Why two mass attracts each other?

[Q-reeus]

Nice hearty chunks of text. Hard to digest though.

A typically deep and meaningful input from you eram. Can't imagine how you could digest anything wearing that silly rocking helmet, but then I'm not a gamer pro!

 

[eram]

A typically deep and meaningful input from you eram. Can't imagine how you could digest anything wearing that silly rocking helmet, but then I'm not a gamer pro!

Oh c'mon. I don't wear a silly helmet, and it's not related to gaming!

What I'm trying to say is, when you include a huge wall of text, it's easy for both you and Markus to get confused and start arguing over something trivial. Or arguing over a definition.
Hence your argument will last longer than necessary. Unless you like arguing.



It's like trying to read through quantum_wave's text.

I can see that you might be saying that no one is interested in the new kind of clock, and that my purpose for bringing it up as if it related to how we could establish and maintain a fixed position relative to the observed redshift and CMB is not clear.

If I look at your posts from that perspective then my conclusion is that the members are not interested in the significance of how the redshift is information about a history of motion going away from all points in the observable universe, and the CMBR is information about a history of motion in the form of radiation coming toward all points in the observable universe.

My point in making that distinction, is that for the separation to be true, the outward motion clearly represents a finite length of time since some initial event (the big bang), but for the inward motion to be entirely connected to that same event is problematic. What is the explanation, within the standard cosmological model, for the source of the inward motion of the CMBR at all points in the observable universe?

I had to read this several times before I could understand what he was saying. I don't think I'm the only one.

 

[Q-reeus]

Oh c'mon. I don't wear a silly helmet, and it's not related to gaming!

Ah yes, sorry, I forgot. it relates to dubstep. But you are a gamer pro - no?

What I'm trying to say is, when you include a huge wall of text, it's easy for both you and Markus to get confused and start arguing over something trivial.

Not a particularly huge wall of text, and i did say preamble to eq'n (1), all of which I'm quite sure Markus is perfectly familiar with.

Or arguing over a definition.

Not at all. Unless you think a fundamental aspect of the very nature of gravitational field is 'just definitional'.

Hence your argument will last longer than necessary. Unless you like arguing.

No I detest it, but argumentation is forced on me by others imo.

It's like trying to read through quantum_wave's text....I had to read this several times before I could understand what he was saying.

Learning curve!

 

[eram]

No I detest it, but argumentation is forced on me by others imo.

If you say so.

Not a particularly huge wall of text, and i did say preamble to eq'n (1), all of which I'm quite sure Markus is perfectly familiar with.

Huge enough to get into a prolonged argument. Well, are you familiar with it too?

Ah yes, sorry, I forgot. it relates to dubstep. But you are a gamer pro - no?

They cover many genres, but a Daft Punk fan would clobber you for saying that.

No, just an average gamer. Don't be a fogey, play some games!

Not at all. Unless you think a fundamental aspect of the very nature of gravitational field is 'just definitional'.

Fundamentals are supposed to be simple, I don't know how you guys manage to blow it up.

Weren't you talking about how a term doesn't just "waltz from the left hand side to the right"? That sounds simple enough.



Oh yeah, I just read PeterDonis' blog post. Talk about giving a straight answer.

 

[IncogNegro]

Rotation is the answer.

Two masses rotating at perpendicular dimensional angles create a point where they are always tangent. They might create this tangence from drag off the "initial force" but quantum entanglement applies over time in such a way as it has the "appearance" of being a like thing that attracts... When it is just a "complete tangent" in the making.

A complete tangent is a significant expansion of rotational energy in a confined area.

 

[Markus Hanke]

Markus - you have been logging in several times each day since my #770 query, so what exactly is the problem in not extending the minimal courtesy of responding? Till now expected better of you than to (non)react with an evident snub. Whatever - have become used to that kind of thing here.

Huh ?! How would you know whether or not I have been present here ? I never log out from any of the sites I am active on, so every time a member of my family opens the browser I will appear as “online” on all of them. As a matter of fact I have been bedridden with a bout of severe food poisoning, and have not been anywhere near my computer since last Saturday morning; so, frankly, your comment is way out of line, and quite ridiculous, especially the bit about an “evident snub”, considering I just saw your post this very minute. You may wish to think first before publicly posting this kind of crap !

