Leibniz v. Newton: Handbags at dawn.

[uwot]

This is where uwot and I part company. My position is basically that gravity is a fundamental force in the same way as the other other forces are fundamental. In other words, said forces cannot be explained in terms of anything else.

I am sure uwot will have a fair bit to day about my statement, and fair enough I might add. This sort of thing is subject to volumes of philosophical debate.

Well, of course. The main difficulty I have with ideas of forces being fundamental is that they are pluralist. To stick just to gravity, that approach faces the same challenge that Cartesian dualism struggles with, ie: how do the two substances, mind/body in the case of Cartesianism, force/matter for current purposes, interact? That pretty much was the point of my opening post.

...Einstein is not postulating any new substance. From my point of view he outlining a more dynamic role for space and time when we add gravity into the mix.
In other words, space and time are no longer the background or backdrop where physical events are played out. As as per Newton. I guess we can say that under Einstein, universality switches from space/time to the idea of gravity being universal. As one would expect this idea is not without problems as well.

Well, I don't think Einstein argued that gravity is fundamental; after all, his model is based on the premise that it is only matter/energy that creates the conditions that give rise to gravity. What I understand Einstein to mean is that matter changes the properties of spacetime. For Newton, space and time didn't have properties, they, like Ginkgo's gravity, were fundamental. It's not that Einstein is postulating a 'new' substance, rather that the old dimensions of space and time, combined are a substance, something with characteristics that can be altered.

Hi Wyman,


Fair enough, none of this stuff is set in concrete. It is quiet possible we are all wrong- laypeople or otherwise.

Seconded.

[uwot]

So I am reading things the same as gingko. That's not to say we're right, but just that that is how I interpret what I have read about physics, which is a 'layperson's' understanding at best (speaking for myself, not gingko). I'll have to think about uwot's position some more and maybe re-read some Einstein and/or Hawking in light of it.

Hi Wyman,

Fair enough, none of this stuff is set in concrete. It is quiet possible we are all wrong- laypeople or otherwise.

Just a quick addendum: I think this neatly demonstrates that it is entirely possible to have different views on the nature of space, time and the causes of forces, but agree that the maths works. That's what physicists do: shut up and calculate.

[Ginkgo]

Just a quick addendum: I think this neatly demonstrates that it is entirely possible to have different views on the nature of space, time and the causes of forces, but agree that the maths works. That's what physicists do: shut up and calculate.

Yes, I go along with that. Perhaps the philosophical disagreements are simply just scientific works to be undertaken as soon as possible.

[uwot]

....Perhaps the philosophical disagreements are simply just scientific works to be undertaken as soon as possible.

To a degree: in the sense that something is metaphysical, because it is beyond current scientific capability. But we can never know that our scientific capability gives us answers that will not be refined, if not contradicted by technological advances. There are also certain metaphysical beliefs that are impervious to scientific investigation; there is no conceivable scientific procedure that could ever prove that a being that cannot be detected by science, yet maintains everything, does not exist. We are stuck with omnipotent deities moving in mysterious ways; the only resolution is for the real god to fess up and say 'Here I am.'

[Wyman]

So I am reading things the same as gingko. That's not to say we're right, but just that that is how I interpret what I have read about physics, which is a 'layperson's' understanding at best (speaking for myself, not gingko). I'll have to think about uwot's position some more and maybe re-read some Einstein and/or Hawking in light of it.

Hi Wyman,

Fair enough, none of this stuff is set in concrete. It is quiet possible we are all wrong- laypeople or otherwise.

Just a quick addendum: I think this neatly demonstrates that it is entirely possible to have different views on the nature of space, time and the causes of forces, but agree that the maths works. That's what physicists do: shut up and calculate.

Let me take another crack at this. There are two, at least, components to my argument that physicists do more than calculate. First, there's the more obvious psychological point that coming up with new conjectures, interpretations and proofs requires more than mere calculation. It requires imagination and association, among other things - that goes to my illustration of Feynman's 'Babylonian' method of mathematics. Think of doing a proof in geometry, for instance. One does not just calculate, as one would perform long division or multiplication. One 'racks' one's brain for similar 'avenues' of thought from similar problems, similarities of aspects of the models - it quite fits Plato's 'knowledge as recollection' conjecture - much of it is associative in nature.

The second component I'd propose is something like Kant's neumena or Wittgenstein's 'that of which we cannot speak...'

