Sagan covers so much ground in this episode ... which is what he does in all the other episodes as well!
Sagan explains relativity to the general audience — I would never have thought that possible. Perhaps, an audience that is not trained in science would not be able to make much of this really.
The spectacular ideas originating with Albert Einstein that the speed of light is the ultimate speed in the universe, that the speed of light stays constant in all frames of reference, that there are no privileged frames of reference, that time slows down as you travel close to the speed of light, all these concepts are such basic concepts of modern physics and yet very little known to the general public.
Sagan talks about the original thinker that Leonardo da Vinci was and how Einstein's special relativity opens the door to the possibility of long distance space and time travel.
Sagan shows sketches of spaceships of the future that utilize nuclear fusion as their power source — surely something that lies hundreds of years in the future from now if not thousands.
And yet we must be thankful to the people who dare to design such things in a world where stupidity of all sorts is all too common.
It astonishes me no end that we are a species that simultaneously conducts space exploration and is still mired in all sorts of religious and ethnic and other sorts of fanaticism.
On the one hand, we have landed robotic spacecraft on other planets and yet on the other hand, the planet still struggles with abject poverty and millions and hundreds of millions of people are still prey to superstitious religious beliefs.