Shouldn't we see faster expansion without dark energy

In summary: The acceleration of the expansion rate is not directly connected to the velocity of galaxies, but it does play a role in how fast they are moving away from us. In summary, before the discovery of dark energy, it was thought that the expansion of the universe was slowing down since the big bang. However, it was found that the expansion rate is actually accelerating, which is causing galaxies further away to have a higher velocity. This acceleration is not directly connected to the velocity of galaxies, but it does influence it.
  • #1
KeplerJunior
25
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I understand that before we knew about dark energy we thought expansion would have slowed down since the big bang but we then discovered the universes expansion rate to be accelerating.

My question is, surely if the universe did expand faster at the big bang we would see it expand faster the further away we looked as you account for the limited speed of light so there would be no need for dark energy (ignoring missing mass etc.)

I'm sure I've missed something or got something wrong and that there is an explanation but i just wanted it to be clarified
 
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  • #3
Kepler, I *think* you are semi-correct. I believe when we looked out and measured lots of supernovas it turned out that galaxies closer to us were moving away faster than they should have been if the expansion had been slowing. Someone correct me if I'm wrong.
 
  • #4
So the velocity of galaxies does increase the further away you look but that's not due to dark energy
 
  • #5
KeplerJunior said:
So the velocity of galaxies does increase the further away you look but that's not due to dark energy

The expansion rate itself is what causes galaxies further away to have a higher velocity. The acceleration is actually an increase in the rate of expansion. I'm not sure if "acceleration" is the correct term for a rate of something. The rate is increasing over time, which we call acceleration.
 
  • #6
Thanks so just that I'm clear galaxies having a higher velocity is just caused by the expansion of the universe the acceleration of the rate of expansion is not connected to that
 
  • #7
KeplerJunior said:
Thanks so just that I'm clear galaxies having a higher velocity is just caused by the expansion of the universe the acceleration of the rate of expansion is not connected to that

Galaxies further away in distance having a higher velocity than those closer in distance is the result of expansion, yes.
 

1. What is dark energy and how does it affect the expansion of the universe?

Dark energy is a hypothetical form of energy that is believed to make up about 68% of the total energy in the universe. It is thought to be responsible for the accelerating expansion of the universe, pushing galaxies away from each other at an increasing rate.

2. Why do we need dark energy to explain the expansion of the universe?

The current accepted model of the universe, known as the Lambda-CDM model, includes dark energy as a necessary component in order to explain the observed accelerated expansion. Without dark energy, the model would not accurately match the observations.

3. Shouldn't we see faster expansion without dark energy since gravity should be slowing down the expansion?

While it may seem logical that gravity would slow down the expansion of the universe, it is important to remember that gravity is a relatively weak force on large scales. The effects of dark energy are thought to be much stronger, causing the overall expansion to accelerate.

4. Is there any evidence to support the existence of dark energy?

Yes, there is observational evidence from various sources such as the cosmic microwave background radiation, the large-scale distribution of galaxies, and the brightness of distant supernovae. All of these observations support the idea of a mysterious force, such as dark energy, driving the accelerated expansion of the universe.

5. Can dark energy be explained by alternative theories of gravity?

While there are alternative theories of gravity that attempt to explain the accelerated expansion without the need for dark energy, they have not been able to fully replicate the observations and are not widely accepted by the scientific community. The current evidence strongly supports the existence of dark energy as the most likely explanation for the observed accelerated expansion of the universe.

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