21cm Cosmology with CHIME
The nature of dark energy remains one of the greatest mysteries in modern cosmology, and has largely eluded efforts over the past decade to constrain anything other than its existence and its current consistency with the cosmological constant. The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a new transit radio interferometer being built in British Columbia that will probe dark energy via a measurement of Baryon Acoustic Oscillations (BAO). We will use redshifted neutral hydrogen as a tracer of BAO to make cosmic variance limited measurements of the expansion history of the Universe. This will allow us to constrain the equation of state of dark energy at redshifts between 0.8 -- 2.5 when dark energy became dynamically important in the Universe. I will discuss the science goals with CHIME, the CHIME instrument, and its current status.