NASA galaxy image

Is nobody phoning home because all the (hypothetical) aliens are extinct?

Contributed by
Apr 15, 2018, 10:24 AM EDT

For as long as we’ve known there are worlds beyond our world, humans have wondered if there are any other life forms out there, and as long as we’ve had the technology to detect radio signals, we’ve been trying to pick up messages from them. What if we do get a message—from a dead civilization?

Astronomer Claudio Grimaldi and his research team believe that any extraterrestrial hands that transmitted a message to Earth could have long since turned to space dust, as NBC Mach found out. Does this mean we're really the only living examples of life in the entire universe? Even the scientist believes there could be someone in a distant galaxy messaging us right now. But.

“The transmissions arriving at Earth may come from distant civilizations long extinct, while civilizations still alive are sending signals yet to arrive,” Grimaldi and colleagues say in a study recently published in Popular Physics.

Will this unknown individual’s people be nothing more than bones (if they even have bones) by the time such a message arrives? It may seem so, because any radio messages shooting through space travel at the speed of light. Say we just got a signal. Since the expanse of space is so vast, a message that has finally reached us can be assumed to have come from somewhere millions of light-years away if it was travelling that fast and hasn’t landed on Earth until now.

NASA image of stars

Anybody out there? Credit: NASA

The reality is that most star systems SETI scientists have their eyes on are hardly more than a few hundred light-years away. There’s no telling whether a hypothetical alien sent that message during the last three hundred years before said alien’s civilization crumbled, but something like that would be unlikely. Several hundred years is nothing when looking at he lifespan of an entire civilization. Some major cataclysmic event would be an exception.

What Grimaldi argues is that alien civilizations come into being at random times and beam out signals just as randomly. Alien radio signatures are assumed to expand in a sort of doughnut form, starting at the outer boundary and ending with the civilization itself at the inner boundary. Their transmitters could crash at any moment, for any reason. It may or may not mean that they have ceased to exist.

Another thing we don’t know is the average staying power of extraterrestrial civilizations. We have a better chance at receiving a message from an extant civilization if they tend to hang around for hundreds of thousands of years, but not so much if they vanish after ten thousand years or less.

So what if we do receive a message from a long-dead civilization? If it had anything to do with an alien takeover of our planet, we could be relieved, but otherwise, it wouldn’t be pointless. Such a signal would tell us that someone was out there—and if someone was out there, maybe someone else still is.

(via NBC Mach)