Little gray men with big black eyes.

They are able to communicate telepathically. They like to abduct humans and perform examinations on them.

You know what I am talking about, right? Maybe you imagine the ones with multiple appendages. Or better yet, suckers and slime and they want to eat you. Those are creepy!

Perhaps you just prefer the cute kind that uses toys to communicate and just wants to go home like Dorothy in The Wizard of Oz?

Aliens. We are all familiar with the concept and even imagery, thanks to Hollywood. They make a great story lighting up our imaginations with spacecraft, unimaginable technology, and exotic worlds. But, have you ever stopped to think about what alien life would really be like?

We are still learning so much about our planet, the earth beneath our very own feet. Consider the diversity of life on Earth. Plants. Bacteria. Jellyfish. Now, consider the definition of life. Even scientists can’t agree on a common definition. Can a computer program be alive? It is a complicated question.

Regardless of these complex issues, it hasn’t stopped us curious humans from wondering if life, as we are familiar with, exists elsewhere. Looking up at the night sky and knowing that it goes on far beyond what we can see or even understand, the mind tends to imagine great things. At least that’s what my mind does! 

Imagination is great for the human experience. The arts, great entertainment, revolutionary thinking, everything really is inspired through imagination. But what if we want concrete answers to the ponderings of our minds? That is where science comes in.

That is also what Frank Drake wanted to do, bring science to the table when talking about life outside of Earth. To do this, he created what has come to be known as the Drake Equation.


What is the Drake equation?

Dr. Frank Drake presented this formula in 1961. At the time, he was a young radio astronomer interested in the search for extraterrestrial intelligence. He called a meeting to discuss the topic and how to approach it scientifically. He wanted to figure out what we need to know to discover extraterrestrial life. Once that has been answered, the next step is to figure out how to get that data.

He developed what became known as the Drake equation to guide the discussion. Now, many years later, the equation and its many variables are still hot topics for debate.

Drake equation

The Drake equation

The equation is intended to solve for the product N. N is the number of civilizations in the Milky Way from which we could receive communication. The right side of the equation consists of factors pertinent to potential extraterrestrial communicators. Each subsequent variable assumes the previous variable is satisfied. In example: A life form must exist before it can have intelligence. See the next section for a detailed description of each variable.


Explain, in English please?

Drake equation variable N

This term represents the number of civilizations in our the Milky Way whose technological communications are detectable.

  • Comments: There is obviously a higher likelihood of extraterrestrial life than there is of communicating with that life form. Is that what is interests us? Are there other ways to know if life exists aside from literally getting a message or visit from them? Does it matter if life is out there if we aren’t able to communicate with them? If we do get communications from some other life form, what are the odds that they still exist? It takes a long time to travel great distances. So. Many. Questions.

Drake equation variable R star

This term represents the rate of star formation in our galaxy.

  • Comments: Scientists have some information to help make estimates. The estimated number of stars divided by the age of our galaxy. However, the rate of star formation has changed over time. More stars were formed during the earlier years of our galaxy and that has slowed over time. If you consider the type of stars that are suitable for life, the number is also smaller.
  • Drake’s estimate: 5
  • Range of estimates: around 0-20, but scientists believe it to be around 1.

Drake equation variable f sub p

This term represents the percentage of those stars that have planets.

  • Comments: In recent years, scientists have started to find many exoplanets(a planet outside of our solar system). As of 6/4/2015, there have been 1852 confirmed exoplanets with many other potential candidates waiting for confirmation. How are scientists able to find exoplanets? Looking at the gravitational effects, scientists can detect tiny wobbles in a star due to planet orbits. Scientists also can notice tiny differences in star brightness because the planets block some of the light as they pass in front of the star.
  • Drake’s estimate: 50%
  • Range of estimates: 0-100%, scientists now believe it to be around 60-100%

Drake equation variable n sub e

This term represents the number of planets that can support life.

  • Comments: Typically, scientists have considered water to be essential to support life, life as we know it anyways. However, other factors also need to be considered such as atmosphere, orbit stability, and age/stage of life of the star.
  • Drake’s estimate: 2
  • Range of estimates: 0 to around 5, scientists believe it to be around 0.5-3


Throwing darts at dartboard

The next variables are more difficult. We don’t have data to help with estimates. All we know is our Earthly experience. This is where personal views come into play.

