Is Gravity a Force?

[studiot]

4 minutes ago, Davy_Jones said:

Er, that's my raison d'etre right now. Hoping for an answer to that question is the reason I started the thread.

 

Edit: How do I remove unwanted items like vids or pics when quoting another member?

Not wanting to hog the screen, I just wanted to quote your sentence at the end.

Two ways.

1) Don't include them in the first place.

Instead of using the quote button, highlight (select) the text you want to quote and hover the mouse for a moment.
That will bring up the option to 'quote'
Click on that.

like this

2) To remove the picture (I nearly always do this) just select it and click delete before to submit or in the edit mode after you have submitted.

The input and edit boxes here are a real pain but this facility does work quite well.

8 minutes ago, Davy_Jones said:

Er, that's my raison d'etre right now. Hoping for an answer to that question is the reason I started the thread.

So how about considering this ?

10 hours ago, studiot said:

Anyway, back to  gravity as a force or not.

Thank you for the excellent discussion recently +1

I have been thinking further and I have to say that now occurs to me that I have already presented a test of sorts.

Is there, even theoretically, a situation where gravity occurs, but no force is exerted ie no force occurs ?

If it is the case that gravity can occur without a force then gravity cannot itself be a force.

Gravity may give rise to a force and seems to do so in some (most) situations, but that is not the same thing.

 

[Davy_Jones]

Re above: That looks like one for the physicists (isn't it?). I'll keep my trap shut for now.

But your logic seems impeccable. If one can exist in the absence of the other then they are not identical.

Thanks for the tips on quoting, etc.

(Though it's awfully tempting to invoke Saul Kripke's "modal argument" which purportedly refutes the psycho-physical identity theory. Aaaaarrrrgggghhhhhh!!!!!!)

 

Edit:

Oh, what the heck, let's just throw Kripke in here and see what happens LOL.

There are those who claim that mental states are identical with physical states. This is the so-called psycho-physical identity theory. Pain, for example, is sometimes claimed to be identical with a particular brain state, which we'll simplistically call C-fiber firings.

Kripke demurs:

1. If pain is identical with C-fiber firings, given that the two terms are rigid designators (i.e., designate the same thing in all possible worlds), then they would have to be necessarily identical, identical in all possible worlds.

2. Pain and C-fiber firings are not identical in all possible worlds (we can conceive of pain without C-fiber firings)

3. Pain and C-fiber firings are not necessarily identical.

Conclusion: They are not identical.

 

 

Now, even supposing this works for psycho-physical identity, would it work for gravity being a force of a certain kind?

 

Edit #2 : Hmm, on second thoughts I don't suppose this is relevant. Seems we're only interested in whether gravity is a force in this world, i.e., contingently identical.

Edited September 5, 2021 by Davy_Jones
committed Saul Kripke to the flames

[Markus Hanke]

9 hours ago, joigus said:

I also miss @Markus Hanke, of course. I know he takes a peek sometimes.

Yes @joigus, I lurk in the shadows and follow proceedings here whenever I get the opportunity  At present I live in the jungles of Thailand, having recently been ordained as a monk, and do not have access to anything other than an old mobile phone with spotty and slow internet access, so I’m not really in a position to participate in discussions. It’s just too slow and painful to type this way. I will return once I get access to better infrastructure - perhaps some time next year.

6 hours ago, Davy_Jones said:

But your logic seems impeccable. If one can exist in the absence of the other then they are not identical.

Satellites in orbit are in free fall - place an accelerometer into them, and it will show exactly zero at all times. No proper acceleration -> no force acting on them. And yet they don’t fly off into space, but remain gravitationally bound into their elliptical orbits. Clocks in them are also dilated wrt to far-away reference clocks, which is also a gravitational effect. Thus, no force, but still gravity.

Newtonian forces are simply bookkeeping devices, and as such they often work well - but only in the right context. Their nature is descriptive, but not ontological. They are not very physical either, given that they are assumed to act instantaneously across arbitrary distances.

The strong, weak, and EM interactions aren’t ‘forces’ in that sense at all, since they work in very different ways. They are only sometimes called ‘forces’ by convention, for historical reasons. They ultimately arise through the breaking of symmetries, with the particles involved being irreducible representations of symmetry groups.

