![]() ![]() So, the stars and galaxies and the conventional matter we observe all around us really only compose 5 percent of what constitutes our universe. Once we accommodate it, we find that dark matter constitutes about 25 percent of the matter/energy inventory of the universe. The trajectories she observed simply did not fit Newton’s laws of gravity there had to be matter that we cannot observe. Rubin helped prove dark matter’s existence through her measurements of its influence on the movement of stars within galaxies. In fact, Vera Rubin, a Carnegie astronomer, was responsible for the verification of the existence of dark matter. Thus, we were presented with a great mystery: why is the universe’s expansion accelerating, and what could possibly be fueling it? To answer these questions, cosmologists rethought the known contents of the universe, determining that about 70 percent of its matter/energy inventory is embodied in dark energy, a substance we have not yet begun to understand.īut even before the discovery of evidence for dark energy, we had already found evidence of dark matter. But contrary to everyone’s expectations, observations of Type Ia supernovae by the High-Z Supernova Search Team in 1998 and by the Supernova Cosmology Project one year later suggested that the expansion of the universe is actually accelerating. Cosmologists had long expected that the force of gravity produced by the matter in the universe would cause the universe’s expansion to slow down, and perhaps eventually to reverse course. We first learned about dark energy about fifteen years ago. There are deep mysteries to be solved, presenting a great challenge to the researchers of our time. But in another sense, this is a time of enormous excitement. In one sense, in this time of scientific achievement, our ignorance is a little embarrassing. Over the last two decades, we have learned that we fundamentally do not understand the stuff that comprises 95 percent of the universe: dark energy and dark matter. And there is perhaps no field today in which that is more evident than in astronomy. One of the defining characteristics of science is the reality that the more you know, the more you realize you don’t know.
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