# About the pointwise or distributed form of matter

• Omega0
In summary: In other words, it's the body of knowledge that explains the behavior of matter and energy as they are observed in the real world.So, Newtonian physics includes everything from the basic laws of motion to the theory of light and color.What is Newtonian gravity if this
Omega0
Please help me in understanding the history of physics regarding the atomic or non-atomic, say continous, structure of physics.
In my years at school I grew up with physics of ultimate simplifications. Everything was a point "particle", like the moon revolving around the earth. Like the apple falling from the tree. Naturally, this wasn't true for Thermodynamics but let us stay with "Newton and friends" for now. I have a bunch of further questions so this will be probably just the starter.
For me, it always felt bizarre in my school times that gigantic planets are just points in a theory. The sun although is a massive point. For me this was Newton, somehow, as it was teached. "Explaining" Kepler somehow.

Nowadays, I have a completely different picture. Let me please cite E. Poisson, Clifford M. Will, "Gravity", Cambridge University Press (2014):

"There are of course, many compelling reasons to begin a study of gravitation with a thorough review of the Newtonian theory... The reason that compels us most of all is that although there is a vast literature on Newtonian gravity - a literature that is accumulated over more than 300 years - much of it is framed in old mathematical language that renders it virtually impenetrable to present-day students. ... One of our main goals, therefore, is to submit the classical literature on Newtonian gravity to a Jacksonian treatment, to modernize it so as to make it accesible to present-days students."

I would say that Jackson may even be more steep in the development of a continous explanation of the relevant model but this doesn't matter. What matters to me is the development in physics generally. The 300 years of literature mean for example thermodynamics to be included.

My point is the following, in this little "survey": What is Newtonian Gravity in a sense of what he originally wrote? What essentially did he write? How was matter structured for him? Was Newtons Gravity an "atomic" thing? What is "Newtonian physics" if this is defined? Or did he write about continous matter distributions? Which he reduced to a point?
One of the (for me) bizarre things is the "Newtonian Fluid". Is this the prove that he although worked in continous matter? Where he didn't think about "particles"? So, what was then a planet for him? And - if he didn't believe in atoms, why should he has been working in Alchemy?

Etc.... thousands of questions waiting for you experts.

Thanks.

You may find this article by a physics prof interesting. He infers from scattered quotes in Newton's works that Newton thought of matter as collections of point particles held together by forces acting at a distance. Previously people assumed bits of matter needed to touch one another to bind together. But Newton introduced the idea of action at a distance through his theory of gravity. Although nobody had discovered yet the electrostatic and nuclear forces that hold solids together, Newton anticipated that something like that would be going on.

Omega0 said:
My point is the following, in this little "survey": What is Newtonian Gravity in a sense of what he originally wrote? What essentially did he write? How was matter structured for him? Was Newtons Gravity an "atomic" thing? What is "Newtonian physics" if this is defined? Or did he write about continous matter distributions? Which he reduced to a point?
You can read some of what he wrote in his Principia. I've linked to an 1846 American edition below, and you can find the relevant work starting in section 12 on page 224 of the pdf (218 as labeled in the book). Note that the force that we call gravity he refers to as a 'centripetal force' throughout the book (or at least the sections I read through) because of how he introduces it in his book.

Omega0 said:
For me, it always felt bizarre in my school times that gigantic planets are just points in a theory. The sun although is a massive point. For me this was Newton, somehow, as it was teached. "Explaining" Kepler somehow.
That's a view based on ignorance of the theory. It's fine not to understand physics, but you shouldn't assume your confusions about a theory are inherent in the theory itself.

Newton proved something called the Shell Theorem, which shows that the gravitational force between two spheres is the same as that between two point masses.

So, it's not an assumption that the Sun and planets are point masses, but that the shell theorem allows us to model the gravitational interaction as though between point masses.
Omega0 said:
"There are of course, many compelling reasons to begin a study of gravitation with a thorough review of the Newtonian theory... The reason that compels us most of all is ...
That Newtonian gravitational gives an extremely accurate model of the solar system. That is, in fact, the main purpose of the theory. It's not an arbitrary intellectual game.

BillTre

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