Finally, it should be noted that physics makes models, that’s what it sets out to do - and as such it is always descriptive rather than ontologically irreducible. So, asking whether gravity “really is” A or B, or whether A or B are “true” is fairly meaningless, since both A and B are descriptions of reality, but not reality itself. Like maps of a territory. The correct question is thus whether models A and/or B are useful in describing gravity, and in what ways and under what circumstances they are useful. So - Newtonian gravity is sometimes useful, but GR is more generally useful, as it gives more accurate predictions for a larger domain. 

So for now the best answer to “what is gravity” that we have is a purely descriptive one: it’s geodesic deviation, and thus a geometric property of space time. To put it flippantly, it’s the failure of events to be causally related in a trivial manner. Future advancements may upend this picture in the high-energy domain, perhaps radically. We’ll see.

I’m sorry I can’t contribute much at the moment, but I’ll leave you with the above thoughts. I could have written much more, but it’s too much of a pain on a small mobile phone screen.

Edited September 5, 2021 by Markus Hanke

[Davy_Jones]

@Markus Hanke

@Markus

Thanks so much for taking the time to share that thoughtful post under trying circumstances (= Thai Telecom lol).

Before proceeding any further, though, I think we all need to get clear on a few essentials here. At certain times, indeed most of the time, I've been getting the impression that we're talking somewhat at cross purposes, probably due to our respective disciplinary backgrounds or interests (simply an uncredentialed philosophical dilettante myself), and perhaps the way certain terms (e.g. realism, observability) are used differently in different domains.

@TheVat is the only contributor who I feel is, if not always in agreement, at least perfectly clear on what I'm saying. And yes, I do appreciate and acknowledge that I'm the philosophical Blood on physicist Crip turf. Don't shoot! I'm unarmed!

1. You say above ". . . since both A and B are descriptions of reality, but not reality itself. Like maps of a territory." Other members have said similar things (e.g. "the model is not the reality" - MigL) earlier in the thread.

Surely this does not even have to be said. Regardless of whether we use the term theory or model or whatever, surely no one confuses a painting of sunflowers with actual sunflowers, no one mistakes a book about Van Gogh for Van Gogh, and no one thinks a model Boeing 747 is a Boeing 747.

The salient question, rather, is whether or not physical theories or models accurately represent reality, or at least endeavor to do so.

 

2. The view has been expressed in the thread that physics does not, or does not try to, represent reality. I'd been assuming that we all tacitly understand this to mean unobservable reality, but I'm beginning to have my doubts.

Where I come from at least (Blood territory), everyone accepts that physics describes observable reality, indeed describes it very well. Fire a cannonball, say, and physicists will tell you what trajectory it will follow.

The dispute between the scientific realists and antirealists, rather, is whether science can or should do more, can or should science try to go behind the scenes, so to speak, can science "lift a corner of the veil" (Einstein's phrase), should science settle for "saving the appearances" (e.g. simply describe the trajectory of the cannonball) or go further and provide us with a causal-explanatory account of why the cannonball does what it does?

And as we've seen, even in physics, universal consensus by no means obtains on these matters. Antirealism ("Don't even ask what's going on backstage. Just shut up and calculate") does appear to be the prevalent position, though, as I've shown, I hope, Einstein and Weinberg constitute two very notable exceptions. It strains credulity to suggest that the realist camp consists of precisely two members; there are surely others of similar persuasion.

 

So to your post . . .

"So, asking whether gravity “really is” A or B, or whether A or B are “true” is fairly meaningless, since both A and B are descriptions of reality, but not reality itself. Like maps of a territory." - Markus

If one assumes an instrumentalist (a form of antirealism) position on these matters then it is indeed meaningless to ask whether A or B is true. The instrumentalist--and you sound like one--holds that scientific theories/models are not even candidates for truth or falsity . . . not unlike a hammer or a screwdriver or an adjustable spanner (er, that's a monkey wrench to my American brethren). It makes no sense to ask whether a hammer is true or not.