Arguing whether gravity is fundamental to Einstein's physics or physics in general is not arguing over whether gravity is 'really' fundamental, but whether gravity is a fundamental (elemental, undefined, simple) term in the system involved - that is, in the collection of rules (axioms, theorems, hypotheses) and the corresponding model or interpretation of those rules. It is the model that is placed up against reality for comparison - agreement or disagreement with observation. But the model may only 'touch' reality at certain very limited points for that comparison. So the model is not coextensive with the reality it is created to describe.

Thus, to say that gravity, or anything else is fundamental is like saying that points, lines and planes are fundamental to plane geometry. Yes, they are undefined terms, elemental to the system of axioms, with a one to one correspondence with their model (dots and lines on a piece of paper being one such model).

The model describes (along with elemental relations such as incidence, congruence, etc.), say, most of what you could draw with a pencil on a piece of paper (in a sense, which 'sense' is a huge subject in itself). But it does not make sense, quite, to say that dots and dashes -pencil marks - on paper (rather than points and lines in theory) are fundamental elements of a piece of paper.

[uwot]

Let me take another crack at this. There are two, at least, components to my argument that physicists do more than calculate.

I agree. There is no point in a physicist's education at which they stop being human beings.

First, there's the more obvious psychological point that coming up with new conjectures, interpretations and proofs requires more than mere calculation.

Thomas Kuhn is the usual reference point here, he argued that there is 'normal' science, which is how most professionals spend their career and involves working with the concepts and mathematical tools of the current paradigm. A large part of the job is calculating, but, said Kuhn, there is also revolutionary science, which becomes necessary as inconsistent data accumulates to a point where the consensus about the paradigm breaks down and scientists start looking for a new model. Kuhn has been criticised for being too conservative, he appears to believe that scientists all agree with a current paradigm, which is more or less the same belief that WanderingLands has, except they have twisted it slightly so that the scientific 'elite', for some reason are defending a paradigm they know to be untrue. I see that Greylorn Ell has posted a similar thesis. The truth is a bit more complicated; if you want results, you use the mathematical tools that work best, you can believe anything you like about what 'reality' is like, but if the sums don't add up, it is useless.
For example, the Copernican revolution changed our view of the world as much as Darwin or Einstein and it very nearly happened 1500 years earlier. Aristarchus of Samos proposed the same heliocentric model as Copernicus. We only really know about it, because Archimedes, who in anyone's book is a proper scientist mentioned it in a book called 'The Sand Reckoner'. It demonstrates a way, basically exponation, to express numbers so large they have no practical applications. For instance, how many grains of sand it would take to fill the universe. He explains to King Gelon of Syracuse, to whom the book is dedicated, that most people are familiar with the geocentric model described by Aristotle, but there is another model, described in a book by Aristarchus of Samos that depicts the cosmos as considerably larger. Aristarchus had worked out that the sun is a lot larger than the Earth and argued that it is improbable that the larger body should orbit the smaller. We know this is true, and clearly Archimedes was sympathetic, but the Aristotelian model had been developed mathematically by Eudoxus and Calippus, two brilliant mathematicians, and the predictive power of their models wasn't matched by Aristarchus. With a few tweaks the Aristotelian model became the Ptolomaic one, which is perfectly adequate for naked eye observations. The metaphysics, the philosophical model on which the mathematical model is based can be complete bollocks, if the maths tells you what you want to know, use it; shut up and calculate.
The point about scientists being human is that they will have all sorts of crackpot ideas about what actually makes the universe tick. I don't know if, for instance, Ed Witten genuinely believes that fundamental particles really are strings or whether they can simply (Ha!) be described that way; it's a lot of effort for something you don't believe to be the case, but hey, some people just like really difficult maths.

It requires imagination and association, among other things - that goes to my illustration of Feynman's 'Babylonian' method of mathematics.

Which is much more like Feyerabends Methodological Anarchy. Yes; people use the tools at hand and sometimes they invent new ones. Some people are labourers, some are craftsmen and some are inventors.

Think of doing a proof in geometry, for instance. One does not just calculate, as one would perform long division or multiplication. One 'racks' one's brain for similar 'avenues' of thought from similar problems, similarities of aspects of the models - it quite fits Plato's 'knowledge as recollection' conjecture - much of it is associative in nature.

This is a reference to the slave in Plato's Meno http://classics.mit.edu/Plato/meno.html . The main problem I have with this is that there are no examples, that I am aware of, of people suddenly just 'remembering' things; they generally have to have it demonstrated, which corrupts the evidence and makes the conclusion unsound.

