An alternative theory
Not everyone is convinced that the new map reveals the presence of dark matter. Some skeptics think there is a good reason dark matter is invisible: It doesn't exist.
According to these scientists, an alternative explanation for the universe's mass discrepancy is that grav-ity does not operate equally in all parts of the universe, as is predicted by Newton and Einstein. "The au-thors here converted their observed wiggles into matter density using Einsteinian formula," said Hong Sheng Zhao, a researcher at the University of St. Andrews in the UK, about the new map. "If we take a different formula, we would get somewhat different densities or clumps." Zhao is an advocate of a theory of modified gravity called TeVeS, in which gravity is stronger in certain regions of space than others. In these gravity-boosted regions, gravitational lensing would work differently. Until a dedicated mission is launched to measure the law of gravity in weak gravity environments, far away from the influence of the Sun and planets, such possibilities cannot be ruled out, Zhao said in an email interview. "If the law does have a factor depending on the environment, then it could explain away much of dark matter," he said. Massey concedes that deviations in the law of gravity across the universe is still a possibility, but says that there is now too much evidence to dismiss dark matter's existence. "No matter what you do, there really has to be some dark matter to match up with all the gravitational lensing measurements," he said. "Of course, there could also be deviations from general relativity on top of that, but the evidence is now piling up that dark matter makes up at least some of this missing mass." |
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