The Milky Way is estimated to contain on the order of one trillion stars, and each of those stars are spaced many light-years in between. This means our galaxy is a gigantic place, and if we were all alone out there, it would be an awful waste of space. That is not even considering the hundreds of billions of other galaxies that exist in the universe.
But just how could one go about estimating how many of these star systems contain planets capable of sustaining life? And, out of those, how many of those extraterrestrial life forms could be expected to be intelligent?
These and similar questions have been pondered by scientists and philosophers throughout history. Luckily, in the modern age, with the invention of high-powered telescopes and new analytical tools, approaches have been developed to begin to narrow in on answers.
One such approach was proposed by radio astronomer Dr. Frank Drake in 1961. At the time, he was working to develop an argument for seeking out extraterrestrial life by searching for artificial radio signals throughout the galaxy. His efforts were the precursor to the Search for Extra-Terrestrial Intelligence (SETI) program that still continues to today.
The Drake Equation
To prepare for a large meeting of the minds on the pursuit of extraterrestrial life, Dr. Drake developed a framework for estimating how many intelligent civilizations may be detected within the galaxy. The concept he presented went on to become known as the Drake Equation.
Where N is the total number of intelligent civilizations in the galaxy in which communication would be possible, R* is the rate of suitable star formation, fp is the fraction of those solar systems that contain planets, ne is the average number of planets capable of supporting life per star that has planets, fl is the fraction of planets where life actually occurs, fi is the fraction of life-bearing planets on which intelligent life emerges, fc is the fraction of those intelligent life forms that develop a civilization which releases detectable signs of their existence into space, and L is the length of time that those civilizations are capable of releasing signals into space.
The Drake Equation contains 7 terms in total, and each of the components can only be estimated with a high degree of uncertainty. Thus, the equation results in array of estimations for the scale of intelligent extraterrestrial life, with answers ranging from as many as 50 million civilizations in the optimistic assessment, to as few as 20 civilizations in skeptical scenarios.
In order to come up with a solution for the equation, a number of assumptions need to be made to assign values to each of the terms. Luckily, recent advances in astronomy have allowed us to take more precise measurements of extrasolar planets, or planets located outside of our solar system. As these tools become more sophisticated, we should be able to further refine the estimates of each of the terms for the Drake Equation.
One interesting takeaway of the Drake Equation is that even the most conservative estimates are non-zero, meaning that it is widely believed intelligent extraterrestrial life almost certainly does exist elsewhere in the galaxy.
BBC has a useful tool posted online for exploring the range of possibilities here.
Another famous thought experiment regarding the possibility of intelligent extraterrestrial life was proposed by famous physicist Enrico Fermi in 1950, while working at Los Alamos National Laboratory in New Mexico.
The Fermi Paradox
Dr. Enrico Fermi was a famous Italian physicist that made breakthroughs in particle physics and quantum mechanics, even receiving a Nobel Prize for his work related to nuclear applications. The story goes that one day Fermi was having an informal discussion with fellow scientists about the possibility of extraterrestrial life. Fermi quickly did some rough order of magnitude estimates in his head and determined that, considering the age of the universe, life should be abundant.
He further concluded that the Earth should have been visited numerous times throughout the past and added a simple question: where are they? His question highlights a perceived conflict between the assumption that life was prevalent throughout the universe and the fact that we have yet to encounter convincing evidence of that extraterrestrial life.
Of course, to arrive at this paradox, a number of assumptions were made, including:
• The Sun is a fairly typical star, and it is relatively young. There are many stars billions of years older than the sun.
• Other sun-like stars have planets capable of supporting life.
• Interstellar travel is possible, and the ability has been achieved by a subset of intelligent civilizations.
• Any interstellar civilizations would attempt to colonize the galaxy, and that this could be accomplished in around 10 million years.
Numerous solutions have been offered to explain the Fermi Paradox, but I will highlight three of the most widely accepted here.
The Rare Earth Hypothesis
One possible solution for the Fermi Paradox is that planets like Earth and the circumstances suitable for creating life are extremely rare across the universe. This Rare Earth Hypothesis became popular in the new millennium in contrast with the theory that life is abundant, as suggested by Frank Drake and Enrico Fermi.
Several recent developments in astronomy make this hypothesis seem unlikely. To date, scientists have now detected over a thousand extrasolar planets, including several that are similar in size to the Earth. Extrapolating on the initial results of the Kepler Space Telescope, Astronomers now project that there could be as many as 40 billion Earth-sized planets located in the habitable zone of suitable stars within the Milky Way alone.
New methods are also being devised to help detect the signatures of chemicals associated with life. Just this year, one research group has proposed a new method for looking for Methane in the atmospheres of remote planets.
Interstellar Travel May Be Impossible
For many years, the prevailing thought in science was that faster than light (FTL) travel is theoretically impossible due to the restrictions placed by Einstein’s theories of relativity. In recent times, however, that paradigm seems to be shifting toward the prospect that FTL travel may be possible after all. Several recent efforts highlight this shift.
The Alcubierre Warp Drive, proposed by Mexican Physicist Miguel Alcubierre, is a theoretical model for a potential warp drive that could effectively allow FTL travel. The drive would effectively create an artificial gravity well to warp space-time and propel a spacecraft vast distances in a short time, while staying consistent with Einstein’s theories of relativity.
Perhaps the 100-Year Starship Plan, whose stated goal is to achieve the technologies needed for interstellar travel within the next 100 years, will make use of this concept to achieve its objective. The 100-Year Starship Program is a joint project with the National Aeronautics and Space Administration (NASA) and the Defense Advanced Research Projects Agency (DARPA).
And just recently, NASA announced that a demonstration project for a controversial new electromagnetic powered space propulsion drive proved successful, counter to the fact that it was theoretically ‘impossible’. The EmDrive concept provides propulsion internally without the need for any propellant, and it appears to violate Newton’s Third Law of Motion.
Perhaps there are other technologies or concepts that have been ignored because they appear to violate known physical laws, when in fact they still might work. Furthermore, maybe there other advanced technologies that have been locked away in hidden black projects but may enable interstellar travel.
The Great Filter Hypothesis
The Great Filter Hypothesis suggests that there may be certain stages of development that are difficult to survive through. It is argued that in order for a species to advance far enough to become a space-faring civilization, it must first pass through an adolescent stage of maturity without extinguishing itself. Interestingly enough, this has been widely displayed in Earth’s current state of affairs. Between threatened nuclear Armageddon and constant war throughout the world, it is a wonder that we haven’t killed ourselves off yet.
Coincidentally, there have been many reports of UFOs taking an interest in nuclear facilities and weapons by a number of former military personnel around the world. Some of these claims have been hotly disputed, but it seems that quality and depth of the claims allows them to persist over time.
Another interesting thing to note is that if you subscribe to the possibility that some UFOs are extraterrestrial craft and/or Ancient Astronaut theory, Fermi’s question is easily resolved. Simply put, extraterrestrial civilizations do visit the Earth and have been doing so throughout history.
Although there has been lots of speculation on the issue of whether or not we are alone in the universe, we are now finally approaching a point where we can definitely prove, as a society, that extraterrestrial life exists.
Maybe this realization will come from a discovery made by one of our various probe programs, such as the Mars Curiosity Rover. Perhaps it will come from programs such as SETI that are trying to locate signs of extraterrestrial life elsewhere in the galaxy. It is, however, important for us not to forget that this realization may come from another source: the full disclosure of UFO-related documents and materials by all governments and private groups.