Calculating Age of Universe Using Redshift: 0.6

Click For Summary

Homework Help Overview

The discussion revolves around calculating the age of the universe using redshift, specifically at a redshift of 0.6. The original poster expresses confusion regarding the necessary steps and concepts involved in this calculation, including the scale factor and its relationship to redshift.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the relationship between redshift and scale factors, with some questioning how to derive the scale factor and whether integration is required. There is also exploration of the functional form of a(t) in a matter-dominated universe.

Discussion Status

The discussion is ongoing, with participants providing insights into the mathematical relationships involved, such as the Friedmann equation and the power law for a(t). Some guidance has been offered regarding the approximation methods, but there is no explicit consensus on the approach to take.

Contextual Notes

There is an indication that the original poster may not have a strong background in science, which could affect their understanding of the concepts being discussed. The complexity of the questions raised suggests a challenging context for the original poster.

b_o3
Messages
52
Reaction score
0
Hi i am confused as to how to calculate the age of the universe with redshift
say for example

The age of the universe now is 13.4 billion years old (and a critical universe).
How do i find the age of the universe if it was a redshift at say 0.6??

Do i have to find the scale factor first?
I am not very sure, please help!
 
Physics news on Phys.org
You need to know the ratio of the scale factors. z=(a0/a)-1 where a is the scale factor then and a0 is the scale factor now.
 
how do i get that? do i have to integrate first
 
No. To a good approximation the universe has been matter dominated all of it's history. What does a(t) look like as a function of t in this case?
 
so how would that work then?
 
What does a(t) look like as a function of t in a matter dominated universe? You can look it up, it's a power law.
 
to the power of 4
 
Nope. Use the Friedmann equation. H^2 is proportional to rho. If a(t)=t^n. H is proportional to 1/t. rho is proportional to 1/a(t)^3. So 1/t^2 is proportional to 1/a(t)^3. So a(t) is proportional to t^(2/3).
 
I'm sorry I'm not an expert on this I don't usually take science courses... but are u saying I'm gna take a(t)= k * t^(2/3) . and that gives me the answer?
 
  • #10
Yes. Since z=(a0/a)-1, this gives z=(t0/t)^(2/3)-1. (t0 is the age of the universe and t is time at redshift z. It's an approximation but it should do. You are asking some pretty hard questions for a non-science course person. What's the course?
 

Similar threads

How to calculate the age of the universe with redshift
  • · Replies 2 ·
Replies
2
Views
4K
Undergrad Could the Universe Be Much Older Than 13.8 Billion Years?
  • · Replies 3 ·
Replies
3
Views
3K
Find the Age of the Universe when Matter and Radiation densities were equal
  • · Replies 14 ·
Replies
14
Views
3K
Calculate the age of the Universe at a temperature
  • · Replies 6 ·
Replies
6
Views
2K
Undergrad An odd result from integrating to calculate the age of the Universe
  • · Replies 21 ·
Replies
21
Views
3K
High School Age of Universe: 13.8 Billion Years
  • · Replies 7 ·
Replies
7
Views
3K
Undergrad New research puts age of the Universe at 26.7 billion years
  • · Replies 6 ·
Replies
6
Views
4K
High School Size of universe - rewinding big bang versus "flat" universe
  • · Replies 54 ·
2
Replies
54
Views
6K
High School Age of the universe: observable or entire universe?
  • · Replies 56 ·
2
Replies
56
Views
7K
Undergrad Seeking reference for math related to the age of Recombination
  • · Replies 3 ·
Replies
3
Views
2K