Scientists discovered that the universe is expanding and it’s not slowing down; instead, it’s speeding up. This is because it is propelled by so-called “dark energy,” which is the form of energy that comprises almost three-fourths of the universe. A new study suggests that the nature of dark energy is dynamical and its contribution to the expansion of the universe is time-dependent. This, however, does not conform to the cosmological constant introduced by Albert Einstein about a century ago.
Space reports that Einstein’s cosmological constant reflects that empty space could have its own energy. In other words, the constant suggests that as more space appears, the more energy would be contributed to the universe, resulting in its expansion.
In addition, in the Lambda-Cold Dark Matter (LCDM) model, dark energy is fundamentally the cosmological constant (i.e. the vacuum energy, represented by a constant Equation of State (EoS) of -1). This model implies that dark energy has no dynamical features.
On the other hand, in the new study, which was published in Nature Astronomy and titled “Dynamical Dark Energy Considering the Latest Observations,” the scientists reveal the dynamical dark energy. In 2016, Professor Gong-Bo Zhao, from the Institute of Cosmology and Gravitation (ICG) at the University of Portsmouth and the National Astronomical Observatories of China (NAOC) and the lead author of the study, and his team made a successful measurement of the Baryonic Acoustic Oscillations (BAO), according to Science Daily.
Based on this measurement and the method created by Prof. Zhao, the scientists discovered an evidence of dynamical dark energy at a significance level of 3.5 sigmas. This means that the nature of dark energy may not be vacuum energy, rather a type of dynamical field, particularly for the quintom model of dark energy whose EoS varies with time and crosses the -1 boundaries during evolution.
In the image above, the cosmological constant, which refers to the straight yellow line, explains the accelerated expansion of the Universe due to dark energy. This was shown on the expanding blue cone in the image. Meanwhile, in the new study, it implies that the influence of dark energy on this expansion is time-dependent, which was shown as the grey-curve.
Professor Zhao said that they are excited to see that current observations can probe the dynamics of dark energy at this level. He further said that they hope future observations will confirm what they see today.
Meanwhile, the dynamics of dark energy might be confirmed by the coming astronomical surveys. The scientists refer to the future Dark Energy Spectroscopic Instrument (DESI) survey that intends to create a 3D cosmic map in the coming year.
[Featured Image by Sakkmesterke/Thinkstock]