Is Gravity a Force?

[Davy_Jones]

32 minutes ago, MigL said:

What does the ideology of scientists, and the purpose of Science, which is being discussed at some length, have to do with the nature of Gravity ???

Because whether or not physicists purport to describe reality is relevant to how we should read a statement such as "Gravity is a fundamental force" or "Gravity is the curvature of spacetime".

Should such pronouncements be understood as a mere façon de parler, not to be taken at face value, or are we being told this the way things really are.

 

 

25 minutes ago, beecee said:

It can, as I said, but that isn't the primary goal of physics and scientific theories . . .

And who has the final word on these things again?

Edited September 3, 2021 by Davy_Jones
added a li'l

[beecee]

6 minutes ago, Davy_Jones said:

Because whether or not physicists purport to describe reality is relevant to how we should read a statement such as "Gravity is a fundamental force" or "Gravity is the curvature of spacetime".

Depends under what model you are operating, and how much accuracy you require for a correct answer. remembering of course that Newtonian is near exclusively used on Earth, and afaik, also in all space endeavours, including the Voyagers and there close encounters with the four outer gas and ice giants.

8 minutes ago, Davy_Jones said:

And who has the final word on these things again?

As designated by the scientific methodology...via the collection of data through observational and experimental data, and the testing of hypothesis.

https://www.researchgate.net/publication/274872618_Physics_reality

Abstract

Editor's Note: There is probably no modern scientist as famous as Albert Einstein. Born in Germany in 1879 and educated in physics and mathematics at the Swiss Federal Polytechnic School in Zurich, he was at first unable to find a teaching post, working instead as a technical assistant in the Swiss Patent Office from 1901 until 1908. Early in 1905, Einstein published “A New Determination of Molecular Dimensions,” a paper that earned him a Ph.D. from the University of Zurich. More papers followed, and Einstein returned to teaching, in Zurich, in Prague, and eventually in Berlin, where an appointment in 1914 to the Prussian Academy of Sciences allowed him to concentrate on research. In November of 1919, the Royal Society of London announced that a scientific expedition had photographed a solar eclipse and completed calculations that verified the predictions that Einstein had made in a paper published three years before on the general theory of relativity. Virtually overnight, Einstein was hailed as the world's greatest genius, instantly recognizable, thanks to “his great mane of crispy, frizzled and very black hair, sprinkled with gray and rising high from a lofty brow” (as Romain Rolland described in his diary). In the essay excerpted here, and first published in 1936, Einstein demonstrates his substantial interest in philosophy as well as science. He is pragmatic, in insisting that the only test of concepts is their usefulness in describing the physical world, yet also idealistic, in aiming for the minimum number of concepts to achieve that description. In 1933, Einstein renounced his German citizenship and moved to the United States, where he lived until his death in 1955. A recipient of the Nobel Prize in physics in 1921, he was elected a member of the American Academy of Arts & Sciences in 1924.

[MigL]

17 minutes ago, Davy_Jones said:

Because whether or not physicists purport to describe reality is relevant to how we should read a statement such as "Gravity is a fundamental force" or "Gravity is the curvature of spacetime".

Should such pronouncements be understood as a mere façon de parler, or as the way things really are.

Descriptions are verbal models and, as such, some are applicable in some circumstances, and some are not.
If I were discussing Gravity with someone versed in GR, I would certainly use the curvature of space-time description.
If I were talking to a high-school student, I would use the force description.

Words are a tool, just like math is, and both can be used to describe ( model ) Gravity. Math is much less subjective and ambiguous, however, and usually doesn't lead to these kinds of discussions.

[Davy_Jones]

20 minutes ago, MigL said:

Words are a tool, just like math is, and both can be used to describe ( model ) Gravity. Math is much less subjective and ambiguous, however, and usually doesn't lead to these kinds of discussions.

 

There are also people (known as instrumentalists) who feel that scientific theories are nothing more than a tool, or a model, or an instrument for calculation, not subject to the predicates true and false.

