Exploring the Mystery of Our Expanding Universe

Scientists may soon uncover new insights about some of the most mysterious phenomena in our universe with the help of the newly launched Euclid mission. Built and managed by the European Space Agency, Euclid will use a suite of instruments developed, in part, by NASA's Jet Propulsion Laboratory to explore the curious nature of dark energy and dark matter along with their role in the expansion and acceleration of our universe.

Read on to learn how the Euclid mission will probe these cosmological mysteries. Then, find out how to use demonstrations and models to help learners grasp these big ideas.

No greater question in our universe promotes wonder in scientists and non-scientists alike than that of the origin of our universe. The Euclid mission will allow scientists to study the nearly imperceptible cosmic components that may hold exciting answers to this question.

Edwin Hubble's observations of the expanding universe in the 1920s marked the beginnings of what's now known as the big-bang theory. We've since made monumental strides in determining when and how the big bang would have taken place by looking at what's known as cosmic background radiation using instruments such as COBE and WMAP in 1989 and 2001, respectively. However, there's one piece of Hubble's discovery that still has scientists stumped: our universe is not only expanding, but as scientists discovered in 1998, that expansion is also accelerating.

How can this be? It makes intuitive sense that, regardless of the immense force of the big bang that launched all matter across the known universe 13.8 billion years ago, that matter would eventually come to a rest and possibly even start to collapse. Instead, it's as if we've dropped a glass onto the ground and discovered that the shards are flying away from us faster and faster into perpetuity.

Scientists believe that answers may lie in two yet-to-be-understood factors of our universe: dark matter and dark energy. Dark matter is unlike the known matter we experience here on Earth, such as what's found on the periodic table. We can't actually see dark matter; we can only infer its presence. It has mass and therefore gravity, making it an attractive force capable of pulling things together. Amazingly, dark matter makes up roughly 27% of the known universe compared with the much more modest 5% of "normal matter" that we experience day to day. However, dark matter is extremely dilute throughout the universe with concentrations of 105 particles per cubic meter.

In opposition to the attractive force of dark matter, we have dark energy. Dark energy is a repulsive force and makes up roughly 68% of energy in the known universe. Scientists believe that the existence of dark energy and the amount of repulsion it displays compared with dark matter is what's causing our universe to not only expand, but also to expand faster and faster.

But to truly understand this mysterious force and how it interacts with both dark matter and normal matter, scientists will have to map barely detectable distortions of light traversing the universe, carefully measuring how that light changes over time and distance in every direction. As JPL Astrophysicist Jason Rhodes explains, “Dark energy has such a subtle effect that we need to survey billions of galaxies to adequately map it.”

And that's where Euclid comes in.

The European Space Agency and NASA each contributed to the development of the Euclid mission, which launched from Cape Canaveral Space Force Station in Florida on July 1. The spacecraft consists of a 1.2-meter (48-inch) space telescope and two science instruments: an optical camera and a near-infrared camera that also serves as a spectrometer. These instruments will provide a treasure trove of data for scientists of numerous disciplines, ranging from exoplanet hunters to cosmologists.

As Gisella de Rosa at the Space Telescope Science Institute explains, “The ancillary science topics we will be able to study with Euclid range from the evolution of the objects we see in the sky today to detecting populations of galaxies and creating catalogs for astronomers. The data will serve the entire space community.”

This graphic illustrates how cosmological redshift works and how it offers information about the universe’s evolution.

Credit: NASA, ESA, Leah Hustak (STScI) › Full image and caption

The cameras aboard Euclid will operate at 530-920 nanometers (optical light) and at 920-2020 nanometers (near infrared) with each boasting more than 576 million and 65 million pixels, respectively. These cameras are capable of measuring the subtle changes to the light collected from celestial objects and can determine the distances to billions of galaxies across a survey of 15,000 square degrees – one-third of the entire sky.

Meanwhile, Euclid's spectrometer will collect even more detailed measurements of the distance to tens of millions of galaxies by looking at redshift. Redshift describes how wavelengths of light change ever so slightly as objects move away from us. It is a critical phenomenon for measuring the speed at which our universe is expanding. Similar to the way sound waves change as a result of the Doppler effect, wavelengths of light are compressed to shorter wavelengths (bluer) as something approaches you and extended to longer wavelengths (redder) as it moves away from you. As determined by a Nobel Prize winning team of astronomers, our universe isn’t just red-shifting over time, distant objects are becoming redder faster.

Euclid will measure these incredibly minuscule changes in wavelength for objects near and far, providing an accurate measurement of how the light has changed as a factor of time and distance and giving us a rate of acceleration of the universe. Furthermore, Euclid will be able to map the relative densities of dark matter and normal matter as they interact with dark energy, creating unevenly distributed pockets of more attractive forces. This will allow scientists to identify minute differences in where the universe is expanding by looking at the way that light is altered or "lensed."

The multi-dimensional maps created by Euclid – which will include depth and time in addition to the height and width of the sky – will inform a complementary mission already in development by NASA, the Nancy Grace Roman Space Telescope. Launching in 2026, this space telescope will look back in time with even greater detail, targeting areas of interest provided by Euclid. The telescope will use instruments with higher sensitivity and spatial resolution to peer deeper into redshifted and faint galaxies, building on the work of Euclid to look farther into the accelerating universe. As Caltech’s Gordon Squires describes it: “We’re trying to understand 90% of our entire universe. Both of these telescopes will provide essential data that will help us start to uncover these colossal mysteries.”

The abstract concepts of the scope and origin of our universe and the unimaginable scale of cosmology can be difficult to communicate to learners. However, simple models and simulations can help make these topics more tangible. See below to find out how, plus explore more resources about our expanding universe.

• Article for Kids: What Is a Supernova?
• Article for Kids: What Is Dark Matter?
• Article: What Is Dark Energy?
• Article: Gravitational Lensing - Shining a Light on Dark Matter
• Facts & Figures: Euclid Mission - NASA
• Facts & Figures: Nancy Grace Roman Space Telescope

NASA's Universe of Learning materials are based upon work supported by NASA under award number NNX16AC65A to the Space Telescope Science Institute, working in partnership with Caltech/IPAC, Center for Astrophysics | Harvard & Smithsonian, and the Jet Propulsion Laboratory.