Expansion rate of the universe measured out to 11 billion years ago using dark energy

In an extraordinary feat of cosmic exploration, astronomers are embarking on a five-year journey to create the most extensive 3D map of the cosmos ever conceived. The Dark Energy Spectroscopic Instrument (DESI) is at the forefront of this endeavor, and its initial findings are already reshaping our understanding of the universe.

Measuring the universe’s expansion with dark energy

Using spectra from nearby galaxies and distant quasars, astronomers from the DESI collaboration have measured the expansion history of the universe with unparalleled precision.

By analyzing the survey’s first-year data, which contains the largest extragalactic spectroscopic sample ever collected, researchers have achieved a precision better than 1% over the last 11 billion years.

“We’re incredibly proud of the data, which have produced world-leading cosmology results,” said Michael Levi, DESI director and LBNL scientist.

“So far we’re seeing basic agreement with our best model of the Universe, but we’re also seeing some potentially interesting differences that could indicate dark energy is evolving with time,” Levi continued.

Mapping the cosmos at an unprecedented rate

DESI’s ability to collect light from millions of galaxies across more than a third of the entire sky is truly remarkable.

By breaking down the light from each galaxy into its spectrum of colors, DESI can determine how much the light has been redshifted, or stretched to a longer wavelength, by the expansion of the Universe during its billions of years of travel before reaching Earth.

Equipped with 5000 tiny robotic ‘eyes,’ DESI can perform this measurement at an unprecedented rate. In its first year alone, DESI surpassed all previous surveys of its kind in terms of quantity and quality, bringing new insight to one of the biggest mysteries in physics: dark energy.

“The DESI instrument has transformed the Mayall Telescope into the world’s premier cosmic cartography machine,” says Pat McCarthy, Director of NOIRLab.

“The DESI team has set a new standard for studies of large-scale structure in the Universe. These first-year data are only the beginning of DESI’s quest to unravel the expansion history of the Universe and they hint at the extraordinary science to come,” McCarthy concluded.

Baryon Acoustic Oscillations: The cosmic ruler

DESI’s first-year data have allowed astronomers to measure the expansion rate of the universe out to 11 billion years in the past, when the universe was only a quarter of its current age.

They accomplished this feat by using a feature of the large-scale structure of the universe called Baryon Acoustic Oscillations (BAO).

BAO are the leftover imprint of pressure waves that permeated the early Universe when it was nothing but a hot, dense soup of subatomic particles.

As the universe expanded and cooled, the waves stagnated, freezing the ripples in place and seeding future galaxies in the dense areas.

With DESI’s unique ability to map millions of objects both near and far, the BAO pattern can be used as a cosmic ruler.

By mapping nearby galaxies and distant quasars, astronomers can measure the spread of the ripples across several periods of cosmic history to see how dark energy has stretched the scale over time.

DESI’s quest continues on its 5-year odyssey

While the expansion history of the universe may be more complex than previously imagined, confirmation of this must await the completion of the DESI project.

By the end of its five-year survey, DESI plans to map over 3 million quasars and 37 million galaxies. As more data are released, astronomers will further improve their results.

“This project is addressing some of the biggest questions in astronomy, like the nature of the mysterious dark energy that drives the expansion of the Universe,” says Chris Davis, NSF program director for NOIRLab. “The exceptional and continuing results yielded by the NSF Mayall telescope with DOE DESI will undoubtedly drive cosmology research for many years to come.”

“We are delighted to see cosmology results from DESI’s first year of operations,” said Gina Rameika, associate director for High Energy Physics at the Department of Energy. “DESI continues to amaze us with its stellar performance and how it is shaping our understanding of dark energy in the Universe.”

Dark energy and the expansion of the universe

A main component of the DESI project, dark energy, a perplexing and invisible force, permeates the universe and plays a crucial role in its accelerating expansion.

Scientists first discovered evidence for dark energy in the late 1990s when they observed that distant supernovae were dimmer than expected, suggesting that the universe’s expansion was speeding up rather than slowing down.

Nature of dark energy

Despite its significant influence on the universe’s evolution, the nature of dark energy remains one of the greatest enigmas in modern cosmology. Researchers have proposed several theories to explain its existence, including:

• The cosmological constant: This theory suggests that dark energy is an inherent property of space itself, with a constant density throughout the universe.

• Scalar fields: Some scientists propose that dark energy arises from scalar fields, such as quintessence, which can vary in space and time.

• Modified gravity: This theory posits that dark energy is not a separate entity but rather a manifestation of modifications to Einstein’s theory of general relativity on cosmic scales.

Dark energy’s impact on the universe

Dark energy’s presence has a profound impact on the universe’s evolution and ultimate fate. As dark energy continues to drive the universe’s accelerating expansion, it counteracts the attractive force of gravity. This has several consequences:

• Galaxy clusters: Dark energy’s repulsive force makes it more difficult for galaxy clusters to form and grow over time.

• The Universe’s fate: If dark energy continues to dominate, the universe may eventually experience a “Big Rip,” where galaxies, stars, and even atoms are torn apart by the ever-increasing expansion.

• The observable Universe: As the universe expands faster, more distant objects will move beyond our cosmic horizon, limiting the observable universe from our perspective.

DESI, dark energy, and the future of cosmology

In summary, the Dark Energy Spectroscopic Instrument (DESI) has embarked on an awe-inspiring journey to unravel the mysteries of the universe.

With its unparalleled precision, innovative technology, and the tireless efforts of an international collaboration, DESI is reshaping our understanding of dark energy and the cosmos as a whole.

As the survey progresses, astronomers eagerly anticipate the stunning discoveries that will emerge from DESI’s ever-expanding 3D map of the Universe.

This monumental endeavor showcases the power of human curiosity and scientific advancement while promising to redefine our place in the grand cosmic tapestry for generations to come.

The full study was published in the journal Current Biology.

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