Approximate LCDM Expansion in Simplified Math - Comments

[Jorrie]

Jorrie submitted a new PF Insights post

Approximate LCDM Expansion in Simplified Math

Continue reading the Original PF Insights Post.

 

[RyanH42]

Great work thank you

 

[RyanH42]

Expansion rate is H.The observable universe radius is R.Now the expansion rate is 0.07% per billion years.And it goes 0.06% per billion year.It means R is now R+ 7R/100 is universe radius for now one billion years later it will be R+7R/100+(6(R+7R/100)/100).

Zeit is 1/17,3.Now time is 0,8 zeit(13.7 Gyr) and Hubble constant 1,2 zeit^-1 which 1,2/17.3 which its 0.07.

I didnt understand mathematical expression between H and zeit.1/H is Hubble time.I know but I camt make the connection.

And how we found 0.07% ? and what's the lamda is zeit units ?


If all this true you said H is equal $H=√(0.44/a^3+1)$ a is now 1(which you said).H=√(0.44/2)=0.46 what's that.

I said Expension rate is 0.07.Is that true ?

I asked so many question.If you help I will be happy
Thanks for help

 

[Jorrie]

Great work thank you

Pleasure, but as a first post in Insights, I'm still struggling with formatting the figures and graphs. When I edited the entry, things got worse, so please be patient while I'm trying to sort it.

 

[RyanH42]

Ok,I can wait

 

[Jorrie]

Expansion rate is H. The observable universe radius is R. Now the expansion rate is 0.07% per billion years. And it goes 0.06% per billion year.

The radius of the observable universe is not directly related to the Hubble constant H. What is directly related is the Hubble radius, because it is c/H, but you will have to wait for Part 2 for more on that.

Even the Hubble radius is not increasing at 0.07% per million years today - it is the distance to some distant galaxy that is increasing at this rate. Contemplate that and I will get back to you once I have the formatting issues cleared out.

 

[RyanH42]

Let me clear things up then.Lets suppose there's a galaxy 5 billion light years away.Now the universe expands 1/144% per billion year so the length will be 5+5.1/14.4 billion light years away.The billion later this distance will be 5+5.1/14.4+(5+5.1/14.4)/17.3 billion light years.

 

[RyanH42]

H_∞=1/173 % per billion year in the future isn't it ? So now H is 1/144 % per billion year.

 

[RyanH42]

0.2 zeit the expansion rate was 4 zeit^-1 which it means 4/17.3 billion years (0.23) means when the universe is 3.46 billion years old the distance will grow 0.23 times ?

If these things are true the I don't have another question

Note for Mentors:After clarification of my questions you can delete my comments

 

[Jorrie]

Let me clear things up then.Lets suppose there's a galaxy 5 billion light years away.Now the universe expands 1/144% per billion year so the length will be 5+5.1/14.4 billion light years away.The billion later this distance will be 5+5.1/14.4+(5+5.1/14.4)/17.3 billion light years.

It's 1/144% per million years, not per billion years. In a million years your 5 Gly distance will increase to 5+5/(144*100)= 5.00347 Gly. In the following million years it will increase to 5.00347+5.00347/(144*100)= 5.000694 Gly, assuming that H will change negligibly over the next million years.

It does not accurately hold for a billion years, because H will be changing noticeably in a billion years, going down to a constant 1/173% per Gy in the very far future. But since the distances are increasing faster than what H is declining, the expansion is accelerating.

 

[Jorrie]

0.2 zeit the expansion rate was 4 zeit^-1 which it means 4/17.3 billion years (0.23) means when the universe is 3.46 billion years old the distance will grow 0.23 times ?

I do not know where you got these values from, but they are wrong. At T=0.2 zeit, H ~ 3.4 zeit^-1, but it is hard read from the first graph (it was just to illustrate the zeit scale). We have not yet dealt properly with H against time, which will follow in Part 2. Part 1 is primarily about H against scale factor a.

 

[RyanH42]

Thank you.I am waiting Part two now.
Again great work.I am amateur in Cosmology so its takes time understand the idea.