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Scientists have discovered that a mysterious pressure called "dark energy" accounts for about 68% of the total amount of energy contained in the cosmos, but until now, we do not know much more.
Exploring the nature of dark energy is one of the main reasons that NASA has built the wide-field infrared geodetic telescope (WFIRST), a space telescope whose measurements will help illuminate the puzzle. dark energy. With a better understanding of black energy, we will have a better sense of the past and the future evolution of the universe.
An expanding cosmos
Until the 20th century, most people believed that the universe was static and remained essentially unchanged for all eternity. When Einstein developed his theory of general relativity in 1915, describing how gravity acted in the tissue of space-time, he was surprised to find that this theory indicated that the cosmos had to either expand or be contract. He made changes to preserve a static universe, adding something that he called the "cosmological constant," even though there was no evidence of his reality. This mysterious force was supposed to counteract gravity to keep everything in place.
However, as the 1920s drew to a close, astronomer Georges Lemaitre and then Edwin Hubble made the surprising discovery that, with very few exceptions, galaxies were fighting over each other. The universe was far from static – it was swelling. Therefore, if we imagine rewinding this expansion, there must have been a time when everything in the universe was almost incredibly hot and close.
The end of the universe: fire or ice?
The Big Bang theory describes the expansion and evolution of the universe from this superhot, superdense initial state. Scientists have speculated that gravity would eventually slow down and possibly even reverse this expansion completely. If the universe contained enough material, gravity would outweigh the expansion and the universe would collapse into a fiery "Big Crunch".
Otherwise, the expansion would never end – the galaxies would grow further and further up to beyond the edge of the observable universe. Our distant descendants might not be aware of the existence of other galaxies because they would be too far away to be visible. Much of modern astronomy could one day be reduced to a mere legend, as the universe gradually fades into a icy black.
The universe does not just grow – it speeds up
Astronomers measured the rate of expansion using ground-based telescopes to study relatively close supernova explosions. The mystery intensified in 1998 when supernova observations further away from the Hubble Space Telescope showed that the universe had actually developed more slowly in the past than today. The expansion of the universe does not slow down because of gravity, as everyone thought. It speeds up.
Fast forward to today. Although we still do not know what is causing the acceleration, it has been given a name: black energy. This mysterious pressure has remained unknown for so long because it is so weak that gravity dominates it on the human scale, planets and even the galaxy. It is present in the room with you as you read, in your very body, but gravity neutralizes it so that you do not fly out of your seat. It is only on an intergalactic scale that the dark energy becomes perceptible, acting as a kind of weak opposition to gravity.
What is black energy?
What is black energy? We know more than we know, but theorists are looking for several possible explanations. The cosmic acceleration could be caused by a new energetic component, which would require some adjustments from Einstein's gravity theory – perhaps the cosmological constant, which Einstein called his biggest mistake , is real after all.
Alternatively, Einstein 's gravity theory can collapse on the cosmological scale. If this is the case, the theory will have to be replaced by a new one integrating the observed cosmic acceleration. The theorists still do not know what the right explanation is, but WFIRST will help us find out.
WFIRST will illuminate black energy
Previous missions have collected clues, but so far, they have not yielded results that strongly favor one explanation over another. With the same resolution as Hubble cameras, but with a field of view 100 times larger, WFIRST will generate large images of the universe never seen before. The new mission will advance the exploration of the mystery of dark energy in a way that other telescopes can not do by mapping the structure and distribution of matter in the cosmos and measuring a large number of distant supernovae. The results will show how dark energy is acting in the universe and if and how it has changed in cosmic history.
The mission will use three survey methods to search for an explanation of dark energy. The high latitude spectroscopic survey will measure distances and precise positions of millions of galaxies using a "standard rule" technique. Measuring how the distribution of galaxies varies with distance will give us a window on the evolution of dark energy over time. This study will link the distances of galaxies to the echoes of sound waves just after the Big Bang and test Einstein 's theory of gravity on the age of the universe.
The high latitude imaging survey will measure the shapes and distances of multitudes of galaxies and clusters of galaxies. The immense gravity of massive objects distorts the space-time and gives the impression that more distant galaxies are distorted. Observing the degree of distortion allows scientists to deduce the distribution of mass in the cosmos. This includes all the material we can see directly, such as planets and stars, as well as dark matter – another dark cosmic mystery that is visible only through its gravitational effects on normal matter. This survey will provide an independent measure of the growth of the large scale structure in the universe and how black energy has affected the cosmos.
WFIRST will also investigate an explosive star type, based on observations that led to the discovery of accelerated expansion. Type Ia supernovae occur when a white dwarf star explodes. Type Ia supernovae usually have the same absolute brightness at their maximum, making them "standard candles". This means that astronomers can determine how far they are by observing their brightness from the Earth – and the farther away they are, the lower their intensity. Astronomers will also examine the particular wavelengths of supernova light to determine how fast the dying stars are moving away from us. By combining distances and brightness measurements, scientists will see how dark energy has evolved over time, allowing the results of two surveys to be verified under high latitude.
"The WFIRST mission combines these three methods in a unique way, it will lead to a very robust and rich interpretation of the effects of dark energy and allow us to make a precise statement about the nature of dark energy", said Olivier Doré, a researcher at NASA's Jet Propulsion Laboratory in Pasadena, California, and responsible for the team planning the first two methods of investigation with WFIRST.
Discovering how black energy has affected the expansion of the universe in the past will better understand how it will influence expansion in the future. If this continues to accelerate the expansion of the universe, we could be doomed to experience a "big tear". In this scenario, dark energy would eventually become dominant over the fundamental forces, resulting in the destruction of everything that is currently linked – galaxies, planets, men. The exploration of dark energy will allow us to study and even predict the fate of the universe.
For more information on WFIRST, visit: www.nasa.gov/wfirst
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