# Doesn't the redshift mean space's expansion has slowed?

If further distance means farther back in time and those farther galaxies appear to be moving faster away.

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• Jon
Lv 6
1 month ago

The universe's rate of expansion isn't the speed at which galaxies recede from us. It's the ratio of speed to distance.

• Anonymous
1 month ago

Galaxies are going increasingly Republican.

• 1 month ago

The larger a galaxy's redshift, the faster the galaxy is receding from earth.

• neb
Lv 7
1 month ago

For the first 7 billion years of the universe, the expansion rate did indeed slow down because of the pull of gravity.

About 6 billion years ago, expansion started to accelerate due to the effects of dark energy. While we don’t know what dark energy is, it’s predicted effect is to create a kind of repulsive gravity that increases the rate of expansion.

So, why the change 6 billion years ago? Dark energy appears to be a property of space itself. As the universe expanded, it increased the volume of space which in turn increased the amount of dark energy. At 6 billion years, we hit the tipping point where it began to dominate and counter the attractive force of normal gravity. The expansion rate began to accelerate.

If we look at redshift as a function of time, we can see this.

• 1 month ago

If expansion *was* uniform, then you'd fully expect to see the more distant objects retreating faster than those closer to you. If red shift is relatively constant, that means that the rate of expansion is constant; if it's accelerating, then red shift is increasing. If it's decelerating, then red shift would be decreasing.

It's been seen in the last few decades that the rate of expansion appears to be increasing.

• 1 month ago

The problem with expansion is that it is not the same as one object moving away from another.  the very distance between objects, even if not moving, is increasing and thus expansion is not linear (not a first-order process).  You need more details than you have. In any expanding system, at any change in rate of expansion as long as it did not reverse direction and start contracting, older objects will appear to be moving faster than younger ones.

• Fuhr
Lv 6
1 month ago