Physicists from France and Belgium have published the first results of an experiment to search for particles arriving on Earth "from a parallel universe." Unfortunately, and perhaps fortunately, the detector created for these purposes did not reveal anything unusual. But the researchers are not discouraged because their work offers a simple, inexpensive way to test some theories outside the Standard Model of particle physics.
A number of quantum theories predict the existence of other dimensions outside of the four-dimensional spacetime we know. In this case, the idea of a Multiverse arises, in which separate four-dimensional universes are collected in stacks, like sheets of paper (if we consider the vertical of this stack as another dimension).
Until now, scientists have not been able to obtain any empirical evidence of the existence of parallel worlds (although attempts have been made). In 2010, physicist Michaël Sarrazin from the Belgian University of Namur proposed a model according to which, according to the laws of quantum mechanics, particles from one universe can be transported to neighboring worlds. According to his theory, electromagnetic forces are an obstacle to such movements, therefore, neutrons devoid of charge are best suited for the role of guests from parallel universes.
The team, led by Sarrazin, teamed up with French physicists from the University of Grenoble to create an experimental detector that is sensitive to atoms of the light isotope helium-3. The assembled installation is located just a few meters from the nuclear reactor of the Laue-Langevin Institute.
The idea was that the neutrons emitted by the reactor are in a state of quantum superposition, simultaneously present in our and the parallel world (and also leaving a trace in other more distant ones). When colliding with nuclei of heavy water in a moderator that surrounds the reactor core, the neutron wave function switches from superposition to one of two states.
As a result, most of them remain in our world, but some go into a parallel universe. Scientists believe that the "escaped" particles will not interact with water and the concrete containment of the reactor, or they will, but very weakly. At the same time, a small part of the wave functions of these neutrons will be retained in our universe, so individual particles can return to our world and make themselves felt when they hit the detector outside the concrete insulation of the reactor.
The problem is that capturing such returned neutrons is not easy, the "background noise" is too great. To minimize the background neutron flux caused by neutron leakage from various instruments inside the reactor hall, the researchers shielded the detector with a double-layer shield. The outer twenty-centimeter layer of polyethylene converts fast neutrons into thermal ones, which then "get stuck" in the inner wall made of boron. This two-layer "package" has reduced the "background noise" by about a million times.
In July 2015, Sarrazin and his colleagues turned on the detector for five days and during this time recorded a small number of events, but they all fit the definition of residual background and cannot be considered as evidence of the existence of parallel worlds.
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However, scientists do not lose hope and plan to conduct new tests, launching the detector for a whole year.
Detailed results of the first phase of research are published in Physics Letters B.