Over ten years ago Dark Energy Study (DES) began mapping the universe to find evidence that would help us understand the character of the mysterious phenomenon generally known as dark energy. I’m one of over 100 scientists who helped develop the outcome DES measurementwhich has just been published in 243rd meeting of the American Astronomical Society in New Orleans.
Dark energy It is estimated to make up almost 70% of the observable universe, and yet we still don’t understand what it is. Although its nature stays mysterious, the influence of dark energy is felt on a grand scale. Its major effect is propulsion accelerating the expansion of the universe.
The announcement in New Orleans may bring us closer to higher understanding this manner of energy. This gives us, amongst other things, the chance to check our observations in terms of the concept called cosmological constant it was introduced by Albert Einstein in 1917 as a way to counteract the results of gravity in his equations to obtain a universe that neither expands nor contracts. Einstein later removed this from his calculations.
However, cosmologists later discovered that the universe was not only expanding, but was actually accelerating. This remark was attributed to a 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 space).
The DES results are the culmination of a long time of work by researchers all over the world and provide one of one of the best measurements yet of an elusive parameter called “w,” which suggests “equation of state“dark energy. Since the invention of dark energy in 1998, the worth of its equation of state has remained fundamental.
This state describes the ratio of pressure to energy density for a substance. Everything within the universe has an equation of state.
Its value tells you whether a substance is gas-like, relativistic (as described by Einstein’s theory of relativity) or not, or whether it behaves like a fluid. Working out this number is the primary step to truly understanding the true nature of dark energy.
Our best theory about w predicts that it ought to be exactly minus one (w=-1). This prediction also assumes that dark energy is the cosmological constant proposed by Einstein.
Challenging expectations
The minus one equation of state tells us that because the energy density of dark energy increases, the negative pressure also increases. The greater the energy density within the universe, the greater the repulsion – in other words, matter repels other matter. This leads to an ever-expanding, accelerating universe. This may sound a bit strange because it goes against the intuition of every thing we experience on Earth.
The work uses probably the most direct probe we have into the history of the expansion of the universe: Type Ia supernovae. They are a kind of stellar explosion and act as a sort of cosmic yardstick, allowing us to measure astonishingly large distances into the universe. These distances can then be compared to our expectations. This is the identical technique that was used to detect the existence of dark energy 25 years ago.
The difference now is the dimensions and quality of our sample of supernovae. Thanks to the brand new techniques, the DES team has 20 times more data over a wide selection of distances. This allows for one of probably the most accurate measurements ever, giving a worth of -0.8
H. Stockebrand/Rubin/NSF/AURARubinObs/NSF/AURA, CC BY
At first glance, this is not the precise minus one value we predicted. This may indicate that it is not a cosmological constant. However, the uncertainty on this measurement is large enough to allow for minus one at a 5% probability, or a betting odds of just 20 to 1. This level of uncertainty is not yet large enough to say anything, but it is an important start.
The detection of the subatomic Higgs boson particle in 2012 on the Large Hadron Collider involved a million-to-one risk of being incorrect. However, this measurement can signal no more “Big Rip” models. which have equations of state more negative than one. In such models, the universe would expand ceaselessly at an ever-increasing rate, eventually tearing away 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 DES results suggest that our recent techniques will prove useful in future supernova experiments ESA’s Euclid mission (launched July 2023) and the brand new Vera Rubin Observatory in Chile. This observatory should soon use the telescope to take its first image of the sky after construction is accomplished, providing insight into its capabilities.
Next-generation telescopes could detect 1000’s more supernovae, helping us make recent measurements of the equation of state and shedding much more light on the character of dark energy.
