Scientists at Uppsala University (Sweden) have developed a new model of the Universe, according to which it is a bubble expanding in an extra dimension. According to the researchers, their hypothesis, combining Friedman's model with string theory, solves the mystery of dark matter. This was announced in a press release on Phys.org.
Friedmann's model describes the Universe, uniformly filled with matter, isotropic and expanding. In a new work, scientists have combined this concept with string theory. The Universe itself is the surface of a four-dimensional sphere, which is expanding, and all the elementary particles in it are represented as strings moving along the brane, which is a two-dimensional surface. In a stack of several D2-branes stuck together, the behavior of strings resembles the properties of protons, mesons and gluons in the ordinary world.
Scientists have used the concept of a brane to describe the boundary between a false vacuum in anti-de Sitter space and a true vacuum. Anti-Desitter Space (ADS) is the opposite of de Sitter space, which describes an exponentially expanding universe with positive curvature, where the sum of the angles of the triangle is greater than 180 degrees. The false vacuum is less stable than the true one, and such a transition in our Universe can lead to the appearance of an expanding bubble of the true vacuum.
Thus, cosmologists conclude, for an observer on the surface of a four-dimensional sphere, everything looks as if the Universe is expanding due to a certain value of the vacuum energy density (cosmological constant).