical massive asymetric  collisions or mergers, affect all other mass that experiences it...as per the aLIGO arms.

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So to speak'? Umm...actually gravity does NOT make gravity within GR. There is nonlinear interactions but that is not synonymous with 'making more gravity'

 No it is synonymous with making gravity and non linearity...In fact GR is said to be non linear.......http://www.einstein-online.info/spotlights/gravity_of_gravity.html "One reason why the physics of general relativity is much more difficult than that of Newton's theory of gravity or the theory of electrodynamicsis a property called non-linearity. In short, gravity can beget further gravity - where gravitational systems are concerned, the whole is not the sum of its parts."

In fact I once argued that point on another forum and had expert E-Mail replies from professionals that also supported that position. 

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Notwithstanding various online articles erroneously claiming otherwise. 

And other professionals also? No, obviously the non linearity of gravity is as most interpret it, including my above link, not withstanding your take on it.

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is actually a sneaky reformulation of GR as something other than 'pure GR'. It's the kind of thing that is inevitable when sticking tenaciously to a theory that has inherent consistency issues.

 

As I have attempted to explain to you in another thread, any new hypothetical must need to run the gauntlet, just as GR has, and while GR matches exactly what we observe, and makes predictions, that are continually verified, as per GW's, then it will always be hard to overthrow, until and unless it is shown to be invalid, or the new kid on the block predicts more.....That's science, that's the scientific methodology, and has far more going for it that any half arsed seemingly conspiracy jibe, or some unnecessary recalcitrance claim, on the part of mainstream and particularly GR.

And if that happens, if,  it won't be first announced on forums such as this, or claims by members of I told you so, that was stupidly trotted out when the BICEP2 error came to light, it will be science, and probably aLIGO or VIRGO at the forefront of such science. In the meantime, GR reigns supreme as our model of how the universe plays out.

https://www.researchgate.net/post/Why_is_GR_highly_non_linear_while_electrostatic_interactions_are_linear_even_in_the_comparatively_stronger_electric_force_limit

Gerard t Hooft

Utrecht University

"I think there was some confusion here because in the discussion it should have been stated clearly what is a linear function of what. Secondly, we are talking of mathematical models of physics; if we add all the dirty side effects nothing is linear anymore. In Maxwell's theory, the em fields are linear functions of the charged sources and currents that are around, but if you take into account that these sources back react, then the combined equations become non-linear.

Only in this sense, the question posed is a meaningful one: if we keep the sources and currents fixed, then our mathematical models say that the em fields are linear but the gravity fields are not.

In mathematical terms, this can be explained by the fact that the local gauge group in electromagnetism is Abelian (i.e. the effect of two consecutive gauge transformations does not depend on the order) while in gravity it is non-Abelian (the effect of two consecutive curved coordinate transformations does depend on the order). Physically, this means that gravity carries energy and momentum (although this depends on the curved coordinates chosen), so gravity generates gravity, while em fields are electrically neutral.

All of this did not require the consideration of quantum mechanics. In ordinary quantum mechanics, what I say above is still valid. But now, even the vacuum has vacuum fluctuations of charged particles and they cause non-linearities in light when you include the back reaction of the vacuum".

http://www.staff.science.uu.nl/~hooft101/gravitating_misconceptions.html

Edited November 28, 2018 by beecee

[Q-reeus]

39 minutes ago, Strange said:

Are you sure? They have energy and so must be a source of gravitation. My understanding is that this self-gravitation is a cause of the non-linearity that makes GR so complex, mathematically. 

Strange - what was not clear in my previous posts? You can easily check for yourself that RHS of EFE's, the SET or SEMT, specifically excludes gravitation as source term(s).
To repeat from my last post - that limitation is routinely circumvented via pseudo tensor formulations that of necessity violate the original formulation. Which basically makes a clean statement:
Effect i.e.spacetime curvature (LHS) = cause i.e. non-gravitational stress-energy-momentum density (RHS).
That's a founding physical statement defining GR. Sure mathematically one can move LHS curvature terms to RHS and make them into a source, but doing so violates the foundational physical meaning of the standard formulation. One of necessity, to 'make gravity gravitate' means removing curvature terms from the LHS over to RHS. Requiring source to produce a reduced set of effect - curvature terms. Where is the fundamental coherency in doing that?
As I wrote, it's an inconsistent situation owing to the original aesthetic choice of AE to make gravity to be purely spacetime curvature. I can certainly back my pov via links to other articles, but where has my earlier posting, which this recapitulates, not been clear to you?

[beecee]

Here is another answer from https://www.researchgate.net/post/Why_is_GR_highly_non_linear_while_electrostatic_interactions_are_linear_even_in_the_comparatively_stronger_electric_force_limit  That re-enforces Professor Gerard t Hooft reply, and adds more legitimate corrections  to some other unsupported statements made in this thread.......