The second component I'd propose is something like Kant's neumena or Wittgenstein's 'that of which we cannot speak...'

Kant realised that there are a priori concepts, notably space and time, that we invent to structure and order our experience: separate things happen sequentially, we imagine this happens 'in' something.
I had to read Ayer's Language, Truth and Logic as preparation for my first degree; it nearly put me off. Inspired by Wittgenstein, the Logical Positivists formulated the verification principle, basically that talk of anything for which there is no empirical evidence is meaningless. But as people on the forum have noted, science makes hypotheses for which there is currently no empirical evidence, and then try to introduce technology that provides the evidence.

Arguing whether gravity is fundamental to Einstein's physics or physics in general is not arguing over whether gravity is 'really' fundamental, but whether gravity is a fundamental (elemental, undefined, simple) term in the system involved - that is, in the collection of rules (axioms, theorems, hypotheses) and the corresponding model or interpretation of those rules.

There is a force, there are different explanations. Whatever your preferred explanation, it makes no difference to the strength of the force.

It is the model that is placed up against reality for comparison - agreement or disagreement with observation. But the model may only 'touch' reality at certain very limited points for that comparison. So the model is not coextensive with the reality it is created to describe.

It doesn't have to be for the purposes of science, it only has to agree with the phenomena.

Thus, to say that gravity, or anything else is fundamental is like saying that points, lines and planes are fundamental to plane geometry. Yes, they are undefined terms, elemental to the system of axioms, with a one to one correspondence with their model (dots and lines on a piece of paper being one such model).

The model describes (along with elemental relations such as incidence, congruence, etc.), say, most of what you could draw with a pencil on a piece of paper (in a sense, which 'sense' is a huge subject in itself). But it does not make sense, quite, to say that dots and dashes -pencil marks - on paper (rather than points and lines in theory) are fundamental elements of a piece of paper.

Well, since you mention Plato, it is more plausible (but not very realistic) to argue for a realm in which mathematical 'truths' exist, rather than our 'memories'. The axioms of geometry are independent of any actual paper or pencils, whereas the 'truth' of gravity is contingent on there being a universe. Gravity is not the way it is for reasons of logic, it is for some 'physical' reason. We don't know what that reason is, but that hasn't stopped us sending probes to planets millions of miles away.
In one sense, Kuhn was right, a lot of professional science is a dreary slog. Which is why it is better to be a philosopher.

[Wyman]

Let me take another crack at this. There are two, at least, components to my argument that physicists do more than calculate.

I agree. There is no point in a physicist's education at which they stop being human beings.

It requires imagination and association, among other things - that goes to my illustration of Feynman's 'Babylonian' method of mathematics.

Which is much more like Feyerabends Methodological Anarchy. Yes; people use the tools at hand and sometimes they invent new ones. Some people are labourers, some are craftsmen and some are inventors.

I feel you pay lip service to this idea, yet you really think that physicists should 'just shut up and calculate.' You'll deny it, but I'll continue to call you on it.

Wyman wrote:

Think of doing a proof in geometry, for instance. One does not just calculate, as one would perform long division or multiplication. One 'racks' one's brain for similar 'avenues' of thought from similar problems, similarities of aspects of the models - it quite fits Plato's 'knowledge as recollection' conjecture - much of it is associative in nature.

This is a reference to the slave in Plato's Meno http://classics.mit.edu/Plato/meno.html . The main problem I have with this is that there are no examples, that I am aware of, of people suddenly just 'remembering' things; they generally have to have it demonstrated, which corrupts the evidence and makes the conclusion unsound.

I take Plato's point here as a psychological observation - with a fantasy, mystical interpretation attached to it which is obviously unverifiable. The observation is that problem solving and recalling something are very similar experiences. Think of when a word is on the tip of your tongue and the mental gymnastics utilized to 'capture' the elusive word or concept. Compare this with solving a word puzzle or finding the solution to a proof. That's what I was getting at. Now, to claim that this observation proves the immortality of the soul, I will admit is a stretch.

Wyman wrote:
Arguing whether gravity is fundamental to Einstein's physics or physics in general is not arguing over whether gravity is 'really' fundamental, but whether gravity is a fundamental (elemental, undefined, simple) term in the system involved - that is, in the collection of rules (axioms, theorems, hypotheses) and the corresponding model or interpretation of those rules.

There is a force, there are different explanations. Whatever your preferred explanation, it makes no difference to the strength of the force.

