Cosmology Theories Come and Go

Cosmology theories come and go as new information becomes available. The geometry and nature of the universe must be one of the most fascinating questions for the human species. Early Egyptians thought the universe was a rectangular box. Alexandrian Greeks pictured the cosmos as a set of concentric crystalline spheres, a view adopted by the medieval Catholic Church, which executed Giordano Bruno for holding that the universe was infinite in extent. In the 20th century Hubble's surveys of receding galaxies supported the idea of an expanding spacetime scaffolding. This model, now called the big bang, is generally the accepted overarching theory, but it has been amended several times to include an early "inflationary" phase and, more recently, the existence of dark energy, an entity or mechanism which apparently allows the expansion of the universe visible to our telescopes to be speeding up, and not slowing down. Also not slowing down is the list of new cosmological ideas. Last year's entrant was the "ekpyrotic" model, according to which our universe and all the energy and matter residing therein arises from the collision of two immense membranes embedded in an even larger multi-dimensional volume. Last week's interesting new cosmology development was the suggestion that the universe is finite and has a dodecahedral (soccerball) geometry (Luminet et al., Nature, 9 October 2003). Meanwhile, this week's leading cosmology news, presented at a meeting in Cleveland, featured observations of very distant (8 to 10 billion light years away) and unusually bright supernovas, recorded by the Hubble Space Telescope. This accords with the dark energy model which holds that the general expansion of the universe was relatively slow 10 billion years ago and afterwards got much faster, owing to the propulsive effects of the dark energy winning out over the attractive and slowing effects of gravity (paper by Adam Reiss; also see Science News Online, 11 October ).