- #1
Chain
- 35
- 3
I've been watching the Stanford lectures on GR by Leonard Susskind and according to him the metric tensor is not constant in polar coordinates. To me this seems wrong as I thought the metric tensor would be given by:
[tex]
g^{\mu \nu} =
\begin{pmatrix}
1 & 0\\
0 & 0\\
\end{pmatrix}
[/tex]
Since [itex]g_{\mu \nu}x^{\nu}x^{\mu}[/itex] is supposed to give the squared length of the vector [itex]x^{\mu}[/itex] and indeed it does:
[tex]
g_{\mu \nu}x^{\nu}x^{\mu} =
\begin{pmatrix}
r & \theta \\
\end{pmatrix}
\begin{pmatrix}
1 & 0\\
0 & 0\\
\end{pmatrix}
\begin{pmatrix}
r\\
\theta\\
\end{pmatrix}
=
\begin{pmatrix}
r & \theta \\
\end{pmatrix}
\begin{pmatrix}
r\\
0\\
\end{pmatrix}
= r^2
[/tex]
I'm not sure if he simply made a mistake in the lecture or if I've misunderstood something. I'd appreciate any feedback :)
[tex]
g^{\mu \nu} =
\begin{pmatrix}
1 & 0\\
0 & 0\\
\end{pmatrix}
[/tex]
Since [itex]g_{\mu \nu}x^{\nu}x^{\mu}[/itex] is supposed to give the squared length of the vector [itex]x^{\mu}[/itex] and indeed it does:
[tex]
g_{\mu \nu}x^{\nu}x^{\mu} =
\begin{pmatrix}
r & \theta \\
\end{pmatrix}
\begin{pmatrix}
1 & 0\\
0 & 0\\
\end{pmatrix}
\begin{pmatrix}
r\\
\theta\\
\end{pmatrix}
=
\begin{pmatrix}
r & \theta \\
\end{pmatrix}
\begin{pmatrix}
r\\
0\\
\end{pmatrix}
= r^2
[/tex]
I'm not sure if he simply made a mistake in the lecture or if I've misunderstood something. I'd appreciate any feedback :)