The end of the Universe.
They used to believe that the universe was constant, and the stars were fixed like a canopy in the sky. Later when theory expressed otherwise, Einstein felt obliged to introduce the so-called cosmological constant, something he later regretting having done. Then they discovered that the universe was actually expanding outwards forever. How could this be possible? Will this go on forever resulting in a cold and dark universe without life or will it eventually reach a point where the gravitational forces take over and pull all matter inwards, resulting in a big implosion? Now they have discovered that the universe is actaully "accelerating" outwards, that is with the passing of time all of matter is speeding faster and faster away from each other. How is this possible? Vacuum is not as we learned an empty sapce, but at the nano-microscopic level it is seething with zillions of particles coming into a fleeting existence and then popping just as quickly out of existence. It is this activity spread out over an ever-expanding distance that produces an energy of pushing all of space outwards, overcompensating any gravitational forces which might be trying to pull things back together. Weird. Check out Is the Universe Infinite?
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