On Sun, Aug 10, 2025 at 10:23 PM Alan Grayson <[email protected]> wrote:
On Saturday, August 9, 2025 at 5:45:01 AM UTC-6 John Clark wrote: > > *Until very recently the most distant object our telescopes can see had a > redshift of about 14, but very recently there are reports that the James > Webb telescope has seen point-like objects that seem to have a redshift of > 25! Whatever these objects are they contain little or no dust as you'd > expect because dust requires elements other than hydrogen and helium which > need to be made in stars, but if we really are looking at an object that > has a red shift of 25 then we're looking at something that existed before > stars did. If confirmed that would be a pretty profound discovery, and > about the only thing that could explain them are Primordial Black Holes > created during the first nanosecond after the Big Bang.* > > > *JWST Found Objects at Insane New Distances (Redshift of 25?!)* > <https://www.youtube.com/watch?v=saL_1R1WitA&t=797s> > > *> How is the red shift related to the velocity of light? How large must it > be to equal c? TY, AG * > > > *Because space is expanding and accelerating, galaxies that have a > redshift greater than about 1.7 are today moving away from us faster than > the speed of light, so we can never reach them or even send a message to > them, they are beyond our causal horizon; however today we can still see > them because at the time the light from them was emitted the galaxy was > closer to us than it is now, and back then it was receding away from us > slower than it is now, slower than the speed of light. For the same reason > today we can even detect the Cosmic Microwave Background even though it has > a redshift of about 1100, but we could never send a message or influence > anything that happens that far away.* > > > *> TY. If it's not too much trouble, can you show me how you do that > calculation? AG * > *For nearby galaxies you can get a good approximation of the recessional velocity with the simple formula v = cz where: v = recession velocity, c = speed of light, and z = redshift. However for more distant galaxies you need to take Special Relativity into account and the formula is more complicated: * *v = c × [(1 + z)² - 1] / [(1 + z)² + 1]* *But for even more distant galaxies the above formula is not good enough because it does NOT take into account the fact that the universe is not only expanding it's accelerating, so the formula only gives a lower bound for how fast the galaxy is moving away from us due to the expansion of space. Calculating an even more precise figure is much more complicated because then you need calculus and you need to take General Relativity into account, and it depends on which cosmological model is being used, usually it's ΛCDM which assumes the existence of Dark Energy and Cold Dark Matter. * *John K Clark See what's on my new list at Extropolis <https://groups.google.com/g/extropolis>* axc -- 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/CAJPayv0weTxfEvj5jSz1ya45DX9mes%3DcVYNZauX8QP12EcAjBw%40mail.gmail.com.
