Scientists from the large international Dark Energy Survey-DES consortium have presented the largest and most comprehensive «map» to date of dark matter in the universe, the invisible matter that is estimated to make up about 25% of the total universe, compared to 5% of visible matter and 70% of dark energy. Remarkably, the distribution of dark matter appears to be such that, according to at least some scientists, it casts some doubt on the validity of the general relativity theory of Albert Einstein.
The 400 researchers from seven countries used the dark energy camera - one of the world's most powerful with a resolution of 570 megapixels - on the four-metre diameter Victor Blanco telescope in Chile, to analyse - with the help of artificial intelligence - 226 million galaxies, thus revealing a «pachwark» with huge all-dark empty regions of very low-density matter (where gravity can behave differently) and brighter regions (where dark and visible matter is concentrated).
What the scientists say
Invisible dark matter - so named precisely because it is invisible - has an effect on visible matter, distorting the light reaching Earth from distant stars and galaxies. The greater the distortion, the greater the concentration of dark matter in a galaxy or other region of the universe is assumed to be. The gravitational force of the dark holds galaxies together in cosmic «web» structures.
Researcher Dr Niall Jeffrey of the Ecole Normale Superieure in Paris and University College London (UCL) told the BBC that the new «map» poses «a real problem for physics» because it shows that «maybe Einstein was wrong». He added that «you might think this is a bad thing, that maybe physics is falling apart. But for a physicist it is something that is extremely exciting. It means we can discover something really new about how the Universe is.».
Professor Carlos Frenk of the UK's Durham University, who helped develop modern cosmological theory based on Einstein's work, said he had mixed feelings about the news. «I've spent my life working on this theory and my heart says I don't want to see it fall apart. But my brain is telling me that the measurements made are correct and so we need to explore the possibility of a new physics,» he said. «This is something that makes me very nervous and scared because we are entering a completely unknown territory and who knows what we are going to find,» he added.
«Galaxies are part of a larger invisible structure»
As Jeffrey noted, the map clearly shows that galaxies (including our own) are part of a larger invisible structure due to dark matter. Until now, scientists had formed an accurate idea of the distribution of matter, starting 400,000 years before the Big Bang creation of the universe, thanks to the European Space Agency's (ESA) Planck orbital telescope, which measured the remnants of cosmic microwave background radiation, also known as the «twilight of creation».
By combining the evidence from Planck and Einstein's theories, astronomers like Frenk have developed a model that predicts what the distribution of matter should look like in the 13.8 billion years since then. The DES consortium's official statement says that the new «map» is consistent with the theoretical predictions. However, some researchers have pointed out that, based on the new observations and the DES «map», there is a slight discrepancy, as matter actually appears to be slightly (by a few percentage points) more evenly distributed than expected on the basis of Einstein and the predictions of the dominant cosmological model.
«We may have discovered something really fundamental to the fabric of the universe. The current theory is based on very imperfect pillars of sand. And what we may be seeing now is the collapse of one of those pillars,» said Frenk.
Others, however, such as Professor Ofer Lahav of UCL, appeared more reserved and reluctant to fault Einstein, at least not yet. As the professor said, «the big question is whether Einstein's theory is perfect. It seems to pass every test, but with a few discrepancies here and there. Perhaps the astrophysics of galaxies needs some minor corrections. In the history of cosmology there are examples where problems were solved, as well as examples where thinking changed. It will be interesting to see if the new “excitement” in cosmology will lead to a new revolutionary scientific change.».
