Green Bank Telescope (GBT)
A new study sought to respond to the famous Fermi paradox and points out that more advanced civilizations will have a theoretical mathematical limit of 5,000 years. Humans have been in this group for about 200 years.
It is one of the most famous questions in science and, according to legend, it was asked during lunch. Enrico Fermithe physicist who helped build the first nuclear reactor and whose name names a unit of measurement so small that it makes an atom seem generous, was talking to his colleagues about the possibility of extraterrestrial life when, suddenly, he asked: “Where is everyone?“.
The universe is 13 billion years old. Our galaxy alone contains hundreds of billions of stars, a significant proportion of which are home to planets. Many of these planets are in the ideal temperature range for liquid water to exist. The numbers, by any reasonable estimate, suggest that life should have come many timesin many places, long before our planet was even formed. And yet, no signal. No visitors. No evidence of any living beings. This is the Fermi paradoxwhich has remained unresolved for 75 years.
Now, two physicists at the Sharif University of Technology in Tehran have approached the question from a new perspective. Instead of asking why we don’t encounter other civilizations, Sohrab Rahvar and Shahin Rouhani asked what silence itself reveals to us, and the answer imposes a hard mathematical limit the probability of survival of technologically advanced civilizations.
If we optimistically assume that intelligent life arises relatively easily on Earth-like planets, and that the enormous number of such planets in our galaxy would imply the existence of an immense number of civilizations, then the absence of any contact with these civilizations must mean that they no longer exist.
The galaxy is old enough, and space is interconnected enough, that a long-lived technological civilization would have eventually manifested itself. We would have detected its signals, found its probes, or discovered some trace of its engineering. We didn’t find anything like that.
The researchers analyzed the calculations carefully, based on the famous Drake equation (the formula that tries to estimate the number of communicating civilizations in the Galaxy at any given time). They also introduced a particularly important restriction related to electromagnetic communication. Our radio telescopes have been in operation long enough that our “cone of light” (the region of space from which signals could have reached us) spans the entire history of the Galaxy, dating back approximately 100,000 years. Any civilization that existed in our Galaxy during this period and was emitting detectable signals should, in principle, already have been heard.
The silence, the authors argue, is not due to our technology being too primitive. This is a genuine absence. Doing the calculations, the team concluded that if intelligent life is common, technological civilizations typically survive maximum for about 5000 years. Not millions of years. Not even tens of thousands. Five thousand years… a number that puts all of recorded human history within the danger zone. We are a technological civilization, in any meaningful sense, only about 200 years ago. Statistically, we are at the beginning of the most vulnerable period of our existence.
The enumerates the threats with uncomfortable directness: asteroid impacts, supervolcano eruptions, climate change, pandemics, nuclear war, artificial intelligence, runaway biotechnology. The authors note that the story is full of civilizations that collapsedsince the Romans, the Mayans and Easter Island, and which have never recovered. In a world as interconnected as ours, a civilization-ending catastrophe can, for the first time, be truly global.
As Rahvar and Rouhani are keen to state, their results “should be interpreted as upper limits derived from Fermi paradoxand not as predictions of real life expectancy.”
The math doesn’t say that civilizations must die at 5,000 years, just that, on average, can’t survive much longer than that if we want to explain the silence we observe. Other explanations remain entirely possible: perhaps civilizations choose not to communicate, perhaps we are one of the first intelligent species to emerge, perhaps distances are simply too vast. The study does not rule out any of these hypotheses.
But the implication underlying the equations is hard to ignore. The Galaxy may be, or may have been, full of civilizations that arose, built remarkable things, reached for the stars, and then fell silent before reaching any other civilization. Whether through war, environmental collapse, or misuse of its own technology, the universe appears to impose a strict limit on the duration of intelligence. We still don’t know which category we belong to.
