What is the boundary of the observable universe in the Milne universe?

[micomaco86572]

What is the difference of cosmological horizon and particle horizon in cosmology?

 

[micomaco86572]

Nobody knows the answer?

 

[chronon]

Take a look at http://www.chronon.org/Articles/cosmichorzns.html and http://www.chronon.org/articles/Cosmological_Event_Horizon.html on my website

 

[micomaco86572]

Take a look at http://www.chronon.org/Articles/cosmichorzns.html and http://www.chronon.org/articles/Cosmological_Event_Horizon.html on my website

Thx Chronon! I benefited a lot from your website, which is really cool! lol!

I have two more question: the cosmological horizon people often talk about actually means the the cosmological event horizon, doesn't it?
You said:"for particle horizons to occur the rate of expansion of the universe (the derivative of the scale factor with time) must be infinite at time zero.", why?

 

[chronon]

the cosmological horizon people often talk about actually means the the cosmological event horizon, doesn't it?

I think that 'people' are sometimes confused about the issue, but that would be the most reasonable interpretation of cosmological horizon.

You said:"for particle horizons to occur the rate of expansion of the universe (the derivative of the scale factor with time) must be infinite at time zero.", why?

Well a freely coasting a universe without large scale gravity or cosmological constant - the (0,0) universe, also known as the Milne universe - doesn't have particle horizons. If you transform to conformal coordinates (See http://www.astro.ucla.edu/~wright/cosmo_03.htm#MSTD) then the conformal time goes back to minus inifinity.

 

[micomaco86572]

But in the Milne universe we still have the boundary of the observable universe, do we? Can we refer to it as a particle horizon? thx