When Did the Universe Start Accelerating?

In summary, we are given a cosmological model with H0=72, Omega_M=1-Omega_lamda=0.3 (with dark energy w=-1) and a flat universe. We are asked to find the redshift z at which the universe starts accelerating and how long ago this happened. To solve this, we need to use the deceleration formula, since accelerating expansion means that the second derivative of the scale factor a(t) is positive.
  • #1
June_cosmo
25
0

Homework Statement


Assume the cosmological model with H0=72,Omega_M=1-Omega_lamda=0.3,(so dark energy with w = − 1) and a flat universe.)
a) Find the redshift z at which the universe starts accelerating (that is, when it transitions from decelerating to accelerating).
b) How long ago did this happen?

Homework Equations

The Attempt at a Solution


I don't quite understand the accelerating here. Does it mean that the expanding rate begins to accelerate? How should I start this problem?
 
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  • #2
Accelerating expansion means that the second derivative of the scale factor ##a(t)## is positive.
 
  • #3
Orodruin said:
Accelerating expansion means that the second derivative of the scale factor ##a(t)## is positive.
Orodruin said:
Accelerating expansion means that the second derivative of the scale factor ##a(t)## is positive.
I see. Should I use the deceleration formula?
 

Related to When Did the Universe Start Accelerating?

1. What is the onset of universe acceleration?

The onset of universe acceleration refers to the time when the expansion rate of the universe began to accelerate, instead of slowing down as predicted by traditional theories. This phenomenon was first observed in the late 1990s and has since been confirmed by various experiments and observations.

2. What caused the onset of universe acceleration?

The exact cause of the onset of universe acceleration is still unknown. However, it is believed to be driven by a mysterious force called dark energy, which makes up about 70% of the total energy in the universe. Dark energy is thought to have negative pressure, which causes the expansion of the universe to accelerate.

3. How do scientists measure the onset of universe acceleration?

Scientists use various methods to measure the expansion rate of the universe, such as using supernovae, cosmic microwave background radiation, and baryon acoustic oscillations. By analyzing these data, they are able to determine the rate at which the universe is expanding and whether it is accelerating or decelerating.

4. Is the onset of universe acceleration related to the Big Bang?

The onset of universe acceleration is not directly related to the Big Bang, which is the event that marks the beginning of the universe. However, it is a crucial factor in understanding the evolution of the universe since the Big Bang. The Big Bang theory does not explain the presence of dark energy, which is believed to be responsible for the acceleration of the universe.

5. What are the implications of the onset of universe acceleration?

The onset of universe acceleration has significant implications for our understanding of the universe and its future. It suggests that the expansion of the universe will continue to accelerate, leading to the eventual separation of galaxies and the cooling and darkening of the universe. It also challenges traditional theories of gravity and has led to the development of new theories, such as the theory of cosmic inflation and the concept of a multiverse.

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