Here’s an interesting graph from the most recent issue of symmetry. As cognocenti well know, there are a number of subject classifications for physics preprints on arxiv.org. These include the original hep-th for formal high-energy theory, hep-ph for more phenomenological theory, hep-ex for high-energy experiment, gr-qc for general relativity and quantum cosmology, and so on. The histogram indicates the percentage of papers in hep-th and hep-ph that cite papers from astro-ph, the astrophysics archive. The connection with phenomenology is no surprise, as issues of dark matter and baryogenesis are driving some of the most interesting questions in particle physics today. But the connection with “formal” theory (largely string theory) is interesting. I’m willing to bet that the biggest driver of this connection is the discovery of the accelerating universe — string theorists are now catching on that they shouldn’t be thinking about compactifications with zero cosmological constant, but rather vacua with a small amount of dark energy. Of course, it took a couple of years to catch on, as the acceleration of the universe was discovered in 1998. But it’s nice to see research in quantum gravity influenced by real data.