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The idea that our universe is embedded in a broader multidimensional space has captured the imagination of scientists and the general population alike. 

This notion is not entirely science fiction. According to some theories, our cosmos may exist in parallel with other universes in other sets of dimensions. Cosmologists call these universes braneworlds. And among that many prospects that this raises is the idea that things from our Universe might somehow end up in another.

A couple of years ago, Michael Sarrazin at the University of Namur in Belgium and a few others showed how matter might make the leap in the presence of large magnetic potentials. That provided a theoretical basis for real matter swapping. 

Today, Sarrazin and a few pals say that our galaxy might produce a magnetic potential large enough to make this happen for real. If so, we ought to be able to observe matter leaping back and forth between universes in the lab. In fact, such observations might already have been made in certain experiments.

The experiments in question involve trapping ultracold neutrons in bottles at places like the Institut Laue Langevin in Grenoble, France, and the Saint Petersburg Institute of Nuclear Physics. Ultracold neutrons move so slowly that it is possible to trap them using ‘bottles’ made of magnetic fields, ordinary matter and even gravity.

One reason to do this is  to measure how quickly the neutrons decay by beta emission. So physicists measure the rate at which the neutrons hit the bottle walls and how quickly this drops.   

There are two processes at work here: the rate of neutron decay and the rate at which neutrons escape from the bottle. So in the case of an ideal bottle, the rate of decay should be equal to the beta decay rate. But the bottles are not ideal so the rate of decay is always faster. 

That leaves open the possibility that there might be a third process at work: that some of the extra decay might be the result of neutrons jumping from our universe to another. 

So Sarrazin and co have used the measured decay rates to place an upper limit on how often this can happen. 

Their conclusion is that the probability of a neutron jumping ship is smaller than about one in a million.

That doesn’t really say anything about whether matter swapping actually takes place. Only that if it does, it doesn’t happen very often.  

However, Sarrazzin and co also say it should be straightforward to take better data that places stricter limits.

According to their theoretical work, a change in the gravitational potential should also influence the rate of matter swapping. So one idea is to carry out a neutron trapping experiment that lasts for a year or more, allowing the Earth to complete at least one orbit of the Sun.

In that time, the gravitational potential changes in a way that should influence the rate of matter swapping. Indeed, there ought to be an annual cycle. “If one can detect such a modulation it would be a strong indication that matter swapping really occurs,” they say.

That would be one of the biggest and most controversial discoveries in modern physics and one that is possible with technologies available today. 

Anyone got an old neutron bottle lying around and a bit of spare time on their hands?

Ref: arxiv.org/abs/1201.3949: Experimental Limits On Neutron Disappearance Into Another Braneworld


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