For as long as humans have lived beneath the mysterious cloak of the cosmos, we have gazed upward and wondered: how did it all begin? Although modern physics succeeds in explaining many of the universe’s enigmas, a fundamental understanding of our origins continues to evade our scientific grasp.
Yet, according to research recently published in Physics Letters B, a new model proposes that space and time might not have a beginning or end. It is possible that the universe has existed all along.
Physicists Saurya Das, of the University of Lethbridge in Alberta, Canada, and Ahmed Farag Ali, of Benha University in Egypt, arrived at this conclusion by applying quantum adjustments to equations derived from Einstein’s theory of general relativity.
Their results indicate a universe without an initial singularity, the super-hot, infinitely dense point from which all matter is thought to have exploded in the big bang. The findings also predict a cosmological constant, a key mechanism that defines dark energy’s elusive role in the expansion of the universe.
The traditional big bang theory posits that some 13.8 billion years ago, primordial fluctuations caused the universe to burst forth from the singularity in a violent surge of matter and energy. Cosmologists widely support the theory because evidence of such an explosion can be perceived in the form of subtle, ubiquitous background radiation.
The model for the big bang arises from general relativity, one of the champion theories of modern physics, which describes how matter warps the fabric of space and time. Imagine, for example, the distortion a bowling ball causes when it’s placed in the middle of a taut sheet. According to general relativity, gravity is a result of this distortion of space-time in the presence of matter.
But general relativity has a serious limitation: although it operates elegantly on large scales, it breaks down in the microscopic, or quantum, realm.
“General relativity is completely classical, or deterministic,” co-author Saurya Das tells BTR, “whereas our world is non-deterministic and full of uncertainties.”
In other words, Einstein’s theory cannot mathematically withstand the singularity that it predicts. The predicament creates quite a snag for big bang cosmology. The singularity becomes a point where math devolves into myth, and where physics more closely resembles philosophy.
“When proving the singularity,” Das says, “one uses classical geodesics that arise from general relativity.”
Geodesics describe the shortest possible path connecting two points on a curved surface. Because general relativity tells us that space-time is curved, these paths eventually intersect at a single point: a singularity.
“The theorems are true,” Das continues, “but not completely applicable to the real-life scenario.”
To get around the problem, Das and Ali replaced the geodesics in their equations with Bohmian trajectories, which predict that two separate points in space will never meet. Bohmian trajectories arise from the equally dominant–but fundamentally oppositional–theory of quantum mechanics. By favoring them over geodesics, the authors created a hybrid, or semi-classical, model that eliminates the initial singularity, and by extension, the beginning of time.
“Quantum mechanics describes the world very differently,” Sean Carroll, a theoretical physicist at the California Institute of Technology and popular science author, explains to BTR. “In the quantum realm, observations are predicted in terms of probabilities rather than certainties.”
Das notes that while general relativity and quantum mechanics are correct in their own domains, they seem to be inherently incompatible with each other. One of the long-standing goals of theoretical physics has been to find a means of reconciling the two theories, though scientists have not yet succeeded in this regard.
“If a unified theory of quantum gravity is found,” Das says, “we should be able to answer most, if not all, of the fundamental questions that the quantum realm poses about the universe.”
One such question is how to account for the fact that the universe is expanding at an accelerating rate.
Prior to this discovery in the late ’90s, astronomers hypothesized that the attractive forces between objects should cause the rate of the universe’s expansion to gradually slow down. That the rate of expansion is actually speeding up reveals an unseen, repellant cosmic energy at play. Scientists call this mysterious force dark energy.
Because the density of matter becomes more diluted as the universe expands, the outward push of dark energy meets with less and less gravitational resistance.
“If dark energy has a constant value,” says Carroll, “then the universe will certainly expand forever toward the future.”
Das and Ali’s quantum-corrected equations propose exactly that.
In their model, the universe is made up of a “quantum fluid” that consists of incredibly small particles called gravitons and axions. These particles, which have long been hypothesized by physicists, are believed to facilitate gravity in the quantum realm. If they exist, they would be key players in the fiercely sought-after theory of quantum gravity. Extraordinarily, the density of the “quantum fluid” described in this model confirms existing measurements of the universe’s dark matter content. Furthermore, the fluid predicts a constant value that can reasonably account for observed behavior of dark energy.
“This is the first time that anyone has shown that these two major problems in cosmology can be solved simultaneously by [this quantum-adjusted] equation,” Ali said.
While these results are compelling, other members of the cosmology community are quick to reiterate that these ideas are speculative, and that they have previously been explored in certain capacities.
Carroll cautions that in similar models where Einstein’s equations are modified with quantum elements, the introduction of even slight perturbations can render the predictions unstable.
As for Das, he feels optimistic that although theoretical, this new model holds the potential to resolve some of cosmology’s greatest mysteries.