Albert Einstein’s been having quite a few weeks! First his “imaginary elevator� thought experiment was confirmed with unprecedented precision, then his theory of relativity was shown to create gravitational lenses as expected even in other galaxies. And today, we learn that a central tenet of relativity still holds even at gravitational extremes. It’s no annus mirabilis, but it ain’t bad.

Today’s news, which appears in the journal Nature, concerns the equivalence principal, which roughly