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Name: Ian
Status: educator
Location: Outside U.S.
Country: Australia
Date: Winter 2011-2012

General relativity says matter curves space and this is what we experience as gravity. No problem. Cosmologists say the universe is flat (or very close to it) rather than closed or open. I take that to mean: ignoring the local dents made by matter, the overall shape is flat - whatever "flat" means in 4D space-time. My question is: How can a flat universe not have an edge? How can there not be planets that are so close to the edge that some nights there are stars in the sky and other nights there are no stars?

Ian, The structure of space within a universe is difficult to imagine. Many view the universe within space and time. Latest measurements and models (such as string theory) indicate the opposite: space and time are within the universe. Beyond the "edge of the universe" might be another universe that we cannot reach. It is possible that nothing exists beyond the edge, not even empty space.

Dr. Ken Mellendorf Physics Instructor Illinois Central College

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