Is Gravity a Force?

[joigus]

I think the word we're all fumbling for here when we say 'reality' is in fact 'ontology'.

One of the most important lessons of 20th-century physics is, I think, Nature doesn't care a great deal about our entities.

I think @swansont, @MigL, @beecee, and myself; and perhaps most eloquently @DrDon have drawn arguments along these lines.

Nature is probably connected all the way down to the most fundamental level. That's why such a thing as unification of physical laws is possible in the first place. But distinctions emerge. It is the business of physics to elucidate what connections/distinctions appear/disappear, and when (at what scale) they are relevant. Entities don't present themselves as 'solid' immovable categories; rather, as useful instruments for the scale of description given.

Terms as bosonization (a fermion can be seen as a pair of bosons with a 'twist' between them), dualities (a strongly-coupled interaction in one region of space can be seen as a weakly-coupled one on the boundary of that region) etc., strongly suggest that any entities that we may propose are simply instrumental, and what emerges as really robust are physical principles, patterns, rather than 'things'.

Lorentz invariance, locality, unitarity, symmetries and conservation laws. Those are the main characters in this play. Weinberg was a master at bringing out how they interplay.

Einstein was one of the most brilliant theorists of all time, but this revolution caught him at a point in his life when he was already too set in his --ontological?-- ways. Weinberg was able to take home the lesson much more efficiently for what the 2nd half of the 20th century physics needed.

Maybe nothing is, and everything emerges, in some kind of bootstrap mechanism of substantiation of entities in a grand cosmic scheme of which the building blocks are actually patterns and principles, and not things. --I'm getting blah, blah.  

I'm also glad that professor Lincoln has spent some time among us, be it ever so briefly.

[Davy_Jones]

@joigus
A very thoughtful post you've offered there with a great deal to ponder.

As it happens, and for all it's worth, my own proclivities in these matters would be located somewhere towards the antirealist end of the spectrum, which would seem to put me in good company here.

That said, the realists do have some pretty powerful arguments on their side that I think have to be acknowledged and addressed. So let me play devil's advocate here for a while. (Bliss on tap! Ooh ah!)

Take a look, if you will, at the following list of subatomic particles which, we are told, have been discovered since the year 1800.

https://en.wikipedia.org/wiki/Timeline_of_particle_discoveries

Now, I assume the entities on the list, with the exception of any serendipitious discoveries (X-rays?) which just kinda popped up out of the blue prior to starring in any bright spark's PhD dissertation, were originally posited as theoretical entities, perhaps regarded as "useful fictions" to begin with, much as atoms were until roughly a century ago.

We might have been told that to enquire into the existence of such spooks was to perpetrate the heinous sin of metaphysical speculation. Science can't answer questions like that. Just shut up and calculate, etc., etc.

Given, however, that these spooks were subsequently "discovered" . . . well, to my untrained ears, discovery pretty much entails reality. And if they're real, is it not the case that physics is--at least to some degree--describing reality for us?

Speaking as a physicist (I assume you are), do you consider the entities on the list to be real?

If not, why not?

If yes, how do you reconcile these additions to our ontological inventory with the passage of yours which I have quoted below?

 

56 minutes ago, joigus said:

Terms as bosonization (a fermion can be seen as a pair of bosons with a 'twist' between them), dualities (a strongly-coupled interaction in one region of space can be seen as a weakly-coupled one on the boundary of that region) etc., strongly suggest that any entities that we may propose are simply instrumental, and what emerges as really robust are physical principles, patterns, rather than 'things'.

 

Edited September 4, 2021 by Davy_Jones

[swansont]

12 hours ago, Davy_Jones said:

Well, things are never quite that simple. When data sits uncomfortably with theory, one option is to declare the theory false like a well behaved Popperian and head off to the pub to drown your sorrows.

There are, of course, other options.

1. Do nothing at all. Scratch your head and wonder why data is so recalcitrant.

Or more commonly . . .

2. Declare the theory to be perfectly healthy and try to find some way to reconcile the awkward data/evidence with the theory. The problem does not necessarily lie with the theory; it may lie with the "auxiliary hypotheses", "background knowledge" or whatever you wanna call them.