But, as I've tried to point out in the thread, not all scientists, indeed not even all physicists, are instrumentalists. There are scientists, I suspect the vast majority (physics being the exception), who do feel that the predicates true and false are applicable to scientific theories. E.g.

 

Quote

Rigidity means here that the theory [GR] is either true or false, but not modifiable

- Einstein, essay "On the Generalized Theory of Gravitation"

 

Quote

Although natural science is intellectually hegemonic, in the sense that we have a clear idea of what it means for a theory to be true or false, its operations are not socially hegemonic -- authority counts for very little.

- Steven Weinberg, "The Science Wars", p220

Edited September 5, 2021 by Davy_Jones
aesthetics

[beecee]

2 hours ago, Markus Hanke said:

I’m sorry I can’t contribute much at the moment, but I’ll leave you with the above thoughts. I could have written much more, but it’s too much of a pain on a small mobile phone screen.

You're being far too modest dear Sir! Excellent rundown and some great examples.

Here's an interesting paper on the subject.......

https://www.researchgate.net/publication/333146650_New_Concept_of_Gravity

Abstract and Figures

For more than a hundred years, discussion has been going on in physics: is gravity a force or a curvature of space? This article shows that gravity is both a force and a curvature of space simultaneously. The forcefield of gravity and space are synonyms. Gravity, like other potential forcefields, has allowed different energy levels.

Conclusions:

Mass is the charge of gravity. Gravity is a force. The forcefield of gravity is space. Space is curved as a forcefield. A gravity forcefield has Allowed Levels of Energy (ALE). All experiments with elementary particles are performed in the gravity field ofthe Earth. It is expected that ALE has different values in the different gravity field on the Moon or on the Mars

:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

I also remember a Sten Odenwald answer on a Q+A  forum a while back........

https://einstein.stanford.edu/content/relativity/a11332.html#:~:text=No.&text=General relativity tells us that,that creates the gravitational field.

Special & General Relativity Questions and Answers

Can space exist by itself without matter or energy around?

No. Experiments continue to show that there is no 'space' that stands apart from space-time itself...no arena in which matter, energy and gravity operate which is not affected by matter, energy and gravity. General relativity tells us that what we call space is just another feature of the gravitational field of the universe, so space and space-time  do not exist apart from the matter and energy that creates the gravitational field. This is not speculation, but sound observation.

---

Return to the Special & General Relativity Questions and Answers page.

All answers are provided by Dr. Sten Odenwald (Raytheon STX) for the NASA Astronomy Cafe, part of the NASA Education and Public Outreach program.

 

PS: The original answer contained a contradiction, that concerned me and prompted me to E-Mail Sten Odenwald. The contradiction was as follows...  "so space and space-time can and do not exist apart from the matter and energy that creates the gravitational field" The above answer is the corrected answer by me.

The highlighted underlined two words were a typographical answer and should not be there, and that he apologised for.

[Markus Hanke]

2 hours ago, Davy_Jones said:

The instrumentalist--and you sound like one--holds that scientific theories/models are not even candidates for truth or falsity . . . not unlike a hammer or a screwdriver or an adjustable spanner (er, that's a monkey wrench to my American brethren). It makes no sense to ask whether a hammer is true or not.

As I mentioned earlier, in the context of GR gravity is defined as geodesic deviation. What it means is that GR tells us about the world lines of test particles - far from gravitational sources, initially parallel world lines remain approximately parallel; in the vicinity of sources initially parallel world lines will deviate in specific ways. GR allows us to calculate this deviation, ie the motion of test particles; in fact this is all it does, since geodesic deviation is precisely what ‘curvature’ means. It does not address the question as to why (in a fundamental ontological sense) the deviation occurs, it simply quantifies it. So it is purely descriptive in that sense, and no deeper mechanism is suggested or implied.

It is also important to remember that the mathematical structures employed in this description (manifolds, connections, metrics, geodesics) where known and existed long before Einstein, who simply put them to use for his model. They do not ‘belong’ to GR, but are just general mathematical entities used in many other contexts as well. It is also possible to use different mathematical tools to arrive at the same results (eg a Lagrangian instead of curvature tensors, or numerical methods). Given this fact, in what sense could the formalism of GR be anything more than instrumental? The only observable of the model is the motion of test particles, but the entities used to calculate that observed motion are not themselves observable or detectable in any way, and can to some extent even be substituted for different ones.

