The universe will soon stop expanding and start contracting

Researchers from Princeton University have published a study on the future of the universe in the journal Proceedings of the National Academy of Sciences, LiveScience reports. Their conclusion is that soon the process of the accelerating expansion of the Universe, which lasted almost 13.8 billion years, may stop, after which it will begin to contract.

The expansion of the Universe is usually explained by the action of dark matter - a hypothetical type of energy, about the essence of which there are several hypotheses. Princeton physicists believe that dark energy is not a constant force of nature, but the so-called quintessence - a dynamic field that can decay over time. Even though the expansion of the Universe has been accelerating for billions of years, the energy field of dark matter will soon weaken. This will happen in the next 65 million years, after which, in the next 100 million years, having ceased to expand, the Universe will enter an era of slow contraction, and in billions of years this process will end with the death of time and space.

By cosmic standards, all this will happen very quickly. For comparison, it was 65 million years ago that the asteroid Chicxulub fell to Earth, which caused climate change and the extinction of dinosaurs. The discovery that the expansion of the universe is constantly accelerating was made in the 1990s. The entity that is the source of the ever-increasing distance between galaxies and repels them from each other in spite of gravity has been called dark energy. If this is a cosmological constant woven into the fabric of spacetime, then the universe must continue to expand and accelerate forever. If dark matter changes over time, then depending on the ratio of kinetic and potential energy at a particular moment, it can be either repulsive or attractive. For the last 14 billion years, the quintessence has been causing a repulsion, and its influence is most powerful in the last 5 billion years: dark energy replaced radiation and matter as the dominant component and accelerated the expansion of the Universe.

The authors of the study modeled the future based on observations of the expansion of the universe in the past and found that over time, dark energy can weaken to such an extent that in the end its anti-gravity properties will finally disappear, and it will turn into a semblance of ordinary matter. Now the repulsive force of dark energy is experiencing a decline that could have begun billions of years ago, so that the expansion of the Universe is already slowing down. When it starts to shrink in 100 million years, it will be a very slow process, and if there are still people left by then, they will not notice it.

In a few billion years, the universe will be halved from its current size. After that, it can collapse, ending space and time, or return to where it started: there will be a Big Bang, and a new Universe will arise. There is a possibility that the universe follows this cyclical pattern of expansion and contraction all the time, so the current incarnation in which we live is not the first nor the last in an endless series of expanding and contracting universes.