Timeline for Which Friedmann equation is redundant?
Current License: CC BY-SA 4.0
9 events
| when toggle format | what | by | license | comment | |
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| S Mar 6, 2022 at 6:54 | history | edited | Níckolas Alves | CC BY-SA 4.0 |
Modified formatting; edited tags
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| S Mar 6, 2022 at 6:54 | history | suggested | user320397 | CC BY-SA 4.0 |
Modified formatting
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| Mar 6, 2022 at 6:49 | review | Suggested edits | |||
| S Mar 6, 2022 at 6:54 | |||||
| Aug 11, 2017 at 14:05 | comment | added | Cham | The Einstein equation is really a second order equation, with some constraints from the Bianchi identity. Thus equation (1) is a constraint on equation (2) (second order equation). Equation (3) is a consequence of the Bianchi identity which implies local conservation of energy-momentum : $\nabla_{\mu} \, T^{\mu \nu} = 0$. This one gives (3). | |
| Aug 11, 2017 at 13:56 | comment | added | Cham | Your equations (1) and (2) are missing some terms. They should be these (with the cosmological constant) : \begin{equation}\tag{1} \frac{\dot{a}^2}{a^2} + \frac{k}{a^2} = \frac{8 \pi G}{3} \, \rho + \frac{\Lambda}{3}, \end{equation} and \begin{equation}\tag{2} \frac{\ddot{a}}{a} = -\: \frac{4 \pi G}{3} ( \rho + 3 p) + \frac{\Lambda}{3}. \end{equation} euqation (1) is a first order differential equation, while (2) is second order. This is why most authors say that (1) is the first equation of FL, while (2) is the second equation of FL. | |
| Nov 12, 2011 at 1:24 | vote | accept | Joss L | ||
| Aug 5, 2011 at 9:39 | history | tweeted | twitter.com/#!/StackPhysics/status/99414115054915584 | ||
| Aug 4, 2011 at 19:11 | answer | added | Benjamin Horowitz | timeline score: 5 | |
| Aug 4, 2011 at 17:27 | history | asked | Joss L | CC BY-SA 3.0 |