The popular account of Einstein inventing the cosmological constant goes like this:
- Einstein finds that the Einstein Field Equations predict an expanding universe
- Unable to accept this, Einstein adds the cosmological constant to his field equations to make the universe static
- Later, when learning of Hubble's evidence that light from galaxies is redshifted in proportion to their distance from Earth, Einstein accepts the idea of an expanding universe and gets rid of the cosmological constant, calling it his "greatest blunder"
I tried reading Einstein's 1917 paper on the cosmological considerations of general relativity to understand his thought process, but I don't really see the above narrative. My understanding of the paper is more like this:
- Einstein claims Newtonian gravity cannot handle the case of an infinite universe with constant mass density $\rho$, as this would give a constant potential $\phi$, and Poisson's equation $\nabla^2 \phi = 4\pi G \rho$ paradoxically tells us the mass density must then be zero.
- Einstein reasons he can "correct" this by adding an additional term $\nabla^2 \phi - \lambda \phi = 4\pi G \rho$, which has a solution of $\phi = \frac{4\pi G \rho}{\lambda}$ that works even out at infinity
- Einstein has similar concerns for general relativity, and wonders what value the metric $g_{\mu\nu}$ would take in an infinite universe with constant mass density
- Einstein solves the problem of boundary conditions by making the spatial part of the universe a "closed" sphere, essentially making a universe with no boundary.
- Using some math I don't understand, he deduces that an additional term $\lambda g_{\mu\nu}$ in the Einstein field equations is required to make the universe closed with constant curvature: $G_{\mu\nu} + \lambda g_{\mu\nu} = \frac{8\pi G}{c^4} T_{\mu\nu}$
To me, it seems like Einstein not at all concerned with the universe expanding, and only concerned with the boundary conditions of the metric $g_{\mu\nu}$ at infinity.
Is the popular narrative about Einstein's cosmological constant wrong? Did he believe the EFE without the cosmological constant predicted an expanding universe? Have I failed to understand something in the paper?
(I would prefer answers avoid referring to the Friedmann Equations, since those came later in 1922, unless you feel those are relevant to the question.)