Weltman became known when she co-authored a 2004 paper titled "Chameleon Cosmology" with Justin Khoury, which proposed a theory to explain
dark energy. Thus, the theory suggests that in regions where matter is relatively dense, the chameleon force is difficult to detect, but in empty regions of space, it acts to push bodies apart and expand the universe. The theory of chameleon gravity can be tested in a range of environments including in laboratory tests. The first searches for dark energy in the laboratory were performed as searches for chameleons. In 2007, Weltman joined an experimental team at
Fermilab on the GammeV experiment which has been designed to search for axion-like particles. The first bounds on chameleon gravity parameters were placed by this experiment in 2008. The experiment was redesigned and rebuilt as a purpose built chameleon detector, the GammeV CHASE (Chameleon Afterglow Search Experiment), with first results constraining chameleon dark energy in 2010. These were the first experiments of their kind and were able to place the first direct experimental bounds on the theory. This work pioneered a new subfield of laboratory experiments searching for chameleon gravity, or dark energy more broadly, in the laboratory. ==Awards and distinctions==