Telling universe time from the stars

[Martin]

Maybe some people will want to try this. It uses the cosmos calculator.

Google "cosmos calculator".

 

Let's say you are an alien somewhere in the universe, in the future, and you want to know what time it is (how old expansion is).

 

You can measure the Hubble rate and you find it is 60.8, instead of the 71 we have today.

 

From that you can determine the critical density for flatness, and you can see the universe is approx flat, and you can measure the average density of matter and find it is 0.01 of critical (instead of the 27 percent it is today it is only 1 percent because this is far in the future.)

 

So you do something very simple: go to cosmos calculator and put in

0.01 for omega and 0.99 for lambda and 60.8 for the hubble rate and press calculate.

 

This will tell you the age of the universe (current expansion phase) for that alien.

========================

 

Keep in mind cosmos calculator is not quite as precise as Wright's so it gives answers that are more ballpark in some cases, but we can still do something interesting.

 

Pretend that alien in the future points his telescope at the Milky Way

and finds that it has redshift z = 2.23.

 

So you already put in Omega = .01

Lambda = .99

H = 60.8

 

So now put in z = 2.23 and press "calculate" and see what you get.

 

What you get is us! The alien sees us. And for us the age of the universe is approx 13.7 billion (it will get it nearly right) and for us the hubble rate is approx 71 (it will say around 70 which is close enough.)

 

http://www.uni.edu/morgans/ajjar/Cosmology/cosmos.html

 

It gives a nice change of perspective because with that calculator we are used to reading "age now" as the present age for us 13.7 and we think of "age then" as the age when some ancient galaxy emitted the light we are seeing now----then is some time in our past.

 

But the calculator lets us look at things from the perspective of someone far in the future, and it says that HIS "age now" is, say, 31.7 billion. And for him "age then" is close to 13.7 billion because he is looking at us, and that is the age of our now.

Edited May 2, 2009 by Martin

[NowThatWeKnow]

Pretend that alien in the future points his telescope at the Milky Way

and finds that it has redshift z = 2.23.

 

So you already put in Omega = .01

Lambda = .99

H = 60.8

 

So now put in z = 2.23 and press "calculate" and see what you get.

 

What you get is us! The alien sees us. And for us the age of the universe is approx 13.7 billion (it will get it nearly right) and for us the hubble rate is approx 71 (it will say around 70 which is close enough.)

 

http://www.uni.edu/morgans/ajjar/Cosmology/cosmos.html

 

A quick peek for those that do not want to try it for themselves.

[NowThatWeKnow]

To look out in space from earth set it up by putting in .27, .73, and 71 as the present matter and DE densities, and the Hubble rate. Try out different z #'s up to z = 1000

[Martin]

As usual I can't say thanks with the button, because of the spread-around quota:D, but thanks anyway.

I put a table here

http://www.scienceforums.net/forum/showthread.php?p=489157#post489157

that makes it easier to tell time either just from measuring background temp or from measuring the Hubble rate.

 

That simplifies everything. If you want to know the time you just have to measure one number. It might be the Background temperature or something else. You have a choice.

 

Long range clock in the sky