iiinova — where your digital self keeps evolving

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 18m

What you do is, you set up your haunted scarecrow, and pretty soon a big feral cat shows up and blesses your stoop.

A scarecrow with a burlap face and flannel shirt holds a flickering lantern and is bathed in orange light from below. A cat sits in the foreground.

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 37m

I have a Tandy 1000 set aside, but I can’t say for sure that it has never been connected to the internet, so I may play it safe and put a Timex Sinclair in my disaster preparedness pack.

000

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 1h

I know it sounds crazy, but an arcane form of governmental intervention called “regulation” can actually PREVENT companies from engineering catastrophes.

1202

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 1h

One wild thing that not a lot of people are aware of, is that we don’t actually have to let these companies do any of this.

2332

Reposted by Robert "The Bobby Yaga" McNees

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 5h

The physicist and astronomer Karl Schwarzschild was born #OTD in 1873. In 1915, while serving in the German army on the Russian front, he found the first exact (non-trivial) solution of Einstein’s theory of general relativity. Among other things, it describes a non-rotating black hole. 🧪 ⚛️ 🔭

Black and white photo of Karl Schwarzschild, seated outside. He wears dark suit with a white shirt and tie, and is holding a small pad of paper on his knee.

29624

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 5h

Happy birthday Karl Schwarzschild, and thanks for the black holes. 🎂⚫️

1334

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 5h

Karl Schwarzschild passed away from complications associated with an illness he acquired on the Russian front, less than a year after sending his letter to Einstein.

2130

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 5h

Anyway, here is a translation of Schwarzschild's paper "On the Gravitational Field of a Point-Mass, According to Einstein’s Theory." zelmanov.ptep-online.com/papers/zj-20...

The title and abstract read:

On the Gravitational Field of a Point-Mass,
According to Einstein’s Theory
Karl Schwarzschild
Submitted on January 13, 1916
¨
Abstract: This is a translation of the paper
Uber das Gravitations-
feld eines Massenpunktes nach der Einsteinschen Theorie by Karl
Schwarzschild, where he obtained the metric of a space due to the
gravitational field of a point-mass. The paper was originally published
in 1916, in Sitzungsberichte der K¨oniglich Preussischen Akademie der
Wissenschaften, S. 189–196. Translated from the German in 2008 by
Larissa Borissova and Dmitri Rabounsk

190

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 5h

Tidal forces eventually (perhaps quickly) become so great that any physical object is stretched out like spaghetti and ripped apart. All trajectories end at a singularity where the spacetime curvature becomes infinite. There’s no way out, for anything.

2110

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 5h

However, closer to the mass its gravitational field becomes so intense that causality conspires to close off a region of spacetime from the rest of the Universe. Light cones are tilted and squeezed so that any object crossing into this region is doomed to move further in.

1110

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 5h

Far away, its gravitational field is no different than any object of the same mass. A (very grating) misconception is that black holes are powerful vacuum cleaners violently sucking in everything around them. But outside the Schwarzschild radius, gravity is the same as for a star or planet.

1150

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 5h

So when the mass of a non-rotating spherical object is confined to a region with radius less than 2MG/c², Schwarzschild’s solution describes a black hole.

1141

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 5h

But something does happen at what we now call the Schwarzschild radius. The causal structure of spacetime changes. Anything crossing into the region r<2MG/c² must move further inward and can never return to the outside. This region of no return is behind an “event horizon”.

1111

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 5h

In one sense this is an artifact of these coordinates. There are perfectly good ways of describing this spacetime which extend beyond this point. Physical stresses or strains don’t become infinite as a free-falling observer passes by r=2MG/c², there’s no violent bump in the road.

190

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 5h

His description of the geometry of spacetime *seems* to go haywire here. Quantities we might expect to be non-zero instead become 0 or infinite.

190

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 5h

If the place where his radial coordinate equals 2MG/c² is *outside* the object, something funny appears to happen to Schwarzschild’s solution. (G is Newton's constant, c is the speed of light. For a solar mass object this is about 3km — much less than the radius of our Sun.)

190

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 5h

Anyway, even in those early exchanges it was clear that something unusual happened to Schwarzschild’s gravitational field near a sufficiently compact mass. One of his very important insights was to work in <🎺chorus of heavenly trumpets🎺> spherical polar coordinates.

1151

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 5h

(Nowadays we can test general relativity with enough precision to tell that that Earth’s gravitational field is not exactly described by Schwarzschild’s solution: einstein.stanford.edu )

einstein.stanford.edu

Gravity Probe B: Testing Einstein's Universe

2140

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 5h

For instance, you can approximate the gravitational field outside the Sun with Schwarzschild’s solution. Its null geodesics — paths followed by light rays — describe the deflection of light in the sun’s spacetime geometry pretty well!

