Spacetime

Einstein's spacetime is a four-dimensional mathematical model with 3 spatial dimensions plus one time dimension. Space and time are deeply intertwined and impossible to separate in the general case.

Mathematically it is a so-called manifold. If you are not mathematical, do not be intimidated.

Consider one spatial dimension and one temporal. Spacetime in this case is a surface, like shown in the figure. Please note the figure more properly represents how space is curved by the presence of mass (considering only two spatial dimensions): representing how time is curved is more complicated.

For each point of the surface (manifold) one can always find an (infinitesimal) region which is flat (an euclidean plane). Think , for instance to our Earth: mathematically we can approximate it as a geoid (more or less a crushed sphere) and a sufficiently small area of the geoid is basically a plane (like the surface of the sea). At each point, we also have a metric which allows one to measure the distance between any other point nearby (infinitesimally close).

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European Space Agency (ESA) - C. Carreau

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Mathematically it is a so-called manifold. If you are not mathematical, do not be intimidated.

Consider one spatial dimension and one temporal. Spacetime in this case is a surface, like shown in the figure. Please note the figure more properly represents how space is curved by the presence of mass (considering only two spatial dimensions): representing how time is curved is more complicated.

For each point of the surface (manifold) one can always find an (infinitesimal) region which is flat (an euclidean plane). Think , for instance to our Earth: mathematically we can approximate it as a geoid (more or less a crushed sphere) and a sufficiently small area of the geoid is basically a plane (like the surface of the sea). At each point, we also have a metric which allows one to measure the distance between any other point nearby (infinitesimally close).