More than a decade ago, the Dark Energy Survey (DES) began mapping the universe in search of evidence that could help us understand the nature of the mysterious phenomenon known as dark energy. I was one of more than 100 contributing scientists who helped produce the final DES measurement announced at the 243rd American Astronomical Society meeting in New Orleans.
Dark energy is estimated to make up almost 70% of the observable universe, but we still don’t understand what it is. Although its nature remains mysterious, the impact of dark energy is felt to a great extent. Its main effect is to ensure the accelerated expansion of the universe.
The announcement in New Orleans may bring us closer to a better understanding of this form of energy. Among other things, it gives us the opportunity to test our observations with an idea called the cosmological constant, which Albert Einstein introduced in 1917 as a way to eliminate the effects of gravity in his equations to achieve a universe that is neither expanding nor contracting. . Einstein later eliminated this from his calculations.
But cosmologists later discovered that not only was the universe expanding, but the expansion was also accelerating. This observation was attributed to the mysterious quantity called dark energy. Einstein’s concept of the cosmological constant could actually explain dark energy if it had a positive value (allowing it to accommodate the accelerating expansion of the cosmos).
The DES results are the result of decades of work by researchers around the world and provide one of the best measurements yet of an elusive parameter called “w,” which stands for “equation of state” of dark energy. Since the discovery of dark energy in 1998, the value of the equation of state has become a fundamental question.
This describes the ratio of pressure to energy density for a substance. Everything in the universe has an equation of state.
Its value tells you whether a substance is gas-like, relativistic (explained by Einstein’s theory of relativity), or behaves like a liquid. Studying this figure is the first step to truly understanding the true nature of dark energy.
Our best theory for w predicts that it should be exactly negative one (w=-1). This prediction also assumes that dark energy is the cosmological constant proposed by Einstein.
Read more: Euclid spacecraft will change the way we look at the ‘dark universe’
subverting expectations
A negative equation of state tells us that as the energy density of dark energy increases, the negative pressure also increases. As the energy density increases in the universe, repulsion also increases, that is, matter repels other matter. This leads to an ever-expanding, accelerating universe. It may seem a little strange because it goes against everything we’ve experienced on Earth.
The study uses the most direct probe we have into the expansion history of the universe: Type Ia supernovae. They are a type of starburst and act as a kind of cosmic measuring device, allowing us to measure surprisingly large distances far into the universe. These distances can then be compared to our expectations. This is the same technique used to detect the presence of dark energy 25 years ago.
The difference now lies in the size and quality of our supernova sample. Using new techniques, the DES team has 20 times more data over a wide range of distances. This allows one of the most precise measurements of w yet, giving a value of -0.8.
At first glance, this is not the exact negative value we expected. This may indicate that it is not a cosmological constant. However, the uncertainty in this measurement is large enough to allow odds of minus one on a 5% chance or only 20 to 1. This level of uncertainty isn’t good enough yet in either case, but it’s an excellent start.
The detection of the Higgs Boson subatomic particle at the Large Hadron Collider in 2012 required a one in a million chance of being wrong. However, this measurement could signal the end of “Big Rip” models with multiple negative equations of state. In such models, the universe will expand more and more rapidly indefinitely, eventually tearing apart galaxies, planetary systems, and even space-time itself. It was a relief.
As always, scientists want more data, and those plans are already underway. The DES results show that our new techniques will work for future supernova experiments with ESA’s Euclid mission (launched in July 2023) and the new Vera Rubin Observatory in Chile. This observatory will soon use its telescope to take the first image of the sky after construction and give a glimpse of its capabilities.
This next generation of telescopes could find thousands more supernovae, help us make new measurements of the equation of state, and shed more light on the nature of dark energy.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
Robert Nichol is a member of the Dark Energy Research collaboration.