1160

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 5h

Einstein promised to present Schwarzschild’s result to a meeting of the Berlin Academy the following week. Both of them understood that actual astrophysical objects rotate, but that this solution would be an excellent approximation to the gravitational field of planets and stars.

1160

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 5h

Einstein was delighted. He confessed in his reply that he suspected the equations were so difficult that exact solutions (besides the flat Minkowski space of special relativity!) might never be found.

1160

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 5h

He sent his solution to Einstein in a letter, expressing surprise at his own good luck and praising the marvelous power of the new theory. “It is quite a wonderful thing that from such an abstract idea the Mercury anomaly emerges so stringently.” – Schwarzschild, to Einstein

1170

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 5h

Returning to the front, Schwarzschild began his investigations into this wild new theory. He quickly found an exact solution of the GR field equations that describes the gravitational field outside a massive and non-rotating spherical body.

1160

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 5h

At first, Schwarzschild was skeptical of general relativity. But then, while on leave from the front, he heard Einstein speak at the Prussian Academy of Sciences. Einstein used his new theory to explain the anomalous precession in the orbit of Mercury, and Schwarzschild was sold.

1161

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 5h

29624

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 6h

Teaching the students how to be bounded in a nutshell, and count themselves kings and queens of infinite space. 🧪 ⚛️

The Penrose diagram for Minkowski space is a grey wedge with thin black curves forming a sort of grid. Colored lines and curves describe different trajectories of moving observers. Several points and lines are labeled.

3310

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 14h

There is no force in the universe more powerful than the allure of the thing that is not the thing you should be doing right now.

3211

Reposted by Robert "The Bobby Yaga" McNees

Thomas Spooks 🎃👻💀 @thomasfuchs.at · 14h

I've a moderation list for these types of accounts here, if anyone wants to mass-mute or block them for themselves. Also, please reports these accounts.

092

Reposted by Robert "The Bobby Yaga" McNees

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 07/09/2026

This scraper account posts other people’s stuff without credit. They grudgingly post a separate attribution after the fact, if enough people call them out. Any time an account says “dm me if you own the original,” just put them on the block list. Don’t let these accounts get a foothold here.

33807291

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 09/10/2026

My wife and daughter were still laughing about this after the drive back to Chicago from Milwaukee.

020

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 08/10/2026

This will probably end up on here somehow, so set a reminder to turn off autoplay on December 2. Go to Settings, click "Content and Media," and make sure "Autoplay videos and GIFs" is not checked.

14014

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 08/10/2026

% I prefer big a3 pages with a tight grid. % Good for long calculations on a tablet. \documentclass{article} \usepackage[pattern=majmin, colorset=std,textarea,patternsize=0.25cm, geometry={a3paper, hmargin=0.5cm, vmargin=0.5cm}]{gridpapers} \begin{document} \thispagestyle{empty} ~ \end{document}

030

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 08/10/2026

% Or copy this post, paste it into your favorite editor, % and compile. \documentclass{article} \usepackage[pattern=majmin, colorset=std,textarea,patternsize=0.125in, geometry={letterpaper, hmargin=0.25in, vmargin=0.25in}]{gridpapers} \begin{document} \thispagestyle{empty} ~ \end{document}

130

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 08/10/2026

I use a *ton* of graph paper, so I try to put this out there once a twice of year for anyone else in the same boat. Making it myself means I can have it just the way I want, and I save a bundle now that pads of paper cost a million dollars.

380

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 08/10/2026

Occasional PSA, 2026 edition: @duetosymmetry.com and I made a graph paper package for LaTeX. Various styles (graph, quadrille, hex, iso, dot grid, etc) with pre-defined or custom colors. Print it or make templates for your tablet. 🧪 Github: github.com/mcnees/LaTeX... CTAN: ctan.org/pkg/gridpapers

A light blue grid on a white background.

A red isometric grid on a pink background.

A brown grid with major and minor lines, on a pale yellow background.

A green hex grid on a light green background.

39530

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 08/10/2026

But Sam Altman assured me that we understand the structure of reality better because there’s a big github repo

170

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 08/10/2026

[Sam Altman jabbing his finger at a preprint on his laptop that he cannot explain or verify] “Don’t you see? We understand more about the structure of reality”

0282

Robert "The Bobby Yaga" McNees @mcnees.bsky.social · 08/10/2026

Altman genuinely thinks that output and understanding are the same thing.

2372