At the end of a lecture on astronomy, describing how the planets orbit the Sun, a little old lady at the back of the room stood up and said: "What you've told us is all rubbish. The world is really a ...
Most of the matter in our universe is invisible. We can measure the gravitational pull of this “dark matter” on the orbits of stars and galaxies. We can see the way it bends light around itself and ...
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