An Optical Bench to Weigh Cosmic Structure

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Dark matter and dark energy remain largely mysterious because -- as their name implies -- they are difficult to see. However, even if we are unable to observe this dark sector directly, we can observe the effects that dark matter and dark energy have on other objects in the Universe. One of the best ways to do this is with strong gravitational lensing -- the bending of light around massive objects that was predicted by Albert Einstein's theory of relativity. Gravitational lenses act as cosmic telescopes, and the strength of the telescope lens is set by dark matter, while the length of the `telescope tube' and the distance between the telescope and the distance source it is magnifying are set by the expansion of the Universe that is driven by dark energy. Uncovering how dark matter and dark energy make these telescopes work requires that they first be found on the sky and, like all telescopes, they must be precisely calibrated. My research employs large public surveys to discover lenses (the new lenses I am adding to the zoo are EELs and CASSOWARYs), and I use spectroscopic follow-up observations to independently learn more about the lens properties. These data allow me to determine the strength of the lens, similar to removing a lens from a telescope to measure its curvature -- and knowing the curvature means knowing where the dark matter is in the lens. Once a lens is calibrated, observations of the sizes of sources it is observing help to pin down relative distances between these objects. Because dark energy causes accelerated expansion of the Universe, larger relative distances imply more dark energy, while smaller distances imply less; with a large enough number of observed sources, the history of dark energy can be mapped out. These properly-calibrated gravitational lens telescopes have `observed' dark matter and dark energy!