On Sat, Aug 16, 2025 at 8:31 AM Alan Grayson <[email protected]> wrote:
*>> 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.* > > > *> Since the CMB isn't receding, what is the physical interpretation of > its huge red shift? AG * > > > *When we look at the Cosmic Microwave Background we're looking at a time > about 380,000 years after the Big Bang when the universe cooled enough for > electrons to become attached to atomic nuclei and to form neutral atoms > which allowed the universe to become transparent. We're seeing light that > has been traveling toward us for 13.8 billion years, coming from regions > that are now much farther away than 13.8 billion light years, not because > they have moved through space but because space itself has expanded. * > *The physical interpretation of the CMB's redshift of 1100 is that since > that time the linear distance of space has stretched by a factor of 1100, > and so the volume of space has expanded by a factor of that number cubed, > or about 1.3 billion.* > > > > *> Do you think the red shift of the CMB implies a universe of finite > volume? If not, why not? AG* > *Unfortunately the CMB gives us no help in answering that question, it might be finite, it might be infinite. The CMB can tell us stuff about the observable universe but not the size of the wider universe in general. * *John K Clark See what's on my new list at Extropolis <https://groups.google.com/g/extropolis>* wug -- 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/CAJPayv02eZeYPfCcGKTu3k%3D0VcgwaAqnXgmt7p%3DJ%3DhQcVkWLvw%40mail.gmail.com.
