A Black Hole Can Be Bigger on the Inside Than the Outside

🎧 Prefer listening with the screen off? The Snoozy Scientist is also on Spotify: https://open.spotify.com/show/0EeRCWD... A black hole can have a perfectly finite event horizon while the geometry hidden beyond it contains an astonishingly large amount of space. In this slow journey into one of general relativity’s stranger consequences, we explore why the familiar relationship between an object’s outside and inside begins to fail when spacetime itself is strongly curved. We’ll look at the Schwarzschild radius, why an event horizon is a causal boundary rather than a physical shell, and why there is no single universal definition of a black hole’s interior volume. We’ll also explore the work of Marios Christodoulou and Carlo Rovelli, whose definition of maximal interior volume shows how the space associated with certain slices through a black hole can continue growing even while its horizon area remains unchanged. Along the way, we’ll see why falling inward becomes unavoidable beyond the horizon, how Roy Kerr’s rotating black holes complicate the picture, and how enormous interior volumes connect to black hole entropy and the information problem. A black hole is not simply a tiny doorway hiding a gigantic ordinary room. The reality is stranger: once spacetime becomes dynamical, a modest boundary can be associated with an immense interior geometry without breaking the laws of physics. SOURCES: American Physical Society — How Big Is a Black Hole? https://journals.aps.org/prd/abstract... American Physical Society — Volume Inside Old Black Holes https://journals.aps.org/prd/abstract... NASA Science — Anatomy of a Black Hole https://science.nasa.gov/universe/bla... NASA Science — Schwarzschild Black Holes and the Schwarzschild Radius https://science.nasa.gov/universe/glo... American Physical Society — Roy Kerr’s Rotating Black Hole Solution https://journals.aps.org/prl/abstract... American Physical Society — Black Holes and Entropy https://journals.aps.org/prd/abstract... Nature Reviews Physics — Black-Hole Thermodynamics https://www.nature.com/articles/s4225... arXiv — The Page Curve of Hawking Radiation from Semiclassical Geometry https://arxiv.org/abs/1908.10996