I find it confusing and strange that a schizophrenic response to 'gravity does/doesn't gravitate' abounds amongst GR trained folks

What do you mean by ‘schizophrenic’ ? To me the matter is very clear, there is no controversy here, except the one that you yourself create. Your very own example, that the Ricci tensor vanishes in empty space-time, illustrates this very well - we get a curved space-time even though the source term in the field equation ( the stress-energy tensor ) vanishes. How is that possible ? Precisely because gravity is self-interacting. If that weren’t so, how could we get a curved space-time even though the Ricci tensor and the stress tensor vanish ? What could be source of this, if not gravity itself ? Mathematically, this happens because the Ricci tensor is a non-linear combination of the metric tensor and its derivatives; if it were linear, and the field was not self-interacting, then a vanishing Ricci tensor would automatically imply a flat space-time. Obviously, that isn't the case.
Also, what do you mean by the "Ricci flat postulate" was built into GR ? It is a natural consequence of the trace-reversed field equations, and not an artificial addition of some kind. Have a look at my GR primer thread, where this is explicitly mentioned.

Btw, none of the links you provided contradicts what I said in any way, shape or form. No matter how you look at it, the gravitational field in GR is self-interacting; in fact it could not be any different, since we are dealing with rank-2 tensor fields here !

 

[Q-reeus]

Huh ?! How would you know whether or not I have been present here ? I never log out from any of the sites I am active on, so every time a member of my family opens the browser I will appear as “online” on all of them. As a matter of fact I have been bedridden with a bout of severe food poisoning, and have not been anywhere near my computer since last Saturday morning; so, frankly, your comment is way out of line, and quite ridiculous, especially the bit about an “evident snub”, considering I just saw your post this very minute. You may wish to think first before publicly posting this kind of crap !

Well sorry for your bout of food poisoning and pardon me please for misinterpreting the situation which is highly unusual in timing and circumstance. Had no way of knowing that when 'Markus Hanke' shows up as on-line it really isn't Markus Hanke at times. But I think you should understand why I drew the conclusion I did, and it wasn't 'crap' to do so.

Your very own example, that the Ricci tensor vanishes in empty space-time, illustrates this very well - we get a curved space-time even though the source term in the field equation ( the stress-energy tensor ) vanishes. How is that possible ? Precisely because gravity is self-interacting. If that weren’t so, how could we get a curved space-time even though the Ricci tensor and the stress tensor vanish ? What could be source of this, if not gravity itself ?

Where on earth are you pulling this from? I don't get your drift here at all. Are you referring to gravitational waves or what? Because in static case it's bleeding obvious that absent the usual stress-energy tensor density there is zero Ricci curvature. Zero source density (of any kind) = zero Ricci curvature. As you know, say for exterior Schwarzschild metric there is only a non-zero Weyl (shear) curvature - Ricci flat. Now if the field were it's own source in GR this would be a nonsense - it should - must - act as a kind of 'atmosphere' having a non-zero source density 'out there' exterior to usual stress-energy tensor source, thus a non-zero Ricci curvature in vacuo. But in GR it doesn't! End of story surely. Tell me otherwise. But you are.

Mathematically, this happens because the Ricci tensor is a non-linear combination of the metric tensor and its derivatives; if it were linear, and the field was not self-interacting, then a vanishing Ricci tensor would automatically imply a flat space-time. Obviously, that isn't the case.

Well my understanding is one is left with a non-zero Weyl curvature - e.g. exterior SC solution above mentioned. Which is not flat in the Minkowski sense but is flat in the Ricci curvature sense.

Also, what do you mean by the "Ricci flat postulate" was built into GR ? It is a natural consequence of the trace-reversed field equations, and not an artificial addition of some kind.

I didn't say or imply artificial addition, and that's not how it's put in that Mathpages article I linked to. How it's put there is that Einstein postulated that condition as a necessary one.

Btw, none of the links you provided contradicts what I said in any way, shape or form.

