Sunday, August 28, 2011

Questions you probably never thought about...

...but are nonetheless fascinating once you consider them.

What would it be like to walk around the earth if it were shaped like a cube?

Cecil from The Straight Dope gives a thoroughly fascinating answer, and it conforms with the 'Ask a Physicist' answer too.

For starters, all the atmosphere and oceans would be concentrated in blobs in the centre of each face. So when you walked far enough, you would be out in space.

The comment thread on Hacker News had a good rough metaphor for it: imagine that you're on a regular spherical planet, but with 8 big three-face pyramid mountains bolted on for the corners. This gives you an idea, but it's not exactly correct - when you think of walking up the side of a pyramid, you imagine a constant slope. Here, the pull of gravity would make it more like walking up the sides of a round bowl (even though it's geometrically a pyramid). So walking towards the corners is like walking up a mountain that keeps getting steeper and steeper.

You should read the straight dope column for the full low-down.

'morsch' at Hacker News also quotes a description of a water moon from 'The Algebraist' by Iain M. Banks
I was born in a water moon. Some people, especially its inhabitants, called it a planet, but as it was only a little over two hundred kilometres in diameter, 'moon' seems the more accurate term. The moon was made entirely of water, by which I mean it was a globe that not only had no land, but no rock either, a sphere with no solid core at all, just liquid water, all the way down to the very centre of the globe.
If it had been much bigger the moon would have had a core of ice, for water, though supposedly incompressible, is not entirely so, and will change under extremes of pressure to become ice. (If you are used to living on a planet where ice floats on the surface of water, this seems odd and even wrong, but nevertheless it is the case.) The moon was not quite of a size for an ice core to form, and therefore one could, if one was sufficiently hardy, and adequately proof against the water pressure, make one's way down, through the increasing weight of water above, to the very centre of the moon.
Where a strange thing happened.
For here, at the very centre of this watery globe, there seemed to be no gravity. There was colossal pressure, certainly, pressing in from every side, but one was in effect weightless (on the outside of a planet, moon or other body, watery or not, one is always being pulled towards its centre; once at its centre one is being pulled equally in all directions), and indeed the pressure around one was, for the same reason, not quite as great as one might have expected it to be, given the mass of water that the moon was made up from.
For some reason, once I read this I've been thinking about the cube-earth for the past two days. Weird but cool stuff.

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