- #1

"...for example, if the Hubble Constant was determined to be 50 km/s/Mpc, a galaxy at 10 Mpc, would have a redshift corresponding to a radial velocity of 500 km/s."

In this illustration provided from the article, if this was the measured observation from earth, this describes a constant rate of expansion, not an acceleration. It only appears to be an acceleration because of our somewhat fixed vantage in the universe. If the expansion is

*actually*accelerating, we would expect to see velocity in addition to the constant every time you measured out another 10 Mpc (to stay within the framework of the provided example). So if the constant rate of expansion was 50 km/s/Mpc , an expansion that was also authentically accelerating would yield 50 km/s/Mpc +X ... with X equaling the velocity added by the acceleration of expansion. One number describing a velocity does not give any indication of acceleration, what is needed is a ratio that shows an increase in velocity over distance beyond what one would expect to observe from a constant expansion.

Hubble's constant is how we know the universe is expanding, but I am not clear how it shows acceleration, if it indeed does.

So... I already know that my observation is not common knowledge because it is never brought up in public explanations about the expansion or conversations about dark energy. There is often a mention of how the expansion is happening everywhere at once, and this is illustrated in several different ways to help confused people understand why it seems we are in the "middle" of the big bang... I get all that, no need to re-hash. What I am saying is, there is a corollary observation of "acceleration" to the expansion that is equally confusing. A universe expanding at a steady rate won't look much different from a universe expanding at an accelerating rate. An authentic acceleration may indeed be occurring, and perhaps it is simply not explained well, because no one has come up with good pictures to paint to describe the difference without thick equations (i'm math illiterate)... I dunno. That's what I'm trying to get to the bottom of.

What is the rate of "acceleration" and how are we differentiating it from the observed "acceleration" of distant objects we would expect to observe given a constant rate of expansion?