Say our universe is a bubble. And there’s another universe in another bubble. Researchers have simulated what it would look like if the two bubbles bumped against each other, and their work could reveal the telltale signs of colliding universes -- suggesting that the multiverse theory isn’t just a wild idea, but a testable hypothesis.
“We’re trying to find out what the testable predictions of this picture would be, and then going out and looking for them,” Matthew Johnson from the Perimeter Institute says in a news release. “We’re now able to say that some models predict something that we should be able to see, and since we don’t in fact see it, we can rule those models out.”
To put multiverse theory to the test, Johnson and colleagues imagined the simplest kind of multiple universe setup -- one in which our universe represents one of two such bubbles. Their research models what would happen if those two universes collided, and what that collision might look like to astronomers here on Earth.
Making a model of everything there ever was sounds like a tall order. But not so! “Simulating the universe is easy,” Johnson says. Because they’re working on the largest scales, they didn't have to account for every atom, every star, or every galaxy -- in fact, they accounted for none of them. “All I need is gravity and the stuff that makes these bubbles up,” he adds.
After colliding the bubbles on a computer, they stick a virtual observer in various places and ask what that observer would see from there. For example, two colliding bubbles would leave a disk on the sky: a circular bruise in the cosmic microwave background. Because the search for such a disk has come up empty so far, researchers are able to rule out certain collision-filled models.
The team is currently trying to figure out what other observable traces a bubble collision would leave behind. While none of those signatures have been found so far, some of them are at least possible to look for.
The work was published in Journal of Cosmology and Astroparticle Physics. Look at all the bubbles in this video!