In 1977, NASA launched two Voyager spacecraft into the sky with the initial goal of exploring the outer solar system. Once the spacecraft had examined Jupiter, Saturn, Uranus, and Neptune, they kept flying for billions of miles, ultimately entering interstellar space. Each carried a copy of the Golden Record, a disc of earthly sounds that are intended to represent humanity to any extraterrestrial civilizations that might encounter it. (To date, the record is the only human-made object to have left the solar system.) Astronomer Carl Sagan chaired the committee that determined the disc’s contents, which include booms of thunder, chirping birds, and snippets of more than 55 human languages. There’s also a lot of music: Compositions by Bach, Beethoven, and Mozart made the cut, as did those by blues legend Blind Willie Johnson, Azerbaijani folk singers, and rock ’n’ roll pioneer Chuck Berry.

Nearly 45 years later, the Voyager probes are still going, and still posing big questions around sound through the discs they carry. In particular: If the records’ sonic selections are discovered, will aliens have the ability to hear them? And if not, are there other ways for otherworldly creatures to experience the sounds? For Daniel K.L. Chua and Alexander Rehding, music professors at the University of Hong Kong and Harvard University, respectively, the answer to the latter is yes. They expand upon these far-out ideas in their new book, Alien Listening: Voyager’s Golden Record and Music From Earth (Princeton University Press). In lieu of merely retracing the Voyager story, the authors use the Golden Record’s proposition—that anyone, even aliens, can make sense of music—as an opportunity to redefine the meaning of listening, what constitutes music, and how the art form can serve as a timeless vehicle for sharing and connecting. Through a mix of lighthearted puns, cartoons, illustrations, and fold-out diagrams, the book rejects stuffy conventions of music theory in favor of more straightforward ways of thinking about music. Here, we ask Chua and Rehding to expand upon the wonders of the record, and what it can teach us about listening.

For those of us who are still Earthbound, can you describe what the tracks on the Golden Record sound like?

Chua: NASA was way ahead of its time, creating a record of “world music” before the term was commercially coined. You can listen to the whole thing as if it were a mix tape.

Rehding: The Golden Record’s makers actually encoded different kinds of material as sounds. There’s the music, as well as spoken word and noise tracks, but the most remarkable part are the one hundred and fifteen sonified images, [in which visual data was converted into sound]. To our ears, they sound like bleeps, but if you’re an alien—and have no concept of what constitutes human music and what doesn’t—there’s no way to know that this is just a bleep, and not a very unusual piece of music. If we, as humans, want to give ourselves an outlandish listening experience, I suggest that we start with the bleeps, and try to listen to them as music.

Are there any artists or tracks you think are missing from the Golden Record

Rehding: It has a few gaps. There’s no music from the Caribbean or from Jamaica, for example. I’d also include some Tuvan throat singing, which for me is one of the most remarkable musical traditions on our blue planet. And hip-hop as well, which was in its infancy when the record was put together.

Chua: I recently saw a video of a diver being scooped up by a whale, and almost swallowed. I’d like to add this to the Golden Record. The Record features a recording of U.N. delegates sharing messages in various languages. But because they were so long-winded, Sagan’s team had to make a mashup of these greetings as a collage, and decided to add a whale’s song in the background. I think this could be quite confusing for the average alien linguist. It’s hard enough having to decipher the different human languages, but to add another species in the mix is asking a lot. So the video may help provide a clue.

Sending a record into space for aliens to hear suggests that music can be enjoyed by anyone, regardless of their place in time or space. What is the value of thinking about music in that way, as opposed to the convoluted ways that traditional musical theory approaches the subject?

Chua: Every culture has music. So the fact that music theory is typically an incomprehensible and exclusive activity is not society’s problem, but the problem of music theorists. This book gets back to basics, jettisons jargon, thinks laterally, and makes the case that music is not difficult to understand.

Rehding: Music theory is interested in the question of how we listen to music. But often, it’s too wrapped up in the things that it’s been doing forever, and doesn’t seem to find a way out. We used the Golden Record as an extreme listening situation to take an outside perspective, quite literally, on what music theory does. The aliens are our avatars here: What would a music theory need to look like if it cannot count on any prior knowledge of anything—of music, of styles and genres, of cultural differences, of human ears? What remains is time, pure and simple. And that’s our starting point for a very different kind of music theory.

We reference the figure of Penelope, from ancient Greece, who weaves a shroud while waiting for her husband, Odysseus, to come home. Listening involves a similar phenomenon: the act is a means to “weave” time to detect patterns and repetitions.

The book makes several references to pop culture, including the TV shows Star Trek and Doctor Who. That’s a fun way to keep the mood light, but it occurred to me that both of those programs are, in part, about cultural diversity through the metaphor of space, which is also what the Golden Record aspires to.

Chua: Inclusiveness is vital in our music theory. We welcome the aliens, after all! Also, these TV shows “come in peace,” like NASA. They offer a vision of a universe that is fundamentally peaceful, or at least, a universe that can be ultimately peaceful. Without a peaceful universe as a premise, there is really no point sending music into space.