Right now, the reason Earth is stable against gravitational collapse is because the forces between the atoms that make i

However, if the material composing the Earth still managed to emit or reflect the ambient light, it would remain opaque, and we’d be able to see what happened to the surface beneath our feet as we fell. Either way, the first thing that would happen would be a transition from being at rest — where the force from the atoms on Earth’s surface pushed back on us with an equal and opposite force to gravitational acceleration — to being in free-fall: at 9.8 m/s² (32 feet/s²), towards the center of the Earth.

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.

Both inside and outside the event horizon of a Schwarzschild (non-rotating) black hole, space flows like either a moving walkway or a waterfall, depending on how you want to visualize it. At the event horizon, even if you ran (or swam) at the speed of light, there would be no overcoming the flow of spacetime, which drags you into the singularity at the center. Outside the event horizon, though, other forces (like electromagnetism) can frequently overcome the pull of gravity, causing even infalling matter to escape. (ANDREW HAMILTON / JILA / UNIVERSITY OF COLORADO)

When a human enters free-fall, such as this 1960 skydive jump by Colonel Joseph Kittinger from over 100,000 feet, they accelerate towards the center of the Earth at a roughly constant rate of ~9.8 m/s², but are resisted by the non-accelerating air molecules around them. After only a few seconds, a human will reach terminal velocity, as the drag force will counterbalance and cancel out the accelerative force of gravitation. (U.S. Air Force/NASA/Corbis via Getty Images)

Which is a good thing, because not only would you fall faster and faster towards the Earth’s center as time went on, but your acceleration would actually increase as you got closer to that central singularity.

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.

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.

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)

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.

That “rising stomach” sensation that you’d feel — like you get at the top of a drop on a roller coaster — would begin as soon as free-fall started, but would continue unabated.

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.

Believe it or not, the physical story that we’d experience in this scenario would be identical to what would happen if we instantly replaced the Earth with an Earth-mass black hole. The only exception is what we’d see: as we looked down, a black hole would simply distort the space beneath our feet while we fell down towards it, resulting in bent light due to gravitational lensing.

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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ons on whether your partner can become more comfortable in recognizing or experiencing their emotions because you may be setting yourself up for heartbreak. Many times, when relationships are at a crossroads that require partners to level up emotionally, those who battle with emotional unavailability may ditch one relationship for a “fresh start” in another relationship where emotions aren’t yet in play.

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)