In either case, where there is mass there is gravity. And where there is gravity there is curved space, according to Einstein’s general theory of relativity. And where space is curved it can mimic the curvature of an ordinary glass lens and alter the pathways of light that pass through. Indeed, distant quasars and whole galaxies have been “lensed” by objects that happen to fall along the line of sight to Earth’s telescopes. Depending on the mass of the lens itself and the geometry of the line-of-sight alignments, the lensing action can magnify, distort, or even split the background source of
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