As the tittle says, I am constantly hearing about spacetime, which I sort of get (it’s a 4D space, with 3 spatial and 1 temporal axis) and curvature, which I do not get. What is curved in spacetime? When we say geodesics, what are they representing? I am getting the feeling that it is something like the spatiotemporal distance between two events that is being modified, but what does it mean in physical terms? Is it even physical, since two observers can disagree in almost everything, except the order of casually linked events?
Or I am thinking it too much, and it’s only a model of interpreting observation that only approximates complex reality up to a point?
In: 5
The space around you is flat. If you make a triangle out of three straight things, laser beams are popular, the angles between the sides add to 180˚.
If you imagine a giant triangle made of string with one point at the north pole and two points on the equator, the angles will sum to more than that because the two equator points are 90˚ angles and the angle at the pole pushes the sum over 180˚. This occurs because the strings are not straight, they follow the surface of a curved planet.
When you go near a very massive object, the laser beams will react to the curved space and give a result equivalent to the string triangle.
The time dimension is more complex, an effect we call Relativity, but at speeds measured in fractions of the speed of light (ultra high speeds) the length and clock speed of objects is different when measured from different points moving at high speed relative to the object.
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