AS FAR as dead ideas go, the luminiferous aether is among the deadest. Over a century ago, it picked a fight with Einstein’s theory of relativity and lost. Few victories in modern physics have been so total. Today, relativity offers us our best picture of the large-scale structure of the universe. It is a byword for human achievement and scientific progress. The aether, if it gets mentioned at all, is an embarrassing footnote in its rise to glory.
But relativity has run into difficulties of its own. Its failure to explain the behaviour of the universe at the smallest scales suggests that some more fundamental theory is waiting to take its place. Einstein’s universe is also plagued by dark forces that his theory cannot cast out.