I Density parameter and curvature index

AI Thread Summary
In cosmology, when the density parameter Ω equals 1, the curvature index κ is defined as 0, indicating a flat universe. If Ω exceeds 1, κ must be positive, reflecting a closed universe, while if Ω is less than 1, κ is negative, indicating an open universe. The value of κ is intrinsically linked to Ω, meaning it cannot exist independently. The curvature index can be defined using different conventions, such as the (-1,0,1) system, which simplifies understanding its relationship with Ω. Thus, κ's value is directly influenced by the density parameter Ω.
Ranku
Messages
433
Reaction score
18
For Ω=1, κ=0. Does the value of κ simply follow from the value of Ω, or can its value have an independent existence? So if Ω>1, does κ have to be 1?
 
Space news on Phys.org
Context would be useful. I don't want to guess what you mean.
 
Ranku said:
So if Ω>1, does κ have to be 1?
Yes, by definition. Since Ω=1 is the critical density - the density at which the universe is flat - any other value of Ω necessitates that the k parameter is not 0 and has the same sign as Ω-1.
 
Reply
  • Informative
  • Like
Likes Jaime Rudas and Ranku
Define k for me.
 
The definition of k seems to have more than one option. For example the (-1,0,1) option simplifies your question.
 

Thread 'Matter density right after the decoupling'

https://en.wikipedia.org/wiki/Recombination_(cosmology) Was a matter density right after the decoupling low enough to consider the vacuum as the actual vacuum, and not the medium through which the light propagates with the speed lower than ##({\epsilon_0\mu_0})^{-1/2}##? I'm asking this in context of the calculation of the observable universe radius, where the time integral of the inverse of the scale factor is multiplied by the constant speed of light ##c##.
View full post »

Thread 'Rutgers finds a transparent Einstein Cross - apparently a dark matter "halo".'

The formal paper is here. The Rutgers University news has published a story about an image being closely examined at their New Brunswick campus. Here is an excerpt: Computer modeling of the gravitational lens by Keeton and Eid showed that the four visible foreground galaxies causing the gravitational bending couldn’t explain the details of the five-image pattern. Only with the addition of a large, invisible mass, in this case, a dark matter halo, could the model match the observations...
View full post »

Thread 'Big Bang and Infinite Universe'

Hi, I’m pretty new to cosmology and I’m trying to get my head around the Big Bang and the potential infinite extent of the universe as a whole. There’s lots of misleading info out there but this forum and a few others have helped me and I just wanted to check I have the right idea. The Big Bang was the creation of space and time. At this instant t=0 space was infinite in size but the scale factor was zero. I’m picturing it (hopefully correctly) like an excel spreadsheet with infinite...
View full post »

Similar threads

I How Does Curvature Density Parameter Affect Universe Flatness?
Replies
9
Views
3K
I Curvature Index in Flat Universe with Cosmological Constant?
Replies
3
Views
2K
I Constant Curvature and about its meaning
Replies
9
Views
3K
I Spacetime curvature and curvature index
Replies
7
Views
2K
I How to Independently Determine the Proportion of Dark Energy Density?
Replies
3
Views
2K
I Dark energy and the kinematic Sunyaev-Zeldovich effect?
Replies
22
Views
2K
I The curvature and size of the Universe
Replies
36
Views
7K
I Questions about Density Parameter and Critical Density
Replies
6
Views
2K
I When was the matter density equal to the vacuum energy density?
Replies
2
Views
2K
I Dark Energy contribution to plasma temperature in galaxy clusters?
Replies
7
Views
2K

Hot Threads

Recent Insights

Back
Top