# Does d/R = v/c ?

1. May 24, 2006

### kmarinas86

Does d/R = v/c ??

Hubble Constant=H
distance = d
recession velocity = v
radius of Universe (light travel distance) = R
speed of light = c

Hd=v
d=v/H
R=c/H

d/R = v/c

Is this still true even with varying H with time?

2. May 24, 2006

### marcus

just to clarify notation. It all makes sense to me if these are PRESENT VALUES. except for c which I assume is constant and you could adjust units so that it is c = 1.

so v is present recession velocity of an object whose present distance from us is d.

and R is the present Hubble radius.

Yes that makes good sense. So if the object's present distance is twice Hubble radius, then its present recession velocity is twice the speed of light.

yes. that is the way I learned it IIRC.

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

now you ask is this different as H varies with time.

I think IMO it is NOT different, as long as you imagine all the variables to be measured at that other time, in the past or future.

Exactly the same relations hold, between the recession speed THEN and the distance THEN and the Hubble radius THEN etc.

=======
No problemo. Or do you see a problem kmarinas?

Last edited: May 24, 2006
3. May 24, 2006

No problemo.