On Sun, Sep 8, 2024 at 9:13 PM Alan Grayson <[email protected]> wrote:
> > > On Sunday, September 8, 2024 at 6:45:59 AM UTC-6 John Clark wrote: > > On Sun, Sep 8, 2024 at 1:23 AM Brent Meeker <[email protected]> wrote: > > *> Given that already since Olaf Römer's observations of 1676 it has been > known that light propagates at a finite speed, it would have been possible > more than 300 years ago to conclude that objects moving at nearly the speed > of light must look distorted. Surprisingly, no such conclusions have been > drawn in the framework of classical physics. * > > > *True. They could also have concluded in 1676 that the universe must be a > finite number of miles across, or created a finite number of years ago, or > space itself must be expanding and so very distant stars must be moving > away from us faster than the speed of light so the light from them will > never reach us. I say that because if none of those three things were true > then if you extended a line from you to any point on the sky it would > eventually hit the center of a star, and so every point on the nighttime > sky would be as bright as the sun. But that's not what we observe.* > > > As for the *unobservable* part of the universe, moving away at faster > than light speed, I conjecture that Inflation is the cause. So if we run > the clock backward, they would eventually come back into view, showing that > the whole universe is finite, and therefore cannot be flat (which implies > spatially infinite). AG > > I disagree with your final conclusion. Even if the universe is infinite, > many stars that are directly in our line of sight, might be too faint to be > seen, as is the case of nearby brown dwarf stars, which comprise 50% of > stars in our relatively nearby neighborhood, but too faint to see. AG > The idea of the sky being bright in an infinite universe which had been around forever is called Olber's paradox (see https://en.wikipedia.org/wiki/Olbers%27s_paradox ), even if all stars were brown dwarfs that would mean the sky should look as though we were enclosed in a spherical shell whose entire inner surface was at the same temperature (and emitting the same blackbody radiation) as the surface of a brown dwarf. The argument for the paradox is based on the assumption of a uniform density of stars, which means the mean number of stars at a given distance increases with the square of the distance, which exactly balances out the fact that intensity of light from any given star decreases by an inverse square law. Similarly if the Earth was enclosed in a non-reflective spherical shell with the same temperature as a brown dwarf surface, we would see the same thing regardless of whether the shell was only slightly larger than the radius of the Earth's atmosphere, or the radius was 100 billion or 100 googolplex light years (again assuming it was had been emitting the same radiation for an infinite time). -- 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 on the web visit https://groups.google.com/d/msgid/everything-list/CAPCWU3JgzM1f9uc%2BX%3D7NpJ4eeWQXutWVJnUJz5wVhu5fQcX3Hg%40mail.gmail.com.
