The Cosmic Rift: How the Expansion Rate Crushes Black Hole Births ✛ ✎ ✦
Cosmologists are like tailors stitching a suit from two different measurements. One tape is telescope data, the other a theoretical pattern. Sooner or later, the jacket stops matching the trousers.
The prime suspects for dark matter — primordial black holes — could have emerged from tiny overdensities blown up by inflation — the newborn universe's instant swelling (idea of Alan Guth). But this requires a special kind of inflation with a stall, which leaves a noticeable imprint on the cosmic microwave background, the ancient glow from the edge of the visible cosmos. That imprint — like a pattern on fabric — must have a very specific curve, but real observations paint a different picture.
New work shows that early dark energy alters the ancient light pattern so that the curve needed for black holes becomes completely impossible. Trying to patch one seam rips another. This doesn't mean primordial black holes don't exist — but the most natural recipe for baking them is coming apart at the seams.
A primordial black hole with the mass of an asteroid would be tinier than a proton, yet could weigh as much as a mountain. If such objects really are whizzing around us, a few pass harmlessly through your body each year.
The idea of primordial black holes as dark matter has inspired sci-fi authors: in Peter Watts’ novel Blindsight, they’re used to explain gravitational anomalies.