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
First of all, it’s not just mass, energy also causes gravity. Secondly, we don’t know exactly why. But picture it this way: Think of how everything is always moving forward in time. Space and time are both dimensions of a unified thing we call spacetime. Mass and energy bend spacetime. When it’s bent, a little bit of that motion forward in time that’s always happening is instead movement in space. The two results are that an object in that bent spacetime will a) experience slightly less time and b) move towards the direction spacetime is bent. “a” is gravitational time dilation, which Einstein predicted and has been measured, “b” is what we call gravity.
We don’t know the answer. We know how much gravity, and roughly how it propagates, but we don’t know why.
We just know that mass/energy create space curvature that is otherwise perceived as an attraction, but we don’t know why it happens.
[Feynman on “why?”](https://www.youtube.com/watch?v=Q1lL-hXO27Q)
Nobody knows. Mass is right now a measurable property of matter, and we understand its effects on itself as well as space/time, but nobody knows why matter has mass, or why it has the properties it does.
I’m probably butchering this as I’m just a random guy that likes to watch space videos online.
But I actually think it’s too simplistic to say two things are attracted to one another. It appears as if gravity is the curvature of spacetime.
From our perspective that curvature makes objects act like they’re attracted to one another… But, that’s not exactly what’s happening.
A simplistic way to think about it would be like if you stretched a bedsheet out tight on 4 poles and threw some marbles on it. Then you jumped in the middle. All the marbles would roll towards you like they were attracted to you. But those marbles aren’t so much attracted to you, they’re more just following the curvature of the sheet.
Spacetime is basically the sheet but only 4-dimensional and it’s unintuitive to our senses to think about it as a thing.
Now WHY does mass appear to be curving spacetime? IDK. It just does. I don’t think anybody has really pinned that part down yet. A lot of people are working on it.
GOOD. FREAKING. QUESTION.
So the explanation given elsewhere here, which I won’t repeat because they’re pretty good, is that spacetime becomes curved in the presence of mass, and all things (apparently so far) curve spacetime the same direction, so when things get near each other, they follow the curvature caused by the distrotion, which pulls object closer to each other.
But what is the “spacetime” that is curving, and why do some particles cause a larger bending than others when not moving is still not particularly well established. The current theory is that some particles, notably bosons which are things like quarks that go on to make up protons and neutrons in matter, interact with a field known as the Higgs Field, like the particle you’ve no doubt heard of, and by interacting with this field they gain mass and curve spacetime. Other particles, like photons the particles that are responsible for light, don’t interact with the field and are thus don’t have mass, only energy.
But this is a huge rabbit hole of particle physics that ultimate remains not decidedly answered. There are several theories for how mass is generated and how they interact with gravity at many different scales, and much of it remains up for investigation. I would argue reconciling the connection between particle mass and gravity is the current holy grail of modern physics, in that even in a purely observational sense we can’t answer all of the relevant questions. This isn’t even bringing up things like dark matter, which is a big screw you question mark in the face of all of this.
don’t listen to the bullshit in this thread. it’s just the way it is and no one understands it. and don’t even think about asking about dark matter.
Ball. sheet,-spacetime. Space is Bent by mass causing objects to fall into another point. Gravity. Fact.
Lol great question. Maybe we can get back to you in another 100 years when we have a better understanding.
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.
Gravity isn’t really a force, that’s just an easy way to describe it. Gravity is actually the result of the bending of spacetime, which mass does. Imagine you place a bowling ball on a mattress. It’s going to make an indentation in the mattress while it sits there, right? Now imagine you put a smaller ball next the the bowling ball. What’s it going to do? It’s going to roll downhill into the indentation created by the bowling ball until it’s touching the bowling ball. Now that smaller ball makes an indentation as well, it’s just a lot smaller than the bowling ball because the bowling ball is a lot more massive.
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