I don’t know if that makes me an instrumentalist, but if it does then I’m ok with that label. I just think it’s dangerous to reify mathematical tools that don’t correspond to physical observables, especially not if we know already that more than one formalism is possible for a given model. You can point to a test particle falling, but you can’t point to a Riemann tensor. That doesn’t diminish its usefulness, but we shouldn’t make more of it than what it is. 

2 hours ago, beecee said:

The forcefield of gravity and space are synonyms.

A force is a vectorial quantity by definition. Vectors are rank-1 tensors; it can be formally shown that it is not possible to capture the necessary degrees of freedom exhibited by gravity by any kind of rank-1 object in general. You need at least a rank-2 tensor for this, hence the necessity for a metric theory such as GR.

So no, force fields are not generally equivalent to space time curvature, on fundamental grounds. Only under very special circumstances (static and stationary spherically symmetric vacuum that admits a time-like Killing field) can you describe gravity using a simple potential, and thus force.

2 hours ago, Davy_Jones said:

The salient question, rather, is whether or not physical theories or models accurately represent reality, or at least endeavor to do so.

Ok, but what exactly is meant by this? As explained, GR models the motion of bodies, so it accurately enough represents that aspect of reality. But do you mean to ask whether all unobservable mathematical entities employed in arriving at that observable result must necessarily also represent aspects of reality? For example semi-Riemannian manifolds, and curvature tensors?

Edited September 5, 2021 by Markus Hanke

[Davy_Jones]

@Markus Hanke

 

1 hour ago, Markus Hanke said:

It is also important to remember that the mathematical structures employed in this description (manifolds, connections, metrics, geodesics) where known and existed long before Einstein, who simply put them to use for his model. They do not ‘belong’ to GR, but are just general mathematical entities used in many other contexts as well. Given this fact, in what sense could the formalism of GR be anything more than instrumental? The observable of the model is the motion of test particles, but the entities used to calculate that observed motion are not themselves observable or detectable in any way

 

Thanks once more for the response.

It seems to me that by using the term "formalism" here you may be guilty of begging the question, presupposing that which we are supposed to be examining (i.e. "Can GR be given a realistic interpretation?"). By speaking of formalism, is it not the case that you've already assumed the answer is no?

That is to say, "formalism", at least as I understand the term, implies precisely a mere mathematical structure or framework; a skeleton, if you like, bereft of any ontological commitments.

Consider, for example, this remark from Murray Gell-Mann:

"Quantum mechanics is not a theory, but rather a framework within which we believe any correct theory must fit" 

"Framework" here seems to me pretty much synonymous with "formalism". Does that sound reasonable to you?

And indeed, under the orthodox Copenhagen antirealist-instrumentalist view, at least as far as I understand, the formalism is all there is to it. Don't ask what's going on behind the scenes. Don't ask what's happening when no one is looking. Don't ask what it all means. Shut up and calculate. Etc., etc.

Of course, not everyone is satisfied with such a purely instrumentalist understanding of QM. Attempts have been made to give it a realist spin (David Bohm, multiple universes, etc), to put some meat on the skeleton, so to speak.

Now, back to GR, is it not the case that the same applies? Yes, it can be treated as simply a mathetical device--as you're doing--prescinding from any ontological affiliation.

On the other hand, Einstein's (the later Einstein) realist position, in this regard, is so well documented as to hardly need rehearsing. But oh, let's give Arthur Fine another twirl . . 

"In particular, following his conversion [from antirealism to realism], Einstein wanted to claim genuine reality for the central theoretical entities of his general theory, the four-dimensional space-time manifold, and associated tensor fields. This is a serious business for if we grant his claim, then not only do space and time cease to be real, but so do virtually all of the usual dynamical qualities."

(I keep repeating Fine because it's the only quote I have at hand LOL. Whole books have been written on Einstein's mature realism, though.)

