When scientists look at a galaxy five million light years away that is red shifted, is that galaxy moving away five million years ago, or right now?
It might be obvious, but I just wanted to double check because my next question would be how do scientists know that the universe is still expanding?

by the time the light reaches us that far out its already in the past. its probably still moving away but we can't see its present positions because we are so far away.

well , its both ( it was moving away 5 millions years ago , and its moving away right now )
however , we are not really " looking at the galaxy " , we are looking at the light that it emitted
its the light that is red shifted , and thats how we know that our universe is expanding

But how do they know that it's moving away right now?
That part I don't really understand.

ahhh , this is one of the biggest misconceptions , that " objects sit in an unmoving space "
the truth is , altho galaxies " move around " , when we say " all the galaxies are moving away from us " , we dont mean that the actual galaxies are speeding along in space

what we mean is , space itself is actually expanding , and as it expands , all the objects " in space " , are getting further and further apart

the classic analogy is of a balloon
u blow it up abit , and with a felt pen , put 2 spots , or marks , on the balloon
now blow up the balloon some more
the spots on the balloon are now further apart than before
if u constantly blew up the balloon ( assuming it would never pop ) , you would see these 2 spots " constantly moving away from each other "

but , ofc , the spots are not actually moving at all

the balloon is space , and the spots are 2 galaxies
so what we are actually measuring is not the galaxies rate of movement , but rather the space fields rate of expansion ( we are not measuring the spots on the balloon , we are measuring how fast the balloon is being blown up )

This post was edited by Matao on Aug 21 2011 03:46am

Thanks.

lol thanks

it was a nice question

This post was edited by SuperLemonHaze on Aug 21 2011 05:51am

A neutron walks into a bar.

"I'd like a beer" he says. The bartender promptly serves up a beer."How much will that be?" asks the neutron. "For you?" replies the bartender, "no charge".

Lets put it this way. We cannot look at 5billion years in the past in real time.

HYUK HYUK HYUK,