Model the Expanding Universe

Students learn about dark matter and dark energy, as well as the role they play in the expansion of the universe. Then, they will model the expanding universe using balloons.

• Gather enough materials to provide each group with a full set of materials.
• Have extra balloons available as some will pop.
• Consider incorporating the demo How Do We See Dark Matter? in Step 2 of the Procedures section to help students understand how scientists know dark matter exists.

Since the moment of the big bang nearly 14 billion years ago, the universe has been expanding. Astronomers first measured this phenomenon in the 1920s and have been refining their measurements ever since. Now scientists know that the universe is not only expanding, but also the rate at which it is expanding is increasing. Before this discovery, scientists had believed that gravity from matter within the universe would eventually slow the expansion.

The matter that makes up the observable universe does not have enough mass to account for the accelerating expansion of the universe. Cosmologists – people who study the origin and evolution of the universe – believe that in addition to the matter we can see, such as planets, moons, dust, and stars, the universe contains dark energy and dark matter.

More is unknown than is known about dark energy and dark matter, but their presence can be inferred by the way they interact with the visible universe. We can determine how much dark energy exists by looking at how it influences the accelerating expansion of the universe. When it comes to dark matter, we can look at the gravitational effects on galaxy formation that can’t be explained by visible matter alone.

Based on theoretical models of the universe, dark matter accounts for approximately 27% of the universe and dark energy makes up 68%. Ordinary matter, like what is found on the periodic table, accounts for less than 5% of the total mass of the universe.

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This animated pie chart shows rounded values for the three known components of the universe: visible matter (5%), dark matter (27%), and dark energy (68%). Credit: NASA's Goddard Space Flight Center | › Full video and caption

There are two complementary space missions seeking to explore the mysteries of dark energy, dark matter, and the accelerating expansion of the universe. The Euclid mission, a European Space Agency (ESA) space telescope with important contributions from NASA, is designed to study the expansion of the universe. Its findings, along with the findings of NASA’s Nancy Grace Roman Space Telescope, launching in 2027, will help scientists gain a better understanding of dark energy and reveal some of the hidden workings of our universe.

• What does your observation about the stretching of lightwaves mean for lightwaves as they travel across space over time?
• What are some limitations of this model of the universe?
  • The model only shows the surface of the balloon. A more accurate model would include galaxies inside the balloon.
  • Expansion of the model universe only occurs when it’s being pumped or being blown into. Actual expansion is continual and accelerating.

• The model only shows the surface of the balloon. A more accurate model would include galaxies inside the balloon.
• Expansion of the model universe only occurs when it’s being pumped or being blown into. Actual expansion is continual and accelerating.

• Students should develop an explanation about what they have measured and observed. Explanations might include things like:
  • As the universe expands, the distance between galaxies grows.
  • As the distance between galaxies grows, galaxies themselves do not expand.
  • As the universe expands, lightwaves traveling through space get stretched out.
• Students should notice that the galaxies are moving apart.
• Students should recognize the stretching of lightwaves as the universe model expands.
• Students may connect the stretching of lightwaves with a change in wavelength and type of energy (e.g., ultraviolet to visible light, visible light to infrared).

• As the universe expands, the distance between galaxies grows.
• As the distance between galaxies grows, galaxies themselves do not expand.
• As the universe expands, lightwaves traveling through space get stretched out.

• Article for Kids: What Is Dark Matter?
• Article: What Is Dark Energy?
• 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.