An article published in the journal “Physical Review Letters” describes a new model of the universe that proposes that it exists on the edge of an expanding bubble in a five-dimension space-time. A team of researchers from the Swedish University of Uppsala used string theory to hypothesize that the matter existing in the universe is accomodated at the edges of strings that extend into the fifth dimension. According to this hypothesis, what is called dark energy is an effect described by a cosmological constant in the four-dimension Friedmann equations.
The problem of dark energy is currently one of the most complex and controversial in the field of physics because its existence was hypothesized to explain the acceleration of the expansion of the universe, therefore because of its effects without knowing anything about its nature. String theory had many improvements through the years but also a lot of criticisms because no model based on it could explain consistently the whole universe. Dr. Souvik Banerjee and his colleagues proposed a model that offers a solution.
One of the problems of string theory-based models is that they hypothesize the existence of further dimensions with the problem of finding a way to verify the existence of dimensions that we can’t perceive. In the hypothesis of Dr. Souvik Banerjee’s team, the universe with four space-time dimensions that we perceive is accomodated at the edge of an expanding bubble that has a fifth dimension but there are five more dimensions that are “rolled up” to obtain the ten dimensions hypothesized by string theory.
These notorious strings extend into the fifth dimension and their ends are the matter of the universe we perceive. This model has the advantage of explaining dark energy starting from the description of five-dimension gravity arriving to the four-dimension Friedmann equations with a positive cosmological constant that describes the behavior that we perceive as acceleration of the expansion of the four space-time dimension universe.
The model proposed by Dr. Souvik Banerjee’s team makes the Big Bang obsolete meaning that it offers the concept of a universe born with a given size when the five-dimension bubble formed. Honestly I don’t understand how the cosmic microwave background radiation would be reinterpreted, as it’s considered one of the main evidence for the Big Bang.
These new cosmological models contain a lot of mathematics but they need to find the way to verify string theory in order to have an effective answer on its validity and in a positive case to understand which model is the correct one. If the model proposed by Dr. Souvik Banerjee’s team is correct, there should be deviations from gravity as described by Einstein’s theory of relativity for the presence of extra dimensions. We’d need very precise verification of measurements connected to effects such as gravitational lensing and gravitational waves.
In this model the bubble that contains our universe might not be the only one. In essence, it’s a model that opens the possibility to the existence of other universes and collisions between bubbles, a further starting point for the continuation of this model’s developments. In these cases it’s really difficult to say whether it’s the right path to achieve substantial progress in our understanding of the universe, and beyond, or it’s another dead end that makes sense from a mathematical point of view but will be debunked by some new discovery. The concepts it proposes are intriguing but that’s not enough.