Measuring Dark Energy Just Got Way More Precise — Dare to Know

Measuring dark energy has always relied on supernovas. Find out about a more accurate technique and how it sheds light on this and other mysteries.

Every once in a while, a scientist makes a discovery that sets the whole scientific community on its head. Darwin did it with evolution. Einstein did with his theory of general relativity and Heisenberg did it with the uncertainty principle.

Thomas Kuhn called them “paradigm shifts.” Peers don’t always welcome them when they first come out because they disrupt a lot of people’s worldviews and ways of working in the physical sciences. Still, if they’re valid, they gain acceptance, especially with the next generation.

Two research teams came up with a milestone paradigm shift in cosmology in 1998. They were called the Supernova Cosmology Project and the High-Z supernova search team.

Researchers were Looking at Type Ia Supernovae

Both groups of researchers were looking at type Ia supernovae (exploded massive stars), to study the expansion of the Universe. Cosmologists had established the increasing size of the Universe with the discovery of the cosmic microwave background in 1965.

These teams were hoping to understand the expanding universe in more detail. They chose to use these supernovas because they all burn at very close to the same brightness.

This stability makes them helpful “cosmic rulers” for measuring large scale distances in space. The two research teams observed the redshift from supernovas. That enabled them to determine how much the Universe had expanded since the supernova’s explosion took place.

They Indicated that the Universe Was Expanding

Nobody was more surprised than the astronomers themselves with the results. They indicated that the Universe was expanding at an accelerating rate.

The expansion is due to the energy released by the big bang. In the vacuum of space, momentum should be driving the growth of the Universe.

You would expect the expansion to gradually slow down due to the effects of gravity from all the matter in the Universe. If the momentum is so intense that gravity isn’t a factor, you might expect the expansion to be at a constant rate.

They Detected that the Universe is Speeding Up

The scientists didn’t observe any of that. Instead, they detected that the expansion of the Universe is speeding up.

To get a moving body to accelerate, you have to add some sort of force or energy to its momentum. That’s why you have to step on the gas pedal in your car to make it go faster-your engine needs more fuel.

In the same way, for the Universe to have an accelerating expansion, it must be taking in energy in some hidden way. Scientists call this mysterious force “dark energy.”

Last week, the journal Physical Review Letters published a new study from a research team at the University of Portsmouth. The study shares the team’s discovery of a more precise way of measuring dark energy and the expansion of the Universe.

New Approach Involves Looking at Cosmic Voids

The researchers’ new approach involves looking at large, expanding bubbles of space that contain very few galaxies. They’re called “cosmic voids.”

Along with cosmic voids, the team also looks at the faint imprints of early universe sound waves they can see in the way baryonic matter affects galaxy clustering. These imprints are called baryon acoustic oscillations (BAO).

Combining these two phenomena gives the cosmologists a much more accurate cosmic ruler. They can use it to measure the acceleration more precisely and get a better handle on measuring dark energy’s effects.

“Galaxy Surveys to Pin Down the Amount of Dark Energy”

Lead author Dr. Seshadri Nadathur, said: “This result shows the power of galaxy surveys to pin down the amount of dark energy and how it evolved over the last billion years. We’re making really precise measurements now, and the data is going to get even better with new surveys coming online very soon.”

Using the Sloan Digital Sky Survey, the team studied over a million galaxies and quasars collected by the survey over the past ten years. Their results confirm that dark energy exists as a cosmological constant and that the shape of the Universe is virtually flat.

The shape of the Universe is controversial. The Planck Space Observatory satellite had found that the Universe has a curved shape, based on its measurements of the cosmic microwave background (CMB).

Measuring the Hubble Constant Gets Two Different Answers

We’ve discussed the Hubble Constant in a couple of stories in these pages. Cosmologists are frustrated by the fact that when they use two methods to measure the rate at which the Universe expands, they get two different answers.

This new technique has the added benefit of being able to measure the Hubble Constant more accurately than ever before. That may put this discrepancy to rest once and for all.

Team member Dr. Florian Beutler explained, “ “We see tentative evidence that data from relatively nearby voids and BAO favour the high Hubble rate seen from other low-redshift methods, but including data from more distant quasar absorption lines brings it in better agreement with the value inferred from Planck CMB data.”

Measurement is Fundamental to Science

Measurement is fundamental to science. If you’re going to base your understanding of the world on facts and evidence, you need to be able to quantify things.

This research team has built a better yardstick for measuring dark energy. The Portsmouth team’s results are going to set a few things straight, including the existence of dark energy and the shape of our Universe.

It’s not a massive paradigm shift like dark matter’s discovery way. Still, it’s going to make quite a few ideas redundant or obsolete, and that’s going to ruffle a few feathers in academia.

Going to Ruffle a Few Feathers in Academia

We owe the team our gratitude for their courage. The researchers are playing a pivotal role in pinning down the details in the story of the Universe.

We all need a science-based story that we can tell one another about our place in the cosmos. This new quantitative method gives us the tools we need to learn why the expansion of our Universe accelerates and what that means for all of us.

We always have more to learn if we dare to know.
Learn more:
New Test of Dark Energy and Expansion from Cosmic Structures
Testing Low-Redshift Cosmic Acceleration with Large-Scale Structure
The 5 Big Questions We Need Cosmology to Answer
Hubble Constant: How Fast Are We Going?
Dark Energy Mystery Solved by Fixing the Math?

Originally published at https://daretoknow.ca on June 8, 2020.