UK GCSE level age ~14-16, ~US grades 9-10 PHYSICS revision notes re-edit 25/05/2023 [SEARCH]

Cosmology: 1. An introduction to several different cosmological models

Doc Brown's Physics exam study revision notes

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There are various sections to work through,

after 1 they can be read and studied in any order.

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(1) An introduction to cosmological models

What is cosmology?  Is the universe contracting, expanding or staying the same size?  How to explain the red-shift and its significance? What is the 'Big Bang Theory of the Universe'? How old is the universe?  What evidence is there for the Big Bang theory of the universe?  I'll build up the arguments in four sections to explain why the 'Big bang Theory' seems to be the best theory we have at the moment to describe the origin of the Universe

Cosmology

Cosmology is a branch of astronomy that involves observing and studying the origin and evolution of the universe, from the Big Bang at the start, its current state and what is it's future?

According to NASA, the definition of cosmology is "the scientific study of the large scale properties of the universe as a whole."

At the moment the evidence suggests the Universe is getting bigger - some sort of expansion is taking place.

Two models have been put forward to explain this expansion and the creation of the Universe itself.

The Steady State model of the universe

The Steady State theory states that the Universe has always existed in its current state and will remain so in the future.

The model is based on the idea that the Universe looks roughly the same in which ever direction you look and has always looked that way.

In order for this to be so, the expansion is explained (but not proved) by new matter being created all the time ie more matter is created to cause the expansion.

In the Steady State model of the Universe, there is no beginning and no end - an interesting philosophical concept!

The Big Bang model of the universe

The Big Bang theory relies on the idea that all the matter of the Universe started out by occupying a very small space (referred to as a singularity).

This tiny space or volume of material would be incredibly dense and hot.

It then 'explodes' and expands to create space distributing the matter in it.

This expansion is considered to be continuous - see evidence for this cosmological expansions in later sections of this page.

Measurements of the rate of this expansion can give you an estimate of the finite age of the Universe - now calculated to be about 13.8 billion years (Our Sun is estimated to be 4.5 billion years old).

Of the two theories, the Big Bang model more is the accepted one because it fits the ever increasing experimental data better than the Steady State model - the latter just does not fit in with several important observations.

NOT for GCSE, BUT at a 'deeper' level - The initial singularity was of apparently infinite density and considered to have contained all of the mass and space-time of the Universe that exists. Eventually some sort of quantum fluctuations caused it to rapidly 'explode' in a 'Big Bang' resulting in massive expansion, creating the present-day Universe as we know it - the mind boggles! (I wish I understood more, but my old grey cells are not up to it these days, and where did the singularity come from in the first place? - mind boggling again!)

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