Curved universe could help explain cosmic conundrum

Modifying the standard model of cosmology to allow for a curved universe could help ease confusion between cosmologists who calculate different ages of the Universe, based on different experiments.

The standard model of cosmology says that the majority of matter is made up of invisible, dark matter. These mystery particles are thought to have moved slowly after the Big Bang, almost 14 billion years ago. “Dark matter is necessary to explain how large-scale structure formed in the early Universe, and the distribution of matter we observe today,” says team member, Jhonny Agudelo Ruiz, a physicist at the Federal University of Espírito Santo (UFES), in Brazil.

Astronomers also know that the universe is expanding at an accelerating rate. The standard model attributes this effect to a cosmological constant— a form of energy that pushes outwards against gravity’s inward pull, with equal strength throughout time.

The trouble comes when cosmologists use this model to interpret measurements. Depending on which experiment you look at, a different age for our Universe may be inferred. The mismatch between estimates can be as large as a billion years—a value too large to be blamed on measurement errors. This suggests the standard model may need refining. “We should think of the model as a guide. It is far from the last word,” says Julio Fabris, a cosmologist and team member also at UFES.

The team decided to tweak the model, allowing the cosmological constant to gradually vary over time. If they also allowed the dark matter to move faster—approaching the speed of light—in the early Universe, their revised model seemed to work. It fits with datasets made by plotting the positions of distant supernova, which are used to measure cosmic expansion. It also matches measurements of the relic radiation from the Big Bang, which gives an estimate of dark matter.

Intriguingly, the modified model re-opens a possibility investigated by cosmologists decades ago, suggesting the Universe is curved. This means that in the future, gravity could counter the expansion and draw the universe back inwards on itself. The standard model rejects this possibility. Taking into account this curvature might help ease the disparity between estimates of the age of the Universe, although it is too early to tell, says team member Ilya Shapiro, a physicist at the Federal University of Juiz de Fora, in Brazil. First the team has to apply the model to other datasets. “Our approach could give new insight,” he says.