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Dark energy seems to make up abut 70% of the universe, but it’s also a scientific mystery. Find out how new discoveries from the Dark Energy Spectroscopic Instrument (DESI) may help explain our universe’s history and future.

By David Morton RintoulPublished about a month ago 4 min read

As the week of the total solar eclipse in this part of the world winds down, I’m reminded of the eerie but sublime darkness and sudden cold we experienced that afternoon.

The dark and stargazing tend to go together, even when the Sun is involved. For example, researchers using the Dark Energy Spectroscopic Instrument (DESI) released the largest and most precise survey of our Universe’s history ever conducted this week.

Dark energy is a relatively recent idea, and it’s a puzzle. At the beginning of the 20th century, most cosmologists, including Einstein, believed that the universe was constant and unchanging.


Then, Edwin Hubble discovered that there were other galaxies. What’s more, those galaxies were all moving away from each other, which means that space, or the entire universe, is expanding.

That led to other discoveries like the big bang, but in this edition, we’re going to focus on its implications for dark energy. In 1998, two research teams, the Supernova Cosmology Project led by Saul Perimutter and the High-Z Supernova Search Team lead by Brian Schmidt, came to realize that the universe was not only expanding, but that its expansion is accelerating.

To make something accelerate, we usually have to add energy or apply a force to it in some way. Yet, the scientists couldn’t identify the energy behind this newly discovered acceleration.


They started calling it dark energy, and scientists still haven’t worked out what it entails. What makes this puzzle even more vexing is that, based on its effects, dark matter seems to make up about 70% of the universe’s total energy density.

The US Department of Energy’s Lawrence Berkeley National Laboratory built and mounted DESI onto the 4-meter Mayall Telescope at the Kitt Peak Observatory in Arizona. It’s an international collaboration involving more than 900 researchers working at over 70 institutions worldwide.

Dr. Michael Levi has been an astronomer for the past four decades. He’s currently serving as the director of the DESI experiment.


Using DESI, professor Levi and his team have created the largest 3D map of the universe ever made. They’ve also measured the universe’s expansion with unprecedented accuracy.

“We’re incredibly proud of the data, which have produced world-leading cosmology results and are the first to come out of the new generation of dark energy experiments,” Professor Levi said.

The team began installing DESI in February 2018 using components from all over the world. They were assembled at the Berkeley Lab and mounted at Kitt Peak.


DESI uses 5,000 tiny robotic positioners, each of which connects to an optical fibre. Astronomers use the fibres to capture the light from various galaxies and quasars.

The heart of DESI is its spectrograph, which uses the light from the optical fibres to produce each observed object’s spectrum. Analyzing the spectrum tells the team how red-shifted the object’s light has become on its travels, which in turn tells them the distance between Earth and the object.

Over its first year of operation, the DESI instrument came up with the world’s largest map of the cosmos by compiling and combining all of those distance measurements. The huge sample of observed objects also enabled the team to measure the expansion history of our universe with better than 1% precision.


“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 that dark energy is evolving with time,” Professor Levi said. “Those may or may not go away with more data, so we’re excited to start analyzing our three-year dataset soon.”

The scientists measure the universe’s history by bumpy spots made by hydrogen and helium nuclei in the early universe. Scientists call them Baryon Acoustic Oscillations (BAOs) and by mapping them, the team could determine how fast the universe was expanding during seven historical periods.

The data variations that Professor Levi mentioned might suggest something very intriguing. In the three most recent periods studied, dark energy doesn’t seem to be constant, which means that the universe’s acceleration may vary over time.


Just as over 30 million people watched this week’s eclipse because of humanity’s passionate curiosity, wonder and awe about the universe and our place within it, understanding dark energy helps scientists piece together our universe’s history and future.

A new story is emerging that’s advancing human knowledge and answering some of our most timeless and fundamental questions. Understanding our universe’s expansion and the energy that drives it might unlock a number of mysteries.

“We are in the golden era of cosmology, with large-scale surveys ongoing and about to be started, and new techniques being developed to make the best use of these datasets,” said Arnaud de Mattia, co-leader of DESI’s data interpretation group. “We’re all really motivated to see whether new data will confirm the features we saw in our first-year sample and build a better understanding of the dynamics of our universe.”

We always have more to learn if we dare to know.

Learn more:

First Results from DESI Make the Most Precise Measurement of Our Expanding Universe

Baryon Acoustic Oscillations from Galaxies and Quasars

Euclid Space Telescope Will Explore Dark Energy

Dark Energy Measured More Precisely Than Ever

Dark Energy Mystery Solved by Fixing the Math


About the Creator

David Morton Rintoul

I'm a freelance writer and commercial blogger, offering stories for those who find meaning in stories about our Universe, Nature and Humanity. We always have more to learn if we Dare to Know.

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