Scientists believe that enigmatic dark energy make up 68% of the universe. But according to a Hungarian-American team, it may not exist at all. The team publish their results in a paper in Monthly Notices of the Royal Astronomical Society. The researchers believe that standard models of the universe fail to take account of its changing structure, but that once this is done the need for dark energy disappears. Hubble's law states that on average, the speed with which a galaxy moves away from us is proportional to its distance.
This law is based on observations of hundreds of galaxies. Our universe was formed in the Big Bang, 13.8 billion years ago, and has been expanding ever since, and the Hubble law is the key evidence of this theory. The concept of expansion of universe came in 1920s, by mapping the velocities of galaxies and by observing the lines of the spectrum, astronomers measure this velocity of stagnation, which shift more towards red the faster the galaxy is moving away.
In the second half of the twentieth century, astronomers found evidence for unseen 'dark' matter. After this they understood that something extra was needed to explain the motion of stars within galaxies. Dark matter is now thought to make up 27% of the content of universe (in contrast 'ordinary' matter amounts to only 5%). After observing the explosions called as Ia supernovae, scientists concluded that dark energy, made up 68% of the cosmos, and is responsible for expansion of the universe.
In the new work, the researchers, led by PhD student Gábor Rácz of Eötvös Loránd University in Hungary, explained that models of cosmology rely on approximations that ignore its structure, and where matter is assumed to have a uniform density. They questioned the conventional concept of existence of dark energy and suggest an alternative explanation.
Dr László Dobos, co-author of the paper, at Eötvös Loránd University, explains: "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. 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."
Usually it is believed that dark matter appear to fill the universe, where galaxies are located on the thin walls between bubbles. Using a computer simulation scientists reconstructed the evolution of the universe, by modeling the effect of gravity on the distribution of millions of particles of dark matter.
Dr Dobos said: "The theory of general relativity is fundamental in understanding the way the universe evolves. We do not question its validity; we question the validity of the approximate solutions. 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. These issues were previously swept under the rug but taking them into account can explain the acceleration without the need for dark energy."
Unlike conventional simulations with a smoothly expanding universe, taking the structure into account led to a model where different regions of the cosmos expand at different rate.
This finding could have significant impact on models of the universe and the direction of research in physics.
The mystery of Dark Energy is unsolved for astronomers and theoretical physicist for the past 20 years. This new model may start a lively debate, now.