Is there any evidence of a universe expansion jerk

Click For Summary

Discussion Overview

The discussion revolves around the concept of a non-zero rate of change of the acceleration of the universe's expansion, often referred to as "jounce." Participants explore whether there is evidence for such a phenomenon, the nature of that evidence, and the implications of varying dark energy density over time.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants assert that there is evidence for a non-zero rate of change of the acceleration of the universe's expansion, noting that the acceleration began a few billion years ago based on observations of redshift versus brightness and angular size of distant galaxies.
  • Others argue that the rate of acceleration has not been constant due to the changing proportions of dark energy and other energy densities, with dark energy remaining constant while matter density decreases as the universe expands.
  • One participant highlights the difficulty in measuring changes in values, suggesting that measuring the change itself introduces noise into the data.
  • It is proposed that earlier in the universe's history, when matter density was higher, the rate of expansion was decelerating, but as dark energy became more dominant, the expansion began to accelerate.
  • A later reply introduces the idea that the Hubble tension might be explained by the possibility that dark energy is not a constant over time.

Areas of Agreement / Disagreement

Participants generally agree that the rate of acceleration has changed over time due to varying energy densities, but there is no consensus on whether dark energy itself has changed or remains constant. The discussion includes competing views and remains unresolved regarding the specifics of dark energy's behavior.

Contextual Notes

Participants note that the measurement of changes in acceleration is complicated by noise and that current data may not sufficiently clarify the nature of dark energy over time.

arusse02
Messages
24
Reaction score
0
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?
 
Space news on Phys.org
arusse02 said:
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.
 
arusse02 said:
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.
 
One possible explanation for the Hubble tension is that dark energy is not a constant
 

Similar threads

Undergrad Relationship Between Expansion and Curvature in the Universe
  • · Replies 3 ·
Replies
3
Views
3K
Undergrad Expansion of the Universe and the cosmological principle
  • · Replies 9 ·
Replies
9
Views
3K
Undergrad Entropy reversal in an infinite static universe?
  • · Replies 1 ·
Replies
1
Views
3K
Undergrad What is the significance of the cosmological jerk in the expanding universe?
  • · Replies 5 ·
Replies
5
Views
3K
Undergrad Age of the Universe and the Cosmological Constant
  • · Replies 18 ·
Replies
18
Views
3K
High School Other lines of evidence for Dark Energy? (Besides supernova data)
  • · Replies 18 ·
Replies
18
Views
3K
Undergrad How do you get to the conclusion that there is accelerating expansion?
  • · Replies 23 ·
Replies
23
Views
4K
Undergrad What is the acceleration of the expansion of the Universe?
  • · Replies 7 ·
Replies
7
Views
2K
Undergrad Observational evidence for expansion of universe....
  • · Replies 2 ·
Replies
2
Views
1K
Undergrad Is Gravitation Responsible for the Stability of the Universe?
  • · Replies 9 ·
Replies
9
Views
2K