The black hole is one of the most fascinating phenomena in the universe, and one of the most misunderstood. The singularity of a black hole is not where, or when, we expect to find it. Writes Carlo Rovelli.

The geometry of the space inside a black hole, down there in the blind world below, is surprisingly similar to that of Dante’s Inferno. Think of a very long funnel. At any given moment, the interior of the black hole can be imagined as this funnel. The older the black hole, the more elongated its interior.

Enormous it might be, the length of the funnel is not infinite: at the bottom there is the star that, by collapsing in on itself, gave rise to the hole.

Unlike Dante’s Inferno, which as far as we know stays the same, the funnel inside the black hole lengthens and narrows with the passage of time.

Deep down where we are falling, there are regions where the distortion of spacetime is extremely strong.

___

But the devil is in the details. Let’s see exactly where the equations stop working. Pay attention. This is the detail that has caused the most confusion among scientists.

___

Here, we expect quantum effects to intervene, as happens in extreme conditions. Einstein’s equations do not take account of such phenomena. They ignore them.

Einstein’s theory does not help us anymore. We call these regions “singularities.”

But the devil is in the details. Let’s see exactly where the equations stop working. Pay attention. This is the detail that has caused the most confusion among scientists.

SUGGESTED READING Black holes could challenge Relativity By Lydia Patton

It may seem natural to think that strange things happen at the bottom of the funnel, down in the center of the black hole.

But this is not the case. In the center of the funnel there is only the falling star; we are not in singularity territory. Here, the equations still work.