The large-scale structure of the Universe supplies crucial information about the physical processes at play at early times. Unresolved maps of the intensity of 21 cm emission from neutral hydrogen HI at redshifts $z\simeq 1–5$ are the best hope of accessing the ultralarge-scale information, directly related to the early Universe. A purpose-built HI intensity experiment may be used to detect the large scale effects of primordial non-Gaussianity, placing stringent bounds on different models of inflation. We argue that it may be possible to place tight constraints on the non-Gaussianity parameter $f_{\mathrm{NL}}$, with an error close to ${\sigma }_{f_{\mathrm{NL}}}\sim 1$.

• Received 30 May 2013

DOI:https://doi.org/10.1103/PhysRevLett.111.171302