Expansion of Universe, do we know the equation?

  • Context: Graduate 
  • Thread starter Thread starter magnetoman
  • Start date Start date
  • Tags Tags
    Expansion Universe
Click For Summary

Discussion Overview

The discussion revolves around the mathematical description of the universe's expansion, particularly in relation to dark energy. Participants explore whether the expansion is linear, exponential, or asymptotic, and question the behavior of dark energy over time.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that the expansion of the universe dominated by dark energy is exponential in nature, while acknowledging that the actual expansion is more complex due to the presence of other components.
  • It is noted that the density of dark energy remains constant as the universe expands, unlike normal matter, which dilutes with volume increase.
  • A participant mentions a specific equation related to dark energy and the expansion, referencing the LCDM model, which approximates the expansion rate based on current dark energy density.
  • Another participant refers to a cosmic calculator that may provide relevant equations, suggesting that there are additional resources available for understanding the mathematical framework.

Areas of Agreement / Disagreement

Participants express differing views on the exact nature of the expansion and the role of dark energy, indicating that multiple competing models and interpretations remain in the discussion.

Contextual Notes

The discussion includes assumptions about the dominance of dark energy and its effects on the universe's expansion, but does not resolve the complexities or provide definitive equations applicable in all contexts.

Who May Find This Useful

This discussion may be of interest to those exploring cosmology, dark energy, and the mathematical modeling of the universe's expansion.

magnetoman
Messages
1
Reaction score
0
Our acceleration universe due to 'dark energy'. Do we have a mathematical equation to describe this? I want to know if it is linear, exponential, asymptotic or something else. Is amount of 'dark energy' increasing or staying the same?
 
Space news on Phys.org
Hello and welcome to PF!

The expansion of the universe, in a universe completely dominated by dark energy alone, is exponential in character. Since our universe is not 100% dark energy, our real universal expansion is slightly more complicated.

Now, the density of dark energy does not dilute as the volume of the universe increase. Think of a box with a finite number of particles in it, say N. Now if I expand the box, the density of particles, N/V, decreases. This does not happen with dark energy. As the volume of the box increases, density stays constant. So while the density of normal matter is falling as our universe expands, the density of dark energy is constant! This means that eventually dark energy will be the main component of the universe, simply because while everything else is decreasing it stays the same.

P.S: The mathematical equations describing the evolution of the universe are known as the Friedmann equations:
http://en.wikipedia.org/wiki/Friedmann_equations
 
magnetoman said:
Our acceleration universe due to 'dark energy'. Do we have a mathematical equation to describe this? I want to know if it is linear, exponential, asymptotic or something else. Is amount of 'dark energy' increasing or staying the same?

I don't know if this thread would be of any help.
There is a specific equation in post #5 that is used in the Ned Wright cosmic calculator.
https://www.physicsforums.com/showthread.php?t=267808
 
If we take the present value of dark energy being 73% of the total density, then a/a0 = .715[sinh(1.28t/t0)]2/3. This is a pretty good approximation that ignores only "light" energy (photons, neutrinos), which is less than 1% now and is decreasing. The subscribt "0" represents the present.
(This is the LCDM model.)
 

Similar threads

Graduate Gravitational Instability and accelerated explanation of Universe?
  • · Replies 19 ·
Replies
19
Views
3K
Graduate Black hole thermodynamics and accelerated expansion
  • · Replies 2 ·
Replies
2
Views
3K
Graduate Models without dark energy
  • · Replies 29 ·
Replies
29
Views
4K
Undergrad Dark energy and the kinematic Sunyaev-Zeldovich effect?
  • · Replies 22 ·
Replies
22
Views
3K
Undergrad Voids, dark energy and tidal forces...?
  • · Replies 0 ·
Replies
0
Views
2K
Undergrad Avoiding heat death in an accelerated expanding universe?
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad Sachs-Wolfe effect in a Dark Energy universe?
  • · Replies 1 ·
Replies
1
Views
2K
Undergrad Hubble Constant, Dark Energy and the Expanding Universe
  • · Replies 20 ·
Replies
20
Views
5K
High School Estimates — True Size of the Universe?
  • · Replies 33 ·
2
Replies
33
Views
8K
Undergrad More extended equilibrium configurations due to dark energy?
  • · Replies 19 ·
Replies
19
Views
3K