The universe is inconceivably large and ancient. Given all that time and space, it seems likely that somewhere, sometime, another spark of intelligence was ignited. But if there are intelligent beings somewhere.
How could we connect with them and, assuming we would like to be friends, how would we give them directions to our planet?
There are several techniques scientists could use to send addresses to distant extraterrestrials, but more importantly, researchers would have to find a way to send a readable galactic map to our guests, which is a tricky problem.
If you’re trying to tell someone where you are, you need to have some common references, right? Ideally fixed references.
Héctor Socas-Navarro, astrophysicist of the Instituto de Astrofísica de Canarias
Stars and planets are in constant flux, moving around each other in a slow cosmic waltz. But even within our ever-changing galaxy, scientists have devised some ways to transmit our location to anyone else who might be out there.
Most people would say, ‘Send out a strong radio wave transmission.
Martin Rees, UK Astronomer
Electromagnetic radiation, which includes everything from visible light to radio waves to infrared, has historically been the number one choice for transmitting information about Earth to the cosmos. By subtly modulating the frequency of an electromagnetic wave, scientists can transmit complex messages in simple binary code. And because electromagnetic waves are directional, any intelligent extraterrestrial intercepting such a signal could simply trace it back to Earth.
Of all the different types of electromagnetic waves, radio waves are the usual resource for this type of communication. That’s because the frequency of radio waves fills a convenient space in the electromagnetic spectrum, known as the “water well,” according to NASA. At this frequency, between 1420 and 1720 megahertz, hydrogen and hydroxyl (oxygen and hydrogen bonded together) molecules, the two components of water, act as a kind of chemical “sound insulation,” absorbing lower and higher vibrations and leaving the channel relatively free of cosmic particles. The frequencies above and below the water well are comparatively “noisy” because they are filled with quantum vibrations and remnants of Big Bang radiation.
Scientists have used radio waves to attempt extraterrestrial communication in the past. In 1974, researchers broadcast a radio frequency message from the Arecibo telescope in Puerto Rico to the star cluster M13, approximately 21,000 light-years away. The message was a simple binary pictogram containing a representation of a DNA molecule, our solar system and a human figure, among other things, according to the Search for Extraterrestrial Intelligence (SETI). Since then, numerous radio messages have been sent into space, including NASA’s “Across the Universe” signal in 2008, which consisted entirely of the Beatles’ song of the same name.
However, a potential problem with radio waves is that they diffract, or broaden as they travel, like a ripple expanding in water. That means they can become too diffuse to carry a discernible message when they reach a distant galaxy, according to MIT Lincoln Laboratory . For a more direct message, said Svetlana Berdyugina, an astrophysicist at the Leibniz Institute for Solar Physics in Germany, we should transmit using visible laser light.
A directed message made of polarized laser light, or light whose vibrations occur in a single plane, has the potential to travel much farther than a radio signal without degrading. However, because optical waves are a more compact signal, they are very narrow. Scientists would have to use incredible precision when sending them. In other words, we would already need to know where our aliens were before we could send them laser directions.
Some scientists have taken a different approach to interstellar communication, one more akin to a “message in a bottle,” Socas-Navarro said. The most famous is the gold “Pioneer plaque,” which astrophysicists Carl Sagan and Frank Drake attached to the Pioneer 10 probe in 1972, according to the Planetary Society. A second identical plaque was affixed to Pioneer 11 the following year. These plaques are inscribed with two human figures, a man and a woman, as well as a “map” pointing the way to our solar system using a series of 14 odd cosmic landmarks: pulsars.
Pulsars (short for pulsating radio source) are extremely dense rotating remnants of dead neutron stars that emit beams of electromagnetic radiation from their poles. As they spin, these beams appear to “pulse” or flicker, like a space beacon. Because pulsars represent a rare metronome-like point in the galaxy, they are extremely useful for navigation, Berdyugina said.
In fact, NASA plans to use pulsars as a kind of cosmic GPS in future manned deep-space missions, according to Nature. By measuring slight changes in the arrival of each pulse of three or more pulsars, a spacecraft can triangulate their position in the galaxy. On Pioneer’s plate, each pulsar is marked with a line indicating its distance from Earth, as well as a series of dashes to indicate how fast it is spinning.
However, pulsars are only directional; their flashes are not visible from all angles. So if an alien civilization were to take the Pioneer plaque and read it like a map, “they would have to figure out what we see,” Berdygina said, lest they miss a pulsar entirely. When they designed the plaque, Sagan and Drake were confident that any civilization advanced enough to find and capture the Pioneer probe would have a deep enough knowledge of pulsars to read it.
But the Pioneer plate is not just a message in a bottle, it is also a time capsule. The shading marks on its pulsar map indicate the rotation rate of each pulsar from the point of view of a 1972 earthling. But those rapidly spinning pulsars are slowing down. In several hundred million years, some of them may no longer be spinning. As Socas-Navarro pointed out, an intelligent civilization could take much longer to find the probe, let alone travel to Earth.
Sources: MIT, WordsSideKick.com