This document contains comments about the article Age of the universe in Wikipedia
• The text in italics is copied from that url
• Immediate followed by some comments
In the last paragraph I explain my own opinion.

### Introduction

The article starts with the following sentence.
Measurements of the cosmic background radiation give the cooling time of the universe since the Big Bang, and measurements of the expansion rate of the universe can be used to calculate its approximate age by extrapolating backwards in time.
It is very important to discuss the uncertainties involved in these physical arguments.

### 1. Explanation

If one extrapolates the Lambda-CDM model backward from the earliest well-understood state, it quickly (within a small fraction of a second) reaches a singularity called the "Big Bang singularity".
It is better to write:
It reaches a state of almost infinite density.
(and not use the word singularity)

### 3. Cosmological parameters

The problem of determining the age of the universe is closely tied to the problem of determining the values of the cosmological parameters.
This is a rather circular argumentation.
Today this is largely carried out in the context of the Lamda/CDM model, where the universe is assumed to contain normal (baryonic) matter, cold dark matter, radiation (including both photons and neutrinos), and a cosmological constant.
The cosmological constant should be argumented from a physical point of view.
The fractional contribution of each to the current energy density of the universe is given by the density parameters omega(m), Omega(r), and omega(lambda).
See the next sentence.
If one has accurate measurements of these parameters, then the age of the universe can be determined by using the Friedmann equation.
In dutch we say: "This is the truth of a cow". The problem is how can you accurately measure these parameters? That is very very tricky.

### 4. 4 WMAP

The paragraph ends with this sentence:
Assuming the validity of the models used to determine this age, the residual accuracy yields a margin of error near one percent
That means there is a big if i.e. uncertainty.

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Created: 17 December 2017

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