DARKSYDE said:
Is our galaxy receding near the speed of light to an observer at the edge of our observable universe?
phinds said:
No, it is receding at 3 times the speed of light.
Darksyde, you may need some background concepts otherwise you could find the information confusing.
There's the idea of PROPER distance at some specified moment which is the distance you'd measure if you could freeze the universe right at that moment, stop the expansion process, so you could measure in some conventional way like radar without the distances changing while you were measuring. Sometimes that present value of that distance is called the "NOW distance" or "current distance" to something.
Many of us use that concept of distance consistently or almost always. Unless otherwise specified like by saying angular-size-distance or luminosity-distance or whatever. Technically those are different. I almost always mean proper distance.
The farthest matter we can see is the matter which gave off the ancient light called the CMB (cosmic microwave background). When we use an antenna to study that light we are seeing that matter. IT IS NOW ABOUT 46 BILLION LIGHTYEARS AWAY. Because of the expansion of distances while the light was traveling to us.
So that effectively marks the EDGE of the currently observable universe---the farthest stuff we can see. We see it as it was when it was still hot gas and had not cooled and condensed into galaxies and stuff.
THE DISTANCE TO THAT MATTER IS INCREASING AT ABOUT THREE TIMES the speed of light.
You might want to get some hands-on experience with the standard cosmo model, so you don't just have people telling you stuff. There is a very good online calculator by a PF member named Jorrie, who posts here occasionally.
The only problem is it tells you too much. You have to focus and just look at the numbers that matter to you and ignore the rest. You might want to try it though.
http://www.einsteins-theory-of-relativity-4engineers.com/cosmocalc_2010.htm
Just go there and press the "calculate" button. He already has it set up to give you roughly the distance to the edge of the observable, and the recession speed of matter at that edge.
It will say something like
Proper distance now = 46000 Mly
Proper recession speed now = 3c
Just look at those two numbers, in those two boxes, and ignore the rest.
Then you can put in a different number for
Redshift of source now
and press "calculate" button again.
That is the key thing, try varying the redshift of source. He has it set to 1088 for starters because that is a good estimate of the redshift of the ancient light coming from the edge of what we can currently observe. Its waves have been stretched out by a factor of around 1100. That is why it is microwaves now, instead of the visible light and heat-glow of hot gas (which it used to be when it started out.)
But put in something else instead of 1088. Say you heard a supernova was observed and the redshift was 2. Put a 2 into the box labeled Redshift of source, and press calculate.
That will tell how far away the supernova is, and how rapidly the distance to it is now expanding.
, but this is somewhat non-standard.