But if you think all scientists subscribe to instrumentalism, think again.

Try asking Richard Dawkins, say, whether he thinks the theory of evolution is merely a tool with no bearing on the way things really are.

You might wanna bring a gun.

 

 

20 minutes ago, MigL said:

If I were discussing Gravity with someone versed in GR, I would certainly use the curvature of space-time description.
If I were talking to a high-school student, I would use the force description.

 

We touched on this earlier in the thread.

Now, if you are treating the two theories as mere instruments (as described above), there is no problem.

On the other hand, if you are presenting the two theories realistically--as the way things really are--then, assuming that the curvature of spacetime is not a force, you would be making two inconsistent statements. You would be contradicting yourself.

Edited September 3, 2021 by Davy_Jones
typos

[MigL]

'True', and 'truth' are subjective, and R Dawkins would be the first to agree.
( and the reason I use the scare quotation marks you previously asked about )

You seem to continuously want to steer the discussion in the Philosophy direction.
I am not well versed in Philosophy, but I have deluded myself into thinking I know a little Physics; and that is guiding the opinion I'm giving you.
My ( subjective ) 'truth', you might say.

[Davy_Jones]

19 minutes ago, MigL said:

'True', and 'truth' are subjective, and R Dawkins would be the first to agree.

 To the contrary, I suspect Dawkins would throw a fit.

If truth is subjective then the Creationists' truth is just as good as his own. It's all relative, eh?

Bring two guns

 

"Gravity is not a version of the truth. It is the truth. Anyone who doubts it is invited to jump out a tenth-storey window." - R. Dawkins

(It's a very silly comment, but gives you some idea what he thinks of truth)

 

19 minutes ago, MigL said:

You seem to continuously want to steer the discussion in the Philosophy direction.

Well, as I hinted at in the OP, I'm not sure it's possible to examine a question of this type without delving into a li'l philosophy.

 

19 minutes ago, MigL said:

I am not well versed in Philosophy, but I have deluded myself into thinking I know a little Physics; and that is guiding the opinion I'm giving you.

And I'm very grateful for it, sir.

 

 

59 minutes ago, beecee said:

Abstract

Editor's Note: There is probably no modern scientist as famous as Albert Einstein. Born in Germany in 1879 and educated in physics and mathematics at the Swiss Federal Polytechnic School in Zurich, he was at first unable to find a teaching post, working instead as a technical assistant in the Swiss Patent Office from 1901 until 1908. Early in 1905, Einstein published “A New Determination of Molecular Dimensions,” a paper that earned him a Ph.D. from the University of Zurich. More papers followed, and Einstein returned to teaching, in Zurich, in Prague, and eventually in Berlin, where an appointment in 1914 to the Prussian Academy of Sciences allowed him to concentrate on research. In November of 1919, the Royal Society of London announced that a scientific expedition had photographed a solar eclipse and completed calculations that verified the predictions that Einstein had made in a paper published three years before on the general theory of relativity. Virtually overnight, Einstein was hailed as the world's greatest genius, instantly recognizable, thanks to “his great mane of crispy, frizzled and very black hair, sprinkled with gray and rising high from a lofty brow” (as Romain Rolland described in his diary). In the essay excerpted here, and first published in 1936, Einstein demonstrates his substantial interest in philosophy as well as science. He is pragmatic, in insisting that the only test of concepts is their usefulness in describing the physical world, yet also idealistic, in aiming for the minimum number of concepts to achieve that description. In 1933, Einstein renounced his German citizenship and moved to the United States, where he lived until his death in 1955. A recipient of the Nobel Prize in physics in 1921, he was elected a member of the American Academy of Arts & Sciences in 1924.

(your own emphasis)

 

And your point is?

Did you notice the bit about "describing the physical world"?

Read that as "describing reality".

Edited September 3, 2021 by Davy_Jones
aesthetics again

[beecee]

1 hour ago, Davy_Jones said:

 And your point is?

Did you notice the bit about "describing the physical world"?

