1
Physics, Astronomy & Cosmology / A new horizon problem and the "missing mass"
« on: 27/07/2009 18:17:58 »
This notion concerns a way by which the Universe can have lots more mass than we observe.
First, the very concept of "curved space" means that we have to talk about geometry in four dimensions. Cosmologists say that if the Universe has enough mass it will be "closed", and its geometry will be equivalent to that of a sphere (except it will be a 4D sphere and not a 3D sphere).
I'm thinking of an analogy between the normal 3D sphere and a 4D sphere (hypersphere): where is the horizon? If we were FlatLanders at some location on the surface of a 3D sphere, things that are some distance away could be distorted, due to the curvature. Suppose the Universe does indeed have the shape of a hypersphere, and we are in its 3D "surface" --and we can only see part-way around it, because red-shift and other effects creates at least an imitation of that purely geometric horizon. Then all the "missing mass", needed to ensure that the Universe is both "closed" and hyperspherical, would simply be out of sight beyond the horizon, filling the rest of its "surface" in a manner very much as we see in our Observable section of the Universe.
First, the very concept of "curved space" means that we have to talk about geometry in four dimensions. Cosmologists say that if the Universe has enough mass it will be "closed", and its geometry will be equivalent to that of a sphere (except it will be a 4D sphere and not a 3D sphere).
I'm thinking of an analogy between the normal 3D sphere and a 4D sphere (hypersphere): where is the horizon? If we were FlatLanders at some location on the surface of a 3D sphere, things that are some distance away could be distorted, due to the curvature. Suppose the Universe does indeed have the shape of a hypersphere, and we are in its 3D "surface" --and we can only see part-way around it, because red-shift and other effects creates at least an imitation of that purely geometric horizon. Then all the "missing mass", needed to ensure that the Universe is both "closed" and hyperspherical, would simply be out of sight beyond the horizon, filling the rest of its "surface" in a manner very much as we see in our Observable section of the Universe.