Matts Roos

University of Helsinki

"As Gerard said (and Stam implied) gravity generates gravity, But gravitons are hypothetical particles which need both the classical gravitational field and quantum mechanics for their description. Such a theoretical description is lacking, no astrophysical effect is known which needs it, thus it is premature to speculate about the interactions of gravitons."

Edited November 28, 2018 by beecee

[Q-reeus]

2 hours ago, beecee said:

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Of course it is, and you have yet to show it isn't, other then denial...

https://en.wikipedia.org/wiki/Self-gravitation"Self-gravity is the gravitational force exerted on a body, or a group of bodies, by the body(ies) that allows it/them to be held together".

 

Oh my. I made a slight technical error in using 'self' together with gravitating. Try and deal with my clear intended usage instead of pressing a technical definition.

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Again gravitational radiation is simply ripples in spacetime and any effect that we feel as gravity is just geometrical spacetime that is curved, warped in the presence of mass/energy, or anything other then flat. So again, the troughs and crests that gravitational radiation exhibits in those ripples, which are caused by astronomical massive asymetric  collisions or mergers, affect all other mass that experiences it...as per the aLIGO arms.

You insist on repeating something earlier dispatched as an irrelevancy. And that in red is another meaningless, disjoint statement.
 

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No it is synonymous with making gravity and non linearity...In fact GR is said to be non linear.......http://www.einstein-online.info/spotlights/gravity_of_gravity.html "One reason why the physics of general relativity is much more difficult than that of Newton's theory of gravity or the theory of electrodynamicsis a property called non-linearity. In short, gravity can beget further gravity - where gravitational systems are concerned, the whole is not the sum of its parts."

In fact I once argued that point on another forum and had expert E-Mail replies from professionals that also supported that position. 

 

An example imo of an erroneous online source. And as you may recall from that other forum, when I confronted that author he admitted his position was not fully self-consistent.

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And other professionals also? No, obviously the non linearity of gravity is as most interpret it, including my above link, not withstanding your take on it.

You always did rely on quote mining and a show of hands as determinant of truth. Which approach and outlook I don't subscribe to.

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As I have attempted to explain to you in another thread, any new hypothetical must need to run the gauntlet, just as GR has, and while GR matches exactly what we observe, and makes predictions, that are continually verified, as per GW's, then it will always be hard to overthrow, until and unless it is shown to be invalid, or the new kid on the block predicts more.....That's science, that's the scientific methodology, and has far more going for it that any half arsed seemingly conspiracy jibe, or some unnecessary recalcitrance claim, on the part of mainstream and particularly GR.

And if that happens, if,  it won't be first announced on forums such as this, or claims by members of I told you so, that was stupidly trotted out when the BICEP2 error came to light, it will be science, and probably aLIGO or VIRGO at the forefront of such science. In the meantime, GR reigns supreme as our model of how the universe plays out.

https://www.researchgate.net/post/Why_is_GR_highly_non_linear_while_electrostatic_interactions_are_linear_even_in_the_comparatively_stronger_electric_force_limit

Gerard t Hooft

Utrecht University

"I think there was some confusion here because in the discussion it should have been stated clearly what is a linear function of what. Secondly, we are talking of mathematical models of physics; if we add all the dirty side effects nothing is linear anymore. In Maxwell's theory, the em fields are linear functions of the charged sources and currents that are around, but if you take into account that these sources back react, then the combined equations become non-linear.

Only in this sense, the question posed is a meaningful one: if we keep the sources and currents fixed, then our mathematical models say that the em fields are linear but the gravity fields are not.

In mathematical terms, this can be explained by the fact that the local gauge group in electromagnetism is Abelian (i.e. the effect of two consecutive gauge transformations does not depend on the order) while in gravity it is non-Abelian (the effect of two consecutive curved coordinate transformations does depend on the order). Physically, this means that gravity carries energy and momentum (although this depends on the curved coordinates chosen), so gravity generates gravity, while em fields are electrically neutral.

All of this did not require the consideration of quantum mechanics. In ordinary quantum mechanics, what I say above is still valid. But now, even the vacuum has vacuum fluctuations of charged particles and they cause non-linearities in light when you include the back reaction of the vacuum".

http://www.staff.science.uu.nl/~hooft101/gravitating_misconceptions.html

 

 

Yes one can go on quoting authorities to bolster a particular pov. That is of course just appeal to authority - as substitute for personally having a clear understanding.

You should also recall from that other forum where I linked to someone who gave a somewhat detailed defense for why gravity does NOT gravitate in GR:
https://www.physicsforums.com/insights/does-gravity-gravitate/
Which analysis is imo rigorously logical. And respects the meaning of the very definition of EFE's.
Later in that series he then proceeds to argues that, contrary to what he shows in above linked, GW's can be made to gravitate. By the process of swapping over from LHS to RHS. Which imo is logically inconsistent with his above. Again - I never slavishly follow authority figures.
Best to actually think things through for oneself. If you can of course. Your quasi-religious devotion to GR and its creator is well known in that other forum.
PS - above will suffice to cover your later quote-mining post.

