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jedishrfu

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http://www.preposterousuniverse.com...never-expands-faster-than-the-speed-of-light/

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George Jones

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Maybe some someone else, like Brian, knows some physical consequences.

Note the scare quotes above. Since speed = distance/time, the definition of "speed" depends on the definitions of "distance" and "time". The definitions used in special relativity do not generalize easily to the curved spacetimes of cosmology. The definitions used in cosmology are, however, are easily applied in special relativity. When this done, cosmological speed turns out to rapidity (also known as the velocity parameter). In special relativity (with ##c=1##), the relationship between speed ##v## and rapidity ##w## is

$$v =\tanh w.$$

Consequently, ##0<v<1## gives ##0<w<\infty##, and ##w=1## (i.e., ##w=c##) has no physical significance.

Note that even though speeds don't add algebraically in special relativity, rapidities do add algebraically in special relativity, just like the cosmological speeds in equation (20) from the paper to which Andrew linked

https://www.physicsforums.com/threads/reason-for-galaxy-fading.869954/#post-5461870

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Moot

http://www.preposterousuniverse.com...never-expands-faster-than-the-speed-of-light/

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jedishrfu

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http://www.dailywritingtips.com/are-you-sure-you-mean-moot/

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jedishrfu

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Thanks for all the great answers.