Now, given that Einstein (just to name one) clearly was able to construe GR as a (or an attempted) representation of how the universe really is, on what grounds do you base your claim that it cannot be read any other way but instrumentally? -- unless, of course, this has already been presupposed to begin with.

Edited September 5, 2021 by Davy_Jones
changed the first paragraph a bit

[dimreepr]

17 minutes ago, Davy_Jones said:

@Markus Hanke

 

 

Thanks once more for the response.

It seems to me that by using the term "formalism" here you may be guilty of begging the question, presupposing that which we are supposed to be examining (i.e. "Can GR be given a realistic interpretation?"). By speaking of formalism, is it not the case that you've already assumed the answer is no?

That is to say, "formalism", at least as I understand the term, implies precisely a mere mathematical structure or framework; a skeleton, if you like, bereft of any ontological commitments.

Consider, for example, this remark from Murray Gell-Mann:

"Quantum mechanics is not a theory, but rather a framework within which we believe any correct theory must fit" 

"Framework" here seems to me pretty much synonymous with "formalism". Does that sound reasonable to you?

And indeed, under the orthodox Copenhagen antirealist-instrumentalist view, at least as far as I understand, the formalism is all there is to it. Don't ask what's going on behind the scenes. Don't ask what's happening when no one is looking. Don't ask what it all means. Shut up and calculate. Etc., etc.

Of course, not everyone is satisfied with such a purely instrumentalist understanding of QM. Attempts have been been made to give it a realist spin (David Bohm, multiple universes, etc), to put some meat on the skeleton, so to speak.

Now, back to GR, is it not the case that the same applies? Yes, it can be treated as simply a mathetical device--as you're doing--prescinding from any ontological affiliation.

On the other hand, Einstein's (the later Einstein) realist position, in this regard, is so well documented as to hardly need rehearsing. But oh, let's give Arthur Fine another twirl . . 

"In particular, following his conversion [from antirealism to realism], Einstein wanted to claim genuine reality for the central theoretical entities of his general theory, the four-dimensional space-time manifold, and associated tensor fields. This is a serious business for if we grant his claim, then not only do space and time cease to be real, but so do virtually all of the usual dynamical qualities."

(I keep repeating Fine because it's the only quote I have at hand LOL. Whole books have been written on Einstein's mature realism, though.)

Now, given that Einstein (just to name one) clearly was able to construe GR as a (or an attempted) representation of how the universe really is, on what grounds do you base your claim that it cannot be read any other way but instrumentally? -- unless, of course, this has already been presupposed to begin with.

Do you think there is an answer?

[Davy_Jones]

Just now, dimreepr said:

Do you think there is an answer?

Almost certainly not. But hey, we might learn something along our merry meanderings.

[dimreepr]

7 minutes ago, Davy_Jones said:

Almost certainly not. But hey, we might learn something along our merry meanderings.

Then why is it here, and not in philosophy? 

[Davy_Jones]

1 minute ago, dimreepr said:

Then why is it here, and not in philosophy? 

See OP. I invited the mods to locate the thread as they saw fit.

[studiot]

24 minutes ago, Davy_Jones said:

And indeed, under the orthodox Copenhagen antirealist-instrumentalist view, at least as far as I understand, the formalism is all there is to it. Don't ask what's going on behind the scenes. Don't ask what's happening when no one is looking. Don't ask what it all means. Shut up and calculate. Etc., etc.

Since you seem to like saying "Shut up and calculate." almost every other post and usually it seems in a disparaging light,

I will say a few words about it.

I believe (though I can't pick it out at the moment, perhaps it was another thread) that swansont already pointed out the need for sufficient study time and effort to appreciate these matters and I agree.

 

The great advantage of 'calculate' is that you gain familiarity with the subject.
You start to know what sort of values to expect in various circumstance.
With enough of this you can step back, gain insights and formulate generalisations of the matter.

Personally I have found this method of learning of great value.
I know there are some who come to understanding by different routes.
But it is a tried and tested route for the majority of us.

 

[dimreepr]

On 9/1/2021 at 3:26 AM, Davy_Jones said:

This question is for the physicists mainly, I suppose, though there may also be a philosophical element to it. (Mods may wish to relocate the thread as appropriate). I ask as an interested layman. 