 

Edited November 28, 2018 by Q-reeus
amend link

[swansont]

9 hours ago, Q-reeus said:

Well within GR paradigm GW's are nothing other than purely spacetime ripples. The better analogy then is one between sound waves and GW's. Both are distortions of a medium, and not something else propagating on top of or through the medium. Anyway there is a logical issue with GR's take on GW's as pure transverse spacetime distortions.

That assumes that spacetime is a physical medium, rather than a geometry. That's a huge assumption.

9 hours ago, Q-reeus said:

Given GW's carry away energy and momentum, they should also self-gravitate like all other forms of energy-momentum-stress do within GR.

Is that a prediction of GR?

9 hours ago, Q-reeus said:

But by definition, the vacuum gravitational field - both static and dynamic i.e. GW's, is NOT a source of further gravity in GR.

The energy already exists, so why would there be further gravity? The conclusion of the events is that mass is reduced, significantly, and that energy is what is contained in the GWs. So there is no "further gravity" since there is no additional energy.

9 hours ago, Q-reeus said:

Hence a self-consistency issue exists - there is an overall loss of gravitating mass when a binary BH or NS merger sheds GW's. That portion converted to GW's no longer gravitates.

Do you have a source that confirms this?

Even if it's the case, I don't see what the self-consistency issue is. There is no conservation of gravity.

9 hours ago, Q-reeus said:

In some other gravity theories, there is no such dilemma. For instance, Svidzinsky's Vector Theory of Gravity posits GW's are comprised of quanta - gravitons. Propagating on a notionally flat background metric. In that scenario gravitons self-gravitate similar to photons do.

Then one needs to see where the theories differ and devise an experiment that differentiates the two. Meanwhile, the signals that have been detected by LIGO are consistent with the predictions of GR.

[Q-reeus]

1 hour ago, swansont said:

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That assumes that spacetime is a physical medium, rather than a geometry. That's a huge assumption.

You disagree that acoustic waves as propagating distortions in a medium is a better analogy with GW's than photons propagating through an absolute vacuum? Bare in mind we are here merely asking 'what is the most obvious analog to GW's' - from purely within GR framework? Imposing e.g. Lorentz invariance on any such 'aether' is separate consideration.

How would you reconcile energy momentum in a GW with 'pure geometry' if the latter is nothing more than a way of relating distortions of clocks and rulers? On an historical note, AE himself, on pondering the different implications of GR vs SR, back-pedalled wrt his earlier total dismissal of existence of any kind of aether - see e.g 13th para and further on here:
http://www-history.mcs.st-andrews.ac.uk/Extras/Einstein_ether.html
"More careful reflection teaches us however, that the special theory of relativity does not compel us to deny ether. We may assume the existence of an ether; only we must give up ascribing a definite state of motion to it, i.e. we must by abstraction take from it the last mechanical characteristic which Lorentz had still left it. We shall see later that this point of view, the conceivability of which I shall at once endeavour to make more intelligible by a somewhat halting comparison, is justified by the results of the general theory of relativity."

One cannot imo achieve self-consistency within GR's insistence gravitation is pure spacetime curvature. As my previous posts argue.

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Is that a prediction of GR?

See my previous response to beecee - especially link to PeterDonis's Insights article: https://www.physicsforums.com/insights/does-gravity-gravitate/

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The energy already exists, so why would there be further gravity? The conclusion of the events is that mass is reduced, significantly, and that energy is what is contained in the GWs. So there is no "further gravity" since there is no additional energy.

You have misunderstood my basic argument it seems. Have a closer re-read. What should be conserved, in accordance with divT_μν = 0, is conservation of NET gravitating source - inclusive of GW emissions. I hope we don't go around in circles here.
 

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Do you have a source that confirms this?

Even if it's the case, I don't see what the self-consistency issue is. There is no conservation of gravity.

 

See above. In particular, please point out specifically any disagreement you may have with the analysis and finding gravity does not gravitate in that article already linked to:
https://www.physicsforums.com/insights/does-gravity-gravitate/

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Then one needs to see where the theories differ and devise an experiment that differentiates the two. Meanwhile, the signals that have been detected by LIGO are consistent with the predictions of GR.

See my contributions in Vector theory of Gravity thread, beginning here:

The matter is currently in dispute and not likely to be resolved real soon.

 

[Strange]

1 hour ago, Q-reeus said:

You disagree that acoustic waves as propagating distortions in a medium is a better analogy with GW's than photons propagating through an absolute vacuum?

Gravitational waves and light waves are both propagating in a field not a medium. (I assume a medium means something material)

1 hour ago, Q-reeus said:

See above. In particular, please point out specifically any disagreement you may have with the analysis and finding gravity does not gravitate in that article already linked to:
https://www.physicsforums.com/insights/does-gravity-gravitate/

Although that series of articles start by saying that gravity does not gravitate, it then goes on to explain all the ways in which it can be considered that it does. 

