Question

How do we know dark matter and dark energy exist when they cannot be observed directly?

a) They can be directly observed through telescopes.
b) Their effects on visible matter and the universe can be observed indirectly.
c) They emit visible light.
d) Dark matter and dark energy cannot be proven to exist.

Answer 1

b) Dark matter and dark energy cannot be observed directly, but their existence can be inferred through indirect observations, such as studying the motion of stars in galaxies and the motion of galaxies in clusters.

Step-by-step explanation:

Dark matter and dark energy cannot be observed directly, but their existence can be inferred through indirect observations. For example, the motion of stars in galaxies and the motion of galaxies in clusters imply the presence of dark matter. The velocities of stars in spiral galaxies can be measured using the Doppler shift in the emitted light, and these measurements indicate the rotation of the galaxy. The graph of velocity versus distance from the galactic centre shows that the velocity does not decrease as expected if the matter were concentrated in luminous stars, suggesting the presence of a massive halo of dark matter extending beyond the visible stars.