The episode begins by noting how the destruction of the Library of Alexandria lost much of humanity’s knowledge.
Tyson then proceeds to describe the discovery of cosmic rays by Victor Hess through high-altitude balloon trips, where radiation increased the farther one was from the surface.
Swiss Astronomer Fritz Zwicky, in studying supernovae, postulated that these cosmic rays originated from these events instead of electromagnetic radiation.
Zwicky’s theory was confirmed by the work of Vera Rubin, who observed that the rotation of stars at the edges of observable galaxies did not follow expected rotational behavior without considering dark matter.
Tyson describes Carl Sagan’s role in the Voyager program, including creating the Voyager Golden Record to encapsulate humanity and Earth’s position in the universe.
Voyager I looked back to take a picture of Earth from beyond the orbit of Neptune, creating the image of the Pale Blue Dot.
The series concludes with the empty-seated Ship of the Imagination leaving Earth and traveling through space as Tyson looks on from planet Earth.