 

[Q-reeus]

31 minutes ago, Strange said:

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Gravitational waves and light waves are both propagating in a field not a medium. (I assume a medium means something material)

If by field you mean a notionally flat background Minkowski 4D spacetime manifold as 'field', I suppose. But then, both GW's and light waves are themselves fields, so what meaning exactly to 'fields propagating within fields'? And I already explained via quote from AE's 1922 Leyden lecture, that one is drawn to the position spacetime itself has to take on some kind of ether/aether 'medium' character. Not a material medium, owing to requirement of Lorentz invariance, but having the similarity of being a disturbance OF that medium - not something else propagating within it. Well that's what GR implies. One that imo cannot be fully consistent with GR's founding definition in EFE's. Unless one thinks non-gravitating GW energy-momentum can be self-consistent with divT_μν = 0 (to repeat yet again).

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Although that series of articles start by saying that gravity does not gravitate, it then goes on to explain all the ways in which it can be considered that it does.

 See above. The gravity as gravitons on flat background = gravity gravitates argument later there is btw a half-way house to Yilmaz gravity, or, with a radical rejection that gravitons must be spin-2, to Svidzinsky's Vector Gravity. Both the latter theories insist, in different ways, something other than pure spacetime curvature is needed for self-consistency. Again, since you have evidently taken over from swansont in responding, I will ask you to point to any logical error in PeterDonis original article - that part dealing strictly with classical GR. Which is what we are supposed to be dealing with. Yes? If you agree he makes no error there, how is subsequently making GW's self-gravitate also self-consistent? I maintain it is not.

 

 

[swansont]

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You disagree that acoustic waves as propagating distortions in a medium is a better analogy with GW's than photons propagating through an absolute vacuum? Bare in mind we are here merely asking 'what is the most obvious analog to GW's' - from purely within GR framework?

Yes. What in GR is analogous to atoms and molecules?

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Imposing e.g. Lorentz invariance on any such 'aether' is separate consideration.

Why? That poses obvious shortcomings to any analogy.

 

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See my previous response to beecee - especially link to PeterDonis's Insights article:

Looks to me that he's saying that gravity is not included as a source term in the EFE.

we write the EFE the way we do in order to ensure automatic conservation of the “source”, and that way of writing the EFE requires the “source” to only include fields other than gravity.

But then goes on to say that it does, indeed contribute, and it's a matter of how the equations are broken down.

 

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See above. In particular, please point out specifically any disagreement you may have with the analysis and finding gravity does not gravitate in that article already linked to:
https://www.physicsforums.com/insights/does-gravity-gravitate/

My disagreement is that the conclusion of that article is that gravity does gravitate. IOW, I disagree with your assessment, not with the article.

 

A request: please learn how to use the editor.

With the cursor at the end of the material you want to respond to, hit return a few times, and you should get a cursor outside of the quote box. That way, your response is not buried inside of someone else's quote, and can then be more easily quoted and attributed.

[Q-reeus]

1 hour ago, swansont said:

Yes. What in GR is analogous to atoms and molecules?

Incorrect comparison. 'Atoms and molecules' would be appropriate analog to a quantized extension of GR - so-called quantum gravity aka quantized spacetime, with GR as 'emergent' classical limit. Instead, stick to what should be the obvious appropriate analog to classical GR spacetime - a continuum elastic 'medium'.

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Why? That poses obvious shortcomings to any analogy.

So explain how your example of photons propagating in vacuum, better captures the essence of GR's picture of GW's as purely propagating ripples OF spacetime WITHIN spacetime, than acoustic wave analogy does. All analogies have limitations. Some are better for the intended purpose than others.

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Looks to me that he's saying that gravity is not included as a source term in the EFE.

we write the EFE the way we do in order to ensure automatic conservation of the “source”, and that way of writing the EFE requires the “source” to only include fields other than gravity.

But then goes on to say that it does, indeed contribute, and it's a matter of how the equations are broken down.

 

My disagreement is that the conclusion of that article is that gravity does gravitate. IOW, I disagree with your assessment, not with the article.

You are too vague. I have differentiated between his application to classical GR, vs application to gravitons on flat background. What are YOU referring to, and where and how?

Look, the situation is not difficult to grasp. Standard GR as expressed in standard EFE's has NO room for gravity gravitating. Period. That situation is routinely skirted by redefining EFE's in a way doing violence to the originally formulated clear distinction between cause and effect. (Hypothesized quantum gravity extensions of GR involving spin-2 gravitons etc. lies outside that arena.)
Evidently you and most others here are happy with that situation. I am not. Is there any point in extending this obviously fundamental ideological impasse on further? Good night.

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A request: please learn how to use the editor.

With the cursor at the end of the material you want to respond to, hit return a few times, and you should get a cursor outside of the quote box. That way, your response is not buried inside of someone else's quote, and can then be more easily quoted and attributed.

 

Edited November 28, 2018 by Q-reeus

[Strange]

1 hour ago, Q-reeus said:

But then, both GW's and light waves are themselves fields

The waves are oscillations in the respective field, surely. 