 

After all, when it was noticed circa 1850 or so that Uranus was not behaving in the manner Newtonian physics predicted (i.e. data/evidence clashed with theory) I doubt it crossed anyone's mind that Newtonian physics might be at fault. What they did instead was say "There must be something wrong with our background assumptions. Hmm, perhaps there's something out there that we're not seeing . . ."

 

Enter Neptune.

 

Irrelevant. GR’s failure to work in the described situations is not analogous to this.

[studiot]

4 hours ago, Davy_Jones said:

A very thoughtful post you've offered there with a great deal to ponder.

Yes I agree, some good stuff in there.

Though I would sound the same warning about the ancient greeks (esp Plato) that swansont has already made.

I am suspicious that this is too easy. It is easy to be seduced by thoughts of "how things ought to be" to the detriment of actually looking to see how things really are.

So I am rather worried about this idea.

4 hours ago, joigus said:

Nature is probably connected all the way down to the most fundamental level. That's why such a thing as unification of physical laws is possible in the first place.

 

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.

 

One further comment.

The comment by your hero that gravity depends upon scale

21 hours ago, DrDon said:

One other piddly point.  Our current understanding of gravity is qualitatively different from the other known forces.  Sure.  Some of you have been discussing the meaning of the word force.  Classically, it means something that has the potential to cause an object's velocity to change according to some reference frame.  At the quantum level, it has a somewhat different meaning.  There it means that the phenomenon can effect some sort of change, be it changing velocity or causing particle decay.  The fact that the word has a nuanced meaning depending on the size scale at which it is being evaluated implies that the word is fuzzy and anybody trying to nail it down, will fail.

is surely in direct conflict with The Principle of Relativity due to Einstein ?

That is about the proposition that the universe is isotropic and homogeous.

I do agree with his statement about fuzzyness however

[TheVat]

5 hours ago, joigus said:

 

Terms as bosonization (a fermion can be seen as a pair of bosons with a 'twist' between them), dualities (a strongly-coupled interaction in one region of space can be seen as a weakly-coupled one on the boundary of that region) etc., strongly suggest that any entities that we may propose are simply instrumental, and what emerges as really robust are physical principles, patterns, rather than 'things'.

 

This is an approach to ontology that is sometimes called a "bundle theory, " and goes way back to David Hume.   Physical entities,  rather than having any sort of substance, are construed as bundles of properties.  They ARE their properties,  rather than some thing that HAS properties.   

(plus one to your whole post,  BTW)  

I think bundle theory is quite germane to modern physics,  which as @swansont noted is pretty much a black box operation insofar as Aristotlean "stuff" is concerned.  

[joigus]

5 hours ago, Davy_Jones said:

Speaking as a physicist (I assume you are), do you consider the entities on the list to be real?

If not, why not?

Yes, I'm a physicist by training, but I don't work as one. I only play one on social networks. Although I'm more up-to-date than quite a number of your average physicists out there. 

Through my years I've learnt to deeply mistrust the term 'real' and what it whispers to my ear, so to speak. I prefer less exalted terms, like 'objective'. To me, a lambda hyperon, which has a lifetime the order 10^-13 s, is no less, no more real than a cloud, or a bee. It's very clear in my mind that it's more fundamental, simpler, less 'composite' than a cloud or a bee. But as doc said, at some point the word is not gonna cut it. Even for the cloud: Is it two clouds, or just one? A moment ago it wasn't there. Now it's come back at about the same position. Is it the same cloud?

2 hours ago, studiot said:

I am suspicious that this is too easy. It is easy to be seduced by thoughts of "how things ought to be" to the detriment of actually looking to see how things really are.

So I am rather worried about this idea.

7 hours ago, joigus said:

Well, yes. There's no guarantee that unification is possible. If it doesn't turn out that way, tough luck; but we must accept it. Somehow it seems hard to believe that the unification program will continue just up to a point, and then stop.

2 hours ago, 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.

I wouldn't invest too much on the concept of force. @MigL before proposed the more encompassing term 'interaction'. And @DrDon explained very clearly the limitations of such concept. The mathematics of physical theories is far less ambiguous in this respect. To me, whenever you have a system with coordinates X, another with coordinates Y, and and a coupling term involving X and Y, that's an interaction. It produces scattering, decay, etc. But again, words are very limited. Example: the cosmological constant: It is no doubt gravitational, but is it a force? An interaction perhaps? I don't think you can call it 'interaction' in any reasonable sense.

