[AnotherGoodName]

It wouldn’t surprise me if at some point in the future we realise mass shields us from a gravitational field that pushes everything in all directions at once as opposed to our current thinking that mass emits a field that pulls us towards it.

Eg. imagine the earth below you shielding you from a force that otherwise pushes all mass in all directions constantly. You’re now more shielded from the push in the direction of the earth so you feel pulled that way.

It’s the same thing. Just a sign change from a convention we had no real basis to believe one way or the other.

[atahanacar]

What you are describing is a meme in my country, used to make fun of religious anti-evolution people who claim "evolution is only a theory and not a proven law, thus doesn't exist".

We call gravity "yer çekimi", which literally means "the pull of ground". The meme is "Ya yer çekimi yoksa da gök itimi varsa?" which translates to "What if the gravity doesn't exist but sky-push does?".

[Joker_vD]

> It wouldn’t surprise me if at some point in the future we realise mass shields us from a gravitational field that pushes everything in all directions at once as opposed to our current thinking that mass emits a field that pulls us towards it.

It would definitely surprise me since I know that this theory — since it's such an obvious hypothesis — has been proposed multiple times since Newton's own (it's now colloquially called "Le Sage's theory of gravitation" [0], but it had many other proponents including Kelvin, H. Lorentz and Thomson) and it has always failed to accomodate the equivalence of graviational and inertional masses: after all, the gravity is not proportional to the cross-section of the bodies, and graviational shielding does not exist — experiments done by Eötvös were quite decisive in that regard.

[0] https://en.wikipedia.org/wiki/Le_Sage%27s_theory_of_gravitat...

[ViktorRay]

Well I guess that explains why "the normal force" is the one that counteracts gravity.

(for those of you who don't know, the super simplified explanation in physics 101 is that the normal force is the vector that pushes up while gravity pushes down for objects that are resting on top of each other)

So I guess the one who named it "the normal force" would be more correct that he ever imagined if your theory of gravity was the real correct one!

[hollerith]

Turn it into a theory that predicts exact quantities (accelerations) and I will start paying attention.

[tzs]

The idea he's describing is Le Sage's theory of gravity, and it does correctly predict many of the things Newtonian gravity predicts. Specifically it predicts an inverse square attraction between pairs of bodies and that the attraction is proportional to the masses of the bodies.

It turns out it doesn't quite work, but it is interesting enough try that does get enough things right that quite a few well known physicists over the years have taken a look at it. The Wikipedia article on it covers a lot of them [1].

Feynman talks about it briefly in section 7-7 of volume I of the Feynman lectures [2]:

> Many mechanisms for gravitation have been suggested. It is interesting to consider one of these, which many people have thought of from time to time. At first, one is quite excited and happy when he “discovers” it, but he soon finds that it is not correct. It was first discovered about 1750. Suppose there were many particles moving in space at a very high speed in all directions and being only slightly absorbed in going through matter. When they are absorbed, they give an impulse to the earth. However, since there are as many going one way as another, the impulses all balance. But when the sun is nearby, the particles coming toward the earth through the sun are partially absorbed, so fewer of them are coming from the sun than are coming from the other side. Therefore, the earth feels a net impulse toward the sun and it does not take one long to see that it is inversely as the square of the distance—because of the variation of the solid angle that the sun subtends as we vary the distance. What is wrong with that machinery? It involves some new consequences which are not true. This particular idea has the following trouble: the earth, in moving around the sun, would impinge on more particles which are coming from its forward side than from its hind side (when you run in the rain, the rain in your face is stronger than that on the back of your head!). Therefore there would be more impulse given the earth from the front, and the earth would feel a resistance to motion and would be slowing up in its orbit. One can calculate how long it would take for the earth to stop as a result of this resistance, and it would not take long enough for the earth to still be in its orbit, so this mechanism does not work. No machinery has ever been invented that “explains” gravity without also predicting some other phenomenon that does not exist.

[1] https://en.wikipedia.org/wiki/Le_Sage%27s_theory_of_gravitat...

[2] https://www.feynmanlectures.caltech.edu/I_07.html

[ViktorRay]

Well why wouldn’t it? The mathematical constants could remain the same as in the current theories.

Both the constant G for gravitation and g for the acceleration for gravity on earth.

I am not a physicist so I may be getting something wrong

[hollerith]

Newton's Philosophiae Naturalis Principia Mathematica (published 1687) contains a mathematical (geometric actually) proof that the gravitational attraction between the Earth an a man standing on the surface of the Earth is the same as it would be if all of the mass of the Earth were at its center. There's another proof that if the man is standing at the bottom of a one-mile hole, and the Earth is assumed to be a perfect sphere, then the attraction is the same as if the Earth's radius were one mile less than it actually is (i.e., the attraction between the man and the shell of mass higher in altitude than the man is exactly zero because the attraction from the various points in the one-mile-thick shell exactly cancel out).

That is that kind of thing I mean: proofs and calculations, not "why wouldn't it?"

[ViktorRay]

Hey thank you for your reply. I learned several interesting examples from your first paragraph in the comment.

I do think your last sentence here was unnecessary though:

”That is that kind of thing I mean: proofs and calculations, not "why wouldn't it?"”

When I said “why wouldn’t it” I was asking out of genuine curiosity. There really wasn’t any need to criticize that part. It came off as maybe more hostile than I think you intended.

Again I most certainly appreciate you taking the time to type up the rest of your comment though because I did learn quite a bit from those examples you posted so I am indeed sincerely grateful for that.

[bequanna]

As a layperson, that makes sense to me. It also explains the time dilation effect when near a large mass.

[AnotherGoodName]

Thinking of it as directional action potentials that are blocked by mass? I agree it does feel intuitively nicer that way honestly.

[bequanna]

Yep. Coming from everywhere and moving outward in all directions at all times and ‘absorbed’ or ‘blocked’ by mass

[marmadukester39]

Physicists: Has anyone ever looked into this?

[abecedarius]

Yes. https://en.wikipedia.org/wiki/Mechanical_explanations_of_gra...

(but I only play a physicist on HN)