Novel Measurements of Starlight from Cosmic Dawn to the Present

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Since the Universe was filled with hydrogen atoms at early times, the

most promising method for observing the epoch of the first stars is to

measure the hyperfine line of hydrogen at a wavelength of 21 cm. Such

an observation of the "cosmic dawn" era was considered speculative

when I helped lay out the theoretical predictions a decade ago, but

there is now an enormous, promising observational effort (in which I

am involved within the Square Kilometre Array). There is also an

important aspect of early cosmic history that can potentially be

probed today. The difference between the early evolution of the

baryons and the dark matter should imprint a specific signature that

can be probed via galaxy surveys. We have recently attempted the first

such measurement; detecting this would provide a novel confirmation of

the standard cosmological model.