1 hour ago, TheVat said:

This is an approach to ontology that is sometimes called a "bundle theory, " and goes way back to David Hume.   Physical entities,  rather than having any sort of substance, are construed as bundles of properties.  They ARE their properties,  rather than some thing that HAS properties.   

I wasn't aware of this. I'll look it up. I find it very intellectually enticing. Thanks a lot.

I'm very nearly philosophically illiterate. --Blush

[studiot]

23 minutes ago, joigus said:

Well, yes. There's no guarantee that unification is possible. If it doesn't turn out that way, tough luck; but we must accept it. Somehow it seems hard to believe that the unification program will continue just up to a point, and then stop.

I think you misunderstood my point.

Edited September 4, 2021 by studiot

[joigus]

23 minutes ago, studiot said:

I think you misunderstood my point.

Most likely my mistake... Could you elaborate?

[studiot]

31 minutes ago, joigus said:

Most likely my mistake... Could you elaborate?

My point is just how wrong Plato and company were in believing they could deduce everything by just thinking about it.

[joigus]

7 minutes ago, studiot said:

My point is just how wrong Plato and company were in believing they could deduce everything by just thinking about it.

Sorry, I misunderstood.  It was Hume precisely who was there to open our eyes, wasn't he?

3 hours ago, studiot said:

So I am rather worried about this idea.

9 hours ago, joigus said:

Nature is probably connected all the way down to the most fundamental level. That's why such a thing as unification of physical laws is possible in the first place.

 

Somehow I saw a colon there.

[studiot]

2 hours ago, joigus said:

I'm very nearly philosophically illiterate. --Blush

Clearly you know more about it than I do.

1 hour ago, joigus said:

It was Hume precisely who was there to open our eyes, wasn't he?

Yes, but I prefer Rutherford.

Quote

Approximate quote on scattering

It was as though we had fired a 20 inch shell at a piece of paper and it had bounced back at us.

He was obviously prepared to make his philosophy fit his observations, not the other way round, despite his suprise.

[MigL]

11 hours ago, Davy_Jones said:

Take a look, if you will, at the following list of subatomic particles which, we are told, have been discovered since the year 1800.

https://en.wikipedia.org/wiki/Timeline_of_particle_discoveries

Now, I assume the entities on the list, with the exception of any serendipitious discoveries (X-rays?) which just kinda popped up out of the blue prior to starring in any bright spark's PhD dissertation, were originally posited as theoretical entities, perhaps regarded as "useful fictions" to begin with, much as atoms were until roughly a century ago.


Given, however, that these spooks were subsequently "discovered" . . . well, to my untrained ears, discovery pretty much entails reality. And if they're real, is it not the case that physics is--at least to some degree--describing reality for us?

Maybe the meaning of 'discovered' also needs some clarification.

What is actually discovered is the effect  these so called particles have on other particles.
Does that make the particles 'real', or is it simply the effect that is real and verifiable ?
Hence, models/theories describe effects ( mechanisms/interactions ), and are not concerned with the particles themselves.

4 hours ago, joigus said:

6 hours ago, TheVat said:

This is an approach to ontology that is sometimes called a "bundle theory, " and goes way back to David Hume.   Physical entities,  rather than having any sort of substance, are construed as bundles of properties.  They ARE their properties,  rather than some thing that HAS properties.   

I wasn't aware of this. I'll look it up. I find it very intellectually enticing. Thanks a lot.

We had a mathematical Physicist member, AJB, whose primary area of research was fibre bundle theory  of fields.

Fiber bundle - Wikipedia

He still posts very interesting stuff in our Blog section, but hasn't contributed to the forum in a couple of years.
It would have been interesting to get his take on the present subject.

[beecee]

4 hours ago, joigus said:

Yes, I'm a physicist by training, but I don't work as one. I only play one on social networks. Although I'm more up-to-date than quite a number of your average physicists out there. 

You do a reasonable job when playing the physicist may I say. 🙂

4 hours ago, joigus said:

I'm very nearly philosophically illiterate. --Blush

I wouldn't hold that against you...I believe action/knowledge speaks louder then words/thoughts.

[joigus]

35 minutes ago, MigL said:

Maybe the meaning of 'discovered' also needs some clarification.

