As you no doubt have realized, I’ve had a recurrence of my crippling writer’s block this week. Rather than continue to fight with it for the third day in a row, I’m taking a day off from frustration in hopes of rebooting my brain. In any case, here are a few links for Wednesday:

• Dark matter is one of the major challenges for theoretical and experimental physics, since it still is proving elusive. However, it also explains a lot about the structure of the Milky Way, as this Scientific American article by Leo Blitz describes.
• Gravitational waves are predicted from Einstein’s general theory of relativity, and their effects have been observed to a high degree of precision in binary pulsar systems. Gravity is the weakest force in the universe, though, so direct detection of gravitational radiation still hasn’t happened. Modern detectors are pushing the limits of our technology to find gravitational vibrations smaller than atoms, using a method known as “squeezed light”. (I think I may have to write about this later!)
• To finish the theme of studying the things that are not seen, gamma-ray bursts — exceedingly energetic explosions of massive stars — may provide another measure of the acceleration of the universe, giving cosmologists a new handle on dark energy.
• The greatest mathematician of antiquity was undoubtedly Archimedes, whose work presaged that of Galileo and Newton. Since he wrote for a technical audience rather than novices (as Euclid did), his work never caught on in the same way. However, modern scientists are appreciating just how sophisticated the old boy was, beyond possibly apocryphal stories about running around without a towel.