No, this is where the heavy lifting comes in. There is a model which has gravity as an element (or a complex of elements perhaps) and there is a differing model (perhaps) that also has something called 'gravity' as an element or concept. But don't say that the two models describe the same 'real' thing called gravity. They may involve in a sense the same concept of gravity, but you can't (or else you haven't justified doing so) claim to be describing reality.

Think of it this way: one model of basic Euclidean geometry interprets a point as the familiar dot on paper. Another interprets it as a member of a set (two such members determine one and only one set, etc.). Hilbert famously said that one could interpret points and lines as chairs and beer mugs.

Now, a dot, an element of a set, and a beer mug can be said to describe the same 'thing,' but only in the sense of describing some very abstract concept.

Similarly, I would argue, saying that different models all interpret 'gravity' in some way or other, does not say that they all describe the same thing, except an abstract concept.

Your insistence that the 'force' is a real thing that is being variously measured and described involves a leap of faith.

I am not advocating for idealism. I am pointing out that one cannot sidestep the problems of 'how do concepts relate to reality' and 'how is knowledge possible' - the age old problems of philosophy - by expanding the field of inquiry to all of science rather than single concepts.

Another way to perhaps shake the determination that gravity is a 'real' force that is variously described is by Einstein's equivalence of gravity and inertial mass and his own examples. When you are accelerating in your sports car or going around on a circular carnival ride, do you interpret your car or the metal frame of the ride as exerting a field of force - or beaming out quantum gravity particles? He said that you can think of gravity (excepting such cases as standing on the Earth) as accelerating, like standing in a constantly accelerating elevator - as the floor pressing up against your feet. But when you think of it as the floor pressing against your feet, are you so sure that a field of force called 'gravity' is a real thing? Or are you now saying that legs and floors and something called 'acceleration' are real things?

[uwot]

I feel you pay lip service to this idea, yet you really think that physicists should 'just shut up and calculate.'

No. I really do think that physicists, and in fact all people, will inevitably have their own visions and that this should be tolerated, and even encouraged. The fact is though, if you want to put a man on the moon, you need to get the sums right.

You'll deny it, but I'll continue to call you on it.

Well, if I can't persuade you that I actually believe what you refuse to believe I believe, it's going to be a struggle, but could I refer you, or remind you of my initial post? The whole premise of this thread is that physicists should have ideas that go beyond the purely empirical and mathematical.

I take Plato's point here as a psychological observation - with a fantasy, mystical interpretation attached to it which is obviously unverifiable. The observation is that problem solving and recalling something are very similar experiences. Think of when a word is on the tip of your tongue and the mental gymnastics utilized to 'capture' the elusive word or concept. Compare this with solving a word puzzle or finding the solution to a proof. That's what I was getting at. Now, to claim that this observation proves the immortality of the soul, I will admit is a stretch.

To be honest, I don't see the similarity between remembering words and problem solving with the same clarity as you apparently do.

No, this is where the heavy lifting comes in. There is a model which has gravity as an element (or a complex of elements perhaps) and there is a differing model (perhaps) that also has something called 'gravity' as an element or concept.

I disagree. Gravity is not an element or concept in a theory, it is a thing theories are about. Aristotle's explanation for 'gravity' was teleological. The four terrestrial elements, he said, had natural movements; straight up for air and fire, straight down for water and Earth, basically there was somewhere they 'wanted' to be, there was no mechanism involved. Newton did a brilliant job of describing 'how badly they wanted it', but left his explanation at 'There is a force, which I call gravity.' It's not an explanation; gravity is just Latin for weight, that things are heavy wasn't news even in Newton's time.

But don't say that the two models describe the same 'real' thing called gravity.

The two models describe the same 'real' thing called gravity. In fact any number of models describe the same thing. Generally speaking, there are three elements to a theory in physics: there is the empirical data, some phenomenon that needs explaining; this is the factual part: either there is a phenomenon or there isn't. Then there is the maths. This is less factual in that it agrees with the empirical data, or it doesn't, but there's necessarily a bit of wiggle room, because a mathematical tool doesn't have to be perfect to be useful and despite the ravings of the more hyperbolic maths realists, it is unlikely that we will ever demonstrate that any mathematical model is 'perfect', much less that we 'know the mind of god'. Finally, there is the metaphysics. This can be useful. Like the idea of warped spacetime, or it can just be an emotional crutch; something to help you make sense of it all, doesn't matter; the phenomena are what they are and the maths works or it doesn't.

