What shape is the universe?
Ari Buchalter, a graduate astronomy student, and David Helfand, professor of astronomy at Columbia, have devised a way to examine radio telescope measurements of distant galaxies to determine whether the universe is ‘open’ and will expand forever, ‘closed’ and will eventually collapse, or ‘flat’ and will attain some kind of equilibrium. They have studied 103 galaxies so far, and believe they can draw valid conclusions if they obtain results from 500 such galaxies, a project that should take another year or so. “There’s lots of evidence pointing to an open universe,” said Mr. Buchalter, who is writing a doctoral dissertation at Columbia based on his research. “Theorists say the universe is flat. Observers say it’s open. If we can get 500 of these galaxies, we should be able to rule in favor of one of them.” Such a study would complement information being gathered by two satellites being launched to study this very question. The National Aeronautics and Space Administration has approved
And if you can do this in two dimensions, why not in three? Draw a cube in space, and simply declare that opposite faces of the cube are actually in the same place, as if you had glued them together. To an occupant of the cube, flying out through one face would mean flying straight back in through the opposite face. And there would be no apparent edges: if you lived in a cubic universe and could see far enough, you would just see the back of your own head, repeated ad infinitum. You needn’t even start with a cube. You can take certain other shapes – a dodecahedron, say – and declare opposite faces to be identical. You can add twists, so that when you look at the back of your own head, it’s tilted sideways, or at some other angle. Some dimensions could be infinite while others are finite. The possibilities are endless. There is one way to trim this embarrassing choice: find out how space is curved. The very possibility that space can curve only emerged with Einstein’s general theory of
Let’s not get confused here. The geometry of our Universe is flat. This means if we throw a triangle out into space, the angles would add up to 180 degrees. Not another number which would indicate a curved or saddle geometry. This is not to be interpreted as the shape of our Universe. The two are completely different topics. The shape of our Universe is spheroidal. http://www.rumormillnews.
All astronomical information comes from our past light cone – a sphere of light of decreasing radius created at big bang and sweeping through space, and focusing on us right now. Everything outside that is unknown. The light cone has finite extent since the universe existed for finite time after the big bang. We have no idea what is outside of our light cone, so questions like weather the universe is finite and what shape it has cannot be answered based on the current observational data. The simplest is to assume it is infinite which we currently do.
Essentially all directions look the same when you observe the universe at large, it’s […] on October 18, 2008 at 3:44 pm | Reply Hubble Telescope at 10x or 100x or 1000x « Auxiliary Memory […] people never ponder the size of reality. They never grasp that we live in space-time. Hell, few people even look at up at the […] on January 11, 2009 at 10:56 pm | Reply How to Introduce Physics to Your Friends? « Auxiliary Memory […] physics chose to have a small view of reality. I referenced my earlier blog post, “What Shape is the Universe?” where I was going to chide my friends for living in a small dinky universe of only a few […
