22
Hubble
Law Example using relative vr and relative d
40 miles
20 miles
0 miles
-70 miles
d relative to B
140 miles
120 miles
100 miles
30 miles
d
2 hr
2 hr
2 hr
2 hr
t0 = 1/H0
20 miles/hr
10 miles/hr
0
miles/hr
-35miles/hr
vr relative to B
D
C
B
A
Car
t0 = 1/H0
vr
2 hr
70 miles/hr
2 hr
60 miles/hr
----
50 miles/hr
2 hr
15 miles/hr
You
get the same result whether you use “absolute” velocities and distances, or measure velocities relative to any
arbitrary car.
Every driver thinks they are at the center of the “car
universe” and the other cars are just heading away from them, all having
left at some
common start time.
Car
“B” is the Highway Patrol – using a radar gun which can find
speed and distance to other cars – but can’t see the ground.