On Monday, September 9, 2024 at 2:09:16 PM UTC-6 Brent Meeker wrote:
On 9/9/2024 12:51 PM, John Clark wrote: On Sun, Sep 8, 2024 at 9:13 PM Alan Grayson <[email protected]> wrote: *>> 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.* *I'm not talking about inflation, just the normal everyday expansion of the universe, which has been known since the mid-1920s, means that stars a finite distance away are moving away from us faster than the speed of light , and so the light from them will never reach us. * *> if we run the clock backward, they would eventually come back into view, * *Yes there are stars that we can see today that we won't be able to see tomorrow, 1 trillion years from now we won't be able to see any stars except those that are in the Milky Way because those stars are gravitationally bound together. * *And not just the Milky Way but also Andromeda, with which we will have collided by then, plus several small galaxies that are part of the local group. https://en.wikipedia.org/wiki/Local_Group <https://en.wikipedia.org/wiki/Local_Group>* Although the rate of expansion of the universe appears to be increasing, is it increasing fast enough to cause galaxies in our local group to become part of the *UN*observable universe? Right now, the local rate of expansion is only about 70 km/s/mpsec. Can expansion *alone* increase that rate so much, that galaxies in our local group are receding faster than light speed, thus becoming out of sight from the perspective of the Milky Way? AG BTW, FWIW, I conjecture that the *UN*observable universe came into being with Inflation. If so, it must have been *initially** finite *in spatial extent, and thus can ever become flat, if flat means infinite in spatial extent. I sent this conjecture to some cosmologists who believe the global geometry of the universe is flat, but they show no interest. 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.* *Sirius A is the brightest star in the sky but it has a companion, Sirius B, which is hotter and, because the light emitted of a hot object is proportional to the size of the object and to the fourth power of the temperature, is much much brighter, and yet it is impossible to see unless you have a fairly large telescope. That is because although its light is very intense Sirius B is far smaller than Serious A. One has a diameter of about 1,000,000 miles while the other has a diameter of only 6800 miles, so even though it's very intense the total amount of light given off is much less than Sirius A. * *I think his idea is that there are dark bodies and so Olber's paradox is resolved by there being enough dark bodies to intercept you line-of-sight and create the dark background of space. I don't believe it, but it could be true in a different universe. Brent* -- 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/06fb41d2-1331-4679-b68f-169c842e20a3n%40googlegroups.com.
