Universe expansion is slowing down

In summary, the standard point of view is that when looking at distant galaxies, the redshift is higher than expected, leading to the conclusion that the universe is expanding at an accelerating rate. The concept of acceleration in cosmology refers to the change over time of the Hubble rate, which is a percentage growth rate of distance between stationary objects. This rate has been decreasing since early days, but is now increasing due to the second derivative of the scale factor being positive. However, this acceleration should not be thought of in terms of conventional motion or velocity, but rather as a change in geometry.
  • #36
According to theorists, if the universe is absolutely flat, the matter density of the universe is, and always will be, equal to its critical density since the end of the inflationary epoch.
 
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  • #37
Chronos said:
According to theorists, if the universe is absolutely flat, the matter density of the universe is, and always will be, equal to its critical density since the end of the inflationary epoch.
While strictly true, I'm pretty sure this isn't the case, as it requires perfect fine-tuning of the initial conditions of our universe.
 

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