In an expanding universe, a black hole isn't so scary: a falling particle reaches its horizon in finite time. But without expansion, infinite tidal forces build up inside the horizon, and an extended body gets torn apart. Could anything survive such a plunge?
Spacetime is a flexible fabric. A black hole presses it into a bottomless funnel, while the expansion of the universe stretches this fabric in all directions. Dark energy—the mysterious force accelerating the stretch—smoothes the funnel’s edges.
New calculations show: a speck of dust is guaranteed to slide into the funnel in a finite time. But the fate of a large body depends on whether dark energy is at play. Where it acts, tidal forces—the stretching stresses—at the funnel’s rim remain finite. Without it, these forces become infinite, grinding up everything that approaches.
So it turns out, the very dark energy that pushes galaxies apart makes black holes “softer.” The ideas of Karl Schwarzschild about black holes and Edwin Hubble about expansion merge into one model. A surprising fact: the black hole’s horizon, usually the point of no return, ceases to be a lethal trap in an expanding universe.
🎯 The supermassive black hole Sagittarius A* at the center of the Milky Way holds onto a gas cloud, despite cosmic expansion—its gravity is stronger than the cosmic stretching.
🎬 In “Interstellar,” astronauts survive inside a black hole; perhaps dark energy in their universe acted as an invisible guardian.