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Recommends Doradus · 2020-08 · Physics Stack Exchange · on “Does the curvature of spacetime theory assume gravity?”

Gravity is not as important to the rubber-sheet analogy as one might think. It is needed for two things: Causing the weights to curve the sheet Causing the weights stay on the sheet as they move Anything that made these two conditions true would work for the demonstration. In fact, gravity is not an ideal mechanism for #2 because it has a component in the direction of the sheet, and so it causes acceleration along the sheet that actual general relativity does not exhibit. In any case, the rubber-sheet analogy only shows how space curves due to mass. In reality, most of the effects we observe are due to the curvature in the time direction. To visualize that, a cone- or horn-shaped curvature i

Cites Matas Vaitkevicius · 2018-06 · Physics Stack Exchange · on “Could dark energy and gravity be explained as same phenomenon?”

I have watched VSouce video on gravity [this video] . The idea is that gravity pulling it is just lots of mass bending space-time, and natural direction of movement becomes moving towards the mass, and since we have earth already there we get to sit on top. This got me thinking what about lack of matter to bend space-time, could it be that space-time bends in the 'opposite' 'direction' like create a slope where everything's natural movement direction is away. Could this be used to explain dark energy's anti-gravity properties? EDIT: Duplicate is about dark matter while this one is about dark energy that are two completely different things...

Cites Chang Hexiang · 2021-05 · Physics Stack Exchange · on “Mathematical description of a conical spacetime”

In multiple explanations of general relativity, the curvature of a cone has been used to explain why objects fall in a gravitational field, like so: [LINK] It also appears in videos like this [LINK] and this one [this video] from Vsauce. I am looking for a mathematical description of this conical spacetime. Obviously, the cone describes a flat spacetime, which is to be expected from a uniform gravitational field on the surface of the Earth. However, I'm struggling to write the metric, because the Euclidean line element for the cone would be: $$ds^2=dr^2+r^2 d\theta^2$$ I'm not sure if this is the correct metric if time is involved. I would like to show intuitively that the coordinate acceleration

Cites Dhanvin Malhotra · 2025-02 · Physics Stack Exchange · on “Does experiencing gravity in general relativity require an object to have length?”

I've recently started studying general relativity and I'm trying to get an intuition for how gravity works. So far I’ve come across two different explanations online: Time dilation explanation: Many explanations, like VSauce's Video [this video] , with it's pencil and cone visual, suggest that gravity arises because different parts of an object (e.g., your head and feet) experience time at different rates. To me this seems to imply that length is a requirement to experience gravity. Geodesic explanation: Other explanations, like this one [LINK] , describe gravity as objects following the shortest path in curved spacetime. This explanation doesn’t seem to require an object to have any length. Is t