For over a hundred years, humans on Earth have been using radio transmissions to communicate with each other. This ability to communicate around the globe has brought people closer together. However, by their very nature, these radio transmissions, such as what leaks from television, cell phones, and satellites, are also detectable from space. This means the Earth is not a closed system. Earth’s ever-expanding detectable radio signature has been coined the radiosphere. Although radio signals weaken the further away they get from the source, faint signals are still detectable with a sensitive enough receiver. In his paper titled “The benefits and harm of transmitting into space,” author Jacob Haqq-Misra explores the potential consequences of broadcasting signals into space.
The search for extraterrestrial life (SETI) is ongoing and has yet to turn up concrete proof of life beyond Earth. Some scientists say that one possible way to find life is to send it a message. Therefore, instead of the search for extraterrestrial intelligence (SETI), it would be called messaging to extraterrestrial intelligence (METI.) However, broadcasting METI comes with a host of ethical and practical issues. Groups or individuals may claim to speak for the entire planet and potentially give away Earth’s location in space.
Humans have already sent multiple intentional METI attempts, usually involving a strong radio transmission targeted at a specific star system. For METI, we assume that any possible extraterrestrials can detect and interpret radio signals. However, Earth’s detectable radio signature includes all METI attempts in addition to the unintentional leakage from TV, radio, and satellites. METI and unintentional radio signatures can be detected if someone is listening. External life forms, or watchers, may be able pinpoint the location of life on Earth without the help of METI. Regardless of METI use or not, the exact implications of extraterrestrial contact are unknown. Therefore, are the potential benefits of METI worth the potential risks?
Signals from Earth travel away in all directions at the speed of light. If humans sent a message starting 5 years ago, those signals would be 5 light years away from Earth. There are concerns that even an internationally agreed upon message would quickly become outdated. The light-years transmissions need to travel before being detected by an extraterrestrial civilization may mean a huge delay between transmission and receipt of the message. Sent METI has been aimed at star systems as close as 10 light-years away and as far as 24,000 light-years away. After such a long time, the message content may no longer reflect the type of life present on Earth at a future date. Therefore, any METI attempts must account for possible changes in human society many years down the road.
The authors of this article explore the positive or negative outcomes that could result from contact with extraterrestrial intelligence. But ultimately, the outcome is unknown. For example, they may receive METI from Earth and choose to do nothing about it or study it but not send a return message. If no action is taken, there may be no way for Earth to know if the message was received. There is also a chance that the message is received but they can’t interpret it. Or, the extraterrestrial civilization could try to make contact with Earth. The ethics of the civilization may determine if this contact benefits or harms humans on Earth. For example, contact from an extraterrestrial intelligence could benefit human life through sharing of knowledge, technology, or resources.
Because the outcome is uncertain, it is therefore hard to determine if METI broadcasting is positive or negative. However, the very act of deciding on a message and sending it out may capture imaginations here on Earth and allow humans to think more deeply about our place in the universe.