14 DAY TRIAL // Even today, most of the scientific communities still believe that the universe might have originated in a Big Bang explosion, but have no way to prove such process ever took place. Furthermore, although singularity-like objects are allowed to exist in the fabric of space-time, models explaining how such structures could experience a rapid expansion are currently unavailable.
Over time, alternative theories have been constructed to specifically fit the 'inflation' model of the universe. Inflation basically means that the universe had originally existed in an ultradense state, which suffered a rapid expansion in space. As matter expands through space, even the tiniest imperfection in the density of material would eventually grow into large perturbations, fact that might have determined the formation of stars, star clusters and the galaxy clusters observed today.
In 2001, four physicists proposed the so-called ekpyrotic cosmology model, which states that our universe may actually exist in two separate branes located in an extra spatial dimension. The branes are supposed to be locked into a perpetual oscillatory motion that causes them to collide with each other at certain periods in time.
Each time the branes collide, massive amounts of energy are released in order to produce an initial ultra dense perturbation in the fabric of space-time. Because our visible universe is mostly flat and the energy conservation laws still apply to the branes, such structures are thought to be flat as well.
Nevertheless, as in the case of the Big Bang, a particular set of problems are experienced with the ekpyrotic cosmology model. This means the collisions between branes would mostly result in the creation of a singularity with infinite density and temperature. Furthermore, as the Microwave Background Radiation seems to imply the perturbations in material density, it should take place at all scales.
In the case of the Big Bang theory, the general belief is that the singularity could have suffered a rapid expansion into space by generating negative-energy particles. The ekpyrotic cosmology model goes around the problems posed by the presence of the singularity by defining a scalar field that could act as a fluid of massless particles which would generate a repulsive gravitational force through the mass of the singularity.
However, there is one problem: the so-called 'ghost condensate' cannot keep the density perturbations scale-invariant. Albeit a recent suggestion argues that the density perturbations scale-invariant could be resolved through the introduction of the entropy fluctuations.
Although the theory has evolved a great deal since its first publication, more than six years ago, critics still argue that, similarly to the Big Bang theory, it requires negative energy particles that may trigger an instability in the space-time fabric, causing the universe to pop out of existence as fast as it appears.
That may be true, but theory critics have failed to observe one small detail. As in the case of singularities, relativistic physics cannot explain the physics of particles when they exceed a certain energy scale. The ekpyrotic model of the universe may be suppressed due to the fact that its rival, the Big Bang theory, is easier to explain, but the ghost condensate - if such state even exists - would have sufficiently low energy to describe the bounce of the universe.