- #36
wabbit
Gold Member
- 1,284
- 208
Hmm I'm confused. You mean, the history of the velocity of a galaxy that is currently at that distance, right ?
But yes if I read it correctly this is a weird and interesting chart, showing in concrete terms the deceleration from gravity then acceleration caused by the cosmological constant, looking at just one observer and one distant galaxy - this is nice, a break from the "all encompassing majestic view" one is easily tempted into when talking cosmology.(*)
It just hit me that that one galaxy not only approaches us faster, but at asymptotically infinite speed as one approaches the big bang. Quite obvious really, its distance scales as a which is vertical at the origin, but somehow I didn't quite see it, was lost in comoving coordinates and scale factors I guess, leaving the poor galaxy alone. Good chart indeed.
But.. Everything is superluminal early on ? Come on, you must be joking ! And yet, it is, every galaxy (or what remains of it) eventually exits our Hubble radius as we approach t=0. Hmmm is that right ?
Another nice chart would be this : the history of the Hubble radius, with the paths of a few selected galaxies, entering it, spending some time visiting, then eventually exiting when aunt lambda calls time to go home (he he, a hint of time symmetry here )
(*) You might add the distance chart as well, d0*a/a0, on the same or nearby plot, as it tells that same story in a complementary way.
But yes if I read it correctly this is a weird and interesting chart, showing in concrete terms the deceleration from gravity then acceleration caused by the cosmological constant, looking at just one observer and one distant galaxy - this is nice, a break from the "all encompassing majestic view" one is easily tempted into when talking cosmology.(*)
It just hit me that that one galaxy not only approaches us faster, but at asymptotically infinite speed as one approaches the big bang. Quite obvious really, its distance scales as a which is vertical at the origin, but somehow I didn't quite see it, was lost in comoving coordinates and scale factors I guess, leaving the poor galaxy alone. Good chart indeed.
But.. Everything is superluminal early on ? Come on, you must be joking ! And yet, it is, every galaxy (or what remains of it) eventually exits our Hubble radius as we approach t=0. Hmmm is that right ?
Another nice chart would be this : the history of the Hubble radius, with the paths of a few selected galaxies, entering it, spending some time visiting, then eventually exiting when aunt lambda calls time to go home (he he, a hint of time symmetry here )
(*) You might add the distance chart as well, d0*a/a0, on the same or nearby plot, as it tells that same story in a complementary way.
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