For decades, the theory of gravity, which stems from the general theory of relativity developed by Albert Einstein, has explained all the processes in space, from the unusual orbit of Mercury to the behaviour of black holes. But in the early 1960s, one discovery called into question the universality of the UTO and the theory of gravity.
At that time, researchers first discovered that the behaviour of distant galaxies did not match the predictions of gravity theory, and the distortion of space-time from distant clusters and star systems was much stronger than the mass of such objects calculated on the basis of observations.
Later in the late 1990s, researchers discovered another unusual fact. It turns out that the rate of expansion of the universe is increasing over time. This effect has further challenged Albert Einstein's theory: the gravitational effects of matter should have slowed down the expansion of the universe rather than accelerated it. A modern cosmological model, the , CRM model, has found answers to these questions, but scientists have no hope of challenging the genius from the first half of the twentieth century.
Why do scientists think that the universe is expanding faster?
The accelerated expansion of the universe was discovered in 1998 as a result of the work of two independent teams: the Supernova Cosmology Project and the High Z Supernova Search Group. Both research groups studied the acceleration of the expansion of the universe by analysing remote star explosions.
Supernova types of la have almost the same standard luminous intensity. When you see the brightness of these objects, you can see how far they are. In addition, when you expand the universe, light shifts from distant objects to the red side of the spectrum. By measuring the red displacement, you can measure how much the universe has expanded since the supernova.
Astrophysics, during these experiments, were convinced that the universe should expand with a slowdown, then the process should either stop or move to compression, but the unexpected result, independently of both groups of scientists, was that the universe would expand with acceleration.
The expansion of the universe was later confirmed by other methods: the measurement of the cosmological microwave background, the gravitational lens effects and the analysis of barion acoustic fluctuations confirm the hypothesis of the expansion of the universe.
In 2007, both teams that had the effect of expanding the universe were awarded the Gruber Prize in Cosmology, and in 2011, three of the participants were awarded the Nobel Prize in Physics.
How can we explain the accelerated expansion?
To explain the observations, scientists introduced two new models — dark matter and dark energy.
Dark matter is a hypothetical form of matter that scientists believe accounts for about 85% of matter in the universe. It is called dark, because it does not interact with the electromagnetic field. In other words, such matter does not reflect, absorb or emit light or other electromagnetic waves. However, it has its own mass, and thus gravitational effects. Adding dark matter to cosmological models can explain the more powerful gravity of distant galaxies.
Dark energy is a hypothetical form of energy, unlike dark matter, which is not yet known. It is believed that dark energy is very homogeneous, not very dense, and cannot interact with any of the fundamental forces except gravity. This energy is associated with the energy of the vacuum. If you assume that as the universe expands and the space of freedom grows, then you can explain the transition from even to accelerated expansion.
Although the theory of dark energy describes well the processes observed in the universe, its very existence and interaction only with the gravitational field are difficult to relate to Einstein's common theory of relativity and gravity theory.
How do you test the theory?
Some scientists believe that if the theory of gravity cannot explain dark energy, perhaps it is incomplete, and it is necessary to add to the equation an additional parameter or variable that will link all observations together. To test this hypothesis, scientists have been looking for signs of a violation of gravity theory in the past.
One such work was an international study of dark energy using Victor Blanco's 4-metre telescope in Chile, the results of which were presented at the International Conference on Particle Physics and Cosmology in Rio de Janeiro in August.
Participants in the study sought evidence that gravity had changed throughout the history of the universe, or in the distant past, using the European Space Agency's "Plank" satellite data in addition to the Blanco main telescope for their work.
Astrophysicists have examined images of galaxies for more subtle distortions due to the distortion of dark matter space, an effect called a weak gravitational lens. The force of gravity determines the size and distribution of the structures of dark matter, and the size and distribution, in turn, determines how curved these galaxies seem to us.
When you measure all these parameters, you can measure the power of gravity in distant galaxies, and since light comes from them to us in millions and billions of years, in fact, scientists learn how gravity has been in the past.
Researchers have reported that gravitational forces and shapes in over 100 million galaxies have already been studied, but in all observation experiments they are fully consistent with Einstein's theory, which means that the nature of dark energy remains a mystery.
In 2023, the European Space Agency planned to launch the Euclid Space Telescope, which would measure the red displacement of galaxies at different distances from the Earth and explore the connection between red displacement and distance.
The developers expect that Euclid will be able to look at 8 billion years ago, and will be able to learn how gravity, dark matter, and dark energy were handled in this era.
I believe that NASA is planning to launch the Nancy Grace Roman Space Telescope into Earth orbit in 2027, and researchers believe that it will be able to study galaxies located at a distance of 11 billion light-years and study the earliest universe.