Good Authors List For nearly a century, astronomers have known that our universe is expanding. For decades, scientists have predicted that this expansion will slow down due to gravity. However, that all changed in the 1990s, when astronomers realized that the universe was not only expanding, but expanding at an accelerated rate, like an out-of-control train going downhill. The universe is literally blowing itself apart.
The main culprit for this expansion is a phenomenon called dark energy. This invisible, undetectable material is actually a gravity-defying force that pushes distant galaxies out of the way, making empty space even more empty. While the scientific community believes in the existence of dark energy, this energy is so weak – equivalent to only a few protons per cubic meter – that it is very difficult to determine its properties. But after a decade of hard work, astronomers have just released very precise measurements of the amount of dark energy that has existed over the past 9 billion years.
The Dark Energy Survey (DES) is a collaborative project of astronomers who used powerful telescopes in Chile to scan about one-eighth of the sky in search of supernovae. A supernova is the ** of a star that causes flashes so bright that it can be seen in billions of light-years. While there are several different kinds of supernovae, there is one particular supernova – called "sn-ia" – that is very special. SN-IA supernovae are all very similar, meaning they all produce roughly the same amount of light. Given that objects farther away appear fainter than nearby objects, astronomers can compare the brightness of a supernova in a telescope to its original brightness and use this information to determine how far away the supernova is from Earth.
Given that light travels at a fixed speed, knowing how far away something is can tell us how old it is. After all, light from objects farther away takes longer to reach Earth. Thus, by observing objects that are getting farther and farther away, astronomers actually have a time machine. Nearby galaxies tell us about the expansion of the universe now, while distant objects tell us what happened in the distant past.
Astronomers can also image galaxies where these supernovae occur to determine the spectrum of light they emit. Due to the Doppler effect, galaxies farther away from Earth will appear redder than at rest, and redness is related to the speed of the galaxy. (The Doppler effect mentioned here is visually equivalent to a change in the tone of a train's whistle as it passes.)
Scientists can combine distance measurements with velocity measurements to calculate the expansion history of the universe – which is how the first observations of the accelerating expansion of the universe were made in 1998.
The initial measurements used only 52 supernovae to discover them. Recently, DES used about 1,500 supernovae for new measurements. The team also used advanced AI technology to ensure that the supernova it sees is the desired SN-IA type. The result is a huge step forward in the understanding of dark energy.
Scientists have known for a long time that dark energy currently accounts for about two-thirds of the energy in the universe. Whether this ratio is a constant is still an open question. It is here that the situation becomes complicated. According to the currently accepted theory of the universe, what does not change is the density of dark energy. As the volume of the universe increases, so does the proportion of the universe made up of dark energy.
Previous measurements have shown that the density of dark energy is constant, but these early measurements have some uncertainties that lead to uncertainty in our understanding of the evolution of the universe. Precisely determining the density of dark energy will have a profound impact on cosmological theory.
If the density of dark energy in the universe is constant, then the theoretical parameter represented by the letter w should be equal to minus 1 (w = -1). When DES scientists used their data to measure this parameter, they found that the value was (w = -0.).80), but the uncertainty range is -066 to -096。The difference between the and measurements is about the same size as the uncertainty, which means that the dark energy density is likely to be constant.
DES isn't the only group focusing on the amount of dark energy. When they combined their measurements with those of Planck's group's earlier measurements, the results were more precise: w = -0955 with an uncertainty range of -0923 to -0992。
On top of that, the measurements were very close to each other, leading scientists to conclude that the dark energy density could be constant, but the small residual differences meant they weren't entirely certain. They will continue to review their data and combine it with other measurements to refine their results.
Dark energy density is one of the most important parameters for the future evolution of the universe: whether the expansion will continue to accelerate as before, or whether the acceleration will slow down or accelerate. Future measurements, such as Vera CThe measurements planned by the Rubin Observatory will help to determine this important measurement.