Dark matter and dark energy are two of the biggest mysteries in
science today. Although we don't know what they are, scientists would
not have added them to our models of the universe without strong
evidence that they represent real phenomena (see the Hallmarks of
Science). In a 2-3 paragraph essay, identify one piece of evidence for
the existence of either dark matter or dark energy, and describe it in
detail. Explain why the observations you have chosen are scientifically
convincing evidence for the existence of dark matter or dark energy.