Read that as "describing reality".

My point is scientific theories are models describing what we observe and according to experimental results. Reality and truth you talk about, and whether they exist at all, are not the objective of scientific theories, but obviously as time progresses, as technology and instruments improve, our results become more accurate.eg: when we finally have a validated QGT. That most probably will answer more questions and be "closer" to any of this vague reality and truth you seem obsessed with. We are enormously successful at this time, with simply being able to describe gravity.

1 hour ago, Davy_Jones said:

 "Gravity is not a version of the truth. It is the truth. Anyone who doubts it is invited to jump out a tenth-storey window." - R. Dawkins

(It's a very silly comment, but gives you some idea what he thinks of truth)

Of course it is true, in that it exists. Dawkins'makes a very valid point, to anyone doubting gravity exists.

1 hour ago, Davy_Jones said:

If truth is subjective then the Creationists' truth is just as good as his own. It's all relative, eh?

Bring two guns

Not really, since by the very nature of ID, it falls outside of science and into the mythical category. The spiritual, supernatural and paranormal are by definition unscientific. I'll stick with the scientific method as Richard Dawkins does.

[studiot]

5 hours ago, Davy_Jones said:

Read that as "describing reality".

The terms real and reality ; exist and existence can be thought of as ill defined.

Instead of asking if something is 'real' can you offer me something that is not 'real'.

How would I test this ?

Can something which is not 'real' affect some things that are 'real' in any way ?

Is Harry Potter Real ?

Harry Potter has certainly affected millions of 'real' people.

This, I would suggest, is the real reason behind why Science shies away from such terms (pun intended)

 

 

[Davy_Jones]

15 minutes ago, studiot said:

The terms real and reality ; exist and existence can be thought of as ill defined.

1: Instead of asking if something is 'real' can you offer me something that is not 'real'.

2: How would I test this ?

3: Can something which is not 'real' affect some things that are 'real' in any way ?

4: Is Harry Potter Real ?

5: Harry Potter has certainly affected millions of 'real' people.

This, I would suggest, is the real reason behind why Science shies away from such terms (pun intended)

 

 

I've added numbers to your points above for convenience.

1. Ok. I hereby offer Harry Potter (Doubtless there are lots of people named Harry Potter out there. I mean the fictional character we both have in mind right now.)

2. We might conduct a search. Pretty sure we'd never find him, though.

3. I don't think so 

4. No (but see 1 above)

5. Many people have been affected by their beliefs about Harry Potter. Said belief corresponds to nothing in reality.

 

I throw these answers out--somewhat diffidently (lol)--to see what happens next. What do you think?

Edited September 3, 2021 by Davy_Jones
typo

[studiot]

2 minutes ago, Davy_Jones said:

I've added numbers to your points above for convenience.

Sounds good.

5.

Many people have been affected in other ways, whatever they believe about HP.
For instance many people have gained $millions on account of HP.
Some people, who have never heard of HP and have no beliefs about him, have had their lives saved by charities funded through HP related donations.

As a matter of interest, related to earlier discussion on belief in this thread, which definition of believe are you using ?

[Davy_Jones]

Your reasoning above is a bit like saying many people have been affected by the Fountain of Youth.

Ponce de Leon (was that his name?) squandered years searching for it. Said Fountain, as far as we can tell, does not exist; it is not real.

But Ponce de Leon believed it existed. It was his belief doing the causal work.

I'm using the term belief in the everyday sense.

[studiot]

13 minutes ago, Davy_Jones said:

Your reasoning above is a bit like saying many people have been affected by the Fountain of Youth.

Ponce de Leon (was that his name?) squandered years searching for it. Said Fountain, as far as we can tell, does not exist; it is not real.

But Ponce de Leon believed it existed. It was his belief doing the causal work.

I'm using the term belief in the everyday sense.

I'm glad you said reasoning ie rational thought.

Yes Harry Potter was merely an example to show why the terms 'real' and 'exist' are not as tightly set at might first appear.

