Probing the Cosmic WebA new mathematical framework based on perturbation theory could yield new insights into cosmic structure and fundamental physics. By Charles Day Matter in the Universe is spread in a vast 3D network of filaments and sheets known as the cosmic web.These structures are dominated by dark matter and include both galaxies and the intergalactic medium: hot, nearly fully ionized hydrogen, with only about one atom in 100,000 remaining neutral.Light emitted by distant quasars travels through this cosmic web, and whenever it encounters neutral hydrogen, it's absorbed at a specific redshifted wavelength.By the time the light reaches an Earthly observer, the spectrum is imprinted with a dense series of absorption lines known as the Lyman-alpha forest.Since the 1990s, astronomers have used the forest to track the evolution of the intergalactic medium and to trace the enveloping dark matter.However, because the medium's dynamics are complex on small scales, extracting data from the forest has required computationally expensive hydrodynamical simulations.Now Roger de Belsunce of MIT and his collaborators have developed a new theoretical description of the Lyman-alpha forest 1.Their perturbation-theory approach rests on a central idea: Although the physics is highly complex on small scales, the large-scale behavior is governed by fundamental symmetries.
Charles Day (Tue,) studied this question.