1 hour ago, Q-reeus said:

And I already explained via quote from AE's 1922 Leyden lecture, that one is drawn to the position spacetime itself has to take on some kind of ether/aether 'medium' character. Not a material medium

As he says, not a material medium. So nothing like sound waves. I can’t see much difference between his characterisation of spacetime and, say, the electromagnetic field. 

(Sorry if I missed some of the points you have made, but it is almost impossible to read your posts, as they are all mixed up with quotes from other people)

1 hour ago, Q-reeus said:

but having the similarity of being a disturbance OF that medium

So, like light waves in the electromagnetic field then?

2 hours ago, Q-reeus said:

Well that's what GR implies. One that imo cannot be fully consistent with GR's founding definition in EFE's.

That sounds as if you are saying GR is inconsistent with GR, so I must have misunderstood. 

[swansont]

53 minutes ago, Q-reeus said:

Incorrect comparison. 'Atoms and molecules' would be appropriate analog to a quantized extension of GR - so-called quantum gravity aka quantized spacetime, with GR as 'emergent' classical limit. Instead, stick to what should be the obvious appropriate analog to classical GR spacetime - a continuum elastic 'medium'.

It's your comparison.  Air is made up of molecules.

53 minutes ago, Q-reeus said:

So explain how your example of photons propagating in vacuum, better captures the essence of GR's picture of GW's as purely propagating ripples OF spacetime WITHIN spacetime, than acoustic wave analogy does. All analogies have limitations. Some are better for the intended purpose than others.

Sorry, where did I say photons?

I said electromagnetic waves. No medium is required. It's the fluctuation of a field.

53 minutes ago, Q-reeus said:

You are too vague. I have differentiated between his application to classical GR, vs application to gravitons on flat background. What are YOU referring to, and where and how?

I am too vague? It's your reference. And in it he says that this applies both quantum mechanically and classically (as it must)

53 minutes ago, Q-reeus said:

Look, the situation is not difficult to grasp. Standard GR as expressed in standard EFE's has NO room for gravity gravitating. Period. That situation is routinely skirted by redefining EFE's in a way doing violence to the originally formulated clear distinction between cause and effect. (Hypothesized quantum gravity extensions of GR involving spin-2 gravitons etc. lies outside that arena.)

And yet you pointed to a reference that says that this is not so.

It says that there is a source term, which does not include gravity, which yields the curvature, and all of the effects of gravity self-interacting is included in the curvature (owing to the nonlinear nature of the equation). It sounds to me like it's set up that way so you don't double-count the effect of the curvature on itself.

 

[Q-reeus]

1 hour ago, Strange said:

The waves are oscillations in the respective field, surely. 

See my reply below.

1 hour ago, Strange said:

As he says, not a material medium. So nothing like sound waves. I can’t see much difference between his characterisation of spacetime and, say, the electromagnetic field. 

As per your above comment, and below, you are mixing up quantum concepts - QFT's electromagnetic field, with classical - EM waves as critters propagating in a distinctly different entity namely classical vacuum. I like to compare apples to apples.

 

1 hour ago, Strange said:

(Sorry if I missed some of the points you have made, but it is almost impossible to read your posts, as they are all mixed up with quotes from other people)

Thanks to swansont's tip last post, I now know to double press Enter key for a clean separation. I had thought using supplied " quote function was sufficient. It certainly seems sufficient in my browser view - a clear vertical bar distinguishes that quoted from my response. So sorry if that was still confusing for you and swansont.

1 hour ago, Strange said:

So, like light waves in the electromagnetic field then?

See above. Classical paradigm vs QFT paradigm. Best not mixed up imo.

1 hour ago, Strange said:

That sounds as if you are saying GR is inconsistent with GR, so I must have misunderstood. 

If you had followed my general drift that statement is more or less accurate. GR is inherently self-contradictory imo. For reasons given ad nauseum. But I refer you to the last main para in response to swansont last post of mine. Take it or leave it. Preferably leave it. When there is clear ideological commitment at play, it becomes time wasting and farcical to go on and on with intent to only point score and/or deliberately misrepresent/undermine the other side's position. Hope that is not actually happening here but looks it to me. Cheers.

 

29 minutes ago, swansont said:

It's your comparison.  Air is made up of molecules.

And? Is air an elastic medium? Does it support shear waves (umm...no) which are the nearest analog to GR's transverse GW's? Nitpicking irrelevant diversions here?

29 minutes ago, swansont said:

Sorry, where did I say photons?

My bad. Still, we do tend to think these days of EM waves as a bunch of coherent photons, no? But that goes against my admonition to keep classical and quantum concepts separated. OK.

29 minutes ago, swansont said:

I said electromagnetic waves. No medium is required. It's the fluctuation of a field.

Rrrright. And this gets back to the matter of GW's gravitating or not how exactly? Maybe if we just referred to what the standard EFE's has to say, analogues can be dispensed with.

29 minutes ago, swansont said:

I am too vague? It's your reference. And in it he says that this applies both quantum mechanically and classically (as it must)

Yes too vague. Like right there. Please - actually quote specific passages, preferably in proper context.

