Black holes born in the big bang could be the dark matter physicists have sought for decades – if they exist. Now there’s an audacious plan to find the scars they would have left as they punched through the moon
29 September 2021
IF YOU hovered above the surface of the moon and studied it up close, you wouldn’t necessarily see anything special. There would be craters, of course, some dusty slopes and a few featureless, ancient volcanic plains. If you were in the right place, you might get a glimpse of Neil Armstrong’s footprints. But if you knew what to look for, you may find something much more extraordinary than all of this. Hiding on the lunar surface could be a scar left behind by a tiny black hole.
We aren’t talking about any old black holes, but remnants from the dawn of the cosmos. Known as primordial black holes, these theoretical beasts are thought to range in size from the width of a single atom to that of our entire solar system. If they exist, they may explain some of our universe’s greatest mysteries, from the origins of supermassive black holes found at the centres of galaxies to the mysterious planet-like mass at the edge of our solar system. They might even account for dark matter – the roughly 85 per cent of the universe’s mass that we are unable to see, but know must be there in some form.
As yet, there is no evidence that these black holes exist. But now, two physicists have come up with an audacious plan to change that. They want to scour the lunar surface in search of craters left behind as these black holes slammed into – and indeed through – the moon. “It sounds a little bit wild,” says Matthew Caplan at Illinois State University. “But you never know until you check.”