IDK how gravity or topology works.
Well, first you have to get the elephants to stand on the turtle’s back
I was hoping to find this
A planetary mass disc would collapse into a sphere. Gravity works towards the centre of mass, so it makes sense that it becomes a sphere once the force is great enough, where the distance from said centre of mass is nearly equal from all points on the surface. it’s the reason why smaller objects are usually oblong and weird shaped (e.g. asteroids) while larger objects are close to spherical (e.g. Pluto!)
And what do you mean by “uniform gravity”? If you mean for a theoretical person on the planet, it would not be uniform on the edges as you have an imbalance of forces towards either side, while in the centre it is symmetrical, an equal amount of mass on either side. On a perfectly spherical planet, it would all add up to a downward force on any point on the surface
One interesting note, some planets like Jupiter and Saturn spin so fast they bulge in the equator, making them a little less spherical than normal!
edit: All the planets spin and have this bulge, but Jupiter and Saturn have the most noticeable bulges of the Solar System planets due to spinning the quickest
Earth, too. By about 43 km.
A planetary mass disc would collapse into a sphere
… but galaxies are “flat”?
Yep, as are solar systems. But when they collapse in to single objects, those objects end up spherical once they’re about a third the size of our moon (or even less than that if they’re icy/gaseous).
Not all galaxies are flat, and the stars in galaxies are sperated by enormous distances.
It’s the difference between Saturn and its rings. Saturn the plantet collapsed into a spheroid. The rings are pieces of stuff, not solid. Of all the stuff in the rings were thrown together into one solid clump, it would be a spheroid, too.
And I think we’re pretty lucky to see Saturn’s rings. Wait a few million years and they will collapse into a moon.
A galaxy isn’t a planet. Planets themselves are rarely perfect spheres. Earth is actually an oblate spheroid. Solar systems also exhibit planar geometry. They all spin. The angular momentum is enough to overcome the gravitational pull. If that momentum was not enough to overcome gravity, all that mass would collapse into a spherical object. Depending on how much mass would determine what kind of celestial body it is.
Earth doesn’t have uniform gravity…
It’s mostly uniform. There is variation by location, but the maximum difference is +/- 0.7% from the nominal value of 9.8 m/s^2.
The answer to your question is illustrated here in the first couple minutes of this old Vsauce video
Now, I’m confused. Does the magnitude of the gravity change or only the direction? Ooterness’s, linked physics analysis seem to show gravity would be super week near the edges. The video seems to suggest otherwise. Or maybe I’m just not understanding anything.
I’m almost certain that the pull of gravity would be weakest while standing at the center of the disc. The majority of the disc’s mass is distributed to your sides, acting evenly on you in all directions, so the net downward vector would be relatively weak.
Although gravity generally acts most strongly when you’re closest to the center of mass, that would surely no longer apply if you’re surrounded by the mass. Imagine there was a hollow space at the center of the earth. You could be at earth’s center of mass and experience no net gravity, since it would be pulling evenly on you in all directions.