29 minutes ago, swansont said:

And yet you pointed to a reference that says that this is not so.

Have I? Please, again, actually quote where and how exactly. Bearing in mind my actual overall position.

29 minutes ago, swansont said:

It says that there is a source term, which does not include gravity, which yields the curvature, and all of the effects of gravity self-interacting is included in the curvature (owing to the nonlinear nature of the equation). It sounds to me like it's set up that way so you don't double-count the effect of the curvature on itself.

It may sound like it to you. To me the situation is as explained by PeterDonis - there is no room for gravity gravitating in standard GR's standard EFE's. Period. Want to keep this up? Play a game of attrition? If so, you 'win'. Right here and now. If otoh there is still genuine misunderstanding at play, it's still a case of 'this will never end happily for both sides'. So - Good night, again.

29 minutes ago, swansont said:

 

 

[MigL]

The requirement for both, a classical theory of gravity, and a quantum field theory of gravity is that it is self-coupling.

For a classical theory, like GR, stress-energy produces curvature in space-time, either static or travelling ( as in GWs ). This curvature of space-time is also a stress-energy and so, contributes to further curvature. IE gravity gravitates.

In a quantum field theory, which is the only place you would expect to find gravitons, self-coupling means gravitons interact with gravitons. IE gravity gravitates.

What exactly is the problem ?

[beecee]

9 hours ago, Q-reeus said:

Oh my. I made a slight technical error in using 'self' together with gravitating. Try and deal with my clear intended usage instead of pressing a technical definition

Don't take it too hard...that is the least of your technical errors of judgement. 

Quote

You insist on repeating something earlier dispatched as an irrelevancy. And that in red is another meaningless, disjoint statement.

I'll keep repeating it as you have done nothing, nor said anything to dispatch it as you claim. Still it looks good for the record. Your highlighted part of my statement was simply referring to flat spacetime....in other words other then  spacetime that isn't curved, warped, waved or twisted in the presence of mass,  thereby exhibiting gravity, which irrefutably shows that gravity is simply the geometry of spacetime.

Quote

An example imo of an erroneous online source. And as you may recall from that other forum, when I confronted that author he admitted his position was not fully self-consistent.

Erroneous in your opinion, which has already been shown to be in error. All my sources are reputable including the Professor t'Hooft, a Nobel prize recipient I might add. And of course there was more then one authority supporting my position, and no, I certainly do not remember any reply inferring the authoritive position as not fully consistent. 

Quote

You always did rely on quote mining and a show of hands as determinant of truth. Which approach and outlook I don't subscribe to

Quote mining?? The link with the full text is there for all to read, and always is in any point I make. Obviously you don't subscribe to your "show of hands"  particularly when that show of hands disputes and/or disagrees with your made up interpretation of GR, gravitational waves, etc, that happens to be supported by an isolated minority of hands. 

 

Quote

Yes one can go on quoting authorities to bolster a particular pov. That is of course just appeal to authority - as substitute for personally having a clear understanding.

Any appeal to authority that is appeal to authority educated and qualified in the relevant discipline under discussion, is admirable appeal to authority and totally justified, in attempting to facilitate your own understanding and the areas where you are simply wrong...and of course, most definitely yes, also to facilitate my own understanding. The usual inferences you are noted for are simply sour grapes and excuses.

Quote

You should also recall from that other forum where I linked to someone who gave a somewhat detailed defense for why gravity does NOT gravitate in GR:

My memories are pretty good for an old bloke, and once again, the bulk of references, and authoritative statements from experts and reputable links, supported the fact that gravity being non linear, means that gravity makes gravity.

 

Quote

. Again - I never slavishly follow authority figures. Best to actually think things through for oneself.

Particularly authoritative figures that just happen to refute your own amateurish opinions. While thinking things through for ones self, is an admirable quality, it is not quite as admirable to make veiled inferences and accusations about science being recalcitrant and stubbornly dishonest, when your limited ability lacking the expertise and professionalism, happens to be in conflict with the well held and justified mainstream position.

Quote

 If you can of course. Your quasi-religious devotion to GR and its creator is well known in that other forum.
PS - above will suffice to cover your later quote-mining post.

Quote

 

 

 Excuse me for laughing, but really, you must be getting desperate. My devotion as you sarcastically put it, is simply adhering and appreciating the scientific methodology, and dismissing the conspiracy nonsense in this regard that you seem obviously taken with....I mean really, it's near as stupid and foolish as the nuts that push the 9/11 and Moon Landing nonsensical conspiracies.

As per the thread I started re V4 gravity, and the other thread that discussion has taken place on, as per aLIGO and other reputable scientific people and orginisations, now considering and working through any possible anomalies with either the GR interpretations or that of the many alternative hypotheticals, all this shows your veiled accusations and  conspiracy claims, as nothing but sheer nonsense and excuses when one is not achieving what his or her agenda dictates.

