Einstein’s revolutionary theory of general relativity has been confirmed in countless experiments, to the point that it is seen within the scientific community itself as one of the theories most often proven by other studies. And it has happened again, with a big one.
An international team of scientists has just finished analyzing the enormous amount of data collected by the Dark Energy Spectroscopic Instrument (Dark Energy Spectroscopic Instrument), or DESI. It is a scientific apparatus operated by the Berkeley National Laboratory and designed specifically for the study of gravity on large spatial and temporal scales, and has confirmed (once again) the incredible accuracy of theoretical predictions of the general relativity of Albert Einsteinformulated more than a century ago and considered one of the cornerstones of modern physics. The results of the study (published here), which “traversed” billions of years of the evolution of the Universe, represent the most precise experimental verification of Einstein’s theories to date: “General relativity,” explains Pauline Zarrouk, cosmologist at the French National Center for Scientific Research (CNRS) and co-author of the article, “has been widely tested at the spatial scale of the Solar System, but it needed to be validated at much larger scales. Study the rate of galaxy formation allowed us to do so, and so far we have observed that everything fits, even cosmological scales“.
What general relativity says
The theory of general relativity was formulated in 1915 by Einstein, and was described by Max Born, another Nobel Prize winner in Physics, as “the most amazing combination of philosophical insight, physical intuition and mathematical skill“. The theory was inspired by the conclusions that Einstein himself had reached in 1905 when he developed special relativityanother theory that resolved the contradictions between Maxwell’s equations related to electromagnetism and Galilean relativity. The problem in question was that special relativity, in turn, was in contradiction with Newton’s theory of universal gravitation: so Einstein, to “correct” gravity, developed a field equation that completely revolutionized its definition. According to this equation, which is the core of general relativity, the gravitational force is nothing more than the manifestation of the curvature, or deformation, of the so-called space-time, the four-dimensional “fabric” of which the Universe is made. As we said, the theory has been widely tested: the first confirmation came in 1919, on the occasion of a solar eclipse. Indeed, the astronomer Arthur Eddington managed to observe some stars very close to the edge of the Sun, which should have been invisible because They were behind the Sun itself (relative to the point of view of a terrestrial observer). The phenomenon occurred because, as Einstein predicted, Starlight is also deflected by the curvature of space-time produced by the Sun’s mass.. This verification was followed by many others: the last, only in order of time, was the observation of a distant supernova whose light is divided into four different trajectories due, again, to the curvature of space-time (in scientific jargon, the effect is called ‘gravitational lensing’), giving rise to the so-called ‘Einstein cross’.
The new DESI results
The DESI experiment was designed to answer a question closely related to a kind of “anomaly” in the behavior of gravity. We know (since Newton’s time) that gravity is a force of attraction; That means that it tends to bring bodies with mass closer together. We also know that, starting with the Big Bang, the Universe began to expand, and that it continues to do so today. However, it also seems that the expansion of the Universe occurs at an accelerated ratefaster and faster, which is apparently incompatible with the “braking” action of gravity, which should instead act to hold matter together. To overcome this problem, physicists have hypothesized the existence of another type of energy, the so-called dark energywhich should be responsible for this action “contrary” to gravity and, therefore, for accelerating the expansion of the Universe. The thing is that we don’t know anything about this energy; We don’t know if it really exists, we don’t know what it’s supposed to be, where it comes from or how it acts. Another possibility is that gravity works differently, perhaps not ‘attractively’, at cosmological spatial scales.
And precisely To test that hypothesis, DESI was designedan experiment involving more than 900 scientists from 60 different institutions around the world. The studies just published refer to the first year of data collected by the instrument, which includes the analysis of more than 6 million galaxies and quasars during 11,000 million years of cosmic evolution. Essentially, we were able to take a look into the Universe’s past, going back to when it was “only” three billion years old, and the scientists’ analysis confirmed that, even on cosmological space and time scales, gravity behaves exactly as Einstein predicted: “We are trying to put limits on how matter moves in the Universe and how galaxy clusters evolve,” he explained. Mustapha Ishak-Boushakiphysics professor the University of Texas at Dallas who co-led the experiment, “and our results, combined with those of other experiments, confirmed that the theory of relativity is true even at these spatial scales. However, we cannot completely rule out other theories of modified gravity“In short, the discourse is not yet closed, and we will have to continue searching.
What will happen next
Experiments and data analysis continue: the DESI collaboration is currently studying another three years of observations, and hopes to publish new results on the expansion of the Universe in the spring of next year. “Dark energy is supposed to make up about 70% of our Universe, and we still don’t know what it is,” explains Mark Maus, a researcher at the University of California Berkeley, who is working on models to validate the new analyses. “The fact that we are now able to ‘take’ such detailed images of the Universe and address such fundamental questions is mind-blowing.”
In addition to its work on gravity and dark energy, among other things, DESI has also provided new information on the neutrino, the only fundamental particle whose mass we have not yet been able to determine precisely: its observations have allowed us to establish an upper limit for the sum of the masses of three types of neutrino, which can no longer be greater than 0.071 eV/c2 (electronvolts over the cosmological constant squared).
Article originally published in WIRED Italy. Adapted by Mauricio Serfatty Godoy.
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