By Jonny Lupsha, News Writer

Scientists conducted a computer simulation of 8 million universes to understand dark matter, the University of Arizona (UA) website announced. The team of UA researchers were testing how each universe would form and what role dark matter would play in galaxy formation. Here’s what science knows about dark matter.

According to the UA announcement, the millions of universes simulated through the use of a supercomputer each “obeyed different physical theories for how galaxies should form.” Dark matter has largely been a theoretical scientific concept. Scientists search for dark matter by trying to detect its gravitational effects observed throughout the universe. The recent UA experiment also aspired to explain “how galaxies evolve over time and how they give birth to stars.” The research findings could fundamentally alter what humanity currently knows about the mysterious nonluminous matter, which is called dark matter.

The Case for Dark Matter

How do we know dark matter exists at all if we can’t directly observe it in any way? As it turns out, dark matter is detectable by its effects on things around it, which have been observed repeatedly and without error.

“The way that we get from observations to the idea that there is dark matter is to use the force of gravity,” said Dr. Sean Carroll, Senior Research Associate in Physics at the California Institute of Technology. “We can detect the force of gravity on other celestial objects. So if there is some ‘stuff’ out there in the universe, some stuff that exists—and there is as much of it or even more of it than there is ordinary matter—that stuff will create a gravitational field. We can detect that gravitational field; that’s what provides us the secret to detecting the ‘dark side’ of the universe.”

If that explanation sounds a bit heady, Dr. Carroll recommended pretending that the Moon were completely invisible. How would we know it’s there? We could detect the changes in Earth’s tides and know that a celestial object relatively near Earth had a large amount of mass and gravitational pull. We could even analyze the tides to the point of learning the Moon’s mass and distance from us. Dark matter is detectable in the same general fashion—we can’t yet observe or measure it, but it definitely affects the universe through its gravitational pull.

The Universe’s Building Blocks

Even more daunting than the probability of locating an undetectable matter, like dark matter, is the theoretical postulate of how much of that matter exists throughout the universe. “Five percent of the universe is what we call ordinary matter,” Dr. Carroll said. “By this, physicists mean every single particle that we’ve ever detected directly in any experiment ever done anywhere on Earth, ever. Every star, every planet, and every bit of gas and dust that we’ve ever seen is ordinary matter, the stuff that you see directly, and it’s only five percent of the universe.”

The other 95 percent is the “dark side” of the universe. “Twenty-five percent of the universe is what we call dark matter,” Dr. Carroll said. “It’s matter—it’s ‘stuff’—and it’s some kind of particle that moves around, but it’s dark; we don’t see it directly. The rest of the universe, 70 percent, is something even more exotic than dark matter, called ‘dark energy.’”

Dr. Carroll defined dark energy as “something that is smoothly spread out throughout the universe.” Like an invisible filler in the spaces between ordinary matter, dark energy exists all around us. “There is the same amount of dark energy here as somewhere in the desolate hole of intergalactic space,” he said. “Seventy percent of the universe is the smoothly distributed kind of energy that we call dark energy.”

Like other once intangible items of scientific theory, such as germs or quarks, dark matter and dark energy sound a bit far-fetched. Even trying to study them—by only being able to study the things they affect—is in its earliest phases of development. However, with tests like the research team’s universe simulation at the University of Arizona, astronomers are inching toward yet another discovery that could change our knowledge of existence.

Dr. Sean Carroll contributed to this article. Dr. Carroll is a Senior Research Associate in Physics at the California Institute of Technology. He earned his undergraduate degree from Villanova University and his Ph.D. in Astrophysics from Harvard in 1993.