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
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)
Newton : Any two mass in the universe pull each other with a force called gravity.
Einstein: Mass bends the space time fabric and the things circles around it falls into it.
Our sun’s mass is itself 99.8% of everything in our solar system.
What’s space-time fabric made up of ? Not sure. They call it waves. Like concentric ripples in a river.
I think Steve Mould has a few videos on visualising gravity. The current theory is that gravity is the distortion of spacetime around an object – the more massive the object, the greater the distortion. For example, if you place a bowling ball on a sheet of fabric, it’ll cause the fabric around it to stretch as it pushes downwards. Imagine that, but on three dimensions.
Honest answer, there is no definitive answer. The leading theory is objects with a higher mass cause a distortion in spacetime. There’s a video on YouTube you can check out called Gravity Visualized, super helpful.
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 why, we just know it does. Right now the best we have are some damn good theories, theories that are so good they almost certainly contain a huge amount of truth in them. But our theories are not the same thing as understanding. We can’t currently answer the question of “are anti-gravity engines possible?” or “can you make a gravity shield, or lens?”
People are not wrong in their explanations here but I think understanding how much we don’t know, and the majesty of that is probably the most important thing you take away from your question.
So you know how electrons and protons have electrical charges? In a sense, something’s mass is its gravitational “charge.” It’s kind of just a way of saying “how strongly does this object interact with a gravitational field?” Now, proving that it is the same mass as the mass that shows up in Newton’s laws of motion and is associated with inertia and everything is actually a non-trivial thing and was one of the first things that Einstein had to prove for his equivalence principle to be valid.
Okay, so that’s kind of the classical story. If you want to talk about relativity, that says that energy densities curve spacetimes. It is actually pretty mathematically beautiful, since the only assumptions that it comes from is that you can have a curved spacetime and matter living in that spacetime. This is what we know from Einstein’s equation. Mass really is just a bunch of energy tied up in one particular place (from E=mc^2 ), so it is really good at creating large energy densities and therefore curving spacetime.
But where does gravity come in? Well, things like to travel in straight lines, or at least they like to take the shortest distance between two points. When your space is curved, this shortest path is also changed from a straight line (think about being trapped on the surface of a sphere: the shortest distance between two points is really a circle). When particles follow these paths in a curved space, the effect looks exactly the same as a gravitational field. So mass curves spacetime because of the energy densities and the curves spacetimes give the effects of gravity.
Isn’t it strange? There’s no definitive answer, but imagine an MMRPG where:
Each player can carry some amount of special mana. The only action for this mana is to trade it, so you‘ll once in a while interact with other players with that special mana, and typically not too far from those players.
Players without mana don’t care about your mana and you don’t care about them.
Players with mana condense into big swarms and trade it in a frenzy. More game servers need to be spun up to handle all the trades for that swarm.
Other in-game mechanics, like NPC bosses, achievement missions, or mini-games, incentivize swarms to stay below a certain sizes.
Mana is mass. Players with mana are particles with mass. The idea that players with mana will congregate is the “force” of gravity. Players without mana are massless particles. The in-game-trades impact on server load represents the impact of gravity on the curvature of space time.
Other game mechanics are like other forces and their agents.
Mass = the ability to distort spacetime, the more you distort it the more gravitational pull you will have. They are less ‘attracted to each other’ and more ‘falling into each other’ like a marble circling a drain. The deeper the drain the faster the marble will fall to the middle, the shallower the slower it will fall. The more mass an object has the deeper that drain will be. That is, incidentally, why they call it a gravity ‘well’. Everything has it but when you are talking about something that has the mass of the sun the well is deep and long so planets as far as pluto are caught in it. That is a super-simplified idea but it might get you thinking in a way that makes more sense.
The simplified definition of gravity is the distortion of spacetime and or the result of differing velocities between bodies. GR is hard to teach to a 5 year old but SR isn’t, and that is where you get the idea of gravity really being the result of motion. An accelerating train feels on your back exactly how gravity feels on your feet.
Note: Not a physicist, but it’s not just a leading theory being talked about. There is some level at which we don’t know what mass has to do with gravity, and things get even weirder when you get to quantum scale. But the General Theory of relativity is one of the best tested and most robust theories out there. It is, for all intents and purposes the explanation linking mass and gravity.
The theory of relativity shows that spacetime is 4 dimensional and distortable. Energy is what causes that spacetime to distort. And since mass and energy are equivalent via E = MC^2, the more mass an object has, the more energy it has, and the more it distorts spacetime. The more distorted spacetime, the stronger the the effect of gravity you see, That Gravity Visualized video on youtube (mentioned by kylye) should give you an intuitive understanding of this.
Now the fun stuff, that we don’t know for sure (but there have been some really cool advances in in the last few years) is how gravity interacts on a quantum scale. All of the other forces (strong, weak and electromagnetic) are mediated by a particle. It is theorized that gravity is too, but gravity is so weak that we haven’t been able to observe that particle. We have seen gravity waves though, which helps to confirm the particle hypothesis. So the answer to your question is that we pretty much know on a macro scale what mass has to do with gravity (distortion in spacetime) but we don’t know on a micro scale for sure.
Latest Answers