Owen Gent
TASKED with telling the universe’s epic story, cosmologists have put on a compelling show. The curtain rises with a bang before a sweeping, unstoppable narrative unfolds. Stars form and explode, galaxies swirl their way into existence. Black holes munch and merge, sending out ripples through the auditorium.
It is a ripping yarn – but the longer we watch it, the more it seems not quite to add up. The story is inconsistent. The pace changes arbitrarily. Some of the characters are ill-drawn, do inexplicable things or are just plain not there on cue. All in all, there is enough in this play that goes wrong to make you think someone has lost the plot.
Increasingly, we think we know how. We had assumed that just four fundamental forces keep the cosmic action bowling along. But hints from theory and experiment are combining to suggest it might not be just four, but five, six – or maybe even more. Sketchy though these indications are, even one new force would be a turn-up for the books. “It would be absolutely momentous,” says Philippe Brax at the Saclay Institute of Theoretical Physics in France.
Forces drive the cosmic narrative. They tell its various actors, from particles to planets, how to move and behave – things that would otherwise seem inexplicable (see “What is a force?”). The four fundamental forces we know of are gravity, electromagnetism, the weak nuclear force and the strong nuclear force (see “The familiar four”). Of these, gravity is the outlier, the only one with no quantum field or particle attached to it and which can’t be described by the …
