John C. Baez's Blog, page 75
February 7, 2016
Rumors of Gravitational Waves
The Laser Interferometric Gravitational-Wave Observatory or LIGO is designed to detect gravitational waves—ripples of curvature in spacetime moving at the speed of light. It’s recently been upgraded, and it will either find gravitational waves soon or something really strange is going on.
Rumors are swirling that LIGO has seen gravitational waves produced by two black holes, of 29 and 36 solar masses, spiralling towards each other—and then colliding to form a single 62-solar-mass black hole!
...
February 4, 2016
Aggressively Expanding Civilizations
Ever since I became an environmentalist, the potential destruction wrought by aggressively expanding civilizations has been haunting my thoughts. Not just here and now, where it’s easy to see, but in the future.
In October 2006, I wrote this in my online diary:
A long time ago on this diary, I mentioned my friend Bruce Smith’s nightmare scenario. In the quest for ever faster growth, corporations evolve toward ever faster exploitation of natural resources. The Earth is not enough. So, ultimat...
February 1, 2016
Corelations in Network Theory
Category theory reduces a large chunk of math to the clever manipulation of arrows. One of the fun things about this is that you can often take a familiar mathematical construction, think of it category-theoretically, and just turn around all the arrows to get something new and interesting!
In math we love functions. If we have a function
we can formally turn around the arrow to think of 
as something going back from 
back to 
. But this something is usually not a function: it’s called a ‘cof...
January 29, 2016
Among the Bone Eaters
Anthropologists sometimes talk about the virtues and dangers of ‘going native’: doing the same things as the people they’re studying, adopting their habits and lifestyles—and perhaps even their beliefs and values. The same applies to field biologists: you sometimes see it happen to people who study gorillas or chimpanzees.
It’s more impressive to see someone go native with a pack of hyenas:
• Marcus Baynes-Rock, Among the Bone Eaters: Encounters with Hyenas in Harar, Penn State University Pre...
January 26, 2016
The Internal Model Principle
“Every good key must be a model of the lock it opens.”
That sentence states an obvious fact, but perhaps also a profound insight if we interpret it generally enough.
That sentence is also the title of a paper:
• Daniel L. Scholten, Every good key must be a model of the lock it opens (the Conant & Ashby Theorem revisited, 2010.
Scholten gives a lot of examples, including these:
• A key is a model of a lock’s keyhole.
• A city street map is a model of the actual city streets
• A restaurant menu...
January 24, 2016
Ken Caldeira on What To Do
Famous climate scientist Ken Caldeira has a new article out:
• Ken Caldeira, Stop Emissions!, Technology Review, January/February 2016, 41–43.
Let me quote a bit:
Many years ago, I protested at the gates of a nuclear power plant. For a long time, I believed it would be easy to get energy from biomass, wind, and solar. Small is beautiful. Distributed power, not centralized.
I wish I could still believe that.
My thinking changed when I worked with Marty Hoffert of New York University on resear...
January 21, 2016
Salar de Uyuni
I just learned about the Salar de Uyuni: the world’s largest salt flat, located in southwest Bolivia. It’s about 10,000 square kilometers in area!
It’s high up, near the crest of the Andes, 3,600 meters above sea level. Once there were permanent lakes here, but no more. This area is a transition zone: the eastern part gets rain in the summer, but clouds never make it past the western part, near the border with Chile. Further west comes the the famously dry Atacama Desert.
The Salar de Uyuni...
January 17, 2016
Glycolysis (Part 2)
Glyolysis is a way that organisms can get free energy from glucose without needing oxygen. Animals like you and me can do glycolysis, but we get more free energy from oxidizing glucose. Other organisms are anaerobic: they don’t need oxygen. And some, like yeast, survive mainly by doing glycolysis!
If you put yeast cells in water containing a constant low concentration of glucose, they convert it into alcohol at a constant rate. But if you increase the concentration of glucose something funny...
Curiosity Meets Martian Dunes
In December, the rover Curiosity reached some sand dunes on Mars, giving us the first views of these dunes taken from the ground instead of from above. It’s impressive how the dune seems to shoot straight up from the rocks here!
In fact this slope—the steep downwind slope of one of “Bagnold Dunes” along the northwestern flank of Mount Sharp—is just about 27. But mountaineers will confirm that slopes always looks steeper than they are.
The wind makes this dune move about one meter per year.
...January 13, 2016
Information Geometry (Part 16)
joint with Blake Pollard
Lately we’ve been thinking about open Markov processes. These are random processes where something can hop randomly from one state to another (that’s the ‘Markov process’ part) but also enter or leave the system (that’s the ‘open’ part).
The ultimate goal is to understand the nonequilibrium thermodynamics of open systems—systems where energy and maybe matter flows in and out. If we could understand this well enough, we could understand in detail how life works. That’s...
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