Timeline of the universe

Makes sense really - I should imagine the overall KE of particles in that era was a little on the high to allow rapid condensation of matter to form stars, etc. Even now, it takes nebulae a significant amount of time to run from an state of 'equal' density to regions forming protostars.
 
why does the change in expansion seem so slow after the dark age? and why is it accelarating now (from the image).

epic
 
why does the change in expansion seem so slow after the dark age? and why is it accelarating now (from the image).

I am hardly an expert in that field (I am sure Chalnoth could explain ;-) ), but I think that the acceleration has something to do with the distribution of matter which is now a lot less uniform and dense than in the dark ages. Kind of like trying to spread out dough: At first is hard, but once it's flat and spread out is a lot easier.
 
Yea... This is a little tricky to explain in this forum if I read the question right, and its a bit technical.

eg I have to explain what a scale factor is, and its dependancies on various things we observe. But let me proceed anyway.

In general you will have a ratio of energy densities like so:
Lambda (Vacuum) / Lambda (Matter) ~ a^3. Where a is the scale factor whose second derivative measures the 'acceleration' of the universe (I hate to use the word acceleration here btw, it can easily lead people astray if they're not careful, and there are several different inequivalent parameters that you might be thinking off). That means in early times matter and radiation are dominant, and vacuum energy irrelevant, whereas at late times the reverse happens.

And yes, acceleration was slower in the past. you'd need to look at the acceleration equation for a FRW universe for the full picture... roughly it looks something like this off the top of my head

acceleration/a ~ -(p(m) + p(vacuum)) > 0 where acceleration is the second derivative of a, and p(m) and p(vacuum) are linear functions of rho matter and rho vacuum (the energy densities).. Theres a bunch of constants and stuff floating around that im neglecting, and im taking some confusing liberties with definitions here, but thats roughly the idea.

You might want to check one of the exhaustive cosmology faqs out there on FRW universes with the concordance model parameters.
 
Back
Top