“The paper introduced a new methodology to deal with what was believed to be (and probably still is) one of the main difficulties for these types of observations.”

The paper helped convince people that a new generation of radio telescopes using the 21 cm line of hydrogen could observe the epoch in the history of our Universe when the first stars and galaxies formed. Moreover, such observations make it possible, in principle, to detect the influence of radiation from these first stars and galaxies on the matter in the Universe.

Ultimately, it might even be possible to use this approach to probe cosmic structure at even earlier times in the history of the Universe, before any luminous sources existed. The first projects that will try to make these challenging observations are now under way and, consequently, a new frontier in observational cosmology is opening, partly in response to our theoretical work.

The paper introduced a new methodology to deal with what was believed to be (and probably still is) one of the main difficulties for these types of observations. Namely, emission from sources in the late Universe (foreground sources) that could be confused with the fainter, cosmological signal from the distant Universe. In the paper we introduced a procedure for removing this contamination and quantified how well it would work.

It provided a theoretical framework for a new frontier in observational cosmology that is now ripe for exploration owing to technological advances, mainly in computer technology.

My main research focus had been in another area of cosmology, the study of the Cosmic Microwave Background (CMB). Lars Hernquist and Steve Furlanetto approached me to discuss these potential 21 cm observations to see if some of the techniques developed for the CMB could be applied in this case. It turned out that the methods could indeed be generalized and used to address some of the outstanding problems, such as the effects of foreground contamination.

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The challenge now involves making detailed predictions of what the observatories will see and hopefully inthe near future use the models we produce to interpret the observational results. This could lead to interesting new insights on the properties of this first generation of stars and galaxies such as their mass and spatial distribution.

There is even the possibility that, in the future, more ambitious missions could use this technique to learn about the birth of our Universe—the epoch known as inflation—when the initial inhomogeneities which resulted in the structure that we see in our Universe were created. Realizing this possibility involves significant work on both the experimental and theoretical sides.

The origin and evolution of the Universe has always intrigued people. In that respect, although cosmology might not have direct political or social consequences, it still captures the imagination of the public at large.