Its outer limit of observation is approximately 3 billion light years, far short of light from the time of the big bang. Furthermore, the chemical composition of the universe has changed since the Big Bang as unstable deuterium has been destroyed in the cores of stars. We are looking at that abundance now. Over the course of time, the quantity of deuterium has changed. It has decreased.
Stars destroy it and convert it to different things.
To find deuterium, scientists will study hundreds of places of varying ages and in varying parts of the nearby universe, where celestial phenomena are better understood and more easily observed. From this information they hope to extrapolate the initial recipe for the primordial soup and plot the different points of the history of the universe. One result of this process, scientists say, will be better information on how galaxies evolve and what the mechanics of star formation are. It would mean that things are much more complicated than we now think and that we really have a lot of work left to do. The Christian Science Monitor.