Dark energy makes up more than 70% of the universe, but no one knows what it is. Its existence was inferred in the 1990s to explain why the expansion of the universe is accelerating, which was determined from observations of supernovae of known luminosity, or “standard candles.” Now scientists want to learn more about how dark energy behaves by using a “standard ruler.”
The standard-ruler approach involves measuring the traces of the primordial baryon acoustic oscillations in the large-scale structure of the universe at different times in history. The oscillations are remnants of sound waves in the first 300 000 or so years after the Big Bang, and are imprinted in the distribution of galaxies.
The Wide-Field Multi-Object Spectrograph (WFMOS), a proposed collaboration between the Gemini and Subaru telescopes (see the story on page 30), will use baryon acoustic oscillations and spectroscopic redshifts to probe dark energy. The most...