# Subatomic particle and space curvature

Can we say that each subatomic particle affects space time such that collectively as big as a planet it explains why there is gravity?

Thank you very much.

Nabeshin
Well, to the big question you're asking the answer obviously has to be yes. Each individual particle does curve spacetime according to general relativity, having its own "gravitational field", and we know the net effect is that of a macroscopic object. You have to be careful in thinking about how you would actually do such a computation. The field equations of GR are not linear (in contrast to, say, the field equations for electromagnetism), so you cannot simply "add" the spacetime curvatures from all the different elementary particles and recover what we know to be the curvature for an object like the earth. Instead, you have to actually consider the system of 10^50 or however many particles you want in the stress energy tensor and then proceed to solve the einstein equations (a tall task indeed!).

But schematically, yes what you're saying is correct, just note that gravity is not an emergent phenomenon but does exist on the smaller scales as well.

Well, to the big question you're asking the answer obviously has to be yes. Each individual particle does curve spacetime according to general relativity, having its own "gravitational field", and we know the net effect is that of a macroscopic object. You have to be careful in thinking about how you would actually do such a computation. The field equations of GR are not linear (in contrast to, say, the field equations for electromagnetism), so you cannot simply "add" the spacetime curvatures from all the different elementary particles and recover what we know to be the curvature for an object like the earth. Instead, you have to actually consider the system of 10^50 or however many particles you want in the stress energy tensor and then proceed to solve the einstein equations (a tall task indeed!).

But schematically, yes what you're saying is correct, just note that gravity is not an emergent phenomenon but does exist on the smaller scales as well.
Then why is there a need for graviton?

George Jones
Staff Emeritus
Gold Member
Then why is there a need for graviton?
It is though that quantum theory applies to everything, but we do not have a quantum theory of gravity. A quantum theory of gravity probably will use gravitons.

It is though that quantum theory applies to everything, but we do not have a quantum theory of gravity. A quantum theory of gravity probably will use gravitons.
So graviton should exist because Einstein can't explain Quantum Mechanics?

George Jones
Staff Emeritus
Gold Member
So graviton should exist because Einstein can't explain Quantum Mechanics?
I woudn't put it this way.

So graviton should exist because Einstein can't explain Quantum Mechanics?
I may have missed something. How can we then reconcile gravitons and spacetime curvature to be one principle that explains gravity?

Massive bodies emit gravitons to tell spacetime how to curve through the stress-energy tensor.

Massive bodies emit gravitons to tell spacetime how to curve through the stress-energy tensor.
If you remove graviton will spacetime be still curved one way or another (or perhaps its curvature will be in a flux)? Does this mean that all subatomic particles have its own graviton?

Hypothetically, right now Einstein's General Theory of Relativity states that mass and energy tell the stress-energy tensor how to curve spacetime, the graviton just appears logical because all other forces have bosonic carriers.

Hypothetically, right now Einstein's General Theory of Relativity states that mass and energy tell the stress-energy tensor how to curve spacetime, the graviton just appears logical because all other forces have bosonic carriers.
Thanks! That does clarify things for me.