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Only 4 percent of our universe is made of ordinary matter like atoms and molecules. The other 96 percent is in entirely unfamiliar forms we know almost nothing about. About 25 percent is dark matter, which holds galaxies and larger-scale structures together; another 70 percent is thought to be dark energy, an even more mysterious entity that appears to be driving the accelerated expansion of the universe.

In the Spring 2017 Hans Bethe Lecture at Cornell, physicist Joshua Frieman introduces the Dark Universe and describes new experiments and observatories that aim to illuminate its enigmas.

Frieman is a founder, and currently serves as director, of the Dark Energy Survey, a collaboration of more than 300 scientists from 25 institutions on three continents that is probing the origin of cosmic acceleration. His research centers on theoretical and observational cosmology, including studies of the nature of dark energy, the early universe, gravitational lensing, the large-scale structure of the universe, and supernovae as cosmological distance indicators.

The Hans Bethe Lectures, established by the Department of Physics and the College of Arts and Sciences, honor Bethe, Cornell professor of physics from 1936 until his death in 2005. Bethe won the Nobel Prize in physics in 1967 for his description of the nuclear processes that power the sun.

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