Will Science Burst the Multiverse's Bubble?

news.discovery.com

Physicists aren’t afraid of thinking big, but what happens when you think too big?

This philosophical question overlaps with real physics when hypothesizing what lies beyond the boundary of our observable universe. The problem with trying to apply science to something that may or may not exist beyond our physical realm is that it gets a little foggy as to how we could scientifically test it.

A leading hypothesis to come from cosmic inflation theory and advanced theoretical studies — centering around the superstring hypothesis — is that of the multiverse, an idea that scientists have had a hard time in testing.

In its most basic sense, the multiverse is a collection of universes popping in and out of existence, bustling around in a foamy mess, embedded in a vacuum of non-zero energy. Through quantum fluctuations, universes are born while others die — each universe taking on different forms and different kinds of physics.

But, if the multiverse hypothesis has any shred of reality behind it, how can scientists prove (or at least gather some observational evidence) that we exist inside one of an infinite ocean of universes?
This question is a tough one for scientists as many critics will argue that the multiverse hypothesis is nothing more than metaphysics, or a philosophical discussion. We are forever cocooned inside our universal ‘bubble’ and can therefore never experience what is going on ‘outside’ — if, indeed, there is an outside — so what’s the point in thinking about it?

But in a thought-provoking news release from the Perimeter Institute for Theoretical Physics, in Ontario, Canada, theoretical physicists are working hard to marry the multiverse with observational science collected from the furthest-most frontiers of the Cosmos.

“We’re trying to find out what the testable predictions of (the multiverse) would be, and then going out and looking for them,” said Matthew Johnson of the Perimeter Institute for Theoretical Physics.

If the multiverse is real, it stands to reason that, in this rampaging mess of neighboring universal “bubbles,” there should be frequent collisions, much like the jostling balls in a ball pit. Johnson’s team has specifically set out to look for observational evidence of neighboring universes colliding with our own, thereby supplying some hint of observational evidence that we may have universal neighbors.

But to do this, Johnson must model the entire Universe.

“We start with a multiverse that has two bubbles in it, we collide the bubbles on a computer to figure out what happens, and then we stick a virtual observer in various places and ask what that observer would see from there,” said Johnson.

“Simulating the universe is easy.”

Although you have to admire his can-do attitude, the team aren’t simulating every atom, star or galaxy in the Universe; in fact, the computer simulation only models the largest scale structures and forces. “All I need is gravity and the stuff that makes these bubbles up. We’re now at the point where if you have a favorite model of the multiverse, I can stick it on a computer and tell you what you should see,” he said.

This is where, according to the researchers, their work is so important if we are to understand what is going on in the regions beyond our Universe.

For example, if we consider a collision-filled multiverse, Jonson’s model predicts that observations of the cosmic microwave background (CMB) radiation should exhibit rings, or ‘bruises’, where next-door universes are pushing against ours. The CMB is the ubiquitous (yet very faint) ‘echo’ of the Big Bang that can be seen at the most distant reaches of the Universe. If there’s some interaction with universal bubbles (as some multiverse hypotheses suggest), these circular bruises should be present in the CMB signal – -representing distortions in the outermost edge of our ‘bubble.’
Through a brief analysis of CMB maps of the entire sky, it appears that these circular rings are not present, potentially disproving a multiverse filled with colliding universes. Or it at least suggests the collisions aren’t happening now — perhaps the multiverse is in some quiescent state?

As pointed out by the Institute press release, this research isn’t setting out to prove whether or not the multiverse exists, it’s merely identifying possible observational cues that we could look out for. And this pulls extra-universal studies into a scientific endeavor rather than leaving it in a metaphysical funk.