They may involve in a sense the same concept of gravity, but you can't (or else you haven't justified doing so) claim to be describing reality.

I've already thrown my hat into the ring: I think the best explanation for 'gravity' is that it is refraction. Oh, yes: I can match Greylorn Ell and WanderingLands for metaphysical fruitloopery, I just don't throw my toys out of the pram when people tell me I'm nuts and I don't think there is an international conspiracy to suppress my hypothesis.
There is a difference between describing what reality does and what it is; you don't have to believe that Spacetime is warped to see the efficacy of the fields equations.

Think of it this way: one model of basic Euclidean geometry interprets a point as the familiar dot on paper. Another interprets it as a member of a set (two such members determine one and only one set, etc.). Hilbert famously said that one could interpret points and lines as chairs and beer mugs.

Now, a dot, an element of a set, and a beer mug can be said to describe the same 'thing,' but only in the sense of describing some very abstract concept.

Similarly, I would argue, saying that different models all interpret 'gravity' in some way or other, does not say that they all describe the same thing, except an abstract concept.

When my bathroom scales groan, that is not an abstract concept. (Although, for pedants, it is a metaphor.)

Your insistence that the 'force' is a real thing that is being variously measured and described involves a leap of faith.

Any leap of faith will result in me plummeting Earthwards. I suppose I could be wrong, but that has been my experience so far; it's the problem of induction.

I am not advocating for idealism. I am pointing out that one cannot sidestep the problems of 'how do concepts relate to reality' and 'how is knowledge possible' - the age old problems of philosophy - by expanding the field of inquiry to all of science rather than single concepts.

As I have said: in terms of knowledge, there are certain analytic truths and there are empirical truths. We will never know that any machine or observation will tell us the whole and final truth.

Another way to perhaps shake the determination that gravity is a 'real' force that is variously described is by Einstein's equivalence of gravity and inertial mass and his own examples. When you are accelerating in your sports car or going around on a circular carnival ride, do you interpret your car or the metal frame of the ride as exerting a field of force - or beaming out quantum gravity particles?

No. I interpret it as a centrifuge.

He said that you can think of gravity (excepting such cases as standing on the Earth) as accelerating, like standing in a constantly accelerating elevator - as the floor pressing up against your feet. But when you think of it as the floor pressing against your feet, are you so sure that a field of force called 'gravity' is a real thing?

Yep.

Or are you now saying that legs and floors and something called 'acceleration' are real things?

Those too.

[Wyman]

I feel you pay lip service to this idea, yet you really think that physicists should 'just shut up and calculate.'

No. I really do think that physicists, and in fact all people, will inevitably have their own visions and that this should be tolerated, and even encouraged. The fact is though, if you want to put a man on the moon, you need to get the sums right.

Fair enough.

You'll deny it, but I'll continue to call you on it.

Well, if I can't persuade you that I actually believe what you refuse to believe I believe, it's going to be a struggle, but could I refer you, or remind you of my initial post? The whole premise of this thread is that physicists should have ideas that go beyond the purely empirical and mathematical.

I'm not convinced, but no matter, it's just a difference of emphasis, I think. I didn't know you were endorsing Liebnitz's view. You usually say that physics is not concerned with first causes. I think I disagree with you and Gingko here - again, to an extent. I don't see a clear difference between pushing for a deeper understanding of the fundamental particles, for instance (which would include finding their causes - i.e. more fundamental particles) and finding first causes.

I take Plato's point here as a psychological observation - with a fantasy, mystical interpretation attached to it which is obviously unverifiable. The observation is that problem solving and recalling something are very similar experiences. Think of when a word is on the tip of your tongue and the mental gymnastics utilized to 'capture' the elusive word or concept. Compare this with solving a word puzzle or finding the solution to a proof. That's what I was getting at. Now, to claim that this observation proves the immortality of the soul, I will admit is a stretch.

To be honest, I don't see the similarity between remembering words and problem solving with the same clarity as you apparently do.

Fair enough. I don't think many people would agree with many of my interpretations of Plato. And it was meant as an aside, really. Chalk it up as a bad illustration of the point I was trying to make.

No, this is where the heavy lifting comes in. There is a model which has gravity as an element (or a complex of elements perhaps) and there is a differing model (perhaps) that also has something called 'gravity' as an element or concept.

