# Insights A Journey Into the Cosmos - The Friedmann Equation - Comments

Tags:
1. Dec 22, 2017

### Arman777

2. Dec 26, 2017

### Greg Bernhardt

Great start @Arman777. This is part of our student series. If anyone has suggestions or feedback for him he would appreciate it!

3. Dec 27, 2017

### Drakkith

Staff Emeritus
Very nice!

4. Dec 27, 2017

### Arman777

Thanks a lot :)

5. Dec 29, 2017

### chasrob

Very interesting post, one that even someone with an art major's understanding of physics can follow along. Like me, heh.

Inre to figure 8 and the crunch; years ago I came across a paper about solving the Friedmann equations by computer and noticed some surprising results. Surprising to me anyway. What do you think of their statement on page 2 --Thus a closed universe, by definition, is one with positive curvature K_0. Closure by itself does not tell us whether or not the universe will recollapse. In Sect. III we will show that in relativistic cosmology some open models recollapse and some closed ones do not."

6. Dec 29, 2017

### Staff: Mentor

It's true if there is a nonzero cosmological constant. Most introductory treatments of the Friedmann equations don't consider this case. If the cosmological constant is zero, then a closed universe will always recollapse and a flat or open one will always expand forever; that's why you often see statements along those lines in introductory treatments.

7. Dec 29, 2017

### Arman777

As PeterDonis said, my case is for $Λ=0$. But in the next chapters, I' ll introduce the $Λ$ and solve some models when $Λ≠0$.