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Did the Universe have to be the way it is?

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Channel: Scientific American
Categories: Astronomy   |   Physics   |   Science  
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If gravity were just a little stronger in our own three-dimensional world, the curvature of spacetime would be greater, and matter could more easily collapse in on itself. This arrangement would make stars, galaxies and planets extremely diminutive, compared with the ones in our reality. Not only would we have less space on Earth, but our sun would deplete its nuclear fuel much more rapidlymeaning that evolution, and life itself, would be greatly curtailed.

If gravity were weaker, Earth would be gigantic, and it might be oddly shaped like some asteroidsor a potato. And rather than walking on the surface of our planet, we might find ourselves, say, jumping to grab a rebound in a basketball game, only to accidentally end up in the upper atmosphere or orbiting the globe as a tiny human space station.

What if we werent three-dimensional at all? (Imagine people as paper cutouts.) If we lived in two dimensions, gravity would act very differently. Although we would still have the spacetime curvature noted in Einsteins general theory of relativity, such curvature would no longer produce gravitational forces. For this sort of flattened universe, we could instead have scalar gravity, in which Newtons description of gravity would have been the final word, and black holes would be relegated to science fiction.

Thankfully, even though 2020 seems topsy-turvy, we still have gravity to keep us grounded.

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