I disagree. Gravity is not an element or concept in a theory, it is a thing theories are about. Aristotle's explanation for 'gravity' was teleological. The four terrestrial elements, he said, had natural movements; straight up for air and fire, straight down for water and Earth, basically there was somewhere they 'wanted' to be, there was no mechanism involved. Newton did a brilliant job of describing 'how badly they wanted it', but left his explanation at 'There is a force, which I call gravity.' It's not an explanation; gravity is just Latin for weight, that things are heavy wasn't news even in Newton's time.

But don't say that the two models describe the same 'real' thing called gravity.

The two models describe the same 'real' thing called gravity. In fact any number of models describe the same thing. Generally speaking, there are three elements to a theory in physics: there is the empirical data, some phenomenon that needs explaining; this is the factual part: either there is a phenomenon or there isn't. Then there is the maths. This is less factual in that it agrees with the empirical data, or it doesn't, but there's necessarily a bit of wiggle room, because a mathematical tool doesn't have to be perfect to be useful and despite the ravings of the more hyperbolic maths realists, it is unlikely that we will ever demonstrate that any mathematical model is 'perfect', much less that we 'know the mind of god'. Finally, there is the metaphysics. This can be useful. Like the idea of warped spacetime, or it can just be an emotional crutch; something to help you make sense of it all, doesn't matter; the phenomena are what they are and the maths works or it doesn't.

They may involve in a sense the same concept of gravity, but you can't (or else you haven't justified doing so) claim to be describing reality.

I've already thrown my hat into the ring: I think the best explanation for 'gravity' is that it is refraction. Oh, yes: I can match Greylorn Ell and WanderingLands for metaphysical fruitloopery, I just don't throw my toys out of the pram when people tell me I'm nuts and I don't think there is an international conspiracy to suppress my hypothesis.
There is a difference between describing what reality does and what it is; you don't have to believe that Spacetime is warped to see the efficacy of the fields equations.

Think of it this way: one model of basic Euclidean geometry interprets a point as the familiar dot on paper. Another interprets it as a member of a set (two such members determine one and only one set, etc.). Hilbert famously said that one could interpret points and lines as chairs and beer mugs.

Now, a dot, an element of a set, and a beer mug can be said to describe the same 'thing,' but only in the sense of describing some very abstract concept.

Similarly, I would argue, saying that different models all interpret 'gravity' in some way or other, does not say that they all describe the same thing, except an abstract concept.

When my bathroom scales groan, that is not an abstract concept. (Although, for pedants, it is a metaphor.)

Your insistence that the 'force' is a real thing that is being variously measured and described involves a leap of faith.

Any leap of faith will result in me plummeting Earthwards. I suppose I could be wrong, but that has been my experience so far; it's the problem of induction.

I am not advocating for idealism. I am pointing out that one cannot sidestep the problems of 'how do concepts relate to reality' and 'how is knowledge possible' - the age old problems of philosophy - by expanding the field of inquiry to all of science rather than single concepts.

As I have said: in terms of knowledge, there are certain analytic truths and there are empirical truths. We will never know that any machine or observation will tell us the whole and final truth.

Another way to perhaps shake the determination that gravity is a 'real' force that is variously described is by Einstein's equivalence of gravity and inertial mass and his own examples. When you are accelerating in your sports car or going around on a circular carnival ride, do you interpret your car or the metal frame of the ride as exerting a field of force - or beaming out quantum gravity particles?

No. I interpret it as a centrifuge.

He said that you can think of gravity (excepting such cases as standing on the Earth) as accelerating, like standing in a constantly accelerating elevator - as the floor pressing up against your feet. But when you think of it as the floor pressing against your feet, are you so sure that a field of force called 'gravity' is a real thing?

Yep.

Or are you now saying that legs and floors and something called 'acceleration' are real things?

Those too.

I guess I just don't see how what you have said is consistent with your original post:

"Like I say; the most likely cause of all the phenomena that give the impression of a universe made of stuff, is some stuff the universe is made of. The problem with Newton is that (thanks to Hypotheses non fingo) he is reduced to asserting that the cause of gravity is the gravitational force, which doesn't explain anything." - (aside) actually, it explained an awful lot - it described it as a 'force', which concept Newton was able to introduce and define and use to explain all sorts of things, including gravity

Yet you keep saying that "The two models describe the same 'real' thing called gravity." I don't see how that is different from Newton.

As I think about it, perhaps my failure to understand what you are getting at involves your distinction between finding causes (metaphysics) and explaining how the world works (physics). I don't think there is a distinction there, at least not a neat distinction that travels through all of the subject matter.

