For nearly half a century, the Big Bang theory has been accepted by many as the best explanation for how the universe began. But what if it was wrong – and the universe’s current expansion was actually preceded by an earlier phase, and there are still traces of that ‘previous’ universe?
Some physicists are now challenging the idea of ‘the beginning of time.’ Instead of a Big Bang event that started it all 13.7 billion years ago, some suspect the universe may experience ‘bouncing’ phases of contraction and expansion.
“I believe the Big Bang never happened,” said physicist Julian Cesar Silva Neves, who works as a researcher at the University of Campinas’ Mathematics, Statistics & Scientific Computation Institute (IMECC-UNICAMP) in Sao Paulo State, Brazil.
In a new study published to the journal General Relativity and Gravitation, Neves argues that there may be no need for the spacetime singularity – or, the Big Bang. Instead of springing into existence, the current expanding universe may have been preceded by a contraction phase. The idea stems from the theory that a ‘Big Crunch’, in which the universe collapses on itself, could lead to an ‘eternal succession of universes.’
The process would create extremes in temperature and density, leading to an inversion and a ‘bounce’ that allows for expansion.
“In order to measure the rate at which the Universe is expanding with the standard cosmology, the model in which there’s a Big Bang, a mathematical function is used that depends only on cosmological time,”said Neves. “Eliminating the singularity or Big Bang brings back the bouncing Universe on to the theoretical stage of cosmology. The absence of a singularity at the start of spacetime opens up the possibility that vestiges of a previous contraction phase may have withstood the phase change and may still be with us in the ongoing expansion of the Universe.”
The new argument is inspired by the behaviour of ‘regular’ black holes. In a black hole, the core contracts to form a singularity, with extreme density and gravitational attraction. But, Neves argues that this singularity does not define a black hole – instead, the event horizon does, or the ‘membrane’ which indicates the point of no return.
“Outside the event horizon of a regular black hole, there are no major changes, but inside it, the changes are deep-seated,” Neves says. “There’s a different spacetime that avoids the formation of a singularity.”
Neves and supervisor lberto Vazques Saa, a Professor at IMECC-UNICAMP, devised a scale factor inspired by physicist James Bardeen, who considered the mass of a black hole not as a constant, but as something dependent on the distance to the center. This modified the solution to the general relativity equations on black holes, and gave rise to what’s known as the ‘regular’ black hole.
“Regular black holes are permitted, since they don’t violate general relativity,” said Neves. “The concept isn’t new and has frequently been revisited in recent decades.”
The researchers used a similar approach to eliminate the singularity. Neves says the hypothesis can be tested “by looking for traces of the events in a contraction phase that may have remained in the ongoing expansion phase.” This could include “remnants of black holes from a previous phase of universal contraction that may have survived the bounce.”