eli5: What creates gravity?


If gravity is what holding the planet together. How did gravity came to be in the first place? Can we visualise gravity? Can gravity be increased or decreased? If a planet is destroyed into chunks, will gravity holds the broken planet together?

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Based on our current understanding Gravity is a warping of spacetime

Gravity is not a force like Magnetism, or an exchange of particles, it is the warping of space itself.

Imagine a trampoline, now place a bowling ball in the center. This warps the material of the trampoline. Now roll a tennis ball beside it and the ball will follow the curvature of the material.

This is one of the ways we can visualize what is going on with gravity, but gravity affects spacetime in 4 dimensions not just two.

Gravity appears to be directly related to mass, as the greater the mass of an object, the more gravity it has.

Gravity is also the only force we know of that can affect space over very vast distances and accumulates rather than cancelling out.

>If gravity is what holding the planet together. How did gravity came to be in the first place?

The mutual attraction of smaller particles caused them to attract and combine. At that scale static electricity would have been more important as it was stronger than gravity. But as these masses crew to asteroid size they started affecting one another gravitationally more and more until they merged into planets.

>Can we visualise gravity?

See above

>Can gravity be increased or decreased?

Yes, it is directly proportional to the mass of an object

We do not currently have a way to modify gravity with technology

>If a planet is destroyed into chunks, will gravity holds the broken planet together?

It can, it depends on how much energy was involved in the explosion.

For example the Moon was formed when the early Earth was struck by a Mars sized object.

Gravity was strong enough to not only hold Earth together but to keep most of the material in orbit until it’s own gravity formed the moon

We don’t actually know what creates it. Its one of the fundamental forces of the universe but we’re still missing a Theory of Quantum gravity that ties things together.

Gravity seems to just come from Mass/Energy causing dips in space time and pulling on everything else nearby. Why does it come from Mass? As far as we can tell, it just does. This is the problem with fundamental forces, there is no why as they’re part of the underlying structure.

Destroying a planet into chunks is actually ludicrously hard because of gravity.

Consider asteroids.

You likely just though of a big hunk of solid rock right? Most asteroids are closer to a pile of variously sized gravel that’s all bunched together. Its held together by its gravity. If you were to crack it in half and pull them a little ways apart, their gravity would pull them right back together. Gravity doesn’t change because its a single object instead of two objects, the gravity comes from each tiny pebble and a given pebble always contributes the same amount

Not a physicist so anyone else correct me if I’m wrong.

Anyway, as far as we can tell, gravity appears to be just a fundamental fact of reality. Anything with mass imparts a curvature on spacetime (whole other ELI5 can of worms there) and the result is that masses tend to get pulled together. Whoever figures out why certain universal constants exist can sit on top of their pile of Nobel prizes.

We can visualize gravity often by reducing reality down to two dimensions in a diagram.

https://www.researchgate.net/profile/Matjaz-Vidmar/publication/332442180/figure/fig1/AS:[email protected]/Gravity-Field-Diagram-and-Gateway-Earth-Space-Access-Architecture-C-Gateway-Earth.jpg

The topic of that diagram is something else but can you see how the earth and moon create a depression in the space around? That’s effectively what’s happening, except the “plane” of space there is 3d in reality instead of 2d there.

If a planet were to go kablooey like Alderaan in Star Wars, it all depends on the power of the explosion. If it’s strong enough to send most or all of the pieces away at faster than escape velocity*, the planet’s gone forever. They may or may not end up creating an asteroid belt around the planet’s sun. But if it were just barely enough to break up the planet, the pieces might fly around and collide with each other for a bit before eventually settling back into place, in a wildly different configuration than they were at first.

Good luck in your further research. 🙂

*I mentioned escape velocity up there, and I suppose the actual value would be less than the intact planet because of the distance between the parts after the initial explosion. But up to a certain point the debris field could be considered to have a single barycenter with its own escape velocity before the sun or other bodies became more important in the calculation.

The best way to visualize gravity (for me!) was when I went to a science museum as a kid. Spacetime is like a blanket. When you put something heavy in the middle, it warps. I didn’t know it as a kid, but the ingenious way to raise funds for the museum was to put a coin in a slot that fed into the top of a metal cone. It would roll and circle around until it met it’s doom. A hole in the bottom that was a “black hole.” Just like planets today.