No Big Bang? Quantum equation
predicts universe has no beginning

Feb 09, 2015 by Lisa Zyga

http://phys.org/news/2015-02-big-quantum-equation-universe.html#jCp

(Phys.org) —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.

More information: Ahmed
Farag Ali and Saurya Das. "Cosmology from quantum potential." Physics
Letters B. Volume 741, 4 February 2015, Pages 276–279. DOI: 10.1016/j.physletb.2014.12.057.
Also at: arXiv:1404.3093[gr-qc].

Saurya Das and Rajat K.
Bhaduri, "Dark matter and dark energy from Bose-Einstein condensate",
preprint: arXiv:1411.0753[gr-qc].

Journal reference: Physics Letters B

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