Hubble Constant

  • Thread starter madness
  • Start date
  • #1
madness
815
70
The Hubble constant v = Hd tells us recessional velocity of galaxies is proportional to distance. But distance is equivalent to looking back in time. So what we are seeing is the recessional velocities of galaxies at different times in the universe? This surely can't be right, because for an expanding universe, recessional velocity should be proportional to physical distance, not time.
 

Answers and Replies

  • #2
Chalnoth
Science Advisor
6,197
447
The Hubble constant v = Hd tells us recessional velocity of galaxies is proportional to distance. But distance is equivalent to looking back in time. So what we are seeing is the recessional velocities of galaxies at different times in the universe? This surely can't be right, because for an expanding universe, recessional velocity should be proportional to physical distance, not time.
The above equation only holds when you have a constant expansion rate. When the expansion rate changes with time, you have to use an integral.
 

Suggested for: Hubble Constant

  • Last Post
Replies
14
Views
710
Replies
8
Views
876
Replies
18
Views
873
Replies
21
Views
679
Replies
6
Views
1K
  • Last Post
Replies
4
Views
1K
Replies
2
Views
133
Replies
17
Views
2K
Replies
8
Views
542
  • Last Post
Replies
11
Views
1K
Top