Practice Questions

1.What is dark matter?

Dark matter is a type of matter that does not emit light or radiation and cannot be seen directly, but its presence is inferred from its gravitational effects on galaxies.

2. Explain why scientists think dark matter exists.

Stars on the edges of galaxies are moving faster than expected based on the mass we can see. This suggests there is invisible matter providing extra gravity — called dark matter.

3.What is dark energy?

Dark energy is a mysterious force thought to be causing the accelerated expansion of the universe.

4.Describe one piece of evidence for the existence of dark energy.

Observations of distant supernovae show that the expansion of the universe is speeding up. This suggests there is a force, called dark energy, pushing galaxies apart.

5.Scientists believe that the matter we can see only makes up about 5% of the universe. What makes up the rest of the universe, and how do we know?

Around 27% is dark matter, which we know exists because of its gravitational effects on galaxies. About 68% is dark energy, which is believed to cause the accelerated expansion of the universe. These components are invisible but inferred from their effects.

6. Explain the difference between dark matter and dark energy, and describe how each affects the universe.

Dark matter is invisible matter that does not emit radiation, but provides extra gravity to hold galaxies together. Dark energy is a force that causes the universe to expand at an increasing rate. Dark matter affects the motion of galaxies, while dark energy affects the large-scale expansion of space itself.