The universe may have existed forever,
according to a new model that applies quantum correction terms to complement
Einstein's theory of general relativity. The model may also account for dark
matter and dark energy, resolving multiple problems at once.

The widely accepted age of the universe, as
estimated by general relativity, is 13.8 billion years. In the beginning,
everything in existence is thought to have occupied a single infinitely dense
point, or singularity. Only after this point began to expand in a "Big Bang"
did the universe officially begin.

Although the Big Bang singularity arises
directly and unavoidably from the mathematics of general relativity, some
scientists see it as problematic because the math can explain only what
happened immediately after—not at or before—the singularity.

"The Big Bang singularity is the most
serious problem of general relativity because the laws of physics appear to
break down there," Ahmed Farag Ali at Benha University and the Zewail City
of Science and Technology, both in Egypt, told Phys.org.

Ali and coauthor Saurya Das at the University
of Lethbridge in Alberta, Canada, have shown in a paper published in Physics
Letters B that the Big Bang singularity can be resolved by their new model in
which the universe has no beginning and no end.

**Old ideas revisited**

The physicists emphasize that their quantum
correction terms are not applied ad hoc in an attempt to specifically eliminate
the Big Bang singularity. Their work is based on ideas by the theoretical
physicist David Bohm, who is also known for his contributions to the philosophy
of physics.

Starting in the 1950s, Bohm explored replacing
classical geodesics (the shortest path between two points on a curved surface)
with quantum trajectories.

In their paper, Ali and Das applied these
Bohmian trajectories to an equation developed in the 1950s by physicist Amal
Kumar Raychaudhuri at Presidency University in Kolkata, India. Raychaudhuri was
also Das's teacher when he was an undergraduate student of that institution in
the '90s.

Using the quantum-corrected Raychaudhuri
equation, Ali and Das derived quantum-corrected Friedmann equations, which
describe the expansion and evolution of universe (including the Big Bang)
within the context of general relativity. Although it's not a true theory of quantum
gravity, the model does contain elements from both quantum theory and general
relativity. Ali and Das also expect their results to hold even if and when a
full theory of quantum gravity is formulated.

**No singularities nor dark stuff**

In addition to not predicting a Big Bang
singularity, the new model does not predict a "big crunch"
singularity, either. In general relativity, one possible fate of the universe
is that it starts to shrink until it collapses in on itself in a big crunch and
becomes an infinitely dense point once again.

Ali and Das explain in their paper that their
model avoids singularities because of a key difference between classical
geodesics and Bohmian trajectories. Classical geodesics eventually cross each
other, and the points at which they converge are singularities. In contrast,
Bohmian trajectories never cross each other, so singularities do not appear in
the equations.

In cosmological terms, the scientists explain
that the quantum corrections can be thought of as a cosmological constant term
(without the need for dark energy) and a radiation term. These terms keep the
universe at a finite size, and therefore give it an infinite age. The terms
also make predictions that agree closely with current observations of the
cosmological constant and density of the universe.

**New gravity particle**

In physical terms, the model describes the
universe as being filled with a quantum fluid. The scientists propose that this
fluid might be composed of gravitons.

In a related paper, Das and another
collaborator, Rajat Bhaduri of McMaster University, Canada, have lent further
credence to this model. They show that gravitons can form a Bose-Einstein
condensate (named after Einstein and another Indian physicist, Satyendranath
Bose) at temperatures that were present in the universe at all epochs.

Motivated by the model's potential to resolve
the Big Bang singularity and account for dark matter and dark energy, the
physicists plan to analyze their model more rigorously in the future. Their
future work includes redoing their study while taking into account small inhomogeneous
and anisotropic perturbations, but they do not expect small perturbations to
significantly affect the results.

"It is satisfying to note that such
straightforward corrections can potentially resolve so many issues at
once," Das said.

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