On Sat, May 31, 2025 at 1:01 AM Alan Grayson <[email protected]> wrote:
*> Sorry for this question, but what puzzles me about your comment is that > the further back in time we observe, the faster galaxies are receding, so > how can a galaxy NOT receding faster than light speed in the past, now be > receding faster than light speed? AG* *Space is expanding, so the further away a galaxy is the faster it will be receding from us. 10.2 billion years ago a galaxy with a red shift of 1.8 was much closer to us than it is now, and it was receding from us much slower than it is now. Today it is much further away and thus receding from us much faster than back then, in fact it has just gone over the line and is now receding faster than the speed of light.* *Remember although Special Relativity says nothing can move faster than light, General Relativity is able to make a more nuanced statement, it says matter energy and information cannot move between two points in space faster than the speed of light, but it places no such limit on how fast space itself can expand. If intelligent life develops on that galaxy then astronomers there looking at the Milky Way will see it as it looked 10.2 billion years ago, but they will never be able to see what it looks like now. * * John K Clark See what's on my new list at Extropolis <https://groups.google.com/g/extropolis>* bd; *>> The James Webb telescope has discovered a galaxy with the red shift of > 14.44. From that you can calculate that it took light 13.5 billion years to > reach us, it started its journey only 280 million years after the Big > Bang. And because of the expansion of the universe the galaxy is now 34.7 > billion light years from the Earth. What I find really fascinating is that > although we can see the galaxy if we tried to send a laser beam to it, > because of the expansion of the universe, the beam would NEVER reach it; in > fact that's true for any galaxy that has a red shift larger than 1.8, and > this one had a red shift of 14.44! * > > *James Webb telescope breaks its own record again, discovering farthest > known galaxy in the universe* > <https://www.livescience.com/space/astronomy/previously-unimaginable-james-webb-telescope-breaks-its-own-record-again-discovering-farthest-known-galaxy-in-the-universe> > > *> Does a red shift of 1.8 imply recession at light speed?* > > > *If you're looking at a galaxy that has a red shift of 1.8 then you're > looking at how that galaxy looked 10.2 billion years ago, back then it was > not moving away from us faster than the speed of light but today it is, so > although we can see it we could never reach it in a finite amount of time, > not even if we could move at the speed of light. And a red shift of 1.8 is > the boundary line for that sort of thing. * > > > *Sorry for this question, but what puzzles me about your comment is that > the further back in time we observe, the faster galaxies are receding, so > how can a galaxy NOT receding faster than light speed in the past, now be > receding faster than light speed? AG* > > > > *> How is that calculated? AG * > > > *The general integral for finding the lookback time tL(z) is complicated > and involves calculus because it depends and a lot of things that are > changing, it's:* > > *tL(z)=∫(1+z′)H(z′)1dz′* > > *where you integrate between zero and the redshift z* > > *H(z) is the Hubble parameter at redshift z* > > *H(z)=H0Ωm(1+z)3+ΩΛ in a flat universe with dark energy* > > *H0 is the Hubble constant today* > > *Ωm is the matter density parameter* > > *ΩΛ is the dark energy density parameter* > > nx > > -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/d/msgid/everything-list/CAJPayv0kTjzSGPT3f583LcPfuTO-WderMONUorpA4NwGkwy9Xg%40mail.gmail.com.
