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—hypothetical massless
particles that mediate the force of gravity. If they exist, gravitons are
thought to play a key role in a theory of quantum gravity.

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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