It has been more than twenty years since dark energy was discovered.
Scientists have therefore had more than twenty years to decipher the secrets of this invisible substance that seems to be pulling the universe apart. Yet they still know virtually nothing about it. Dark energy may not even be a substance. It could be a force or even an intrinsic property of the space itself.
For example the standard model of cosmology – our leading theory of cosmic evolution – suggests that dark energy is steadfast throughout the universe and throughout time, making it a fundamental property of room. If it were constant, the mysterious dark energy that makes up as much as 70 percent of the universe would push everything away stars and galaxies. However, the largest overview of the cosmic history of the universe may indicate that dark energy, also known as a hypothetical “anti-gravity” forcemay evolve over time rather than remain constant, hinting at a less lonely future for the inhabitants of the universe.
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If this early result matches future observations, cosmologists may need to at least investigate the systematic uncertainties in the prevailing Lambda CDM (LCDM) model, a mathematical model of the universe where lambda represents dark energy. They may also have to search through dozens of other models of our universe to find the best match. Still, the evidence is preliminary: It doesn’t reach what’s known as the “5-sigma threshold,” which determines whether a signal can be celebrated as an official discovery. So the continually emerging interpretations about the evolution of dark energy could change as more data emerges in the coming years.
“If this is true, this just turns cosmology upside down,” says Dillon Brout of Boston University, who measures the acceleration of the universe with supernovas. Such a discovery would represent a “paradigm shift in our thinking about what our best understanding of our universe is.”
Street lights of the universe
Located atop the Nicholas U. Mayall 4-meter telescope in Arizona Kitt Peak National Observatorythe Dark Energy Spectroscopic Instrument, or DESI, locates the positions of a million galaxies every month. These observations allow cosmologists to measure the expansion rate of the universe as it has increased over the past 11 billion years. These distant galaxies, which can be compared to the “street lamps of the universe”, thus helping cosmologists study the universe-pervading riddle of dark energy.
And on Thursday (April 4), the DESI collaboration shared the largest-ever 3D map of the universe. It also includes extremely precise measurements of the expansion rate of the universe over the past 11 billion years. In its first year of existence alone, DESI has proven to be twice as powerful at measuring the expansion history of the early universe as its predecessor, the Sloan Digital Sky Survey, which took more than a decade to complete. to create a similar 3D map.
This “is the next generation of data that we have been waiting for for a long time, so it is very nice to see that it has arrived,” says Brout, who is not involved in the DESI collaboration.
In addition to countless galaxies clustered together like knotted threads, DESI’s new 3D map highlights a faint pattern in the early universe known as Baryon Acoustic Oscillations, or BAO. These subtle 3D ripples had flown through the matter that existed for the first 380,000 years of our universe’s history, freezing over time and turning into remnants of a young cosmos. By mapping the sizes of these frozen BAOs, researchers managed to estimate the distances to galaxies and deduce how quickly the universe was expanding at different times.
Because the light from typical galaxies is too weak to observe, because these galaxies are very far away from us and the light they emit is relatively low, the DESI collaboration also studied more than 400,000 intensely bright objects, called quasars. As the light from these objects passes through interstellar spaceit is absorbed by clouds of gas and dust, allowing cosmologists to map regions of dense matter in a similar way to mapping galaxies.
“It lets us look further back to the time when the universe was very young,” said Andreu Font-Ribera, a scientist at the Institute for High Energy Physics in Spain and member of the DESI collaboration, in a rack. “It’s a very difficult measurement to do, and very cool to see that it works.”
‘If this is real, we are in uncharted territory’
The preliminary conclusion with which dark energy could evolve time comes from an early analysis of DESI data combined with data from other cosmological records. The researchers found that a varying dark energy model fit the data better than the standard model. To be clear, no single dataset on its own convincingly reveals the time-evolving nature of dark energy, but the signal becomes slightly stronger when all datasets are combined.
“It’s not such a strong bias that I would say Lambda CDM is wrong,” Kyle Dawson, the co-spokesperson for DESI at the University of Utah, told Space.com. “We’ve actually never found deviations from that model with any real significance.”
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However, from early analysis, it appears that dark energy is moving from being a strong driver of the acceleration of our universe to some degree of deceleration, Dawson said.
“If this is real, we are in uncharted territory,” Brout said. The DESI collaboration used the second simplest model of our universe after Lambda CDM, which is unremarkable aside from its ability to help cosmologists check for deviations from the standard model. If future observations indeed show that dark energy evolves over time, dozens of other models would also become viable, and cosmologists would have to start testing each one individually, Brout said.
“If it’s not Lambda CDM, who knows?”