Is the Speed of Light Truly Constant in General Relativity?

  • Thread starter Thread starter MetricBrian
  • Start date Start date
  • Tags Tags
    Constant Gr Light
Click For Summary
The discussion centers on whether the speed of light remains constant in the context of General Relativity (GR). Participants agree that while the speed of light is constant for all observers in local, flat regions of spacetime, its measurement can vary depending on the observer's state of motion and gravitational influences. The distinction between speed (a scalar) and velocity (a vector) is emphasized, noting that while speed remains constant, velocity can differ due to direction changes in a gravitational field. The complexities of measuring light speed in curved spacetime are acknowledged, highlighting that there is no standard way to define it globally. Ultimately, the speed of light is a fundamental aspect of both special and general relativity, but its measurement can be context-dependent.
  • #31
These issues are fairly complex and explaining them accurately and unambiguously to someone who is asking a "simple" question is not so simple. Dr Greg's posts above are, I believe, precisely accurate. Rereading my own initial post, I would now change a few words, but likely the poster would not have gained any additional insights anyway...

The speed of light being constant to all observers is one of the fundamental aspects of special relativity, so it can't be different in general relativity, as it arose from special relativity.

This statement is not precisely accurate because special relativity implies constant velocity and no curvature of space (no gravity); general relativity involves curvature of space and acceleration and only simplifies to special relativity under certain circumstances...no gravity, no acceleration...
 

Similar threads

High School Meaningfulness of the speed of light
  • · Replies 25 ·
Replies
25
Views
2K
Undergrad I want a good reference to a discussion of the meaning of "the speed of light is constant"
  • · Replies 60 ·
3
Replies
60
Views
4K
Undergrad Conventionality of the One-Way Speed of Light
  • · Replies 6 ·
Replies
6
Views
818
High School Can Motion Exceed the Speed of Light in General Relativity?
  • · Replies 20 ·
Replies
20
Views
1K
High School Problem about postulate of the invariance of the speed of light
  • · Replies 33 ·
2
Replies
33
Views
4K
High School Questions about the Speed of Light, Time, etc.
  • · Replies 74 ·
3
Replies
74
Views
5K
Undergrad Confused about time dilation -- motion vs energy
  • · Replies 9 ·
Replies
9
Views
745
Undergrad The Einstein Clock aka Light Clock
  • · Replies 34 ·
2
Replies
34
Views
2K
Undergrad SR vs GR: Logical Necessity of Signal Propagation
  • · Replies 27 ·
Replies
27
Views
3K
High School Constant Speed of Light: Low Speed Explained
  • · Replies 18 ·
Replies
18
Views
2K