If one person tells me that something unbelievable happened, I am skeptical. If a second person gives me the same story, I’m less skeptical. And if a third, independent source offers the same account, that pretty much convinces me that the event indeed happened.
Science often advances with a similar philosophy as demonstrated by the development of dark energy models.
For many years, the prime evidence pointing toward the existence of dark energy relied on measurements of distant supernovae. A special class of these objects, Type Ia supernovae, emit essentially the same amount of light so that the observed brightness tells astronomers their distance. Astronomers use this standard-candle-nature of Type Ia to determine the expansion history of the universe and the results indicate strongly that some form of dark energy started dominating the expansion roughly 6 billion years ago. While the supernova evidence for dark energy is strong, it is possible that scientists made a mistake and dark energy does not exist after all.
A few years ago, research into the clustering of galaxies across the universe provided a second voice affirming dark energy’s existence. The Sloan Digital Sky Survey (the largest survey of galaxies to date) revealed the baryon acoustic oscillation peak expected if the ripples in the cosmic microwave background (CMB) radiation grew into the galactic structures seen throughout the universe. More significantly, the shape of the acoustic peak provided a way to detect the existence of dark energy using the size of the universe at two different epochs. Again, the results affirmed the presence of dark energy.
More recently, a third voice corroborates the dark energy story. When he proposed the theory of general relativity, Einstein boldly asserted that the type of mass/energy in the universe determines its geometry. Conversely, measuring the shape of the universe tells astronomers what types of mass/energy comprise the universe. Using observations of distant binary galaxies, a pair of astronomers measured the geometry of the universe. Their results affirm previous measurements indicating a flat universe.1 Given a flat geometry, the composition of the universe must include roughly 4 percent normal matter, 23 percent dark matter, and 73 percent dark energy.
All three witnesses, using different observations, principles, and calculations, agree: dark energy exists. (For completeness, the CMB provides a fourth witness.) Thus, the evidence continues to grow for dark energy and the extraordinary fine-tuning for life it requires.
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- Christian Marinoni and Adeline Buzzi, “A Geometric Measure of Dark Energy with Pairs of Galaxies,” Nature 468 (November 25, 2010): 539–41.