We may not hear from aliens for another 400,000 years says new paper

The earliest could be 2,000 years.
Ameya Paleja
Alien life visiting us could be far into the futurePetmal iStock

Human civilization, eager to go and explore new planets and set up colonies, may have to wait for 400,000 years for their first contact with an alien species capable of communicating, according to a recently published paper, Universe Today reported. This rules out a Star Trek-like scenario from occurring anywhere in our lifetimes, or even our grandchildren's, for that matter. 

Last month, we reported how a consortium of astronomers was working actively to send messages to a nearby star system with the hope that alien life exists on one of its planets. These approaches rely on the assumption that the star system not only has alien life but is also civilized enough to communicate back. The other question worthy of exploring is how many such civilizations possibly exist.

The Drake Equation

Often criticized for its limitations, the Drake Equation provides a starting point to determine the number of Communicating Extraterrestrial Intelligent Civilizations (CETIs). The researchers used a previously made estimate based on this equation in their analysis. The estimate takes into consideration many factors, such as the history of galactic star formation, the metallicity distributions, and the likelihood that the star has planets in the habitable zone. 

While the Drake Equation is more of a thought experiment rather than an actual calculation, the authors of the new study take the thought experiment a little further and explore the likelihood of the planets being in the habitable zone and life evolving into a CETI. It also attempts to determine at what stage of the star's evolution would a CETI be born. By treating these parameters as variables, the authors computed an optimistic and a pessimistic outlook of the scenarios.   

How long would be the wait? 

In an optimistic scenario, a CETI could emerge as early as 25 percent of the star's lifetime, and each planet carries only a 0.1 percent chance that the life-form develops into a CETI. Under such a scenario, there would be over 42,000 CETIs spread out through the galaxy in different stages of their evolution. Theoretically, it would only require a wait time of 2,000 years to achieve two-way communication with them. 

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In the pessimistic scenario, the sun would have to cool down much more and may have crossed 75 percent of its life, while there is only a 0.001 percent probability that a CETI would emerge. This would reduce the probability of CETIs occurring in the Milky Way to just 111, and two-way communication with one of these would happen in the next 400,000 years. 

That's twice the amount of time human civilization has existed on the Earth, which could possibly see major disruptions from climate change, a rogue undetected comet strike, or even nuclear annihilation. It could very much be possible that human civilization will be long gone before we even make contact and declare our existence.   

The study was published in The Astrophysical Journal.


As the only known intelligent civilization, human beings are always curious about the existence of other communicating extraterrestrial intelligent civilizations (CETIs). Based on the latest astrophysical information, we carry out Monte Carlo simulations to estimate the number of possible CETIs within our Galaxy and the communication probability among them. Two poorly known parameters have a great impact on the results. One is the probability of life appearing on terrestrial planets and eventually evolving into a CETI (fc), and the other determines at what stage of their host star's evolution CETIs would be born (F). In order to ensure the completeness of the simulation, we consider a variety of combinations of fc and F. Our results indicate that for optimistic situations (e.g., F = 25% and fc = 0.1%), there could be ${\mathrm{42,777}}_{-369}^{+267}$ CETIs and they need to survive for ${3}_{-2}^{+17}$ yr (${2000}_{-1400}^{+2000}$ yr) to achieve one-way communication (two-way communication). In this case, human beings need to survive ${0.3}_{-0.298}^{+0.6}$ Myr to receive one alien signal. For pessimistic situations (e.g., F = 75% and fc = 0.001%), only ${111}_{-17}^{+28}$ CETIs could be born and they need to survive for ${0.8}_{-0.796}^{+1.2}$ Myr (${0.9}_{-0.88}^{+4.1}$ Myr) to achieve one-way communication (two-way communication). In this case, human beings need to survive ${50}_{-49.6}^{+250}$ Myr to receive one signal from other CETIs. Our results may quantitatively explain why we have not detected any alien signals so far. The uncertainty of the results has been discussed in detail and would be alleviated with the further improvement of our astronomical observation ability in the future.