What is actually discovered is the effect  these so called particles have on other particles.
Does that make the particles 'real', or is it simply the effect that is real and verifiable ?
Hence, models/theories describe effects ( mechanisms/interactions ), and are not concerned with the particles themselves.

We had a mathematical Physicist member, AJB, whose primary area of research was fibre bundle theory  of fields.

Fiber bundle - Wikipedia

He still posts very interesting stuff in our Blog section, but hasn't contributed to the forum in a couple of years.
It would have been interesting to get his take on the present subject.

LOL. That's a different bundle, and includes non-orientable surfaces. Very interesting stuff, and very relevant in gravitation, by the way. I did learn about those quite a bit. Yeah, I know who AJB is. It would be nice to have him around. I also miss @Markus Hanke, of course. I know he takes a peek sometimes.

14 minutes ago, beecee said:

You do a reasonable job when playing the physicist may I say. 🙂

LOL. Thanks. I did manage to peer-review publish some of my speculations long ago! Not very noticeable though... or noticed perhaps. I do teach physics, but on another level.

[beecee]

2 minutes ago, joigus said:

LOL. Thanks. I did manage to peer-review publish some of my speculations long ago! Not very noticeable though... or noticed perhaps. I do teach physics, but on another level.

Interesting. Any chance of a link to your stuff? 

[joigus]

44 minutes ago, beecee said:

Interesting. Any chance of a link to your stuff? 

Sure, if you're interested. Let me PM you as soon as I have the time to write some words to explain what it's about. It would be quite off-topic and improper here.

[Davy_Jones]

3 hours ago, MigL said:

Maybe the meaning of 'discovered' also needs some clarification.

What is actually discovered is the effect  these so called particles have on other particles.
Does that make the particles 'real', or is it simply the effect that is real and verifiable ?
Hence, models/theories describe effects ( mechanisms/interactions ), and are not concerned with the particles themselves.

I'd say so. To have an effect on other things is to have causal powers, and to have causal powers seems to me a sufficient condition (though not a necessary condition - see * below) for being granted reality status.

Conversely, that which does not exist (i.e., is not real) has no causal powers; can affect nothing.

You may have noticed the brief ramble @studiot and myself took near the bottom of page 4 into the reality of Harry Potter and the luminiferous ether.

Studiot, I think (correct me if I'm wrong), was suggesting that both Harry and the ether are somehow real, on the grounds that many people have been affected by them.

What I said to that, perhaps naively, is that (as far as we can tell) neither exists, neither is real. And if that's so, no one has ever been affected by either inasmuch as non-existent entities have no causal powers. What has had a causal effect on people is their beliefs about these things.

(As others have noted, it's mighty awkward to even discuss these matters without apparent contradictions arising; just to call them things seems to confer reality upon them.)

 

* There is a position in the philosophy of mathematics known as Platonism (him again!) which holds that numbers are real, but they exist in some ethereal (that again!) Platonic realm. If true, this would be a case of something being real, though devoid of any causal powers.

 

Philosopher of science Ian Hacking, meanwhile, defends scientific realism, unlike any other I know of, from the perspective of actual experimental practice in science, his maxim being "If you can spray them, they're real". More generally, we might say if you can manipulate these . . . um, thingies, or whatever you want to call them, then they're real.
 

7 hours ago, joigus said:

Through my years I've learnt to deeply mistrust the term 'real' and what it whispers to my ear, so to speak. I prefer less exalted terms, like 'objective'. To me, a lambda hyperon, which has a lifetime the order 10^-13 s, is no less, no more real than a cloud, or a bee. It's very clear in my mind that it's more fundamental, simpler, less 'composite' than a cloud or a bee. But as doc said, at some point the word is not gonna cut it. Even for the cloud: Is it two clouds, or just one? A moment ago it wasn't there. Now it's come back at about the same position. Is it the same cloud?

Ah, it's the old "Cloud of Theseus" conundrum all over again . . .

https://en.wikipedia.org/wiki/Ship_of_Theseus

 

Edit: The Ship of Theseus conundrum elicits different intuitions in different people as to whether it's the same ship.

I don't think anyone denies, however, that both ships (or is it one ship?) are real.

Same, presumably, applies to your clouds.

The problem is one of individuation, not reality.

