Undergrad Galaxy recession and Universe expansion

Click For Summary
The discussion centers on the complexities of measuring galaxy recession and universe expansion within the framework of general relativity. It highlights that in curved spacetime, unlike flat spacetime, defining relative velocities between distant objects becomes ambiguous due to the lack of global inertial frames. The concept of "recession speed" is clarified as a calculated value based on redshift and other observational data, rather than a direct measurement. Comoving coordinates are identified as a useful framework for understanding the universe's expansion, allowing for a defined expansion rate. Ultimately, the conversation emphasizes the nuanced differences between ordinary velocity and the metric expansion of space.
  • #91
Moderator's note: A subthread based on an unacceptable reference has been deleted. Please do not give pop science articles as references.
 

Similar threads

Undergrad About the meaning of "expanding universe"
  • · Replies 17 ·
Replies
17
Views
2K
Undergrad Determining a stationary point of reference to base all absolute motion
  • · Replies 57 ·
2
Replies
57
Views
3K
Undergrad 2 objects of enormous volume each in relative motion very close to c
  • · Replies 8 ·
Replies
8
Views
1K
High School Relative speed between Galaxies
  • · Replies 13 ·
Replies
13
Views
3K
Undergrad How fast were distant galaxies moving?
  • · Replies 7 ·
Replies
7
Views
2K
Undergrad Deviations of conservation laws in cosmological evolution?
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad How do you get to the conclusion that there is accelerating expansion?
  • · Replies 23 ·
Replies
23
Views
3K
High School Expansion of the Universe
  • · Replies 9 ·
Replies
9
Views
3K
Undergrad Edwin Hubble and the Evidence for Universe Expansion
  • · Replies 49 ·
2
Replies
49
Views
5K
High School Speed of Light & Space: Exceeding the "Universal Speed Limit
  • · Replies 3 ·
Replies
3
Views
2K