by More than ten years ago, the Dark Energy Survey (DES) began mapping the universe to find evidence that could help us understand the nature of the mysterious phenomenon known as dark energy. I am one of more than 100 scientists who helped produce the final DES measurement, which was just released at the 243rd meeting of the American Astronomical Society 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 influence of dark energy is felt on large scales. Its main effect is to drive the accelerated expansion of the universe.
The announcement in New Orleans may take us closer to a better understanding of this type of energy. Among other things, it gives us the opportunity to test our observations against an idea known as the cosmological constant that Albert Einstein introduced in 1917 as a way to counteract the effects of gravity in his equations to achieve a universe that did not have expanding than contracting. . Einstein later removed it from his calculations.
However, cosmologists later discovered that not only was the universe expanding, but that the expansion was accelerating. This observation was attributed to the mysterious quantity known as dark energy. Einstein’s concept of the cosmological constant could actually explain dark energy if it had a positive value (allowing it to follow the accelerating expansion of the cosmos).
The results of the Department of Education and Skills are the culmination of many years of work by researchers around the world and provide one of the best measurements yet of an elusive parameter known as “w”, which stands for “equation of state”. the dark energy. Since the discovery of dark energy in 1998, the value of its equation of state has been a fundamental question.
This state describes the ratio of pressure to energy density of a substance. Everything in the universe has an equation of state.
Its value tells you whether or not a substance is gas-like, relativistic (described by Einstein’s theory of relativity), or behaves like a liquid. Working out this figure is the first step to really understanding the true nature of dark energy.
Our best theory for w predicts that it should be exactly minus 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
The minus one equation of state tells us that as the energy density of dark energy increases, so does the negative pressure. The greater the energy density in the universe, the more it is pushing away – in other words, matter pushes against other matter. This creates an ever-expanding universe. It might be a bit strange, because it is counter-intuitive to everything we have experienced on Earth.
The work uses our most direct probe of the universe’s expansion history: Type Ia supernovae. These are a type of starburst and act as a cosmic yardstick, allowing us to measure vast distances far into the universe. Those lengths can then be compared to our expectations. This is the same technique used to detect the existence of dark energy 25 years ago.
The difference now is the size and quality of our supernovae sample. Using new techniques, Department of Education and Skills staff have 20 times more data, over a wide range of areas. This allows one of the most precise measurements of w ever, giving a value of -0.8
At first glance, this is not the exact minus one value we had predicted. This may indicate that it is not the cosmological constant. However, the uncertainty in this measurement is large enough to give minus one a 5% chance, or betting odds of only 20 to 1. This level of uncertainty is still not good enough to say either way, but it’s a great start.
When the subatomic particle Higgs Boson was detected in 2012 at the Large Hadron Collider there was a million to one chance that it was wrong. However, this measurement may signal the end of “Big Rip” models with equations of state more negative than one. In such models the universe would expand indefinitely at a faster and faster rate – eventually pulling apart galaxies, planetary systems and even space-time itself. That’s a relief.
As usual, scientists want more data and those plans are already well underway. The results from the Department of Education and Skills suggest that our new techniques will work for future supernova experiments with ESA’s Euclid mission (launching in July 2023) and the new Vera Rubin Observatory in Chile. This observatory should soon use its telescope to take the first image of the sky after construction, giving a glimpse of its potential.
These next-generation telescopes could detect tens of thousands more supernovae, helping us make new measurements of the equation of state and shedding more light on the nature of dark energy.
This article from The Conversation is republished under a Creative Commons license. Read the original article.
Robert Nichol is a member of the Dark Energy Survey collaboration.
