Believe it or not, the physical story that we’d experience in this scenario would be identical to what would happen if w

Right now, the reason Earth is stable against gravitational collapse is because the forces between the atoms that make it up — specifically, between the electrons in neighboring atoms — is large enough to resist the cumulative force of gravity provided by the entire mass of the Earth. This shouldn’t be entirely surprising, as if you considered the gravitational versus the electromagnetic force between two electrons, you’d find that the latter force was stronger by about a factor of a whopping ~10⁴².

If you begin with a bound, stationary configuration of mass, and there are no non-gravitational forces or effects present (or they’re all negligible compared to gravity), that mass will always inevitably collapse down to a black hole. It’s one of the main reasons why a static, non-expanding Universe is inconsistent with Einstein’s relativity. (E. SIEGEL / BEYOND THE GALAXY)

First off, the material composing the solid Earth would immediately begin accelerating, as though it were in perfect free-fall, towards the center of the Earth. In the central region, mass would accumulate, with its density steadily rising over time. The volume of this material would shrink as it accelerated towards the center, while the mass would remain the same.

As it turns out, gravity doesn’t need to be the only force: just the dominant one. As the matter collapses, it crosses a critical threshold for the amount of mass within a certain volume, leading to the formation of an event horizon. Eventually, some time later, any object at rest — no matter how far away from the event horizon it initially was — will cross that horizon and encounter the central singularity.

If, somehow, the electromagnetic and quantum forces holding the Earth up against gravitational collapse were turned off, Earth would quickly become a black hole. Here’s what we would experience if that were to happen.

One of the most remarkable facts about the Universe is this: in the absence of any other forces or interactions, if you start with any initial configuration of gravitationally bound masses at rest, they will inevitably collapse to form a black hole. A straightforward prediction of Einstein’s equations, it was Roger Penrose’s Nobel-winning work that not only demonstrated that black holes could realistically form in our Universe, but showed us how.

In the cores of stars that are massive enough, however, neither the electromagnetic force nor even the Pauli exclusion principle can stand up to the force inciting gravitational collapse; if the core’s radiation pressure (from nuclear fusion) drops below a critical threshold, collapse to a black hole becomes inevitable.

Over the timescale of mere minutes, the density in the center would begin to rise fantastically, as material from all different radii passed through the exact center-of-mass of the Earth, simultaneously, over and over again. After somewhere between an estimated 10 and 20 minutes, enough matter would have gathered in the central few millimeters to form an event horizon for the first time.

Although it would take some sort of magical process, such as instantaneously replacing Earth’s matter with dark matter or somehow turning off the non-gravitational forces for the material composing Earth, we can imagine what would occur if we allowed this to happen.

After just a few minutes more — 21 to 22 minutes total — the entire mass of the Earth would have collapsed into a black hole just 1.75 centimeters (0.69”) in diameter: the inevitable result of an Earth’s mass worth of material collapsing into a black hole.

If that’s what the Earth beneath our feet does, however, what would a human being on Earth’s surface experience as the planet collapsed into a black hole beneath our feet?

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e concept: Force app developers to reveal exactly when and how they’ll collect and share user data and what they might do with it. Front load that information on App Store pages, during app install and loads, and, ostensibly, give users the option to opt out.

One of the most important contributions of Roger Penrose to black hole physics is the demonstration of how a realistic object in our Universe, such as a star (or any collection of matter), can form an event horizon and how all the matter bound to it will inevitably encounter the central singularity. (NOBEL MEDIA, THE NOBEL COMMITTEE FOR PHYSICS; ANNOTATIONS BY E. SIEGEL)

When matter collapses, it can inevitably form a black hole. Penrose was the first to work out the physics of the spacetime, applicable to all observers at all points in space and at all instants in time, that governs a system such as this. His conception has been the gold standard in General Relativity ever since. (JOHAN JARNESTAD/THE ROYAL SWEDISH ACADEMY OF SCIENCES)

If a black hole were to appear between the Earth and an observer, the Earth would appear gravitationally lensed in a fashion similar to this, dependent on the Earth’s position relative to the black hole and the observer. If a black hole were to form from the Earth itself, it would create an event horizon just 1.7 centimeters in diameter. (ANDREW HAMILTON / JILA / UNIVERSITY OF COLORADO)