- #1
jstrunk
- 55
- 2
What is the meaning of r in the Schwartzschild metric?.
[tex]
ds^2 = \frac{{dr^2 }}{{1 - \frac{{2GM}}{{c^2 r}}}} + r^2 (d\theta ^2 + \sin ^2 \theta d\varphi ^2 ) - c^2 \left( {1 - \frac{{2GM}}{{c^2 r}}} \right)dt^2
[/tex]
If you were to actually measure the radius, your observation would be affected by the factor
[tex]
\frac{1}{{1 - \frac{{2GM}}{{c^2 r}}}}
[/tex]
So where would you get r from if its not the radius you would measure?
I am used to special relativity where you have two different observers that measure different
values but there are no different observers here. It seems like you are supposed to measure
some space to find r, then move a star there and measure it again to see how r is affected.
That hardly seems practical. Assuming there is already a star there, are you supposed to just
measure the circumference and divide by 2 pi to estimate what r would be if the star wasn't there?
[tex]
ds^2 = \frac{{dr^2 }}{{1 - \frac{{2GM}}{{c^2 r}}}} + r^2 (d\theta ^2 + \sin ^2 \theta d\varphi ^2 ) - c^2 \left( {1 - \frac{{2GM}}{{c^2 r}}} \right)dt^2
[/tex]
If you were to actually measure the radius, your observation would be affected by the factor
[tex]
\frac{1}{{1 - \frac{{2GM}}{{c^2 r}}}}
[/tex]
So where would you get r from if its not the radius you would measure?
I am used to special relativity where you have two different observers that measure different
values but there are no different observers here. It seems like you are supposed to measure
some space to find r, then move a star there and measure it again to see how r is affected.
That hardly seems practical. Assuming there is already a star there, are you supposed to just
measure the circumference and divide by 2 pi to estimate what r would be if the star wasn't there?