Why is the gravitational constant used in GR?

  • #1
Zak
15
0
(precursor: I have not formally studied GR)

I have noticed that the gravitational constant found in classical gravitation is also used in GR. Why is this the case? Am I correct in thinking that the constant was determined by Cavendish and was for the classical theory of gravitation? So, my question: how do we know that the same gravitational constant is suitable for GR and why did we not have to, say, measure a new constant?
 

Answers and Replies

  • #2
491
189
(precursor: I have not formally studied GR)

I have noticed that the gravitational constant found in classical gravitation is also used in GR. Why is this the case? Am I correct in thinking that the constant was determined by Cavendish and was for the classical theory of gravitation? So, my question: how do we know that the same gravitational constant is suitable for GR and why did we not have to, say, measure a new constant?

We get ##G## into the Einstein equations by requiring that they reduce to the classical gravitation law in the limit of slow (test-)particles in low gravitational fields.

Essentially the reason is that we want GR to supersede Newtonian gravity.
 
  • #3
Dale
Mentor
Insights Author
2021 Award
32,774
9,883
I have noticed that the gravitational constant found in classical gravitation is also used in GR. Why is this the case?
As JorisL mentioned, you can look at is as a requirement so that GR can reduce to Newtonian gravity in the appropriate limit.

Another way to look at it is that G is just a universal conversion factor between different units, so any time that you will convert between the same units you will get a the same conversion factor.
 
  • #4
Dale
Mentor
Insights Author
2021 Award
32,774
9,883
I have noticed that the gravitational constant found in classical gravitation is also used in GR. Why is this the case?
You can think of it in terms of reducing to Newtonian gravitation in the appropriate limit. You can also look at it as a conversion factor between different units. So then it is the same in both theories as long as you use the same units.
 

Related Threads on Why is the gravitational constant used in GR?

Replies
7
Views
1K
  • Last Post
Replies
2
Views
2K
Replies
10
Views
10K
Replies
11
Views
1K
Replies
11
Views
1K
Replies
12
Views
3K
Replies
2
Views
3K
Replies
1
Views
1K
Replies
3
Views
883
Replies
1
Views
2K
Top