 

2 hours ago, Q-reeus said:

It may sound like it to you. To me the situation is as explained by PeterDonis - there is no room for gravity gravitating in standard GR's standard EFE's. Period. Want to keep this up? Play a game of attrition? If so, you 'win'. Right here and now. If otoh there is still genuine misunderstanding at play, it's still a case of 'this will never end happily for both sides'. So - Good night, again.

If as you say, gravity is not simply geometry of spacetime, and if as you say gravity is not non linear, and if as you say gravity does not make gravity, and if as you claim V G4 is superior to GR, why not simply take the time, and write up a scientific paper for peer review and possible publishing if successful? I believe we/I have given enough evidence to show that if what you claim is superior, and if what you claim is correct, then in time, your model will be embraced and you will be in line for the Nobel. 

Quote

You should also recall from that other forum where I linked to someone who gave a somewhat detailed defense for why gravity does NOT gravitate in GR:
https://www.physicsforums.com/insights/does-gravity-gravitate/

I never participated in that forum, but isn't it the one where you were banned? Anyway you keep referring to "that other forum" and I suggest to you that this is vastly different and far better, and the reason why I am here. So lets conduct ourselves in accordance with the far better rules and regulations here, without any references to that questionable other place, literally open to any and all nonsensical claims and conspiracies.

[Q-reeus]

5 hours ago, MigL said:

The requirement for both, a classical theory of gravity, and a quantum field theory of gravity is that it is self-coupling.

For a classical theory, like GR, stress-energy produces curvature in space-time, either static or travelling ( as in GWs ). This curvature of space-time is also a stress-energy and so, contributes to further curvature. IE gravity gravitates.

And you have made that (admittedly very widespread) assertion without looking through all that was previously posted in particular by myself?! Why should I bother further here.
OK, one last stab, from a slightly different but equivalent perspective. See single simple expression under 1.6 here:
www.pas.rochester.edu/~rajeev/phy413/Grav13.pdf
Please - actually THINK about it some. If you cannot see a direct contradiction to what you wrote above, then forget it. I will have totally wasted time and effort trying to get through to anyone here. Testament imo to just how effective has the GR brigade been in presenting it as an internally consistent 'perfect' classical theory of gravity.

5 hours ago, MigL said:

In a quantum field theory, which is the only place you would expect to find gravitons, self-coupling means gravitons interact with gravitons. IE gravity gravitates.

Again, you did not read my earlier remarks on that? You know, where I wrote to leave it out as we are really focusing on classical gravity. Sigh.

5 hours ago, MigL said:

What exactly is the problem ?

Sigh

5 hours ago, beecee said:

Don't take it too hard...that is the least of your technical errors of judgement. 

I'll keep repeating it as you have done nothing, nor said anything to dispatch it as you claim. Still it looks good for the record. Your highlighted part of my statement was simply referring to flat spacetime....in other words other then  spacetime that isn't curved, warped, waved or twisted in the presence of mass,  thereby exhibiting gravity, which irrefutably shows that gravity is simply the geometry of spacetime.

Erroneous in your opinion, which has already been shown to be in error. All my sources are reputable including the Professor t'Hooft, a Nobel prize recipient I might add. And of course there was more then one authority supporting my position, and no, I certainly do not remember any reply inferring the authoritive position as not fully consistent. 

Quote mining?? The link with the full text is there for all to read, and always is in any point I make. Obviously you don't subscribe to your "show of hands"  particularly when that show of hands disputes and/or disagrees with your made up interpretation of GR, gravitational waves, etc, that happens to be supported by an isolated minority of hands. 

 

Any appeal to authority that is appeal to authority educated and qualified in the relevant discipline under discussion, is admirable appeal to authority and totally justified, in attempting to facilitate your own understanding and the areas where you are simply wrong...and of course, most definitely yes, also to facilitate my own understanding. The usual inferences you are noted for are simply sour grapes and excuses.

My memories are pretty good for an old bloke, and once again, the bulk of references, and authoritative statements from experts and reputable links, supported the fact that gravity being non linear, means that gravity makes gravity.

 

Particularly authoritative figures that just happen to refute your own amateurish opinions. While thinking things through for ones self, is an admirable quality, it is not quite as admirable to make veiled inferences and accusations about science being recalcitrant and stubbornly dishonest, when your limited ability lacking the expertise and professionalism, happens to be in conflict with the well held and justified mainstream position.

 

 Excuse me for laughing, but really, you must be getting desperate. My devotion as you sarcastically put it, is simply adhering and appreciating the scientific methodology, and dismissing the conspiracy nonsense in this regard that you seem obviously taken with....I mean really, it's near as stupid and foolish as the nuts that push the 9/11 and Moon Landing nonsensical conspiracies.

As per the thread I started re V4 gravity, and the other thread that discussion has taken place on, as per aLIGO and other reputable scientific people and orginisations, now considering and working through any possible anomalies with either the GR interpretations or that of the many alternative hypotheticals, all this shows your veiled accusations and  conspiracy claims, as nothing but sheer nonsense and excuses when one is not achieving what his or her agenda dictates.

