I was watching a Vsauce video and learned that any two objects, like two baseballs, are attracted to each other because of their mass, and the bigger the mass, the more gravity an object has. What does mass have to do with gravity, and what causes gravity? Why does something just attract other things around it?
In: Physics
The idea that objects with mass are attracted to each other is the old Newtonian model of gravity. However, Einstein developed a more accurate model with General Relativity and in General Relativity things work differently. (However, Newton’s Universal Gravitation is a very close approximation of General Relativity in most cases and it’s a lot simpler to work with so it’s still very useful).
The ELI5 of General Relativity is that all mass and energy causes space-time to curve, and objects will try and follow a straight line in that curved space-time. So a very massive object will curve space-time in towards itself and other objects that get nearby will follow that curve towards the object.
A common analogy that’s used is the rubber sheet analogy where a heavy object makes a dent in a rubber sheet which causes things going near the object to follow the curve made by the dent. However, keep in mind that space-time is 4-dimensional and one of those dimensions is time so it’s a lot more complicated than that.
Incidentally, this means that the common explanation for black holes being something that you can’t escape because the escape velocity is faster than light isn’t quite complete. What actually happens at the event horizon is that the curvature of space-time gets so extreme that things get really weird. Specifically, what happens is that the curvature of space-time gets so twisted that all straight lines that go towards the future point towards the singularity so no matter which way you face or how fast you go, you can only ever go towards the singularity.
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