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I was doing a little poking around about just what is a massless particle and what that means when I came across this paragraph:

If we hop in a spaceship that can go 90% the speed of light, we are now going through spacetime with only 10% dedicated to the time dimension which means time slows down for us (relative to slower moving observers) by an equivalent amount. So, for light, using 100% of the speed of light, there is nothing being used in the time dimension so time is not a part of light’s eternal journey through spacetime.

The full page can be found on the Ask a Mathematician/Physicist web site.

Anyway, that got me thinking. If this is true, then is there a reverse? Light is a constant, a speed limit which nothing can exceed. Not only that, anything at that speed will always move that speed relative to an observer slower than that speed. My questions then are, is there anything that will always be stationary relative to an observer? If light is the cosmological constant of speed, is there a cosmological constant of rest? And if so, would that have infinite mass? And exist wholly in time and not in space? I'm not a mathematician or a physicist, but I do like thinking and would love to hear some answers to these.

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  • $\begingroup$ The answers to your first two questions are no and no, but a proper answer would explain a bit about the subject, and unfortunately I don't have time for that. $\endgroup$ – Erik Jörgenfelt Aug 27 '16 at 8:26

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