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The famous 1939 paper by Oppenheimer (and Snyder) that proved that stars could collapse into Black Holes has me puzzled. I can’t get the signs to match in his first 2 field equations for the same metric, and those particular signs are crucial for his very first conclusion.

$$ds^2 = e^\nu dr^2 - e^\lambda dr^2 - r^2 (d\theta ^2 + \sin^2 \theta d\phi ^2).$$

Oppenheimer: (His spherical coordinates appear to be: 1,2,3,4 = radius,$\theta$,$\phi$ and time.)

$$-8\pi T_1^1 = e^{-\lambda} \left(\frac {\nu'}{r}+\frac{1}{r^2}\right)-\frac{1}{r^2}.$$

$$8\pi T_4^4 = e^{-\lambda} \left(\frac {\lambda'}{r}-\frac{1}{r^2}\right)+\frac{1}{r^2}.$$

Maxima program: (Maxima’s spherical coordinates are: 1,2,3,4 = time,radius,$\theta$,$\phi$)

$$E_2^2 = e^{-\lambda} \left(\frac {\nu'}{r}+\frac{1}{r^2}\right)+\frac{1}{r^2}.$$

$$E_1^1 = e^{-\lambda} \left(-\frac {\lambda'}{r}+\frac{1}{r^2}\right)+\frac{1}{r^2}.$$

The opposite signs on the one-over-radius-squared terms in each field equation are what he bases his very first conclusion on – “…that unless lambda vanishes at least as rapidly as radius-squared when $r$ goes to 0…” Can anyone explain what is going wrong? Maxima has never failed any of my hand-checks of its calculations.

I also cannot find Oppenheimer and Snyder’s arguments in any of the many physics textbooks I have bought from Amazon after retiring from engineering. If anyone knows where that might be in recent publications, please let me know.

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  • $\begingroup$ Different references may have many different signs on the definitions of the Riemann tensor and of the Einstein tensor (in addition to the obvious difference in the metric). See this post. I'm not sure, but perhaps this is related to your issue. $\endgroup$ Commented Aug 24 at 0:26
  • $\begingroup$ I found my error – in my input to Maxima! How embarrassing. Oppenheimer’s field equations are correct of course. Thanks to whoever edited my input to make it readable. I can’t seem to find out how to run “MathJax” is it? $\endgroup$
    – BenB
    Commented Aug 29 at 13:52

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