This is also why I hold that English is more versatile than either Science or Philosophy because it can allow the existence of Harry Potter as an abstract concept.

Science, of course, has branches that study the effects of HP on the 'real world'.

 

As a matter of interest can you not think of a better offering , whose unreality is undisputed, to point 1,

Edited September 3, 2021 by studiot

[Davy_Jones]

1 minute ago, studiot said:

As a matter of interest can you not think of a better offering than HP to point 1, whose unreality is undisputed ?

 Ok, how about the luminiferous aether?

2 minutes ago, studiot said:

This is also why I hold that English is more versatile than either Science or Philosophy because it can allow the existence of Harry Potter as an abstract concept.

Hmm, the history of science also has no shortage of concepts which turned out to refer to nothing.

[studiot]

3 minutes ago, Davy_Jones said:

 Ok, how about the luminiferous aether?

Has that concept not affected many people for several centuries in their search for it, like your holy grail or perhaps the Physicist's TOE?

 

Just now, studiot said:

Has that concept not affected many people for several centuries in their search for it, like your holy grail or perhaps the Physicist's TOE?

I hope you will agree this is a more difficult question.

 

Edited September 3, 2021 by studiot

[Davy_Jones]

20 minutes ago, studiot said:

Has that concept not affected many people for several centuries in their search for it, like your holy grail or perhaps the Physicist's TOE?

 Of course it has. But note: what affected people was their beliefs about the aether, not the aether.

On the assumption (current scientific orthodoxy, I believe) that the aether does not exist (i.e. is not real) then it never affected anyone.

Edited September 3, 2021 by Davy_Jones
highlighted one word, changed a couple

[studiot]

1 minute ago, Davy_Jones said:

 Of course it has. But note: what affected people was their belief in the aether, not the aether.

On the assumption (current scientific orthodoxy, I believe) that that aether does not exist (i.e. is not real) then it never affected anyone.

But some (Stokes) never believed in the aether. And yet others held an open mind.

Yes they wrote mathematical works about it.

Stoke's maths is interesting because he discusses the application of negative mass to gravity in that work.

There is a summary in Berkson, that I referenced earlier.

 

Let me play philosopher, or at least what I call the philosopher's favourite game; that of combining at least two incompatible statements to make a paradox.

 

I offer that there is no such object as a four sided triangle.

 

[Davy_Jones]

6 minutes ago, studiot said:

I offer that there is no such object as a four sided triangle.

Fine. Go on . . .

6 minutes ago, studiot said:

But some (Stokes) never believed in the aether. And yet others held an open mind.

Quite so.

I edited my previous post before seeing this.

I changed "their belief in the aether" to "their beliefs about the aether".

Not all scientists believed in it, but they all (the ones relevant to us) had beliefs about it.

Edited September 3, 2021 by Davy_Jones

[studiot]

14 minutes ago, Davy_Jones said:

Fine. Go on . . .

Another problem with 'real ', which can be overcome in English but less well in Philosophy or Science is the fact that nouns come in many guises.

Some nouns are simple and occur all at once, at the same time and in the same place. For example a rich tea biscuit.

Others develop over time. This leads to the moral argument about when is an embryo / a foetus/ a human.

Yet others change over time but are always recognisable, for example the answer to the question What is the gravitational field of an object, varies depending upon what place and time you are asking it about.

 

 

Edited September 3, 2021 by studiot

[Davy_Jones]

Ok. Still listening . . .

[studiot]

Just now, Davy_Jones said:

Ok. Still listening . . .

So we come right back to my original question

How do we say what we mean by a force ?

Possibly our recent discussion leads to the suggestion that one good way to a fruitful discussion is to consider how the force interacts with other better known (defined) quantities.

Then we can limit our consideration to those quantities of interest, and state that "for our purposes", whatever those purposes may be, the quantity under consideration (gravity) is or is not a force.

 

[Davy_Jones]

Well, you're the scientist and I'm here to learn. Is there a universally agreed upon definition of force in science at present?

