Funny stuff of the universe


Tegmark uses a bendable grid to demonstrate how space curves.

Photo by Daniel R. Burke


Max Tegmark, who recently helped quantify the universe’s list of ingredients, came to his field by accident.

“My interest in cosmology is the product of a failed relationship,” said the assistant professor of physics and astronomy. “She was doing physics and I was doing econ, and all her books looked much more interesting than mine.”

Today, Tegmark is contributing research and discoveries to the sorts of books that captured his heart as an undergraduate in his native Sweden. His latest work gives us the most precise measurements of what the universe is made of.

“The coolest thing of all is that although people have been wondering about these questions for as long as humans have walked the earth, we’ve been making real progress over the past 10 years,” Tegmark said, progress due to advances in technology.

According to his latest calculations, recently published in the journal Physics Review D, only five percent of the universe is ordinary matter made of atoms. Thirty-three percent is cold dark matter, a slow-moving class of matter detectable only by its gravitational force. One-tenth of one percent is hot dark matter.

And the remaining 62 percent is “this funky dark energy — which is really just a fancy word for ignorance,” said Tegmark. Ask him what is known about dark energy, and he answers, laughing, “That it exists.” And that it accounts for nearly two-thirds of the universe’s total stash of matter. Despite that impressive number, scientists didn’t know this 62 percent even existed until recently.

The dark energy idea, which has recently gained wide acceptance, comes from Einstein’s theories about how much gravity — and therefore how much matter — exists in the universe. The more matter, the more gravity.

Gravity holds all the universe’s matter together, so the amount of gravity in the universe affects how parts of the universe are pulled to each other, and accordingly affects the curvature of space.

Based on observations of the amount of matter in the universe, scientists until recently assumed that space was very curved. But the most recent observations have revealed that space is, in fact, quite flat. This implies that the universe contains more gravitational force, and therefore more unobservable matter, than previously thought.

As for the detailed breakdown of the different types of matter, that was a job for Tegmark and his two collaborators — Matias Zaldarriaga of the Institute for Advanced Study in Princeton and Andrew Hamilton of the University of Colorado. They used software to combine two sets of data: one, a new three-dimensional map of the placement of galaxies in the universe, and, two, photographs of a Big Bang by-product called microwave background radiation, the glowing inner surface of a spherical wall of hydrogen and other primordial matter that surrounds us at a distance of 14 billion light years.

And amazingly, the three scientists’ results matched figures another research team produced two years ago by different methods.

“The biggest surprise for this particular project is that things actually fit together and agree,” said Tegmark. “We have this whole zoo of different observations and you find a simple model that explains everything. It’s almost too good to be true.”

Originally published on March 22, 2001