Science fiction has long played with ideas of other, parallel dimensions that are dark mirrors of our own, from that episode of Star Trek where Spock has an evil pointy beard to Stranger Thing’s terrifying ‘upside-down.’

But truth can be at least as strange as fiction and a team of researchers in the USA, led by Leah Broussard, may be on the verge of proving that our Universe is far from alone.

For many decades several theories in physics have relied on the possibility of ours being just one of possibly infinite numbers of connected universes. This isn’t just because scientists are sometimes sci-fi nerds too (although we’re sure plenty are) but rather that the existence of other parallel dimensions, or connected universes, could answer some of the remaining fundamental mysteries in physics.

As long ago 1957 Hugh Everett claimed that the implications behind quantum theory meant that there had to be an infinite number of parallel universes.

The physics behind his thinking is pretty complicated, but mostly this is his explanation for the famous Schrodinger’s Cat experiment – the cat in a box that is simultaneously dead or alive depending on the quantum state of a single electron.

Put simply, all electrons are simultaneously in one of two opposing positions (either spinning clockwise or anti-clockwise) and only when they are observed do they ‘choose’ one single location.

Everett’s Many Worlds theory allowed every electron in existence to simultaneously be both, by allowing for parallel realities to be created by each possible action that could be made. This means that, after being put in the box, Schrodinger’s cat would split reality into two new parallel realities, one where it dies and one where it survives.

Given the number of particles in the Universe and the number of different states they could enter, this quickly creates a nearly infinite number of parallel possible realities, all existing side by side.

Other physicists have used parallel realities to explain how a finite possible arrangement of matter could exist in a potentially infinite universe. Brian Greene, for instance, draws on string theory for his explanations.

Writing in his book The Hidden Reality, he explores how the ten or eleven dimensions of superstrings (compared to the four dimensions we humans are aware of) help to bring together the models of Newtonian and quantum physics but also suggest that we may exist on one of many membrane Universes, which individual fundamental particles can move between.

Even the legendary Stephen Hawking’s final, posthumously published, paper dealt with the multiverse (an idea he confessed to never having been very comfortable with) with particular focus on string theory.

But it’s not just string theory, or attempting to bring together quantum and Newtonian physics, that causes physicists to look to alternate dimensions. There are big cosmological questions based on our observations of the Universe beyond our planet that cause us to query whether unseen realities may be impacting our own.

One of the most significant of these is the so-called ‘cold spot’ in the Universe, first observed in 2004 and confirmed in 2013, which the inflationary principle (the most commonly accepted model for the creation of our Universe) is at a loss to explain.

The most exotic explanation so far, offered by Tom Shanks of Durham University, suggests that it may be evidence of a collision between our Universe and a Bubble Universe, a parallel universe created by the nature of the expansion of our own.

There is also the tongue-twisty ‘cosmological lithium problem.’ This is based on a discrepancy in the amount of lithium-7 that exists in our Universe compared to the amount that any modeling of the Big Bang should have created.

And, while the amount of helium and hydrogen in our Universe is utterly consistent with the mathematical models, physicists are still scratching their heads as to where the lithium has got to. Not all theorists would agree, but parallel Universes are certainly considered a possibility by some.

One of the critical arguments against theorizing about multiple universes and parallel realities, as much as they might help the mathematical models work, is the impossibility of testing whether, or in what form, they exist.

Recent articles in the New York Times and Scientific American by Paul Davies and George Ellis prove that the multiverse skeptics have a voice too, as well as a challenge to all those hidden dimension theorists – they want evidence. Testable evidence.

If so, those skeptics should now be turning their eyes to a laboratory in eastern Tennessee. Because 2019 could finally be the year when the walls between our realities are broken down. That may sound like hyperbole, but Leah Broussard and her team of physicists at Oak Ridge National Laboratory are currently preparing to make (or change) history.

The team at Oak Ridge, in east Tennessee, has designed an experiment to test for extra-dimensional travel, building on observations of the behavior of neutrons made in the 1990s in two anomalous findings.

The unexpected state change observed in those neutron experiments in the ‘90s has had physicists wondering for decades. Leah Broussard admits that, if her experiment were successful, it would be “pretty wacky,” but it could also uncover a secret shadow dimension existing parallel to the Universe we can see all around us.

In two separate experiments back in the ‘90s, neutrons were released and left to break down. Neutrons, when they decay, should all turn into protons. They should also do this within a consistent period of time.

However, the experiment in the 1990s saw one set of neutrons trapped in a magnetic field and funneled into a so-called ‘bottle trap’ and the other left free to be detected once they appeared as protons in a nuclear reactor stream.

The laws of physics would suggest that all things being equal, these fundamental particles should have decayed at the same rate as each other. But, in reality, the bottle trapped neutrons were 9 seconds quicker in turning into protons (at 14 minutes and 39 seconds) than the positively lazy free neutrons (which took 14 minutes and 48).

The difference may seem negligible to an outsider, but to physicists, who had no natural explanation for the difference, it left a lot more questions than answers.

The answer hit upon by Leah Broussard and her team at Oak Ridge is that the slow neutrons have not just been sitting around waiting to change states, but rather that they have been on a journey – to another dimension.

It may sound like a wild hypothesis, but there is solid physics behind it, based on the theory that some of the neutrons have been able to oscillate themselves into briefly becoming mirror neutrons, leaving our Universe for a few seconds before returning again to finally decay into a proton.

In the 2019 Oak Park experiment, a stream of neutrons will be fired at an impenetrable wall, with a neutron detector set up on the far side. Broussard has made it clear that she expects the sensor to measure zero hits. After all, there’s a literally impenetrable wall stood in between it and the stream of neutrons.

However, if any of the neutrons are able to oscillate into a mirror state if only briefly, this could see them slip into a parallel dimension long enough to clear the impenetrable wall (which won’t exist in the parallel reality) and reach the neutron detector.

As such, if the detector registers anything at all, this would mean something truly profound for 21st Century physics – evidence of the existence of other dimensions.

In an interview with NBC in the US, Leah Broussard was cautious but excited. How would she feel, after all, to be proving the skeptics wrong? What would it mean for the conception of our Universe?

“When you discover something new like that,” Broussard said, “The game totally changes.”

Evidence of other dimensions truly would utterly transform the game of physics and cosmology combined. And, with it, our very idea of existing in a singular, lonely Universe.

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