So, who's begging the question?

[Davy_Jones]

6 minutes ago, dimreepr said:

So, who's begging the question?

I don't see the problem myself. If the thread offends you, can't you just ignore it?

And I've no objection at all to the mods relocating the thread if they feel it's misplaced here. I just felt if I was going to get some intelligent input to my question it would most likely come from physicists. That's all.

9 minutes ago, studiot said:

Since you seem to like saying "Shut up and calculate." almost every other post and usually it seems in a disparaging light,

 

Not meant that way at all. Hey, it was you guys that came up with the phrase.

Edited September 5, 2021 by Davy_Jones

[studiot]

2 minutes ago, Davy_Jones said:

Not meant that way at all. Hey, it was you guys that come up with the phrase.

Not by me it wasn't.

A great strength is that 'calculate' provides definite testable outcomes.

Hand wavy dreaming and short quotes their own lacking context much less often,

though sometimes we all like to 'shoot the breeze'.

But at some point you can't discuss this subject without firm mathematics.

Note firm does not have to be advanced.

There is nothing that can be said in Mathematics that cannot be said in English, but English can also provide rational thinking that is not available in Mathematics.

 

 

[dimreepr]

1 minute ago, Davy_Jones said:

I don't see the problem myself. If the thread offends you, can't you just ignore it?

I'm not offended, I'm interested.

3 minutes ago, Davy_Jones said:

And I've no objection at all to the mods relocating the thread if they feel it's misplaced here. I just felt if I was going to get some intelligent input to my question it would most likely come from physicists. That's all.

But you placed it here, while thinking it has no answer... Challenging the mod's to change it to philosophy, is an exuse not a reason... 

[swansont]

1 hour ago, Davy_Jones said:

See OP. I invited the mods to locate the thread as they saw fit.

The OP asked a physics question (which was answered) so there’s no reason to relocate it. You might be thinking of a question asked in a later post.

[TheVat]

On 9/4/2021 at 7:36 AM, studiot said:

 

 

 

Is there, even theoretically, a situation where gravity occurs, but no force is exerted ie no force occurs ?

If it is the case that gravity can occur without a force then gravity cannot itself be a force.

 

Sorry I didn't catch this earlier.   One (possibly dumb) answer is: freefall.   When an object is freely following a space-time geodesic,  say around the earth's CoG.   While the object may be said to "obey" gravity,  one can also say that the object in freefall is experiencing no force and is simply following the curvature of spacetime.   OTOH,  one may also say that matter is forcing the space around it to bend.  

I think this directs us to the point others have made,  that gravity, whatever it is,  cannot be pinned down narrowly by words.  And underscores how insufficient the word "force" is in labeling all the nuances and properties.   That's one reason why I am leery of terms like "pseudoforce, " which try to tweak our conceptual understanding without really getting us anywhere.  

.  

And I see that @Markus Hanke  in the nighttime (on this spot on Earth), came along and expanded beautifully on this point already.  

16 hours ago, Davy_Jones said:

 

Oh, what the heck, let's just throw Kripke in here and see what happens LOL.

There are those who claim that mental states are identical with physical states. This is the so-called psycho-physical identity theory. Pain, for example, is sometimes claimed to be identical with a particular brain state, which we'll simplistically call C-fiber firings.

Kripke demurs:

1. If pain is identical with C-fiber firings, given that the two terms are rigid designators (i.e., designate the same thing in all possible worlds), then they would have to be necessarily identical, identical in all possible worlds.

2. Pain and C-fiber firings are not identical in all possible worlds (we can conceive of pain without C-fiber firings)

3. Pain and C-fiber firings are not necessarily identical.

Conclusion: They are not identical.

 

 

Now, even supposing this works for psycho-physical identity, would it work for gravity being a force of a certain kind?

 

Edit #2 : Hmm, on second thoughts I don't suppose this is relevant. Seems we're only interested in whether gravity is a force in this world, i.e., contingently identical.

OK,  whew.   You got there.   And if there are any besides us here who are familiar with Kripke (do not confuse with the cop in West Side Story), then congratulations on having a foot in both universes. 

