I am twelve years old I did not understand if gravity is a force or a consequence of the curvature of spacetime caused by the uneven distribution of mass/energy; and resulting in time dilation
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2 Answers
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Physics uses several levels of description for many kinds of observations. In classical mechanics gravity is an acceleration that is usually written in the form of a force. This is being done for historical reasons, only (Newton understood it that way), but don't get too comfortable with the Newtonian force of gravity description. Technically it's false, even in Newtonian physics. In general relativity the same physics is being described with a geometric distortion of spacetime and we learn how to describe gravity with much higher precision than Newton could. Technically this completely invalidates the Newtonian ideas about gravity as a long range force, but you have to remember that there is no rule in physics that one has to use a single description for a phenomenon all the time, especially when it is as complex as GR. That's why Newtonian gravity is still being taught and used. It is "good enough" for a great many applications (like flying spacecraft to Mars, for instance). Sometimes, when it is not, like for the operation of the GPS system we use a linearized version of GR, which is also called a post-Newtonian approximation. And when that doesn't work, either, as in the case of cosmology and neutron star and black hole physics, then we have to work with the entire toolset of general relativity.
answered Oct 29, 2015 at 20:19
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In quantum mechanics forces are replaced with the more general idea of an interaction.
Interactions can do more than accelerate, they can cause particle destruction and particle creation and so forth. We have figured out how to model the weak interaction, the strong interaction, and the electromagnetic interaction. But not the gravitational interaction.
In General Relativity you model classical (not quantum) gravity through a curvature of spacetime. This happens even when everything is distributed uniformly. There is still curvature when everything is distributed uniformly. And there is still time dilation even when everything is distributed uniformly.