Except they do. Or do want me to make verbatim quotes here? You surely cannot deny PeterDonis did say a definite NO in the classical GR case! And btw that first quote I gave back in #770 was from a Sascha Vongehr (Alpha Meme) of Science20.com (he also strongly disagrees with your position that conservation of energy holds in GR in general). If you like, I can provide a direct link to the exact passage where he makes that point re gravity not gravitating, just so you can be sure there was no taking things out of context. There wasn't. But look I'm not out to argue this matter, just arrive at the truth.

No matter how you look at it, the gravitational field in GR is self-interacting; in fact it could not be any different, since we are dealing with rank-2 tensor fields here !

Self-interacting then apparently is not synonymous with 'being it's own source'. Unless you mean as in GW's. But how is that different to saying an EM wave 'is it's own source'?

 

[Markus Hanke]

Because in static case it's bleeding obvious that absent the usual stress-energy tensor density there is zero Ricci curvature. Zero source density (of any kind) = zero Ricci curvature. As you know, say for exterior Schwarzschild metric there is only a non-zero Weyl (shear) curvature - Ricci flat. Now if the field were it's own source in GR this would be a nonsense - it should - must - act as a kind of 'atmosphere' having a non-zero source density 'out there' exterior to usual stress-energy tensor source, thus a non-zero Ricci curvature in vacuo. But in GR it doesn't! End of story surely. Tell me otherwise. But you are.

I honestly don’t know what you are saying here - the possibility of the Ricci curvature vanishing whereas the Weyl curvature doesn’t ( i.e. the Riemann tensor being non-zero in the absence of stress-energy ) is present precisely because of the self-interaction of the field, i.e. the non-linearity in terms of the metric tensor. If the field wasn’t self-interacting ( meaning the dependency was linear ), that simply wouldn’t be possible. That holds true in general, not just for the static case.

Tell me, what exactly is your understanding of the Ricci and the Weyl tensors ? To put things very simply, the Ricci tensor is just a contraction of the full Riemann tensor across two indices; this of course reduces its rank from 4 down to 2, resulting in an overall loss of information. That “missing” curvature information is precisely what is encapsulated in the Weyl tensor. In essence what this means is that while the Ricci tensor vanishes with the stress-energy tensor, the Riemann tensor in general does not - meaning that the vacuum space-time can have curvature, even though there is no stress-energy present, precisely because it is self-interacting. It is in fact possible to construct solutions which represent non-trivial topological structures in the complete absence of any stress-energy; these are called geons, and are “held together” purely by their own self-interaction.

Well my understanding is one is left with a non-zero Weyl curvature - e.g. exterior SC solution above mentioned.

Correct, but you need to bear in mind that Ricci curvature is a “reduced” form of curvature in that it does not contain all relevant information. The only complete description of all aspects of curvature on a Riemann manifold is the Riemann curvature tensor, which most certainly does not vanish in the case of the SM. See above also.

If you like, I can provide a direct link to the exact passage where he makes that point re gravity not gravitating

“Gravity is gravitating” would be a very misleading statement, and it is not what I said, because that would imply that gravity itself appears as a component in the stress-energy tensor, which clearly it doesn’t. Perhaps this is where the confusion lies - all I said is that gravity is self-interacting, which is not the same thing.

Self-interacting then apparently is not synonymous with 'being it's own source'.

No, it’s not, see above. Come to think of it, I might have carelessly used that expression once or twice - in that I was clearly wrong, and apologize. It is self-interacting, but not it’s own source. So long as it is stated this way, there is no confusion.

But how is that different to saying an EM wave 'is it's own source'?

It’s different in that the wave equation for an EM wave is a linear, uncoupled partial differential equation, whereas the GR field equations are non-linear; in other words, the EM wave equation for the E field contains no terms referring to the B field ( they are uncoupled ), and vice versa. In GR, all components of the metric tensor are mutually dependent in a non-linear way. This is why I earlier on equated non-linearity to self-interaction, which seemingly you don’t agree with.

You surely cannot deny PeterDonis did say a definite NO in the classical GR case!

The “classical GR sense” would be that gravity appears as a term in the energy-stress tensor; obviously that is not the case. However, self-interaction does not require this to be the case, so to me this is a non-argument; the field can be self-interacting without appearing in the source terms - see aforementioned geon solutions.

