The Library of Alexandria was a prominent virtual location on Carl Sagan’s original Cosmos series. It is fitting, therefore, that the final episode of Neil deGrasse Tyson’s Cosmos series should begin in that location. Tyson uses it as both a tale of caution and one of inspiration. Before its destruction, the Library of Alexandria was one of the greatest repositories of knowledge in the world. It was a representation of the incredible things humanity could achieve. Yet it was only available to a privileged few, unlike the knowledge that we can download at our fingertips today. There were very few to defend it when the time came.
One of the key themes in “Unafraid of the Dark” is that scientific knowledge should be freely available to all, for that is the only way to ensure that it is used responsibly. Scientists are human beings and capable of error. They’re also capable of corruption. Only by others cross-checking data and theories can the errors be found and corruption weeded out. But there’s a bigger, more encompassing theme, to this final episode, and that is the fact that human knowledge is incomplete. There is so much about the cosmos that we simply don’t know. In fact, when Martin Behaim made the very first globe of the Earth in 1492 (a globe that only contained the three continents of Europe, Asia, and Africa), people then knew relatively more about the Earth than we know now about the universe as a whole. Yet we shouldn’t be ashamed of this. Indeed, Tyson presents this fact as a point of inspiration, a reason for us to continue the search and to learn more, for there can be nothing more exciting than discovering something new—something that seems to rewrite reality as we know it.
To illustrate this, Tyson takes us back to the origins of one of the biggest mysteries of science. In the early twentieth century, Victor Hess investigated the presence of radiation in the atmosphere to determine where it was coming from. He expected the sun to be the source, but his experiments in high-altitude balloon trips revealed the existence of cosmic rays. These high-energy sources of the radiation did not come from the sun, and he could not determine where they originated from other than somewhere in space. Later, Fritz Zwicky, who first predicted the existence of neutron stars and coined the term supernova, postulated that these were the source of cosmic rays. However, although his prediction of the existence of neutron stars turned out to be true, we now know that they can only account for the least energetic cosmic rays. The source of the more energetic ones remains a mystery.
However, Zwicky’s study of supernovae led him to uncover a greater mystery. He studied the movements of stars and galaxies and discovered that there had to be more mass in the universe than we were able to observe. He called his unobservable mass dark matter. His idea was initially forgotten, but years later Vera Rubin discovered that the movement of stars on the outside of galaxies did not conform with what was expected unless you took into account Zwicky’s dark matter. But just what is this dark matter? We just don’t know. We only know it’s there because of its gravity, but we cannot find it. Dark matter remains perhaps the second biggest mystery in science. But there’s a bigger one.
Tyson goes on to discuss something I remember reading quite a bit about when I was young. The universe began with an event we call the Big Bang. This cataclysmic explosion sent all the particles that would become the stars and planets hurtling out away from one another, an expansion that continues to this day, 14 billion years later. For the longest time, there were competing views over what the ultimate outcome of this expansion would be, and it depended on the amount of dark matter in the universe. With enough dark matter, eventually gravity would overcome the expansion, which would slow down and then reverse. Over billions and billions of years, the universe would collapse back in on itself (called the Big Crunch). On the other hand, with less dark matter in the universe, gravity would slow expansion but not enough to stop it. The universe would expand forever. Although the outcomes were very different, proponents of both sides could agree on one thing: the expansion of the universe would get slower over time. All they really disagreed on was how much slower. Both sides studied the expansion of the universe, and then in 1998, both sides independently came to same startling conclusion: the expansion of the universe was not slowing down! It was getting faster. This made no sense unless there were some other, unknown force propelling the universe outwards, and so the term dark energy was born.
Like dark matter, we have no idea what dark energy is. Indeed, even the names are just code words for our ignorance. In this interview for IO9, Tyson explains that we’d be better off calling them Fred and Wilma, since the term dark matter conveys the idea that it’s matter, which may not be the case. It’s a source of gravity; that’s all we know. Likewise, using dark in both names conveys the idea that dark matter and dark energy are related. Maybe they are, or maybe they’re not. We just don’t know. But that’s okay. There’s nothing wrong with admitting what we don’t know. The only problem comes when we try to pretend we have all the answers.