Edited September 4, 2021 by Davy_Jones

[studiot]

54 minutes ago, Davy_Jones said:

You may have noticed the brief ramble @studiot and myself took near the bottom of page 4 into the reality of Harry Potter and the luminiferous ether.

Studiot, I think (correct me if I'm wrong), was suggesting that both Harry and the ether are somehow real, on the grounds that many people have been affected by them.

This invitation to 'correct' is too tempting to pass up.

'ether' is an organic compound containing an oxygen bridge - that is a C-O-C part.

Luminiferous aether was proposed by european scholars as a medium to transmit electrodynamic effects.

 

Now for the more serious stuff.

54 minutes ago, Davy_Jones said:

To have an effect on other things is to have causal powers, and to have causal powers seems to me a sufficient condition (though not a necessary condition - see * below) for being granted reality status.

 

No, I think causal is to strong a word and not what MigL or I meant.

I prefer MigL's interact or my affect. (MigL's is better)

'Causal' has special meaning in theoretical Physics, that a simple interaction does not.

 

But you are wrong to suggest I think that 'affect' automatically means reality; you are trying to oversimplify my points.

I was actually asking not stating, except that I stated this was in the context of seeking a test (I meant but did not say an objective test).

I proposed a test derived from the common slogan "If it can't interact with us the difference between not existing and existing is moot"

Philosophy and Science (and many other disciplines) tend to define away matters they can't or don't wish to deal with.

I pointed out that English Language is not so restrictive and provides the apparatus to many forms of 'reality' and non reality.

 

I was disappointed in the paucity of response.

Edited September 5, 2021 by studiot
spelling

[Davy_Jones]

3 minutes ago, studiot said:

Philosophy and Science (and many other disciplines) tend to define away matters they can't or don't wish to deal with.

Oh, certainly true, at least some philosophers.

The compatibilist notion of free will comes immediately to mind.

Next up, the eliminativist stance towards consciousness (e.g. Daniel Dennett). 

Seems to me a copout. "It's a tough problem so let's just explain it away".

[studiot]

But I am also disappointed in that this latest round of discussion is veering rapidly off topic whilst there is a real paucity of response to my most recent offering of new thoughts on the issue of is gravity a force or not.

At least I didn't say don't worry about force and use the term the force of gravity together in one post.

[Davy_Jones]

22 hours ago, Davy_Jones said:

I'd like to quote once more from Prof. Don Lincoln's marvellous lecture series (see above).

Lecture 16, "The Hunt for Gravitational Waves", 5:50 mins . . .

"Gone are the days of Newton's force of gravity. According to Einstein's equations, gravity is literally the bending of space"

 

Two questions for Don and everyone else:

It has been expressed in this thread that science cannot answer the question "What is gravity?" (on the grounds that it's metaphysical).

Q1: Isn't Einstein doing exactly that? Isn't Einstein saying the answer to the question "What is gravity?" is "the bending of space"?

(Even if the answer is wrong, he is still providing an answer.)

 

It has also been expressed in this thread that no one knows what gravity is.

Q2: If Einstein's theory is correct, is it not the case that lots of people know what gravity is? Namely, all those who believe his theory.
 

I'm a little disappointed myself at the paucity of responses to the above (from the previous page).

[studiot]

5 minutes ago, Davy_Jones said:

I'm a little disappointed myself at the paucity of responses to the above (from the previous page).

Prefessor Who ?

I suggest you read Nobel Physicist Frank Wilczek's book

The Lightness of Being

You might find more than one surprise in this book, relevant to this thread.

For one thing he devotes a whole chapter to resurrecting the lumineferous aether.

For another chapter he discusses gravity and some of the matters raised in this thread.

 

 

Edited September 5, 2021 by studiot

[Davy_Jones]

I'll check it out . . . just as soon as I'm allowed back in the library again. Grrr! 

[studiot]

2 minutes ago, Davy_Jones said:

I'll check it out . . . just as soon as I'm allowed back in the library again. Grrr! 

 

Now what about my comments on the issue of is gravity a force ?

[Davy_Jones]

8 minutes ago, studiot said:

 

Now what about my comments on the issue of is gravity a force ?

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.

 

Edit #2: Sorry, Studiot. I misread. Can you direct to the exact post you're referring to, please?

I do read everything that's posted, even if I don't always respond . . . often because the more technical parts fly over my layman's head.

Edited September 5, 2021 by Davy_Jones