Lumps In the Cosmos

Not many people spend time worrying about the fact that the universe is lumpy. Galaxies are lumps of matter surrounded by empty space. They cluster in groups--lumps of lumps--surrounded by even vaster stretches of space.

This raises two questions. First of all, why should we care? This one's easy: the Milky Way is a lump, as is our solar system, as are all of us. No lumps, no you. The second question is, Where did all the lumpiness come from, given that the universe shortly after the Big Bang was a pretty uniform sea of particles? This is a puzzle that's had a complicated history, but it may be a little closer to getting solved, thanks to an anomalous spot in a photo recently taken by a space-observing satellite.

Cosmic textures--weird tangles in the fabric of space-time that could help account for a lumpy universe--were a rage in the physics community in the 1990s, before satellite observations seemed to rule them out. "I lost interest in textures more than a decade ago," says Neil Turok, chairman of the department of mathematical physics at Cambridge University and one of the fathers of the field.

But in a recent paper in the journal Science, Marcos Cruz of Spain's Institute of Physics of Cantabria, along with Turok and others, reported they had detected an irregularity in the glow of radiation still smoldering from the Big Bang. It's by no means a sure confirmation of the texture theory, but they are encouraged, particularly because basic physics argues that textures should exist.

To understand why, think of an ice cube. It starts out as water, but as it cools below 32ºF (oºC), it undergoes what's called a phase transition--the same stuff assumes a whole different structure. An ice cube doesn't solidify all at once; the freezing starts in several spots, which grow until they meet. Unless the crystals are perfectly aligned, you get a defect--one of those white streaks inside most ice cubes.

Something similar may have happened to the newborn universe as it expanded and cooled from trillions of degrees to millions to thousands. While this was happening, it went through several phase transitions. Flaws in the fabric of space, similar to the ice streaks, could have remained, acting as gravitational seeds for the growth of galaxies.

Within a few years, new telescopes being built in the Chilean Andes could confirm if some of these flaws are indeed still out there. If so, that's one more nod to Sir Arthur Eddington, the early-20th century physicist who said, "Not only is the universe stranger than we imagine, it is stranger than we can imagine."