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Originally Posted by hardyivan007 Light. in secondary school, we were taught that light travels ion straight line. but some people say light follows the curvature of spacetime. does it mean light do not travel in straight? can u help mi explain this? |
light travels along geodesic lines for each particular spacetime geometry.
For 4D Euclidean geometry, this geodesic is the straight line of plane and solid geometry.
For 4D elliptic, spherical or Riemannian geometry, these geodesics are the great circles.
For 4D hyperbolic Gaussian geometry, the geodesics are envelopes of hyperbolae.
Geodesic lines are shortest paths between two points for each particular geometry.
the physical reason why light travels along the shortest paths is to spend as little energy as possible in going from here to there. This is also the reason why water always flow downstream, why heat travels from hot to cold, why the entropy of the universe increases.