Two bodies shielding each other from ultramundane corpuscles, creating a net attraction that we observe as gravity. Illustration by Georges-Louis Le Sage, ca. 1758.
Newton may have described the laws of gravity, but he couldn’t explain them. Le Sage had a mechanical explanation of gravity. He theorized that the universe is permeated by streams of small, unseen particles he calls ultramundane (originating from outside our observable universe) corpuscles. These particles impact on bodies from all directions. When a body stands by itself, the corpuscles impact on it equally from all directions, creating no net movement. But when two bodies, as above, stand close to each other, they both serve to partially shield each other from particles from one direction. This creates an imbalance in the force exerted on the object, more force from the direction not shielded by the other body, which results in a net movement or attraction towards the other body, which we observe as gravity. The apparent gravitational “attraction” between bodies is simply diminished push in the opposite direction.
To account for the proportionality of gravitational pull to mass, not surface area, we must make some further assumptions:
From the premises outlined so far, there arises only a force which is proportional to the surface of the bodies. But gravity is proportional to the masses. To satisfy the need for mass proportionality, the theory posits that a) the basic elements of matter are very small so that gross matter consists mostly of empty space, and b) that the particles are so small, that only a small fraction of them would be intercepted by gross matter. The result is, that the “shadow” of each body is proportional to the surface of every single element of matter. If it is then assumed that the elementary opaque elements of all matter are identical (i.e., having the same ratio of density to area), it will follow that the shadow effect is, at least approximately, proportional to the mass.
This isn’t some crackpot theory. Newton spoke favorably of the work of Nicolas Fatio, whose work Le Sage built on, although he appears to have had mixed feelings. There are many problems with it, but it took several centuries for the last serious attempts to rehabilitate it were abandoned.
I came across this theory after I read Greg Brown’s comment over at Mills’s blog:
I would love to see a book of intellectual dead-ends. We have chronicles of what lasted, but are sorely lacking in tales of what didn’t.
And he is right. This is really interesting. I can’t provide a book, but there are several other interesting scientific dead ends I’d like to explore in the future. (One is phlogiston theory, which has the unique characteristic of having been 1) widely accepted in the scientific community, and 2) almost the precise opposite of the theory that turned out to be correct.)
