Is the baryon acoustic oscillation peak a cosmological standard ruler?
  In the standard model of cosmology, the Universe is static in comoving
coordinates; expansion occurs homogeneously and is represented by a global
scale factor. The baryon acoustic oscillation (BAO) peak location is a
statistical tracer that represents, in the standard model, a fixed
comoving-length standard ruler. Recent gravitational collapse should modify the
metric, rendering the effective scale factor, and thus the BAO standard ruler,
spatially inhomogeneous. Using the Sloan Digital Sky Survey, we show to high
significance (P < 0.001) that the spatial compression of the BAO peak location
increases as the spatial paths' overlap with superclusters increases. Detailed
observational and theoretical calibration of this BAO peak location environment
dependence will be needed when interpreting the next decade's cosmological
surveys.
