![]() ![]() Turn 90 degrees once more and walk back to your starting point. Then, turn 90 degrees and walk back to the equator. This time, start at Earth’s equator and walk to the North Pole. This is the standard Euclidean geometry that we all learned in high school, and if you add one more dimension you get a flat universe.īut conducting this experiment on a positively curved space that’s representative of a closed universe would create a different outcome. Do this twice more and you’ll find yourself back where you started - you’ve completed a square. Walk another 10 feet and turn 90 degrees again. Walk 10 feet along the wall to the next corner, then turn 90 degrees. ![]() Say you’re standing in one corner of a square room. What does a flat universe mean, though? This flatness isn’t the two-dimensional kind we often encounter in everyday life, but you can envision it with a few analogies. (Perhaps this will come as some consolation to anyone disappointed by our planet’s roundness.) Flat in 3D Most cosmological evidence points to the universe’s density as being just right - the equivalent of around six protons per 1.3 cubic yards - and that it expands in every direction without curving positively or negatively. There’s also a Goldilocks scenario for the universe, which scientists say is the most plausible. This would form an open universe with negative curvature resembling a saddle. On the other hand, if the universe’s density is low and unable to stop the expansion, space will warp in the opposite direction. An intergalactic Ferdinand Magellan could circumnavigate it, traversing space forever without hitting a wall or falling over an edge. A mind-boggling property of this universe is that it is finite, yet it has no bounds. This is known as the closed model, with positive curvature resembling a sphere. If the universe’s density is great enough for its gravity to overcome the force of expansion, then the universe will curl into a ball. The universe’s density refers to how much of this matter is packed into a given volume of space. The remainder is normal matter, which accounts for planets, stars and other bodies. Roughly 68 percent of the universe is dark energy and 27 percent is dark matter. The ultimate structure of the universe depends on just two factors: its density and its rate of expansion. This astronomical geometry is no trivial matter - the fate of the cosmos depends on it.Īs Princeton University cosmologist David Spergel puts it, “The shape of the universe tells us about its past and its future.” Whether the universe will expand forever or eventually collapse, and whether it’s finite or infinite - all are questions that tie back to its shape.įor a matter that bears on such grand questions, its components are remarkably simple. The theory of general relativity, under which space itself can curve, allows for the universe to take one of three forms: flat like a sheet of paper, closed like a sphere, or open like a saddle. ![]()
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