# Space time curvature and gravity [duplicate]

Is Space time curvature responsible for gravity or Gravity responsible for the curvature in space-time.

• Gravity is a physical phenomenon. Spacetime curvature is merely a human description for how it behaves. – CuriousOne Apr 17 '16 at 2:45
• oh can you explain the phenomenon of gravity just tell me why gravity exists – Faisal Iqbal Baba Apr 17 '16 at 2:53
• Science finds descriptions for reality, not existential reasons. Having said that, some people believe gravity is one of the remnants of one fundamental force, from which every other force can be derived, others think that space, time and gravity are one emergent phenomenon that has something to do with either quantum physics or thermodynamics (probably both, actually). The problem with that is that we don't know what "the thing" is that all these are emerging from and nature hasn't given us any clues, yet. If you answer "We don't know, yet." to your own question, you make a true statement. – CuriousOne Apr 17 '16 at 2:59

If we were discussing electromagnetic forces, you might be asking whether electromagnetism causes the forces or vice versa. To make this less of a chicken-egg question, I'd assume "electromagnetism" here means the existence of nonzero values for electric charges and the electric and magnetic fields. The electromagnetic force on a particle of charge $q$ of velocity $v$ in an electric field $E$ and a magnetic field $B$ is $q\left(E+v\times B\right)$. It makes sense to say the force is caused by the aforementioned details of electromagnetism rather than vice versa. In the special case of a force due to a point charge $Q$ a distance $r$ from the charge $q$, the force has magniture $\frac{k_C qQ}{r^2}$, where $k_C :=\frac{1}{4\pi\varepsilon_0}$ is the Coulomb constant. This is because the charge $Q$ generates an electric field proportional to $k_C$.
The analogous constant for gravity is Newton's constant $G$. In general relativity, the equivalent of a "force" is the expression $G_{\mu\nu}+\Lambda g_{\mu\nu}$ (note that only the first $g$ should be capitalised). The Einstein field equation equates this expression to $\frac{8\pi G}{c^4}T_{\mu\nu}$, where $T_{\mu\nu}$ is a description of the space's matter content. This is analogous to a charge distribution that would generate electromagnetic fields. In short, our equivalent of a "force" is due to matter and proportional t the gravitational constant $G$. This is what people mean when they say matter tells space how to curve (that's what the "force" side really described) and space tells matter how to move.