[uwot]

I think we are all just trying to make sense of an extraordinary experience. As far as we can tell, human beings have always told stories about where the world came from and how it works. For most of our history, those stories were about supernatural beings; for many people, they still are. A little over two and a half thousand years ago, this bloke called Thales decided to try and explain how the world works without reference to gods. In doing so, he inspired the fragmentation of thinking about the world into empiricism, mathematics and metaphysics. (I won't go into details here as there is an article on precisely that topic in the next issue of Philosophy Now, which should be out in a few weeks.) They are the foundations, the primary colours, if you wish of western thought. Some people can't let go of spirituality; others see dark forces, but most people make do with some blend of those three, including professionals in any single discipline.
As I mentioned in the OP, this thread was inspired by a book I took on holiday because of something Ginkgo had said about Leibniz. This bit sums it up:
"As significant as his critique of Descartes' mechanics was Leibniz's attack on Newton's account of force. In the Principles , Newton limited himself to describing interactions between bodies in terms of general mathematical laws. This limitation was both a strength and a weakness. Newton succeeded in making the complexities of nature amenable to mathematical description only by simplifying the phenomena: by treating material particles as if they were infinitely hard, yet infinitely elastic, concentrated at points, capable of exchanging any amount of force all at once, connected by forces operating instantaneously at a distance, and so on.
Leibniz complained that this made Newton's system an idealised abstraction, which could not possibly be true of the real world. In reality, nothing was absolutely hard or elastic, nothing happened instantaneously, and every causal interaction was mediated by a complex mechanism. In general terms, Newton would have agreed with Leibniz's comment. He too believed in underlying mechanisms, but he refused to comment about them in the Principles (his famous, 'I do not invent hypotheses.')
A more damaging criticism which Leibniz brought against Newton was that he gave pseudo-explanations in terms of magical 'occult virtues'. Just as Molière had joked about the scholastic explanation that opium sends one to sleep because of its 'dormative virtue', so Leibniz laughed at Newton for explaining the gravity of things as due to a gravitational force. The trouble was that Newton's forces were defined in terms of directly measurable masses and changes in velocity. This meant that these masses and velocities themselves were the primary realities. The forces he postulates added nothing new to reality, and therefore explained nothing."

I think this is where Ginkgo and I differ; from what Ginkgo has said, it would appear that he is content to treat 'gravity' as a fundamental force, and the fact is that for physics to work, you don't have to know how gravity works. In terms of empiricism, mathematics and metaphysics, you can do science perfectly well with just the first two.
MacDonald Ross goes on:

"Leibniz held that it is not enough to formulate mechanical laws to describe and predict the behaviour of physical systems. A genuine science also had to explain the phenomena by postulating underlying mechanisms and powers of which perceptual motions were the results."

Thanks to the influence of Newton, with support from Mach and Bohr in particular, there is a strong 'positivist' element in science that don't feel they have to explain, and they are right. But any scientist that doesn't wonder, at least privately, how it all works, beyond the observation and the maths is missing all the fun.

[Wyman]

"Leibniz held that it is not enough to formulate mechanical laws to describe and predict the behaviour of physical systems. A genuine science also had to explain the phenomena by postulating underlying mechanisms and powers of which perceptual motions were the results."

I think Leibniz is making a mistake by taking metaphysics seriously and as something different from physics. If I explain matter as made of atoms stuck together, I have postulated 'underlying mechanisms and powers of which perceptual motions were the results.' When I then make observations which lead me to infer that atoms are made up of smaller particles, I postulate neutrons, electrons and protons and mark how they interact, which then explains some of how atoms interact. Etc.

Physics is constantly in search of mechanisms and powers which are foundational to what they already know from observation. They don't stop at molecules, or atoms, or atomic particles. They keep searching.

I see your position, and perhaps Leibniz', as claiming that at the end of the process, there will still be something more to 'explain.' I don't think there is an end of the process (of physics) nor something meta - physical that needs explaining.

So Newton's explanations were the beginning of a process and Leibniz did not have the perspective, as a contemporary, to see how this process would unfold, with the discovery of atoms, Einsteins' revamping of gravity and special relativity. Without that perspective, it still seemed as if 'all' physics could accomplish was a broad description of the movement of bodies. It proceeded to be much more than that, filling that explanatory void which Leibniz perceived.

