Aliens & The Fermi Paradox? A Physics Answer
Updated: 2 days ago
“Where is everybody?” asked physicist Enrico Fermi, as he lunched with several of his physicist friends. It was 1950, and he was talking about aliens. The conversation had been an interesting one, as it often is between Nobel Laureates, and Fermi had been questioning the technological possibility of interstellar travel. In popular culture, the Fermi Paradox is sometimes expressed in another way: If, as many people contend, there are other intelligent extra-terrestrial species in our galaxy, why do we not detect any radio transmissions when they communicate?
In 1961, Dr. Frank Drake formulated the now-famous Drake Equation, which was designed to express the probability of other intelligent and communicative life existing elsewhere in our galaxy. While his ‘equation' is not an exact model, it evokes the idea that there should be a very large number of possible candidate civilizations out there. If so, why are we not picking up their communication signals?
One candidate signal was detected in 1977. It has become known as the ‘Wow’ signal because the astronomer who detected it wrote the word ‘Wow’ beside the data on his print-out. That location in the heavens has been revisited many times since, but no repeat of the Wow signal has been detected. It is therefore possible that it was not a candidate signal at all, but rather some other anomaly.
There are several approaches to answering the Fermi Paradox. One might be that intelligent life is too rare in the universe, and it is therefore not out there communicating. Another might be that they are out there but have not yet developed advanced communication technology. And other possibilities, including those entertained by Fermi himself: that interstellar flight might not be possible, that it might not be worth the resources and effort, or that civilizations do not survive long enough to achieve it.
In my novel The Intrepid: Dawn Of The Interstellar Age, a different approach is suggested: (The following is a brief excerpt from chapter 19.)
Ohr looks at Suco. “You think the ‘Wow’ signal came from them?” he asks. “The one in 1977?” “Yes.” “I don’t think so,” she says. “Why not?” “Because they’ve been right in our backyard and they haven’t been contacting us during all the time they’ve been collecting this stuff, so why send us a radio signal? That tells me these guys don’t want to be in communication with us. Which begs the question, ‘why not?’” “So someone else sent it.” “Probably. Also the ‘Wow’ signal looked like it came from somewhere in Sagittarius, probably Tau Sagittarii, which is over a hundred light years away. These guys look like they’ve been going back and forth a lot, so I’d say they live closer.”
“That makes at least two other civilizations,” he says. “At least. I’m sure there’s plenty, I just don’t know why we wouldn’t have picked up more signals from them over the years.” “The Fermi Paradox?” She nods. “Don’t intelligent races also have to use electromagnetic waves to communicate? Well, some could use telepathy maybe.” “But not all.” “Right, and there’s a lot of radio astronomers and a lot of horns pointed at the sky every night, for decades already. And only a half dozen candidate signals in a century?” "Ok, so, what everyone expects to see is wrong. Look. We’re less than five light years from Earth and we’re hardly picking up any signals. Why not? Shouldn’t we be getting at least a hundred sports channels?” “Ok, I see where you’re going. So a long distance message has to be a specially strong broadcast?” “Yes, and also a narrow and well-directed beam. So, basically, you have to know who and where you’re calling, and you have to put a lot of power into it. No one is going to be sending out signals like that everywhere all the time. It’s not practical. That would be like having every TV station on Earth sending narrow-band, high-powered transmissions, individually, to every star system around us. That’s a lot of broadcasting resources. And who’s going to put in all that time?” “So there could be dozens of intelligent civilizations jabbering away in our galactic back yard, without any of our scopes picking up any of it?” “Yup.” Suco ponders this. A beat, then Ohr asks, “Didn’t we send a reply? To the ‘Wow’ signal?” “Yeah, in 2012. Ok, so now what you’re saying makes more sense. Astronomers have been looking for a repeat of the ‘Wow’ for years from that same point in the sky, but they never heard anything from there again. If it was a message, maybe they were just sending out a ‘hello’ to us or even to a whole bunch of stars.” “Maybe.” “And they’ll only get our reply in a century or two, so no use checking back or sending another one ’til then.” “I suppose not,” he says. “Geez. Talk about taking a relationship slow.”
Contrary to popular belief — and to the the beautiful portrayal at the beginning of the movie “Contact” — radio and television signals from Earth will not go on forever into deep space, or at least, not without becoming increasingly distorted.
Space is not empty. It contains atomic particles, dust particles, and radiation. It is an environment in which photons (such as radio waves) experience interference and scattering. In addition, gravitational fields redshift photons, decreasing their energy. The consequence is that radio signals traveling through space will become less clear with distance. After a long enough distance, they will have become very difficult to distinguish from the background photonic noise of space. Long distance transmissions will therefore require special and high-powered broadcasts in order to reach a distant receiver. Without that extra power, Earth-based television signals will probably not even make it to our nearest neighbor, the Alpha Centauri star system.
Sorry, Proxima b sports fans!