And all this is only the result of an elementary intuition: that spacetime and the gravitational field are one and the same thing. And a simple equation that I can’t resist copying out here, even if most of my readers will certainly not be able to decipher it. I do so anyway, in the hope that they might be able to catch a glimpse of its beautiful simplicity: Rab – ½ Rgab + Λgab = 8πG Tab In 1915, the equation was simpler still, because the term “+ Λgab,” which Einstein added two years later (and which I discuss in the next section) did not yet exist.* Rab depends on Riemann’s curvature, and
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