 

[Q-reeus]

No, it’s not, see above. Come to think of it, I might have carelessly used that expression once or twice - in that I was clearly wrong, and apologize. It is self-interacting, but not it’s own source. So long as it is stated this way, there is no confusion.

Markus, methinks above represents a more or less convergence of viewpoint on this, and here's where I'd like to leave it. Trust there are no hard feelings and hope you accept my explanation for unfortunate and misplaced judgement call I made earlier.

 

[Undefined]

Guys, very interesting discussion (specifically the "self-interacting gravity field" side discussion between Q-reeus and Markus Hanke), and rare in that a consensus between you two was reached and the discussion ended in mutual understanding and respect. Very heartening for observer like me and everyone else interested in discussion rather than conflict for ego's sake! Thankyou both for that very good read/conversation on self-interaction of gravity field "free-space components" terms etc.

Edit/---By the way, I recall reading Farsight somewhere also maintained and explained that gravity was self-interacting as has just been concluded between you two. For trying to discuss that idea, Farsight was (hastily and unfairly?) lambasted by some of the "experts" here and elsewhere. I guess that Farsight will feel pretty much vindicated against his attackers on this particular idea when he reads/hears about your discussion and its conclusion here! Where is Farsight, anyway? I haven't seen him on the board for some time? Is he ill too?

 

[Markus Hanke]

Markus, methinks above represents a more or less convergence of viewpoint on this, and here's where I'd like to leave it. Trust there are no hard feelings and hope you accept my explanation for unfortunate and misplaced judgement call I made earlier.

Q-reeus, I agree that this is a mutually acceptable way to resolve the issue, and in any case it is the only way to resolve it that I am aware of. It is also a good demonstration of how important it is to use the correct terminology to avoid unnecessary confusion.
There are absolutely no hard feelings - so please do not worry about it. These things happen sometimes

 

[Markus Hanke]

For trying to discuss that idea, Farsight was (hastily and unfairly?) lambasted by some of the "experts" here and elsewhere.

Again, just like in this case here it would have very much depended on how exactly the idea was formulated and put forward. There is no denying the fact that in GR gravity is "self-interacting", but it is definitely not "it's own source". So again, it would have depended on the exact circumstances of the discussion.
In general, it would seem to me that this particular feature of GR is a source of considerable confusion and misunderstanding. I have had many such discussions on different forums, and this one will certainly not be the last.

 

[Farsight]

Guys, very interesting discussion (specifically the "self-interacting gravity field" side discussion between Q-reeus and Markus Hanke), and rare in that a consensus between you two was reached and the discussion ended in mutual understanding and respect. Very heartening for observer like me and everyone else interested in discussion rather than conflict for ego's sake! Thankyou both for that very good read/conversation on self-interaction of gravity field "free-space components" terms etc.

Edit/---By the way, I recall reading Farsight somewhere also maintained and explained that gravity was self-interacting as has just been concluded between you two. For trying to discuss that idea, Farsight was (hastily and unfairly?) lambasted by some of the "experts" here and elsewhere. I guess that Farsight will feel pretty much vindicated against his attackers on this particular idea when he reads/hears about your discussion and its conclusion here! Where is Farsight, anyway? I haven't seen him on the board for some time? Is he ill too?

No, just busy. I haven't read this current discussion, but I did spot this:

"And btw that first quote I gave back in #770 was from a Sascha Vongehr (Alpha Meme) of Science20.com (he also strongly disagrees with your position that conservation of energy holds in GR in general)."

I disagree with Markus about a fair few things, but can I say that I'm certain that conservation of energy holds in GR. I don't recall being lambasted by experts about that.

 

[Markus Hanke]

No, just busy. II haven't read this current discussion, but I did spot this:

"And btw that first quote I gave back in #770 was from a Sascha Vongehr (Alpha Meme) of Science20.com (he also strongly disagrees with your position that conservation of energy holds in GR in general)."

I disagree with Markus about a fair few things, but can I say that I'm certain that conservation of energy holds in GR. I don't recall being lambasted by experts about that.

I think he is referring to the fact that gravity in GR ( and also in QFT, btw ) is self-interacting, unlike in Newtonian gravity.
The question about energy conservation is a whole different beast again.

