Our Ignorance About Gravity
Why Physics Stack Exchange recommends it
Physics Stack Exchange users link it, and often ask about it, when questions come up about whether Newtonian gravity really holds for small objects and short distances.
Recommended by 1 people across 1 different months, 2019 to 2021.
What it is
A five-minute minutephysics explainer arguing that we have little experimental evidence for how gravity behaves at very short distances and tiny masses. It reviews what is known about the inverse square law at human, microscopic and atomic scales, and notes that Newton's law is only well constrained at solar system scales and larger.
What people said
Recommends John Rennie · 2020-01 · Physics Stack Exchange · on “Newtonian gravity in small objects and Cavendish Experiment”
The video you link [this video] is making the point that we cannot measure the gravitational force if the masses are too small. Cavendish used two lead spheres weighing $158$ kg as his large masses, and even though gravity is a weak force this mass is large enough to produce a detectable force. But suppose the masses were $158$ g, $158$ mg or $158\mu$ g. At some point the gravitational force is going to get too small to be measured, and if we cannot measure the force we cannot know for certain that it obeys Newton's equation. In fact there have been suggestions that the inverse square law might break down at very short distances. This would happen if there were large extra dimensions [LINK] as su
Cites Keis · 2019-09 · Physics Stack Exchange · on “Newtons law of gravity universal?”
Im a bit puzzled about the video from “One Minute Physics” claiming that Newtons law of gravity is not universal, but breaks down on very heavy objects and are not really confirmed on very light ones. [this video] I found the topic interesting, also because I teach basic physics in primary school (children age 13-16), and dont want to use wrong information. We do use some pretty odd examples just to make it a little more fun. But trying to read more on the subject just added confusion, because most places (books, web etc.) treats the gravitational law as a fundamental universal law. Any takes on this? Is it fair to apply Newtons law using the weight of a student and the weight of a grain of dust
Cites Publius Staticus · 2020-01 · Physics Stack Exchange · on “Newtonian gravity in small objects and Cavendish Experiment”
Going through the internet I've found claims (like the ones found on this MinutePhysics video [this video] ) that Newton's law of gravitation could not be applied to small, everyday objects. However, after reading about the Cavendish Experiment for calculating the gravitational constant, how could these claims be considered true if at Cavendish's time the understanding of gravity was based solely on Newtonian Gravity? P.s: If possible please mention scientific sources.
Cites Charles Hudgins · 2021-04 · Physics Stack Exchange · on “According to general relativity planets and Sun bend the spacetime (explaining gravity), but does this hold true for smaller objects?”
Smaller objects *may* warp spacetime, but for all we know they don't. Indeed, very small objects clearly require some theory other than general relativity. In short, general relativity is a great theory for large massive bodies, but we're quite ignorant about how gravity works for smaller objects because experiments are so difficult to perform and because the theory becomes so delicate. Cf [this video]