John C. Baez's Blog, page 5

Azimuth News (Part 7)

In 2023 the director of the Fields Institute asked me to lead a program on climate change. For quite some time I’ve been meaning to say what happened to that.

Briefly, I quit when I realized that I couldn’t get myself motivated to do the job, no matter how hard I tried.

It turned out the job was mainly to apply for grants. There were various options for what these grants could be. At the small end, a grant could be for a meeting or series of meetings at the Fields Institute, focused on a spec...

Category Theorists in AI

Applied category theorists are flocking to AI, because that’s where the money is. I avoid working on it, both because I have an instinctive dislike of ‘hot topics’, and because at present AI is mainly being used to make rich and powerful people richer and more powerful.

However, I like to pay some attention to how category theorists are getting jobs connected to AI, and what they’re doing. Many of these people are my friends, so I wonder what they will do for AI, and the world at large—and wha...

Backing Up US Federal Databases

 

I hope you’ve read the news:

• Ethan Singer, Thousands of U.S. government web pages have been taken down since Friday, New York Times, 2 Feburary 2025.

Some of the things taken down mentions diversity, equity and inclusion, but they also include research papers on optics, chemistry, medicine and much more. They may reappear, but at this time nobody knows.

If you want to help save US federal web pages and databases, here are some things to do:

• First check to see if they’re already backed up...

Obelisks

Wow! Biologists seem to have discovered an entirely new kind of life form. They’re called ‘obelisks’, and you probably have some in you.

They were discovered in 2024—not by somebody actually seeing one, but by analyzing huge amounts of genetic data from the human gut. This search found 29,959 new RNA sequences, similar to each other, but very different from any previously known. Thus, we don’t know where these things fit into the tree of life!

Biologists found them when they were ...

The Formal Gardens, and Beyond

I visited an old estate today
Whose gardens, much acclaimed throughout the world,
Spread out beyond the gated entranceway
In scenic splendors gradually unfurled.
Bright potted blooms sprung beaming by the drive,
While further off, large topiary yews
Rose stoutly in the air. The site, alive
With summer, traded sunned and shaded views.
This composition—classical, restrained—
Bespoke the glories of a golden age:
An equilibrium perchance ordained
By god-directors on an earthly stage.
I ...

Problems to Sharpen the Young

 

A farmer with a wolf, a goat, and a cabbage must cross a river by boat. The boat can carry only the farmer and a single item. If left unattended together, the wolf would eat the goat, or the goat would eat the cabbage. How can they cross the river without anything being eaten?

You probably know this puzzle. There are two efficient solutions, related by a symmetry that switches the wolf and the cabbage.

But what you might not know is that this puzzle goes back to a book written around 800 A...

Magnetohydrodynamics

Happy New Year!

I recently wrote about how the Parker Solar Probe crossed the Sun’s ‘Alfvén surface’: the surface outside which the outflowing solar wind becomes supersonic.

This is already pretty cool—but even better, the ‘sound’ here is not ordinary sound: it consists of vibrations in both the hot electrically conductive plasma of the Sun’s atmosphere and its magnetic field! These vibrations are called ‘Alfvén waves’.

To understand these waves, we need to describe how an electrically conducti...

The Parker Solar Probe

Today, December 24th 2024, the Parker Solar Probe got 7 times closer to the Sun than any spacecraft ever has, going faster than any spacecraft ever has—690,000 kilometers per hour. WHEEEEEE!!!!!!!

But the newspapers are barely talking about the really cool part: what it’s like down there. The Sun doesn’t have a surface like the Earth does, since it’s all just hot ionized gas, called ‘plasma‘. But the Sun has an ‘Alfvén surface’—and the probe has penetrated that.

What’s the Alfvén surface? ...

Epicycles

Some people think medieval astronomers kept adding ‘epicycles’ to the orbits of planets, culminating with the Alfonsine Tables created in 1252. The 1968 Encyclopædia Britannica says:

By this time each planet had been provided with from 40 to 60 epicycles to represent after a fashion its complex movement among the stars.

But this is complete nonsense!

Medieval astronomers did not use so many epicycles. The Alfonsine Tables, which the Brittanica is mocking above, actually computed planetary o...

Martianus Capella

In 1543, Nicolaus Copernicus published a book arguing that the Earth revolves around the Sun: De revolutionibus orbium coelestium.

This is sometimes painted as a sudden triumph of rationality over the foolish yet long-standing belief that the Sun and all the planets revolve around the Earth. As usual, this triumphalist narrative is oversimplified. In the history of science, everything is always more complicated than you think.

First, Aristarchus had come up with a heliocentric theory way back...