 

[rr6]

Gravity = Integrity = Finite Set = essence of ourphysical/energy existence

The question about energy conservation is a whole different beast again.

Perhaps the conservation of energy, in regards to gravity, we see that in multi-verse theories--- not bubble-universes -- is accepted that gravity is the only force that interact with all others verses.

This might appear to us as the creation or destruction of quasi-phyiscal/energy gravity

The essence of our finite Universe we call energy/physical is interference of the ultra-micro, quasi-physical gravitational spacetime.

If were to think of bubble-like Universes of occupied space, existent in macro-infinite non-occupied space, we either see this finite set--- erg integrity i.e. integral set ---interconnected via ultra micro gravitational spacetime, or,

these bubble-like universes are not connected ergo not integral set and finite set becomes irrelevant.

If God/Universe does not play dice, then there exists a finite set of all multi-verse's or a finite set of bubble-like universes.

I agree with Einstein on this one i.e. God/Universe does not play dice with the Universe. Ultra-micro, quasi-physical gravity is the odd-bird out of the bosonic catagory. imo

r6

 

[hansda]

... There is no denying the fact that in GR gravity is "self-interacting", but it is definitely not "it's own source". ...

If something(say mass or as you say 'gravity in GR') does not interact with self(or its own source), then how it( GR gravity) becomes "self-interacting"?

 

[Markus Hanke]

If something(say mass or as you say 'gravity in GR') does not interact with self(or its own source), then how it( GR gravity) becomes "self-interacting"?

You are mixing up terms - self-interaction of the field is not the same as the field being its own source. That is the main point. This is because all components of the metric tensor, which can be considered the "field" in GR, are mutually interdependent, unlike for example in Newtonian gravity.
You can also look at it from a quantum field theory point of view, which is perhaps simpler - (hypothetical) gravitons don't just interact with their sources, but also with each other, because they couple to rank-2 tensor fields.

 

[hansda]

You are mixing up terms - self-interaction of the field is not the same as the field being its own source. That is the main point. This is because all components of the metric tensor, which can be considered the "field" in GR, are mutually interdependent, unlike for example in Newtonian gravity.
You can also look at it from a quantum field theory point of view, which is perhaps simpler - (hypothetical) gravitons don't just interact with their sources, but also with each other, because they couple to rank-2 tensor fields.

Let us not talk about hypothetical(graviton) things. Let us talk practical things. Can a gravity-field exist in isolation without its mass?

 

[hansda]

Do you know, why perihelion precession happens? Due to attractive force or repulsive force(consider the Sun at the centre of the orbit)?

there is no such thing as repulsive force, you have been told this repeatedly, you need to stop trolling.

See post #717. It is explained there, how repulsive forces(from the Sun point of view) causes perihelion precession of Planet Mercury.

You can also see this link where a 'repulsive force' is predicted for anomaly of Mercury perihelion precession.

A quote from the link is as follows:

The discovery and attempts to find classical causes for the precession of the perihelion of the planet Mercury are well known.1 In the 19th century, the French astronomer Le Verrier found that the perihelion of Mercury advanced by 43 arc- seconds/100y, an amount which could not be accounted for in terms of the gravitational forces exerted on Mercury by the other known planets. Le Verrier assumed another planet, which he named Vulcan, existed between Mercury and the Sun. However, observations failed to establish that Vulcan existed. Another explanation put forth by astronomers was that Newton's law of gravitation was not correct but, if additional terms were added, these could account for the excess rate of turning of the orbit of Mercury. For example, it is known that if a repulsive force C/r3 is added to Newton's law it would provide a correct value for precession of the perihelion of planet Mercury.2 A different explanation is offered by Einstein's theory of gravitation which calls for an extra term A/r4 which, if added to Newton's law, gives the excess turning rate of 43 arcseconds/100y. Importantly, A was not adjusted to give this value. It emerged uniquely out of Einstein's theory. Thus, classical explanations, which could not be found since the 19th century were replaced by Einstein's theory in the 20th century.

 

[Tach]

These "interplanetary gravitational interactions" can be considered as "repulsive" from "the Sun" point of view.

This is just your fringe misinterpretation.