Register to reply

Help a mature student! Friedmann equation!

by stormymouse
Tags: equation, friedmann, mature, student
Share this thread:
stormymouse
#1
Nov7-07, 11:16 AM
P: 2
Anybody like to help a physics student who did their BSc six years ago and has forgotten all their maths!
Its a problem from Andrew Liddle's Introduction to cosmology 5.5

The Friedmann eqn is

(a'/a)2 = 8TTG/3 P - k/a2

Consider the case k>o, with the universe containing matter only, so that p =p0/a3

Demonstrate that the parametric solution

a(y) = 4 TT G p0/3k (1-cos y) ; t(y) = 4TTGp0/3k3/2 (y-siny)

solves this equation where y runs from 0 to 2TT

Sorry about the crassness..I hope you can deciphere my symbols...

I know I should differentiate them and use the chain rule..but really my maths is rubbish!!

Any fellow physicists I would much appreciate it...maybe I shouldn't be doing my masters..I need to dig out my old calculus book...
Phys.Org News Partner Science news on Phys.org
Study links polar vortex chills to melting sea ice
Lab unveil new nano-sized synthetic scaffolding technique
Cool calculations for cold atoms: New theory of universal three-body encounters
cristo
#2
Nov7-07, 03:34 PM
Mentor
cristo's Avatar
P: 8,317
You need to show some work before we can help you. (This really belongs in the homework section too). You are correct that you need to differentiate and use the chain rule. Perhaps you should have a go and post what you get.
cristo
#3
Nov10-07, 06:34 AM
Mentor
cristo's Avatar
P: 8,317
Ok, so either you're not coming back, or you still can't attempt the problem. I'll give you a few hints: You vasically have two parametric functions a(y)=L(1-cos(y)) and t(y)=M(y-sin(y)), for some constants L and M. In the Friedmann equation, we have a term [itex]a'=\frac{da}{dt}[/itex]. Using the chain rule we can write [tex]\frac{da}{dt}=\frac{da/dy}{dt/dy}[/tex] from which you should be able to solve.

stormymouse
#4
Nov11-07, 11:08 AM
P: 2
Help a mature student! Friedmann equation!

Sorry, thank you for all your help..that helps a lot!


Register to reply

Related Discussions
Guidance on completing an Engineering Degree as mature student! Electrical Engineering 2
Friedmann Equation Advanced Physics Homework 3
Newtonian derivation of Friedmann equation Cosmology 2
Friedmann equation Cosmology 3
Failure of Friedmann equation? Astronomy & Astrophysics 3