The episode then turns away from dark matter and dark energy and looks at the journey of the Voyager probes as they make their way towards the furthest reaches of the galaxy. Voyager 1 and 2 are, in many ways, symbols of humanity’s search for knowledge. These two probes provided some of our first close-up views of the planets and showed the existence of the sun’s heliosphere which protects the solar system from interstellar winds. But as well as a search for knowledge, the probes also represent our search for immortality, for they contain records of who we are and where we come from—samples of our languages, music, and more, for any extraterrestrial civilizations that might one day discover them. These probes carry our legacy into the unknown.
The Voyager probes have also helped demonstrate our place in the universe by showing us a perspective we could never have before. When people first went into space, we were able to see the Earth as a whole for the first time. Those pictures gave us a new perspective, but Carl Sagan recognized that there was still another. He convinced NASA to turn Voyager 1’s camera back towards Earth when it went beyond Neptune, to take a picture of the Earth at a distance where it looks like nothing more than a pale blue dot in an ocean of blackness. It’s humbling to think of things that way, and the episode drives it home by using Carl Sagan’s own narration about the pale blue dot as the visual animation pans away from Earth until it is nothing more than a literal dot on the screen. While this segment is certainly meant to make us rethink our importance and to realize our insignificance in the grand cosmic scene, this segment is also there to inspire us to cherish what we have and to reach out and leave some sort of noteworthy stamp upon our insignificant corner of the universe.
And that really is what Cosmos has been all about, not just in this episode, but in every episode. It is meant to inspire. It educates, yes, but only enough to compel us to learn more. You cannot teach everything there is about the universe in just thirteen 45-minute episodes. No one is going to pass any science courses just by watching Cosmos. But what the series does beautifully is give an overview and draws attention to what there is to know and to learn. Because science is important. Learning is important. But more than that. Learning is fun, and Cosmos makes that abundantly clear.
Cosmos teaches us to question ourselves and others. The scientific process helps stop us from fooling ourselves and clinging to beliefs in spite of evidence against them. As Tsyon says, “If a favourite idea fails a well-designed test, it’s wrong. Get over it.” But what does it matter? some might ask. Why should we care about the age of the earth or the distance to the stars? Some might be surprised by how much relevance it all really does have, how a discovery in one area can lead to another discovery somewhere else, making something seemingly irrelevant very relevant. But I’ll also quote Tyson’s closing monologue on these very questions, because what he says so closely echoes my own thoughts.
Part of it depends on how big a universe you’re willing to live in. Some of us like it small. That’s fine. Understandable. But I like it big, and when I take all of this into my heart and my mind, I’m uplifted by it. And when I have that feeling, I want to know that it’s real, that it’s not just something happening inside my own head, because it matters what’s true, and our imagination is nothing compared with nature’s awesome reality. I want to know what’s in those dark places and what happened before the Big Bang. I want to know what lies beyond the cosmic horizon and how life began. Are there other places in the cosmos where matter and energy have become alive and aware? I want to know my ancestors—all of them. I want to be a good, strong link in the chain of generations. I want to protect my children and the children of ages to come.
We who embody the local eyes and ears and thoughts and feelings of the cosmos, we’ve begun to learn the story of our origins—star stuff, contemplating the evolution of matter, tracing that long path by which it arrived at consciousness. We and the other living things on this planet carry a legacy of cosmic evolution spanning billions of years. If we take that knowledge to heart, if we come to know and love nature as it really is, then we will surely be remembered by our descendants as good, strong links in the chain of life, and our children will continue this sacred searching, seeing for us as we have seen for those who came before, discovering wonders yet undreamt of in the cosmos.
I’m going to miss Cosmos: A Spacetime Odyssey—well, the thrill of new episodes at any rate, as I have it on DVD now, so can watch it whenever I want. I hope it inspires some people to seek out more, through reading or taking classes or watching other science programmes. There’s lots out there, waiting to be read and seen. And I hope it inspires a new generation of scientists, who will take us on the next step of the journey. It truly has been an odyssey across spacetime, but there is so much more of that odyssey still to come.