Undergrad Is there any evidence of a universe expansion jerk

[arusse02]

As stated in the question--is there any evidence of a non zero rate of change of the acceleration of the expansion of the universe. What is the evidence for it and is it negative or positive? Also if there is what would it take to determine if there was a jounce?

 

[PeterDonis]

is there any evidence of a non zero rate of change of the acceleration of the expansion of the universe

Yes. The expansion only started accelerating a few billion years ago (based on the curve of redshift vs. brightness and angular size for distant galaxies), so the rate of acceleration has obviously not been constant. The reason it has not been constant is that the relative proportion of dark energy vs. other types of energy density has not been constant, because the density of dark energy remains the same as the universe expands (as far as we know), while the density of matter (ordinary and dark) decreases.

 

[kimbyd]

As stated in the question--is there any evidence of a non zero rate of change of the acceleration of the expansion of the universe. What is the evidence for it and is it negative or positive? Also if there is what would it take to determine if there was a jounce?

Also, bear in mind that values are easier to measure than how much those values change: looking at the change instead of the value adds noise.

As PeterDonis mentioned, the rate has changed over time for sure because the matter density drops as the universe expands. Earlier, when matter density was higher, the rate at which objects moved apart was decelerating. As dark energy has become more dominant (because it doesn't drop in density much if at all as the universe expands), the distances between objects have started accelerating.

What we can't tell right now is whether or not dark energy has changed over time: that measurement is far too noisy at the moment.

 

[windy miller]

One possible explanation for the Hubble tension is that dark energy is not a constant