The observation that type Ia supernovae (SNe Ia) are fainter than expected given their redshifts has led to the conclusion that the expansion of the universe is accelerating. The widely accepted hypothesis is that this acceleration is caused by a cosmological constant or some dark energy field that pervades the universe. We explore what the supernovae data tell us about this hypothesis by answering the question: Can these data be explained with a model in which the strength of gravity varies on a cosmic timescale? We conclude that they can and find that the supernovae data alone are insufficient to distinguish between a model with a cosmological constant and one in which varies. However, the varying-G models are not viable when other data are taken into account. The topic is an ideal one for undergraduate physics majors.
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2011
American Association of Physics Teachers
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