One thing we can say, I think, is that these things do tend to change, even in science.

If I'm not mistaken, Newton's action-at-a-distance concept of force was fiercely resisted for quite some time, especially on the continent.

"You call THAT a force!!??" - the French

Correct me if I'm butchering the history.

Edited September 3, 2021 by Davy_Jones
darn typos, and removed a dubious sentence

[studiot]

20 minutes ago, Davy_Jones said:

Well, you're the scientist and I'm here to learn. Is there a universally agreed upon definition of force in science at present?

One thing we can say, I think, is that these things do tend to change, even in science.

If I'm not mistaken, Newton's action-at-a-distance concept of force was fiercely resisted for quite some time, especially on the continent.

"You call THAT a force!!??" - the French

Force, to the continentals (and everyone else for that matter), had previously always involved contact.

Correct me if I'm butchering the history.

No your history is correct, but incomplete.

No there is no universal definition of force, it needs qualifiers ( basically selective filters of interactions)

An electromotive force creates current in an electric circuit.

Does gravity do this ?

Are there other differences between an EMF and gravity ?

In an isolated universe containing one single solitary massive body ( a massive body is a body with mass, not necessarily a large mass)  there is expectd to be gravity, but is there any mchanical force ?

So the contact boys have a point. It takes two to tango.

A force is applied between at least two bodies.

Gravity can do this when our test universe contains at least two bodies.

But how does it do this ?

Gravity is a distributed force, so if the region of operation is large can it be considered the same as a traditional line vector force ?

 

You see I am being 'scientific' in trying to narrow things down, using my preferred method of considering interactions.

What about action at a distance?

Well consider a small ring (small means small enough for our considerations)

How does gravity act on it ?

Gravity acts through the 'centre of gravity' of the ring, which is actually in the middle of the hole, and not a material part of the ring at all.

 

Edited September 3, 2021 by studiot

[Davy_Jones]

Ok, thanks for explaining that.

[swansont]

9 hours ago, Davy_Jones said:

What you seem to be saying, swansont, if I'm understanding you right (please correct me if I'm wrong), is that we should not believe anything physicists have to say about unobservable reality (quarks, bosons, and all the rest). After all, it's all--on your account-- just models, and "making up stuff", and "we know physics isn't trying to describe reality".

No, that's way off base. I never said we shouldn't believe what physicists say. I never came close to it. 

I'm saying that there is no basis to say that these discoveries show the underlying reality of the world. (Are you familiar with Plato's allegory of the cave?). Physics tells us how nature behaves, not how it is. Many of the parts of physics are calculational tools that let us more easily describe this behavior.

quarks, bosons, etc. aren't "unobservable reality"

We observe them, just not with the naked eye. And we are describing behavior. How they interact, and the rules of interaction . The interactions in QCD, for example - do you really think the physicists are claiming quarks and gluons are actually blue, green and red? That's reality? Can you explain how color has a meaning at that scale?

Or perhaps, as I'm claiming, it's a convenience, used because of the details of the interaction, i.e. the behavior. We make models that make some kind of sense to us, and use them if they work.

 

 

[studiot]

24 minutes ago, Davy_Jones said:

Ok, thanks for explaining that.

 

29 minutes ago, studiot said:

Gravity is a distributed force, so if the region of operation is large can it be considered the same as a traditional line vector force ?

 

I don't know if you understand what is meant by a traditional line vector force ?

Gravity is a distributed force, also called a body force.

This means it acts on each an every particle of a body individually.

The combined effect of all these individual actions can often be modelled as a single line vector, acting therough the centre of gravity.

So we have that bane of the schoolboy, 'a brick or block resting on a table', behaves (to use swansont's word) like this sort of line vector.

But the dam I offered way back could well topple over if it has been designed as though the dam behaviour under the influence of gravity was the same as that of the block.
It is necessary to consider the distribution of forces in such a case.

So where does that bring us to ?

Edited September 3, 2021 by studiot