A specific area of my expertise is using a process which maps the intensity of neutral hydrogen to probe the large scale structure of the Universe. Neutral hydrogen, or HI (pronounced H-one), refers to a particular form of hydrogen where it’s negative and positive electric charges are balanced so it is ‘neutral’. Generally, HI is very abundant in galaxies so if we can detect neutral hydrogen, we can trace where large amounts of galaxies are in space.
A quirk of hydrogen is that it spontaneously emits a photon at fixed energy, and therefore at a fixed wavelength which is 21cm. By conducting low angular resolution radio telescope surveys, we can scan large swathes of the sky for this 21cm signal. By measuring how the HI wavelength (or frequency) changes we can make a redshift measurement which we use for a distance estimation. This allows us to build 3-dimensional maps of our Universe.