This is about as accessible as it can get: https://faculty.math.illinois.edu/~jms/Papers/isama/eversions.pdf

The magic happens at the center-point of the surface where the three self-intersections meet. When you ply the surface apart, a tiny cube forms at the triple-point and begins to grow.

Morin’s surface is slightly less complex than splitting the boy’s surface apart, in that sphere eversion halfway model, a trapezoid forms instead of a cube. Inverting a trapezoid in this way is the minimum complexity required to turn a sphere inside out.

Videos I enjoy:

Outside in , which uses a technique different than those above (there’s also a parody out there where the narrators get snarky at eachother)

The optiverse , which uses Morin’s surface mentioned above, but is as ‘smooth’ as mathematically possible.

You haven’t lived till you comprehended this one! If you peel this entire surface into two surfaces like 2ply toilet paper, this is also a halfway point for one way of turning a sphere inside out, depending on which surface peels which way!

I DO think that word means what you think it means!

If wild kangaroos existed in Greece we’d have completely different systems of philosophy.

You may have heard that you can survive a short while after falling below the event horizon of a supermassive black hole. If we extend general relativity further in, for rotating black holes there is an inner-horizon where escape velocity falls back below that of light.

As you approach this inner horizon though, all the matter and spacetime that has ever fallen in and will fall in gets compressed into a single moment at the surface. The dying star matter from its creation would be just in front of you, and everything that falls in in the future would rush up behind you. (Spaghettification would still kill you before getting that close though.)

Infalling matter also experiences an effect called ‘mass inflation’ where energies near the cauchy horizon approach that of the big bang. This also makes the horizon catastrophically unstable, but I haven’t seen how this instability might resolve.

Also, depending on whether you are moving inwards or outwards as you cross the cauchy horizon, GR predicts you will end up in one of two disconnected inner-universes.

Google ‘black hole cauchy horizon’ to go deeper!

You may have heard that you can survive a short while after falling below the event horizon of a supermassive black hole. If we extend general relativity further in, for rotating black holes there is an inner-horizon where escape velocity falls back below that of light.

As you approach this inner horizon though, all the matter and spacetime that has ever fallen in and will fall in gets compressed into a single moment at the surface. The dying star matter from its creation would be just in front of you, and everything that falls in in the future would rush up behind you. (Spaghettification would still kill you before getting that close though.)