[uwot]

I think Leibniz is making a mistake by taking metaphysics seriously and as something different from physics. If I explain matter as made of atoms stuck together, I have postulated 'underlying mechanisms and powers of which perceptual motions were the results.' When I then make observations which lead me to infer that atoms are made up of smaller particles, I postulate neutrons, electrons and protons and mark how they interact, which then explains some of how atoms interact. Etc.

The way the Greeks splintered thinking reduces to three activities:
1. Description.
2. Calculation.
3. Speculation.

In their purest forms you have:
1. Science which is impotent.
2. Maths which is irrelevant.
3. Philosophy which is incoherent.

The bottom line is:
1. If you are not talking about the phenomenal world, you are not doing science.
2. If you are not manipulating precisely defined abstract entities, you are not doing maths.
3. If you are not examining concepts, you are not doing philosophy.

In the real world, those disciplines are blended to imprecise and changeable formulae by practitioners of all three, which is why it is difficult to define any one of them. Leibniz and Newton worked to different formulae. I have heard talk about 'hard science', by which some people seem to mean science that is unadulterated by speculation: 'hard science' is the stuff we 'know'. Newton was one of them.
My game is philosophy. One thing I have learnt is that if all you do is manipulate concepts, you are likely to end up with nonsense like Parmenides' Monism or Anselm's Ontological Argument. For that reason, I have worked very hard to understand the concepts of physics. I couldn't give a monkey's about the maths (it is vital for making things work, but that isn't my interest); as I said, if it isn't about the phenomenal world, it's irrelevant.

Physics is constantly in search of mechanisms and powers which are foundational to what they already know from observation. They don't stop at molecules, or atoms, or atomic particles. They keep searching.

Indeed, but what they are looking for is more observations. It is quite possible that the particles we currently think fundamental really are. But then if you accept some version of modern field theory, QCD and QED being examples, the best candidate for what particles are is that they are, perturbations, excitations, ripples, waves, knots or some other disturbance in a field. If that is so, then, while it is foolish to say never, there is no currently conceivable way that an undisturbed field can be detected; it simply cannot be seen. The best analogy I can think of is that it is like trying to understand water and the only information you have is the churning of the surface.

I see your position, and perhaps Leibniz', as claiming that at the end of the process, there will still be something more to 'explain.'

I'm not sure what you mean here. Surely the "end of the process" would be a point where there is nothing left to explain; I'm not so contrary to think that there would then be something left to explain, when there is nothing left to explain.

I don't think there is an end of the process (of physics)

I agree with that. It is possible that we will reach the limit of usefulness, but I don't think it is possible to know that there is nothing left to find out. In practical terms, for all that physicists make predictions about what particle accelerators will find, they don't know until they find them.

nor something meta - physical that needs explaining.

It depends what you mean by need. We don't currently need to know the process or mechanism that is responsible for gravity, nor do we need to know what fundamental particles are made of, although if you ask me, it the same stuff the Big Bang was made of (what else could it be?), which is why such a small amount can make such a mess.

So Newton's explanations were the beginning of a process and Leibniz did not have the perspective, as a contemporary, to see how this process would unfold, with the discovery of atoms, Einsteins' revamping of gravity and special relativity. Without that perspective, it still seemed as if 'all' physics could accomplish was a broad description of the movement of bodies. It proceeded to be much more than that, filling that explanatory void which Leibniz perceived.

Bit harsh on Leibniz. None of us can predict the future.

[Wyman]

My final passing thought (Well, I could talk about this stuff endlessly actually, but you'd get bored and everybody else has lost interest):

I couldn't give a monkey's about the maths (it is vital for making things work, but that isn't my interest); as I said, if it isn't about the phenomenal world, it's irrelevant.

Back to the Feynman lectures I noted earlier. Watch the one on the relation of math to physics. He claims that you cannot know the physics without knowing the math. It's discouraging actually to watch it, because I, like you, don't aspire to know the math, but am very interested in the subject nonetheless.

[uwot]

Back to the Feynman lectures I noted earlier. Watch the one on the relation of math to physics. He claims that you cannot know the physics without knowing the maths.

True, but then physics without maths isn't physics.

It's discouraging actually to watch it, because I, like you, don't aspire to know the math, but am very interested in the subject nonetheless.

If you mean you are interested in physics, you're out of luck. Physics really is the mathematical description of the phenomenal world; there is no option but to learn the maths. But don't despair; if it is the philosophical questions that interest you, like: 'What is the universe made of?' you are wasting your time with maths anyway.