Really,  I think the same can be said of Kripke's pain fibers example.  We define the "C-fibers" on their functional role in the brain,  so it may be that pain and C-fibers firing ARE necessarily identical.   

And the same for gravity, as a rigid designator.  Whatever attraction between large masses there is in a universe,  that is gravity.  Gravity is simply the short handy term we use for am aspect of a process where matter/energy gives rise to space-time and the bending of geodesics in proximity to massive objects.   

Edited September 5, 2021 by TheVat
nothing is ever finished

[swansont]

1 hour ago, TheVat said:

One (possibly dumb) answer is: freefall.   When an object is freely following a space-time geodesic,  say around the earth's CoG. 

Gravity isn’t a force in GR, so this is moot.

In Newtonian terms, something in freefall is still experiencing a force - it’s accelerating.

[TheVat]

3 minutes ago, swansont said:

Gravity isn’t a force in GR, so this is moot.

In Newtonian terms, something in freefall is still experiencing a force - it’s accelerating.

That was the point of the rest of my post.  Is something in my style constantly causing people to read one or two lines and then pull them out of context?  I would certainly like to remedy this.   

[swansont]

4 minutes ago, TheVat said:

That was the point of the rest of my post.  Is something in my style constantly causing people to read one or two lines and then pull them out of context?  I would certainly like to remedy this.   

If that were the case then you’re reiterating a point that’s been made several times, and studiot spoke of the force of gravity, putting us in the Newtonian realm, so I figured that can’t be it.

[studiot]

2 hours ago, swansont said:

In Newtonian terms, something in freefall is still experiencing a force - it’s accelerating.

I would add to this comment my own about a possibly more alarming misconception.

3 hours ago, TheVat said:

Sorry I didn't catch this earlier.   One (possibly dumb) answer is: freefall.   When an object is freely following a space-time geodesic,  say around the earth's CoG.   While the object may be said to "obey" gravity,  one can also say that the object in freefall is experiencing no force and is simply following the curvature of spacetime.   OTOH,  one may also say that matter is forcing the space around it to bend.  

I hope you are not implying that you consider the Earth's gravity to 'bend' spactime into a complete loop or shell around itself as your description of an orbiting object would imply.

 

Personally I don't like the term bend or curvature since that implies the existence of a dimension that we have no evidence for.
As with special relativity, imposing a coordinate system in general relativity implies addional information that is not needed for the relativity physics of the manifold.
Topologically speaking the extra dimansion is not needed if the presence of mass simply imposes additional relations between the members of the set which makes the manifold. Particularly if these are local rather than global relations.

[MigL]

The original Physics question, as I understood it, asked which of the two models of gravity is 'true', and accurately describes 'reality'.
( yes, I have a problem with both of those words )

We know for a fact that neither is 'true' or 'real'.

The Newtonian concept of a force fails on many levels ( not to undermine its usefulness ), such as discrepancy between force and acceleration ( free fall ), direct observation ( Mercury's orbit ), or even instantaneous information tranfer between masses.
GR, on the other hand, fails at scales of energy ( large ) and separation ( small ), while being exceedingly accurate in between these extremes.
Invoking A Einstein, and his quotes, doesn't help the situation, as he didn't know about Black Holes, nor about gravitational effects on approaching Planck scales.

So I don't see the point of quoting A Einstein, and his beliefs, nor about expecting one theory or the other to fully describe 'reality' or be 'true'.
Obviously neither is, and we are faced with two prospects ...
1 - We don't have a full description of 'reality' yet.
2 - We may never be able to fully describe 'reality.

 

Good to hear from you Markus ...

 

[swansont]

5 minutes ago, MigL said:

The original Physics question, as I understood it, asked which of the two models of gravity is 'true', and accurately describes 'reality'.

The original question was (emphasis added) “Anyway, the question in short: Is gravity a force or not? (In layperson's terms, insofar as possible)”

[MigL]

8 minutes ago, swansont said:

The original question was (emphasis added) “Anyway, the question in short: Is gravity a force or not?

That bolded question was answered, at which point it 'evolved' to which model, force or geometric, is true or real