 

If as you say, gravity is not simply geometry of spacetime, and if as you say gravity is not non linear, and if as you say gravity does not make gravity, and if as you claim V G4 is superior to GR, why not simply take the time, and write up a scientific paper for peer review and possible publishing if successful? I believe we/I have given enough evidence to show that if what you claim is superior, and if what you claim is correct, then in time, your model will be embraced and you will be in line for the Nobel. 

I never participated in that forum, but isn't it the one where you were banned? Anyway you keep referring to "that other forum" and I suggest to you that this is vastly different and far better, and the reason why I am here. So lets conduct ourselves in accordance with the far better rules and regulations here, without any references to that questionable other place, literally open to any and all nonsensical claims and conspiracies.

Given you are simply a GR fanboy with no real grasp of the issues, it's not worth my while responding to each irrelevant point you make. Feel free to consider yourself 'the winner'. That's what matters to you, is it not? I well recall your enthusiasm for keeping arguments going non-stop back in that other forum. Bye bye.

[beecee]

1 hour ago, Q-reeus said:

Given you are simply a GR fanboy with no real grasp of the issues, it's not worth my while responding to each irrelevant point you make. Feel free to consider yourself 'the winner'. That's what matters to you, is it not? I well recall your enthusiasm for keeping arguments going non-stop back in that other forum. Bye bye.

Given that I simply follow the scientific method, and latest science news, given that I am giving reputable links from reputable experts, who you as an amateur chose to be in conflict with, given that like the vast majority, I see the mainstream as the best explanation by far,  given that it is you being contrary and quite arrogant as per your reply to Migl and others, given that you are known to dabble in conspiracies on that other forum you keep raising, given all that, I can safely say that I never chose to be a "winner" as you put it....simply letting you know that any alternative to GR and any incumbent model, will by necessity and rightly so, need to run the gauntlet. Nothing as yet has succeeded. Will something overtake GR? probably, one day, but it certainly is not going to do it by someone running a crusade on two or more forums, irrespective of his or her interpretations. Call me a fan boy, call me a science cheer leader, call me what you like, on this current issue, I'll stand by the incumbent until professionally invalidated in the professional way by a professional.

http://www.staff.science.uu.nl/~hooft101/gravitating_misconceptions.html

 

The above probably applies every day on every science forum, when some upstart or smarty that believes he can or has invalidated GR and/or Einstein. I mean knocking over the crowning ultimate top position will most certainly gain the notoriety or otherwise that these individuals seek for whatever reasons and/or whatever agenda.

from the link.....

 Examples of the claims that professional scientists regularly encounter are:
- "Einstein’s equations for gravity are incorrect",
- "Einstein’s equivalence principle is incorrect or not correctly understood",
- "Black holes do not exist",
- "Einstein’s equations have no dynamical solutions",
- "Gravitational waves do not exist",
- "The Standard Model is wrong",
- "The Big Bang never occurred; Hubble's Law for the cosmic red shift is being mis-understood",
- "Cosmic background radiation does not exist",

and the list goes on and on and on...........

Edited November 29, 2018 by beecee

[Q-reeus]

1 hour ago, beecee said:

Given that I simply follow the scientific method, and latest science news, given that I am giving reputable links from reputable experts, who you as an amateur chose to be in conflict with, given that like the vast majority, I see the mainstream as the best explanation by far,  given that it is you being contrary and quite arrogant as per your reply to Migl and others, given that you are known to dabble in conspiracies on that other forum you keep raising, given all that, I can safely say that I never chose to be a "winner" as you put it....simply letting you know that any alternative to GR and any incumbent model, will by necessity and rightly so, need to run the gauntlet. Nothing as yet has succeeded. Will something overtake GR? probably, one day, but it certainly is not going to do it by someone running a crusade on two or more forums, irrespective of his or her interpretations. Call me a fan boy, call me a science cheer leader, call me what you like, on this current issue, I'll stand by the incumbent until professionally invalidated in the professional way by a professional.

http://www.staff.science.uu.nl/~hooft101/gravitating_misconceptions.html

 

The above probably applies every day on every science forum, when some upstart or smarty that believes he can or has invalidated GR and/or Einstein. I mean knocking over the crowning ultimate top position will most certainly gain the notoriety or otherwise that these individuals seek for whatever reasons and/or whatever agenda.

from the link.....

 Examples of the claims that professional scientists regularly encounter are:
- "Einstein’s equations for gravity are incorrect",
- "Einstein’s equivalence principle is incorrect or not correctly understood",
- "Black holes do not exist",
- "Einstein’s equations have no dynamical solutions",
- "Gravitational waves do not exist",
- "The Standard Model is wrong",
- "The Big Bang never occurred; Hubble's Law for the cosmic red shift is being mis-understood",
- "Cosmic background radiation does not exist",

and the list goes on and on and on...........

As do you. Always having to have the last word. And - see my last post.