Changeover from deceleration to acceleration

In summary, the conversation discusses the concept of the universe transitioning from deceleration to acceleration and the role of the repulsive force and gravitational force in this change. The experts confirm that the acceleration begins when the mass density of the vacuum becomes larger than half of the mass density of matter. They also mention the proposed experiment SNAP and its potential impact on understanding the expansion of the universe. However, it is noted that SNAP has not been built or taken any data yet. A recommended review for current observational evidence and future surveys is provided as well.
  • #1
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Did the universe changeover from deceleration to acceleration exactly after the moment when the increasing repulsive force became equal to the decreasing gravitational force?

[Would like to confirm if that would be consistent with the fact that acceleration starts when the mass density of the vacuum becomes bigger than half of mass density of matter.]
 
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  • #2
It's a constant repulsive "force", if you will, not an increasing one. Otherwise you're correct.
 
  • #3
Ich said:
It's a constant repulsive "force", if you will, not an increasing one. Otherwise you're correct.

But doesn't the repulsive force of the cosmological constant increase in proportion to distance?
 
  • #4
But doesn't the repulsive force of the cosmological constant increase in proportion to distance?
So does gravitation. I was referring to DE being constant over time, while matter gets diluted.
 
  • #5
Ich said:
So does gravitation. I was referring to DE being constant over time, while matter gets diluted.

I know ;). So then I assume I can confirm my original query about the universe accelerating just after repulsive force overtakes gravitational force.
 
  • #6
Yes. Expansion accelerates when [itex]\Omega_{\Lambda}>\Omega_M/2[/itex].
 
  • #7
SNAP suggests expansion began accelerating a few billion years ago. You can search for SNAP on Arxiv.
 
  • #8
SNAP was a proposed experiment that hasn't been built, let along put into space. It's currently not likely that it will ever fly (though something similar probably will at some point). It certainly hasn't taken any data yet though...

If you're after a good, reasonably current, review of observational evidence and probable future surveys try http://arxiv.org/abs/0803.0982" .
 
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FAQ: Changeover from deceleration to acceleration

What causes a changeover from deceleration to acceleration?

The changeover from deceleration to acceleration is caused by a change in the direction or magnitude of the force acting on an object. This results in a change in the object's velocity, which can be either a decrease (deceleration) or an increase (acceleration).

How does this changeover affect an object's motion?

The changeover from deceleration to acceleration will cause a change in the object's motion, specifically in its velocity. If the changeover results in an increase in velocity, the object will speed up and move in the direction of the force. If it results in a decrease in velocity, the object will slow down and move in the opposite direction of the force.

What factors can influence the timing of the changeover?

The timing of the changeover from deceleration to acceleration can be influenced by several factors, such as the magnitude and direction of the force, the mass of the object, and the presence of other forces acting on the object. Additionally, the type of surface the object is moving on and the object's initial velocity can also affect the timing of the changeover.

Is there a specific equation to calculate the changeover from deceleration to acceleration?

There is no specific equation to calculate the changeover from deceleration to acceleration, as it depends on various factors and can vary in different situations. However, the change in velocity can be calculated using the equation Δv = at, where Δv is the change in velocity, a is the acceleration, and t is the time interval.

Can the changeover from deceleration to acceleration be controlled?

The changeover from deceleration to acceleration can be controlled to some extent by adjusting the magnitude and direction of the force acting on the object. However, other factors such as the object's mass and initial velocity may also play a role in the changeover. In some cases, external factors such as friction may also affect the changeover and make it difficult to control.

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