[LINK] "The Pioneer Plaque: Science as a Universal Language"

[rfmcdonald]

At the Planetary Society Blog, Jake Rosenthal writes about the importance of the Pioneer Plaque, as the first intentional message of humanity to extraterrestrial intelligences.

The Pioneer Plaque is a physical, symbolic message affixed to the exterior of the Pioneer 10 spacecraft. At the core of this message is a fundamental concept that establishes a standard of distance and time, which, thereafter, is employed by the other components of the plaque. The design team postulated that hydrogen, being the most abundant element in the cosmos, would be one of the first elements to be studied by a civilization. With this in mind, they inscribed two hydrogen atoms at the top left of the plaque, each in a different energy state. When atoms of hydrogen change from one energy state to another—a process called the hyperfine transition—electromagnetic radiation is released. It is this wave that harbors the standard of measure used throughout the illustrations on the plaque. The wavelength (approximately 21 centimeters) serves as a spatial measurement, and the period (approximately .7 nanoseconds) serves as a measurement of time. The final detail of this schematic is a small tick between the atoms of hydrogen, assigning these values of distance and time to the binary number 1.

The most prominent figures on the plaque are those of two adult humans: a man and woman. The man bends his arm and displays an open palm—an international greeting, but one that, admittedly, may be meaningless to an extraterrestrial civilization. The woman hangs her arms by her sides and stands with her weight shifted rearward as to dispel any misunderstandings regarding a fixed body and limb position; we are mobile and flexible. Beside the illustrations of the humans is the binary number 8, inscribed between two ticks, indicating the height the woman. The civilization could then conclude that the woman is 8 units tall, the unit being the wavelength (21 centimeters) described by the hyperfine transition key; thus, the woman is 8 times 21 centimeters, or about 5.5 feet tall.

At the heart of the plaque is an array of lines and dashes—a cosmic address on the interstellar letter. In the center is our home star; the radial spokes signify the relative distances and directions to pulsars—rapidly rotating neutron stars that emit electromagnetic radiation at regular intervals. Accompanying each line is the period of the respective pulsar—once again, in binary. Not only does this map communicate position, but time as well—an epoch in the lifetime of the universe during which the message was sent. The rate of electromagnetic bursts from pulsars changes over time; thus, the period of the pulsars denoted on the plaque serves as a timestamp. It is presumed that a civilization that has developed radio astronomy will have the capability to comprehend the nature of pulsars. Given the information presented in the pulsar map, it is feasible that such a civilization could date back the message and triangulate our position. As further confirmation of our locale, our solar system’s planets (nine at the time) are depicted in the bottom margin of the plaque with their respective distances to the sun in binary. Supposedly, in the history of the Milky Way, only one star has ever fit the characteristics displayed on the plaque.