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WFIRST will help reveal the fate of the universe



Scientists have found that a mysterious pressure called "dark energy" represents about 68% of the total energy content in space, but we don't know much about it yet.

Exploring the Nature of Dark Energy is one of the main reasons NASA is building a Wide Range Infrared Telescope (WFIRST), a space telescope whose measurements will help illuminate a dark energy puzzle. With a better understanding of the dark energy, we will have a better sense of the past and future development of the universe.

Expanding Space

By the 20th century, most people believed that the universe was static, remaining essentially unchanged throughout eternity. When Einstein developed his general theory of relativity in 1915, describing how gravity acts on the fabric of space-time, he is perplexed to find that the theory shows that Space must either expand or shrink. He made changes to preserve the static universe, adding something he called a "cosmological constant", although there was no evidence that it actually existed. This mysterious force had to counteract gravity to keep everything in place.

However, as the 1

920s approached, astronomer Georges Lemaytre and then Edwin Hubble made the startling discovery that, with very few exceptions, galaxies were racing far apart. The universe was far from static – it was ballooning out. Therefore, to imagine rewinding this extension, there must have been a time when everything in the universe was almost impossible to hot and close to one another.

The End of the Universe: Fire or Ice?

The Big Bang theory describes the expansion and evolution of the universe from this initial super-super-dense state. Scientists have theorized that gravity will eventually slow down and probably even reverse this extension. If the universe has enough matter in it, gravity will overcome expansion and the universe will collapse into a fiery "Great Crisis."

If not, expansion will never end – galaxies will grow farther and farther as they cross the edge of the observable universe. Our distant descendants may not have knowledge of the existence of other galaxies as they would be too far away to be visible. Much of modern astronomy can one day be reduced to a mere legend as the universe gradually fades to icy black.

The universe is not simply expanding – it is accelerating

Astronomers measure the rate of expansion using ground-based telescopes to study relatively near supernova explosions. The mystery escalated in 1998, when observations of the Hubble Space Telescope on farther supernovae helped show that the universe is actually expanding more slowly in the past than it is today. The expansion of the universe is not slowing down due to gravity, as everyone thought. It is accelerating.

Fast forward to today. Although we do not yet know exactly what causes acceleration, it is given the name – Dark Energy. This mysterious pressure remains undetected for so long because it is so weak that gravity overwhelms it on a scale of humans, planets and even the galaxy. It is present in the room with you as you read, within your body itself, but its gravity counteracts that you do not fly out of place. It is only on an intergalactic scale that dark energy becomes noticeable, acting as something like a slight counter to gravity.

What is Dark Energy?

What exactly is dark energy? It is not known more than known, but theorists pursue several possible explanations. Space acceleration can be caused by a new energy component that will require some adjustments to Einstein's theory of gravity – perhaps the cosmological constant that Einstein called his biggest fallacy is real after all.

Alternatively, Einstein's theory of gravity can be decomposed on a cosmological scale. In this case, the theory will have to be replaced with a new one, incorporating the space acceleration we have observed. Theorists still don't know what the right explanation is, but WFIRST will help us understand.

WFIRST will illuminate dark energy

Previous missions have collected some clues, but so far they have not produced results that are highly favorable to one explanation over another. With the same resolution as Hubble's cameras, but a field of view 100 times larger, WFIRST will generate never-before-seen large images of the universe. The new mission will encourage the exploration of the mystery of dark energy in ways other telescopes cannot, by mapping how matter is structured and distributed in space, as well as by measuring a large number of distant supernovae. The results will show how dark energy works in the universe and whether and how it has changed throughout space history.

The mission will use three research methods to seek an explanation for dark energy. High latitude spectroscopy will measure the exact distances and positions of millions of galaxies using the "standard ruler" technique. Measuring how the distribution of galaxies varies with distance will give us a window into the evolution of dark energy over time. This study will link the distances of galaxies to the echo of sound waves immediately after the Big Bang and test Einstein's theory of gravity over the epoch of the universe.

The study of high latitude imaging will measure the shapes and distances of sets of galaxies and galactic clusters. The huge gravity of massive objects distorts space and time and causes distorted galaxies to appear. Observing the degree of distortion allows scientists to make a conclusion about the distribution of mass throughout space. This includes all matter that we can see directly, like planets and stars, as well as dark matter – another dark cosmic mystery that is only visible through its gravitational effects on normal matter. This study will provide an independent measurement of the growth of a large-scale structure in the universe and how dark energy has affected the cosmos.

WFIRST will also investigate one type of exploding star, based on observations leading to the discovery of accelerated expansion. Type Ia supernovae arise when a white dwarf star breaks out. Type Ia supernovae typically have the same absolute brightness at their peak, making them so-called "standard candles". This means that astronomers can determine how far they are by seeing how bright they look from Earth – and the farther they are, the smokier they appear. Astronomers will also look at the specific wavelengths of light coming from supernovae to determine how fast the dying stars are moving away from us. Combining distances with brightness measurements, scientists will see how dark energy has evolved over time, providing a cross-check with both large-scale studies.

"The WFIRST mission is unique in combining these three methods. This will lead to a very sound and rich interpretation of the effects of dark energy and will allow us to make a strong statement about the nature of dark energy, "said Olivier Dore, a researcher at NASA's Jet Propulsion Laboratory in Pasadena, California, and a team leader, planning the first two methods of testing with WFIRST.

Discovering how dark energy has influenced the expansion of the universe in the past will shed some light on how it will affect expansion in the future. If it continues to accelerate the expansion of the universe, we may be destined to experience the "Big Break". In this scenario, dark energy will eventually become dominant over the core forces, causing everything currently linked together – galaxies, planets, humans – to disintegrate. Exploring dark energy will allow us to explore and possibly even predict the fate of the universe.

For more information on WFIRST, visit: www.nasa.gov/wfirstgether19659023SensePlease follow SpaceRef on Twitter and like us on Facebook.


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