lecture2

Distant Universe: 

Seb Oliver Lecture 2: Homogeneity andamp; Isotropy Distant Universe

Main Topics: 

Main Topics Standard Hot Big Bang Model Classical Observational Cosmology Galaxy Evolution The Hunt for the First Galaxies Background Light Structure Formation

Standard Hot Big Bang Model: 

Standard Hot Big Bang Model Assumptions of Homogeneity and Isotropy Nearly-Newton Cosmology Equations of State Geometry and fate of the Universe The Early Universe

Copernican Principle: 

Copernican Principle The earth does not occupy a special position in the universe This principal was possibly first formulated by Giordano Bruno and not Copernicus, but in any case it was a rather radical proposition with profound implications for the thinking of the universe at the time

Definitions: 

Definitions A fundamental observer is someone who is at rest with respect to the rest of the Universe in their locality Homogeneous: at any given time the Universe appears the same to fundamental observers, e.g. the observers will measure the same mean density or any other scalar quantity Isotropic: the Universe appears the same in all directions

Homogeneity: 

Homogeneity Homogeneous Not homogeneous

Isotropy: 

Isotropy Isotropic at Not isotropic

Homogeneous  Isotropic: 

Homogeneous  Isotropic

Isotropy + Copernican Principle  Homogeneity: 

Isotropy + Copernican Principle  Homogeneity Isotropy about A Isotropy about B

Cosmological Principle: 

Cosmological Principle The cosmological principle is that the universe is isotropic and homogeneous Equivalently is isotropic for every fundamental observer The cosmological principle alone can tell us some very useful things

Cosmological Principle implies a cosmological time: 

Cosmological Principle implies a cosmological time The Cosmological Principal implies a cosmological time. Since the Universe appears the same to all fundamental observers at any given time, they can all synchronise their watches to some event which occurs in the history of the Universe, thereafter all the watches measure the same cosmological time

Cosmological Principle & Hubble’s Law: 

Cosmological Principle andamp; Hubble’s Law 2,3,4

Cosmological Principle & Hubble’s Law: 

Cosmological Principle andamp; Hubble’s Law including a t dependence

Cosmological Principle & Hubble’s Law: 

Simply assuming that the universe is homogeneous andamp; isotropic has lead us to the conclusion that i.e. the universe is either: Static h(t) = v = 0 Uniformly expanding h(t) andgt; 0 Uniformly contracting h(t) andlt; 0 Cosmological Principle andamp; Hubble’s Law H(t) is Hubble parameter 7

Cosmological Principle & Hubble’s Law: 

Cosmological Principle andamp; Hubble’s Law comoving position proper position scale factor trial solution 8 9

Slide16: 

We have gone a long way with very little to go any further we need some physics .... but how do we know how H (or a) varies with time?

Standard Hot Big Bang Model: 

Standard Hot Big Bang Model Assumptions of Homogeneity and Isotropy Nearly-Newton Cosmology Equations of State Geometry and fate of the Universe The Early Universe