The universe we live in is expanding, and this expansion is accelerating. In 2011, three researchers who proved that the universe’s expansion was speeding up by studying Type Ia supernovae — which are objects that always explode with the same brightness, making them one of the “standard candles” astronomers use to gauge distance in the cosmos — were even awarded the Physics Nobel prize.
The problem is, we don’t know what’s driving this accelerated expansion.
This is where “dark energy” comes in. According to the Lambda Cold Dark Matter (Lambda-CDM) model, which is the framework that governs our current understanding of the origin and evolution of the universe, dark energy and dark matter make up nearly 95 percent of the cosmos. Dark energy, which is an as-of-yet undetected force that comprises 68 percent of the universe, is believed to be responsible for its accelerated expansion.
However, a study published in the latest edition of the Monthly Notices of the Royal Astronomical Society, has now posed an intriguing question — what if dark energy doesn’t exist?
According to the authors of the study, dark energy may merely be the result of approximations that conventional models of cosmology rely on to calculate the universe’s rate of expansion. These models assume — incorrectly, according to the researchers — that the density of matter in the cosmos is uniform and that the universe is expanding smoothly.
“Einstein’s equations of general relativity that describe the expansion of the universe are so complex mathematically, that for a hundred years no solutions accounting for the effect of cosmic structures have been found,” study co-author László Dobos from the Eötvös Loránd University in Hungary said in a statement released Thursday. “We know from very precise supernova observations that the universe is accelerating, but at the same time we rely on coarse approximations to Einstein’s equations which may introduce serious side-effects, such as the need for dark energy, in the models designed to fit the observational data.”
In order to overcome these “side-effects,” the researchers used a computer simulation to model the effect of gravity on the distribution of millions of particles of dark matter, and to reconstruct the evolution of the universe. Although the model thus created, named Avera, showed different regions of the cosmos expanding at different rates, the average rate of expansion was found to be consistent with present observations.
“Our findings rely on a mathematical conjecture which permits the differential expansion of space, consistent with general relativity, and they show how the formation of complex structures of matter affects the expansion,” Dobos said. “These issues were previously swept under the rug but taking them into account can explain the acceleration without the need for dark energy.”
Of course, the researchers’ findings are still far from conclusive, especially since they need to be reconciled with observations that tell us that the universe we live in is homogenous and isotropic. However, if the need for dark energy to explain the universe’s expansion is removed, it could, according to the authors of the study, change “the direction of research in physics.”