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Originally Posted by renormalised
Any object that is beyond the horizon distance of the Local Universe will, by definition, be traveling faster than the speed of light w.r.t. our local reference frame. However, once enough time has passed and the horizon distance has increased in size, we will begin to see those objects as they were when they emitted the light coming to us at that particular point in time (when the horizon distance has reached them).
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That would only be true if we lived in a matter dominated flat Universe where the Universe expands forever but at a decreasing rate until it reaches an asymtopic value.
Since the expansion of the Universe has been recently found to be accelerating the opposite is true. The Universe is becoming progressively more "unobservable" as more and more distant objects slip beyond the event horizon as the recession velocity of these objects
due to space-time expansion exceeds the speed of light. Unless space-time expansion slows down these objects will never be observed again.
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What they (cosmologists) are trying to say is that the reason why gravity is so weak compared to the other forces, is that most of its strength is being bled off into higher dimensional space. They theorise that it all depends on the geometry of cosmic strings w.r.t. to M-Brane Theory. If you consider that the universe we live in is the surface of a large, multidimensional object called a brane, then it's how the cosmic strings interact with the brane that determines whether gravity leaks away into the higher dimensions or is trapped within the brane itself. It depends on the geometry (shape) of the strings and how they attach themselves to the brane.
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A fundamental problem with cosmological string theories is that multi-dimensional space is a solution for flat space-time.
One possibility of an accelerating universe is that space time rather than being flat has an open geometry. How do the cosmological string theories deal with this?
Regards
Steven