The product of space and time is not exempt from the effects of gravity. Plop in the weight and space-time around it, not unlike what happens if you put a bowling ball on a trampoline.
This dimple in space-time is the result of what we call gravity, and was first described over 100 years ago by Albert Einstein’s field equations in his theory of general relativity. To this day, the equation stands. We want to know what Einstein put in his soup. In any case, general relativity remained intact.
One of the ways we know this is because when light travels through curved space-time, it gets twisted along with it. This results in the light that reaches us all being twisted and stretched and refracted and enlarged, a phenomenon known as gravitational lensing. This periodic quirk is not only observable and measurable, it is an excellent tool for understanding Nature.
But a group of researchers have recently found that predictions of the depth of space-time calculated using relativity don’t always match what we see, using data from the Dark Energy Survey which is currently mapping hundreds of millions of galaxies in the universe. This does not mean that anything is broken – but it does mean that there may be something out there that we haven’t read.
“Until now, the Dark Energy Survey data has been used to measure the distribution of matter in the Universe,” explains physicist Camille Bonvin of the University of Geneva in Switzerland. “In our study, we used this data to directly measure the error in time and space, enabling us to compare our findings with Einstein’s predictions.”
The Dark Energy Survey is an international collaboration using a powerful optical instrument mounted on the 4-meter Victor M. Blanco Telescope at the Cerro Tololo Inter-American Observatory in Chile. Its main task, as the name suggests, is to study dark energy, the mysterious force driving the rapid expansion of the Universe.
To do this, the instrument has been exploring the Universe in as much detail as possible. This means that it sees light in different time periods, peering deep into the history of the Universe to galaxies whose light has traveled billions of years to reach us.
Led by astronomer Isaac Tutusaus of the University of Toulouse in France, a group of researchers realized that they could use this wealth of data to test the predictive power of Einstein’s physical description of the Universe. They specifically measured time-lapses due to gravity wells, at four different times: about 3.5 billion years ago, 5 billion years ago, 6 billion years ago, and 7 billion years ago.
Then, they compared these measurements with what Einstein’s equations predict it should be. Fortunately, some of the measurements are in line with the predictions – but not all.
“We found that in the past – 6 and 7 billion years ago – the depth of the wells coincides with Einstein’s predictions,” Tutusaus explains. “However, closer to today, between 3.5 and 5 billion years ago, they are somewhat slower than Einstein predicted.”
The difference is small, but it can be significant. It could mean, for example, that gravity wells have a slow growth rate in recent times in the Universe. In addition, measurements of the expansion of space-time show that the expansion of the Universe is accelerating, and has increased significantly recently.
This discrepancy may, therefore, indicate a connection between the acceleration of the Universe driven by dark energy and the slow growth of gravitational wells at the same time. Further observations will need to be made to confirm, and add to, the team’s findings.
“Our results show that Einstein’s prediction has a discrepancy of 3 sigma with the measurements. In the language of physics, such a threshold discrepancy arouses our interest and requires us to further investigate,” says physicist Natassia Grimm of the University of Geneva.
“But this inconsistency is not big enough, at this time, to undermine Einstein’s theory. For that to happen, we would need to reach the threshold of 5 sigma. So it is important to have well-organized measurements to confirm or reject these new beginnings. , and to see if this theory still works in our Universe , at very great distances.”
Research published in Nature Communications.