On Thursday, December 4, 2025 at 5:39:31 AM UTC-7 John Clark wrote:
On Wed, Dec 3, 2025 at 2:05 PM Alan Grayson <[email protected]> wrote: > *Distances to galaxies is measured using standard candles. So the attenuation in brightness compared to intrinsic brightness is a true measure of distance even though the universe is expanding. So there doesn't seem to be any problem with Hubble's values for distances.* *Distance between what, and when? If Hubble gives a figure of 10 billion light years that is the distance the light from a distant galaxy needed to travel through space to reach us, it tells us what the galaxy look like 10 billion years ago, but because space had been expanding while light had been making its journey it is NOT the distance the Earth is from that galaxy now, and is NOT the distance between the two when the light was first emitted.* *But when we use standard candles to measure distance from Earth to some galaxy, don't we get the ACTUAL distance NOW, since light attenuates in intensity due to expansion, just as its wavelength increases (and its energy decreases)? AG * *> If gravity is slowing the rate of expansion, it must have been higher in the past than now. On the other hand, Hubble's law seems to claim that when galaxies are close to each other, the rate of expansion is slow. How do you resolve this contradiction,* *You're confusing the amount of expansion and the change in the amount of expansion. * *I don't think so. See below. One thing that confused me was your claim a few days ago that the expansion rate was slow in the very early universe. I think you were comparing its rate at that time with the rate during Inflation. AG* *Except for the first 10^-32 seconds, until about 5 billion years ago the universe was expanding faster than it is now but the RATE of expansion was negative, things were decelerating. Things changed 5 billion years ago, the RATE of acceleration became positive and the universe started to accelerate. The universe experienced a cosmic jerk. * *Brent explained my confusion. Hubble's law compares galaxies near and far from us, and states that those far away, are receding the fastest. That FACT does NOT imply that galaxies in the very early universe were receding from each other at a low rate just because they were relatively close to each other at that time. AG * *> If the universe is infinite, as seems likely, most of it was always unobservable, since the observable part is necessarily finite.* *Yes but in the past we could see more of the universe than we can now, and today there are parts of the universe that we can see but we can never affect, if we sent a radio message to it moving at the speed of light it would not arrive there in any finite number of years. * *While I agree with your statement, you're responding to Brent's comment which I disagree with it. IMO, the unobservable region came into existence during Inflation, when the universe expanded at a rate hugely greater than light speed. So, it seems plausible that the entire universe, that which arose from a substratum which might be infinite, is finite in spatial extent. AG* * John K Clark See what's on my new list at Extropolis <https://groups.google.com/g/extropolis>* 3// 9ii *this would make sense IF Dark Energy is an intrinsic part of space because as space expands matter, which wants to retard the expansion gets diluted but space, which wants to increase the expansion, does not. * *However that might not be true, Dark Energy might not be caused by space itself, maybe it's produced by some sort of field that can change with time. Very recently there have been indications that the rate of change of the acceleration of the universe (believe it or not called a cosmic jerk) might be decreasing, but the evidence is not yet strong enough to claim a discovery. * -- 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/1fea9c05-9a3e-40c0-a853-8be7183254c9n%40googlegroups.com.
