A universe expanding faster than it ought to be? What's up with that?
Instead, he suggests, it's the signal that a fourth dimension – beyond the height, width, and depth humans are geared to experience – has opened up in a universe that is adding physical dimensions as it evolves.
This possible explanation for dark energy results from applying a new "framework" for looking at the evolution of the universe that he and colleagues have developed over the past two years. Working backwards in time, the concept also implies that the universe did not begin its existence in a three-dimensional form, but as a one-dimensional structure that added dimensions as it evolved.
Some support for this may be found in high-energy cosmic rays, according to Dr. Stojkovic, a physicist at the State University of New York at Buffalo, who along with colleagues first proposed the idea last year.
In a paper published recently in Physics Review Letters, Stojkcovic and colleague Jonas Mureika of Loyola Marymount University in Los Angeles write that further tests of the framework's validity could come from the Large Hadron Collider in Geneva as well as from planned space missions to detect gravity waves thought to be rippling through the cosmos.
If he and his colleagues are correct, Stojkovic says, their work could help break a 30-year logjam in efforts to demonstrate that the four fundamental forces in nature – electromagnetism, the weak force (governing radioactive decay), the strong force (binding atomic nuclei), and gravity – are low-energy relics of one unified force that briefly held sway over the cosmos during the first, tiniest fractions of a second after the big bang.
The big bang is a sudden release of an enormous amount of energy that physicists and cosmologists credit with giving birth to the universe some 13.8 billion years ago.
Gravity remains the stubborn hold-out in this grand-unification effort. It's the only one of the four forces that has defied an explanation within the so-called standard model of physics. As the decades have passed, many researchers have developed ever more complicated ideas to fit gravity into the quantum-physics world inhabited by the rest of the forces and their associated subatomic particles. Scientists' calculations suggest that the solution may lie in "new physics" – beyond the standard model.
Stojkovic is part of a subgroup of physicists collectively tapping their "new physics" colleagues on the shoulder and saying: The solution many not require new physics at all, but merely a new way of looking at the standard model.
"The standard lore for years was to make things more complicated, introducing more structures, more particles, extra dimensions," says Stojkovic, a physicist at the State University of New York at Buffalo. His work "is quite the opposite. This is saying no, no, no, we don't need anything else. We don't need more dimensions" in the early universe, as some propose. "We need less dimensions," he says.
A shift from one to two, and then to three dimensions would have occurred long before a cosmic stopwatch recorded the first full second of the universe's existence.
Why the universe would have started as a one-dimensional structure, or what took place during the transitions as new dimensions emerged, have yet to be worked out, Stojkovic acknowledges.
But, he says, if one could view the event from a distance and in excruciatingly slow motion, his calculations suggest that the big bang initially yielded a single rapidly-stretching one-dimensional thread. That energetic thread snaked back and forth across itself, forming a kind of two-dimensional fabric. With time, that fabric finally yielded the three-dimensional structure that humans experience.
The size scale of the nascent universe during this process, whose progress took place within the first trillionth of a second following the big bang, would have been vanishingly small.
This approach to viewing these early actions resolves several longstanding issues that have been vexing physicists and cosmologists, Stojkovic says.
With each step backward in dimension, the mathematical gap – between gravity as Albert Einstein described it in his theory of general relativity and as quantum mechanics would try to describe it – narrows until, in a one-dimensional fledgling universe, it vanishes, he says.
Likewise, general relativity can yield a dark-energy-like expansion of the universe without having to invoke a so-called cosmological constant, which Einstein did and later retracted. Merely have general relativity play out in four dimensions, rather than three, Stojkovic says.
Finally, in a one-dimensional early universe, no one needs need to fine-tune values of the mass for the Higgs boson – an object physicists are trying to detect at CERN and whose interactions are said to give all other particles their mass – to get the equations describing the particle to fall within the standard model.
At this stage, Stojkovic says, the notion of vanishing dimensions as one looks deeper into the universe's fiery beginning falls far short of a full-blown theory.
But within the realm of physics and cosmology, it's "a respectable proposal," says Sean Carroll, a cosmologist at CalTech in Pasadena, whose own preferred picture of the universe's evolution starts with more dimensions at the outset that disappear over time.
That picture, however, is a bit too complicated for Stojkivic's sense of scientific aesthetics, where if several ideas can explain the available experimental data, make a beeline for the simplest one. Whether simplicity reigns as Stojkovic and colleagues work to fill out their framework remains to be seen. But at the least, it's efficient, he says. It appears to solve several longstanding conundrums simultaneously. And seems far simpler than invoking a universe that started out with 11 dimensions and an unfamiliar zoo of additional subatomic particles.
Stojkivic's aesthetic echoes that of Roger Penrose, renowned Oxford University physicist and cosmologist, who once wrote, "A beautiful idea has a much greater chance of being a correct idea than an ugly one."