The Milky Way Should Be Full of Intelligent Civilizations

Plugging new measurements into the famous Drake Equation suggests our galaxy should be bustling with activity.

In the fall of 1961, while working at the National Radio Astronomy Observatory, Dr. Frank Drake combined the factors for determining the likelihood of detecting intelligent civilizations into one, concise equation. Since then, it has garnered both love and hate, as it is a useful tool yet extremely imprecise. This imprecision comes from difficulties in measuring its 7 variables, with estimates for intelligent civilizations in our galaxy ranging from 0 to the millions, depending on the measurements and assumptions of the astrophysicists using it. 

However, we’ve gotten better in recent years. In particular, a team from the University of Sheffield claims Earth-like planets are much more common than previously thought, and a team from University of Arizona overturned the notion that organic molecules need the energy from a star to form, as they found them in clouds of gas and dust that would eventually form into stars and planets.

Calculating the Likelihood of Detecting Intelligent Life

The Drake Equation uses 7 variables to calculate N, the number of civilizations that can produce detectable communication.

N = R_* x f_p x n_e x f_l x f_i x f_c x L

R_* = the average rate of star formation in the galaxy. Drake and his colleagues originally put this at 1, meaning 1 star formed per year on average over the lifespan of the galaxy. However, recent measurements suggest that this could be as high as 3.

f_p = the fraction of stars with planets. This was originally thought to be .5 or less, meaning only half or less of the Milky Way’s stars have planets. Now, because of techniques like microlensing and equipment like NASA’s James Webb Space Telescope this is thought to be closer to 1, meaning virtually every star has planets.

n_e = the number of planets with conditions for life. A lot of considerations go into determining this variable, including the type of star, distance to the star, having the the proportion of elements, being in a safe part of the galaxy, having low density to not attract asteroids, having geological activity, having seasonal activity due to the planet’s tilt, among others. In fact, this variable is heavily debated, with some giving it a high value of 5, although some such as those that subscribe to the rare Earth hypothesis favor a much lower value.

f_l = the fraction of planets on which life appears. Of course, this is highly debated, as it is merely based on speculation. Because there is only one known example of life emerging–life on Earth–it is difficult to form any conclusion with a solid foundation. However, some suggest the emergence of life on Earth happened once there were favorable conditions, meaning it seems life is likely given a high value for n_e.  

f_i = The fraction of planets with life becoming intelligent. Again, values for this variable are highly speculative. One point to consider, though, is that the emergence of complex life happened when conditions were optimal, as shown by the Cambrian explosion. Again, this suggests that given the right conditions intelligent life is ready to emerge.

f_c = The fraction of intelligent that send signals into space. Humans have been broadcasting electromagnetic signals for about 100 years. Most of these are meant for communicating with ourselves, and some have been purposefully sent with the hope of contacting another intelligent civilization. It is assumed by most that other civilizations would do the same, but, for unknown reasons, they may have chosen not to. It’s also possible they communicate in ways we are not aware of or their signals are not able to reach Earth with enough strength to be discernible. 

L = The length of time intelligent civilizations send signals into space. Values for this variable are also controversial. A civilization that is capable and willing to transmit detectable signals may do so for a short time or, if they overcome threats to their existence, indefinitely.

As can be seen, there’s a lot of debate about which values each of the 7 variables should have. Fortunately, the teams mentioned above have provided some unique insight.

New Measurements

In their paper published in the Astrophysical Journal, the team from the University of Sheffield explained that they used the Gaia telescope to look at clusters of young stars in the Milky Way and found that there were far more stars similar to our own than previously thought. This means that n_e = the number of planets, per solar system, with an environment suitable for life can be given a much higher value, as our sun is considered ideal for fostering life. This also means that planets of similar size to Earth are more likely to form around these stars, again increasing the favorable conditions for life.

In another paper from the Astrophysical Journal, a team from the University of Arizona claimed to have found signatures of methanol and acetaldehyde, two complex organic molecules that are the building blocks for life, in collapsing prestellar cores, which are the nurseries for stars. It was thought that complex organic molecules would need to form in the presence of a heat source like a star on a solid surface such as a planet. However, this shows that not only are complex organic molecules more mysterious than we realize, it shows they are also far more prevalent. Therefore, if these are part of the cloud of gas and debris that forms planets, then it is far more likely than previously expected that they are scattered across the surface of the planet. With this information we can increase the value of f_l = the fraction of suitable planets on which life actually appears quite a bit.

So, as Enrico Fermi once asked, if there’s supposed to be so many intelligent civilizations out there, why is it so quiet? 

Maybe their signals haven’t reached us yet because the Milky Way is some 100,000 light years across. Maybe we can’t detect their signals. Maybe intelligent civilizations don’t last that long and they are long dead. Maybe they’re just not interested enough in us to send a signal. Maybe they have contacted us and it’s being covered up. Maybe we are actually alone. Maybe it’s all just a simulation. 

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