region of space. The basis of his general theory of relativity, it demonstrates how matter affects the universe itself. Not only does it predict the Hubble expansion, it also yields precise forecasts for what happens if the mixture of dark matter, visible matter, and energy is altered. Moreover, it even includes an antigravity term, called the cosmological constant, that can be interpreted as representing the impact of dark energy on universal dynamics.

The route Einstein took to his grand equation was extraordinary. Putting forth bold insights about gravitation, accelerated motion, and the roles of space and time, he crafted this raw material through the machinery of mathematics into a beautiful edifice unmatched for its elegance and simplicity. Showing little wear for its age—at least until recently—this construction has provided sturdy support for the burgeoning field of cosmology.

Although one is loathe to tamper with success, it could be that Einstein’s construct will require reinterpretation or even modification to bear the added weight of contemporary astrophysics. Before considering such options, however, let us retrace Einstein’s steps and examine how he assembled various physical suppositions into a masterpiece of mathematical architecture.

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