Time Map

By Joel Hoekstra

Carleton astronomy professor Joel Weisberg imagines a way to communicate with space travelers a billion years or so from now


A brief time ago, in a galaxy we call our own, a satellite was launched into space bearing a five-inch-wide, gold-plated medallion. Inside the medallion were 100 photographic images representing late 20th- and early 21st–century human history, etched onto a silicon disk through the magic of nanotechnology. On the outside of the medallion was a diagram filled with circles, triangles, dashes, and squares, as well as a map of Earth, the outlines of each continent recognizable—at least to our planet’s current inhabitants.

This sleek time capsule, intended to be found by space travelers who might visit our solar system eons from now, owes its existence in part to a collaboration between New York–based artist Trevor Paglen and Carleton astronomy professor Joel Weisberg.


The Last Pictures silicon disk is encased in a gold-plated shell. Etched onto the cover is a time map that Weisberg designed to indicate the medallion’s epoch of origin. 

Paglen, perhaps most famous for his photographs of top-secret military testing sites, spent four years interviewing scientists, anthropologists, philosophers, and artists to develop this project, called The Last Pictures, an effort he likens to cave paintings in Lascaux, France. Discovered in 1940, those prehistoric images of archers and animals illuminate an ancient age in a way that transcends time and language. Paglen hopes his “message in a bottle” will do the same. He arranged to attach the medallion to an EchoStar XVI telecommunications satellite, which Dish Network launched from Kazakhstan last November. It is expected to remain in geostationary orbit, hovering over South America about 24,000 miles above our planet, for some 5 billion years—until the sun swallows Earth.

Weisberg, the Herman and Gertrude Mosier Stark Professor of Physics and Astronomy and the Natural Sciences, who has taught at Carleton since 1984, met Paglen in 2011. The artist was in Northfield to attend the opening of the exhibit Seeing Is Knowing: The Universe at the Perlman Teaching Museum in the Weitz Center for Creativity. At a dinner hosted by museum curator Laurel Bradley, Weisberg asked Paglen about his practice of identifying and photographing spy satellites. “I’ve been a satellite tracker since high school, so we had much in common,” says Weisberg.

Paglen was surprised to discover that Weisberg had been friends with the late Val Boriakoff, an Argentine astronomer whose image was included in a similar time capsule—dubbed the Golden Record—that was placed aboard the Voyager twin space probes in 1977.

With The Last Pictures project, Paglen faced a number of challenges—and there was one in particular that Weisberg thought he could solve. The artist wanted discoverers to know where and when the medallion was created.  A picture of Earth, of course, could suggest the origin of the disk, but conveying time was more difficult. The discoverers would likely have a different way of measuring time than Earthlings do. “What could be understood in a thousand years?” Weisberg says, summarizing the challenge. “What could be understood in a million years? A billion? What could endure?”

Weisberg set about creating a series of “clocks” that he hoped future finders could decode. Some had been used on earlier time capsules launched in the 1970s, while others were based on new discoveries. He started with the assumption that any beings sophisticated enough to travel through space would have an advanced understanding of science and technology. 

The simplest “clock” was a map of Earth, with the continents outlined. Weisberg and Paglen reasoned that future space travelers could compare their view of Earth with the sketch, apply their own scientific theories about plate tectonics, and thereby estimate the time it had taken for continents to shift their configuration. He also included a map of the universe as seen from Earth. By comparing the position of the stars, galaxies, and planets on his map with their own diagrams, and then factoring in what they knew about the rate of change, the travelers might deduce when the map was created.

Other “clocks” were more complex. Using an elaborate series of dots, dashes, and geometric diagrams, Weisberg devised a way to convey the spin cycles of the Earth, the moon, and several pulsars. (Base 2 serves as the numbering system, and time is measured in intervals associated with the spin-flip transition of atomic hydrogen.)

The medallion, which was manufactured at MIT, also contains a handful of personal messages from the scientists that contributed to it. Weisberg wrote: “My family and I wish you peace and social justice.” He estimates he spent about 150 hours on the project overall.

Of course, Weisberg will never know if future space travelers ultimately decode his messages. But that doesn’t bother him. “To me, the beauty is in the creation. This was a very creative process, thinking about what would be understandable,” he says. “I think of astronomy as a manifestation of what humans are capable of—like art. Even if no future civilization discovers it, the act of creating it was a profound experience.”


Web Extra: Learn more or read a paper about the project.

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