The fate of our Universe

Chandra's X-ray image of dark energy. Image: NASA/CXC/SAO/A.Vikhlinin et al.

Doomsday is still a long way away, but this is what might happen.

Have you ever wondered where we and our planet originally came from or what might happen to our galaxy billions of years from now? These aren’t just philosophical questions — scientists have been looking for clues to our origins and our fate for the last few decades. However, five Chinese scientists say that we need to understand the nature of dark energy to truly foresee the destiny of the Universe.

Scientists believe that dark energy makes up 70 per cent of the Universe’s current content, thanks to calculations about how it affected expansion after the Big Bang. But its properties, which have not been completely defined, may decide the fate of the Universe. One scenario is that everything will end in a big rip, when dark energy density grows to infinity in finite time, and its gravitational repulsion will tear apart all the objects in the Universe.

Scientists from the University of Science and Technology of China, Northeastern University, and Peking University have examined the possibility of this cosmic doomsday in a study published in Sci China-Phys Mech Astron. “We want to infer from the current data what the worst fate would be for the Universe,” the authors said in the study.

To explore this scenario, they needed to find a parametrisation that would cover the overall expansion history of the Universe. They eventually settled on a divergence-free parametrisation for dark energy, called the Ma-Zhang parameterisation, to predict the evolution of the Universe and how far away we are from doomsday.

Using the current cosmological observations, the authors found that in the worst-case scenario, our Universe can still exist at least 16.7 billion years before it ends in a big rip. However, this is the worst-case scenario — the best-fit result suggested that the Universe would last another 103.5 billion years. But the researchers wanted to see what would happen in the worst case scenario. “The question of ‘where are we going’ is an eternal theme for human beings, so we should have courage to explore this theme.”

They then focused on this scenario and considered the fate of stars and galaxies. In the event that dark energy increases until it can overcome the forces holding objects together, the Milky Way will be torn apart 32.9 million years before the big rip. The Earth will be ripped from the Sun and the moon from the Earth two months and five days before doomsday respectively. The Sun will be destroyed 28 minutes before the end of time, with the Earth exploding only 16 minutes from the end.

“Even microscopic objects cannot escape from the rip,” the authors state. “For example, the hydrogen atom will be torn apart 310-17 seconds before the ultimate singularity.” But even this violent, worst-case scenario is still billions of years in our future.


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