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It's a rather difficult concept to grab but, in short, the image of expansion you have in your mind is wrong. It's not your fault, it's everywhere out there, the inflatable balloon etc. And it's terrible :) Another way to look at it is that the universe properties are changing. Whether it is infinite or finite, its size (as measured within itself) changes. ...

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There is no boundary there is no outside to be expanding into. Only slightly misleading is the usual analogy of the expansion of the universe is that of the surface of a balloon as it is blown up, which just gets larger but has no boundary. One problem with the balloon analogy is that with a balloon we can see that it is embedded in a 3-space, but there is ...

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Most of the Astronomers and the community of Astrophysics, will agree that the fate of planet earth is "The Big rip, most comparable to The Big Bang;but polar opposites.Where the universe is expanding to it's breaking point, total expansion of the know universe.

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The short answer is no, with some caveats to the effect of sort of, depending on how loose an analogy you want to make. Sound propagation in a fluid is limited by the speed of sound, which can be used to define a "sound cone" structure analogous to the causal light cone structure in spacetime. This is a described by an acoustric metric, which could have an ...

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If you're asking whether it's sufficient to use a retarded (time-delayed) positions to calculate gravitational forces, then no, that would be much worse than Newtonian gravity. For example, that would predict that the Earth should spiral into the Sun on the order of about 400 years. See also this question. Most small-scale N-body simulations (e.g., ...

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In very a general post-Newtonian metric for a two-body system with the first body oblate, where $M\equiv m_1+m_2$ is the total mass, $\mu\equiv m_1m_2/M$ is the reduced mass, and $p\equiv a(1-e^2)$ is the semi-latus rectum of the orbit, the perihelion advance per orbit is \small\delta\varpi = ...

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