The enigma of our dark Universe has baffled both astronomers and theorists for nearly a century. Even with the most advanced telescopes, what we can see on a clear night is just a tiny fraction of the vast cosmos.

Dark matter, comprising 20% of the universe, does not emit or absorb light but exerts gravitational attraction on normal matter. Dark Energy, responsible for the inexplicable acceleration of our expanding universe, accounts for a staggering 76% of the cosmos. In contrast, normal matter, which includes stars, planets, and living organisms, makes up less than 4% of the known universe.

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Fortunately, a mission called Euclid is poised to shed light on this mysterious realm.

The European Space Agency’s (ESA) Euclid Mission, equipped with NASA’s infrared detectors, is scheduled for launch next month. While it may not have all the answers, this 1.2-meter telescope mission will provide valuable data for theorists to analyze.

What makes this telescope so remarkable?

According to ESA, Euclid will map the large-scale structure of the universe over the past 10 billion years. This mission will image 1.5 billion galaxies with the same resolution as the Hubble Space Telescope. It will also collect spectroscopic redshift data on around 50 million galaxies.

Euclid’s science instruments include one that utilizes visible light and another that employs infrared light, as explained by U.S. Euclid science lead Jason Rhodes. An optical element called a ‘dichroic’ splits incoming light into visible and infrared components, directing them to the appropriate instruments. Both instruments contain high-resolution cameras capable of simultaneous sky observation and data collection.

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Assuming a successful launch in July, Euclid’s six-year science mission will commence in December from L2, a gravitationally stable position about a million miles from Earth. It will survey 15,000 square degrees of the sky, providing an extensive atlas with detailed resolution in visible and near-infrared wavelengths.

What major technical challenge does Euclid face?

Euclid’s focus on dark energy involves statistical studies, explains Jason Rhodes. Even a slight systematic offset in the measurements of shapes or distances could bias the results. This is why the decision was made to employ a space telescope, located above Earth’s atmosphere, for these crucial observations.

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The hope is that Euclid’s precise measurements will narrow down the margin of error in current estimations, potentially ruling out certain causes of the accelerating expansion and bringing us closer to understanding the essence of dark energy, Rhodes adds.

Euclid’s measurements are two-fold: first, it assesses how galaxies are affected by dark matter, and then it utilizes these measurements to gain a better understanding of dark energy.

As René Laureijs, the Euclid Project Scientist at ESA ESTEC in The Netherlands points out, the distortion observed in the shape of galaxies hints at the influence of dark matter. From the distribution of dark matter, researchers can derive the accelerating expansion of the universe.

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The precision of our knowledge regarding the clustering of galaxies is such that we can determine the presence of dark energy in the universe, states Hans Winther, a Euclid science consortium team member from the University of Oslo. Thus, regardless of distance measurements to Type 1a supernovae, we possess substantial evidence supporting the accelerated expansion of the universe.

How does dark energy influence the large-scale structure of the universe?

To comprehend the nature of dark energy, we study the universe’s large-scale structure, explains Hans Winther. Structure formation involves the interplay between gravity, the attractive force between objects, and the universe’s expansion. It’s essentially a competition between these two factors.

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In 1917, before our understanding of the big bang theory and universal expansion, Einstein temporarily incorporated what he called the Cosmological Constant (a repulsive force) into his theory of general relativity. This addition aimed to account for a static universe and counterbalance gravity’s impact on ordinary matter. However, Einstein promptly discarded this aspect of his equations after observational evidence of an expanding universe emerged, known as the Hubble expansion.

By the late 1990s, theorists resurrected the cosmological constant as quantum mechanics’ repulsive force known as vacuum energy. In 1997 and 1998, two Nobel Prize-winning teams established that approximately five to seven billion years after the big bang, our universe mysteriously began accelerating its expansion.

In the present era, the cosmological constant has become a temporary solution, serving as an ad hoc fix to explain dark energy’s driving force. As we strive to better comprehend the nature of dark energy, it is possible that the universe contains vacuum energy embedded within the fabric of spacetime, causing this acceleration. The question remains: why did dark energy’s influence only become apparent billions of years after the big bang?

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How is the value of the cosmological constant calculated?

University of Oslo theoretical physicist David Mota, a Euclid science consortium team member, explains that the value we measure represents the amount of dark energy or cosmological constant prevalent in our current universe. There is a significant discrepancy between the value that physics calculations predict and the value observed astronomically, Mota notes, with the vacuum energy calculated to be up to 120 times larger than the measured value.

Regarding the dark theories, which one poses the greatest puzzle?

I would place my bet on dark energy because our knowledge about it is even more limited than our understanding of dark matter, despite it being a more dominant component of the universe, states Jason Rhodes. In the distant past, dark energy played a negligible role, but in the future, it will dominate, with dark matter becoming a relatively minor element. The nature of dark energy will ultimately determine the fate of the universe.

Mota takes it a step further, suggesting that all the theories currently defining our understanding of the cosmos are likely flawed. He observes that from Newton to Einstein, humanity has progressed in discerning the curvature of space and time. However, he hopes that in a million years, our species will adopt different mathematical and physical theories. At present, we are merely taking our first tentative steps.

 

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