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Cosmology
Hello All,
Please reduce my level of ignorance. I am not a physicist, but I am a mathematician. (number theorist). I can deal with tensors. And Riemann surfaces. I have several questions. (1) Apparently, recent supernova observations have lead to the conclusion that omega = 1. I do not see why this must lead to the conclusion that the (topology of) the universe is necessarily Euclidean. Can't it be Elliptic (i.e. positively curved ) yet still forever expanding with omega = 1? One obvious way to prove that it is Euclidean is to show that the angles in a triangle add to exactly Pi. However, we can't possibly have sufficiently accurate observations to verify this. Or can we? (2) Let us assume it is Euclidean. How do we know that the observable universe is NOT the entire universe? Theoretical models may suggest an infinite universe, but there is no way EVER to confirm it by observation. And from a practical point of view, if something can NEVER be observed, than it doesn't really exist. (3) If the universe is Euclidean and infinite, how is this possible? The universe is a finite age and the speed of light is finite. There simply hasn't been enough time for it to expand to infinity. Furthermore, inflation does not seem to provide for an infinite universe either, for even a sudden (finite) period of exponential expansion in the very early universe does not lead to an infinite one. How do we know (or how CAN we know) that the Universe is not Euclidean and bounded? How do we know that Mach's principle must apply at a point in space 13 billion LY away? How can we know that at an observer there sees that in some directions there are no stars? (because beyond the boundary there is literally nothing) Bob Silverman [[Mod. note -- Ed Wright's Cosmology FAQ, http://www.astro.ucla.edu/~wright/cosmology_faq.html gives a nice general introduction to cosmology, and would probably provide insight into (3), and possibly also (1) and (2). -- jt]] |
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