How do you perceive humans? Are we special? Are we the norm? Given the approximately 13.7 billion years our galaxy has existed, is it likely for life, intelligence, and technology to evolve in many places in our galaxy?

Let’s go ahead and entertain the thought and throw some darts at the board.



Drake equation variable f sub l

This term represents the percentage of those planets that actually develop life.

  • Comments: Again, the question of what is considered life comes up. If we take what we know from our own solar system, it seems that life does evolve given the chance. Scientists are split on this, but most believe that given the right conditions life will emerge.
  • Drake’s estimate: 100%
  • Range of estimates: 0-100%, on the higher side? possibly over 50%?

Drake equation variable f sub i

This term represents the percentage of the life that is intelligent.

  • Comments: How do you define intelligence? It is relative. Frankly, sometimes I question whether humans are intelligent. *wink* Considering the many kinds of life there have been on Earth, an exceedingly low number are considered intelligent. Biologists tend to believe it is rare to develop intelligence, while astronomers believe intelligence is so useful it is inevitable. I am going to place my bets with the biologists on this one, it is their field after all.
  • Drake’s estimate: 20%
  • Range of estimates: 0-100%, on the lower side? possibly less than 50%?

Drake equation variable f sub c

This term represents the percentage of the intelligent life that transmit technology communications in space.

  • Comments: If we assumed intelligence to include the ability to create things, then this seems more likely based solely on our experience. If your assumptions are less than this, than it looks far less likely. Perhaps, other life forms use/have used/will use a communication process much different than anything we recognize.
  • Drake’s estimate: 100%
  • Range of estimates: 0-100%, throw a dart on this one

Drake equation variable L

This term represents the length of time the communications are operating.

  • Comments: The Milky Way is around 13.6 billion years old. The Earth is around 4.55 billion years old. We have been transmitting for about 100 years. That is minuscule considering the context of our planet in our galaxy. Whether it is leaking communications unintentionally through technology like radio or intentionally sending communications like the Golden Record. Discussions tend to turn dark quickly raising issues like gamma-ray bursts, asteroids, and self-destruction of species or environment (atmospheric changes, disease, famine, and nuclear destruction). Ugh!
  • Drake’s estimate: 10,000
  • Range of estimates: 1-many billion, I would image closer to 1 than many billion

Drake equation

Plugging in the values for Drake’s original estimates, we have…

N = (5)(50%)(2)(100%)(20%)(100%)(10,000)

N = 10,000 civilizations in the Milky Way whose communications we could receive

Plugging in pessimistic/low estimates, we have…

N = (1)(60%)(0.5)(0.1%)(0.1%)(1%)(100)

N = 0.0000003 civilizations

Plugging in optimistic/high estimates, we have…

N = (7)(99%)(3)(100%)(100%)(100%)(1,000,000,000)

N = 20,790,000,000 civilizations


  • Range from pessimistic and optimistic estimate: 0.0000003 – 20,790,000,000, obviously a huge disparity
  • Pessimistic approach. We know that the pessimistic estimate is too low because we exist and therefore N should be at least 1 to account for us. As we can remember from math class, anything multiplied by 0 is 0. So, even if only one of the variables is 0 or close to 0 we all know what that means, N=0 or is really really close to it. So, pessimistic estimates on the life, intelligence, and communication variables will render an extremely low N.
  • Optimistic approach. The estimate is likely too high otherwise a civilization would be approximately 3.6 light years away. If that were the case, we may have heard from them by now. For optimists, the equation roughly boils down to N=L. Unfortunately, L is a HUGE unknown. But with 200 billion stars in our galaxy, that is a lot of possibilities for life. I am certainly happy to avoid the suggestions of masses of self-destruction for intelligent beings.
  • There are online calculators available where you can plug in your guesses. The calculator at NOVA is nice because it gives you some context for your estimates. The calculator at University of Texas, Austin is fun because it tells you how close the average distance is to the nearest civilization.


Stirring up the Drake debate

Here are some items that add fuel to the heated discussions of the Drake equation. I present a quick synopsis to give you something to mentally chew on. If you want to learn more, you can visit my resources.

  1. The Wow! Signal. Have you heard about this? Back in 1977, Jerry Ehman, a radio astronomy researcher noticed something unusual on the data from the Big Ear radio observatory at Ohio State University. There was a 72 second signal at a peculiar frequency that was exceptionally strong. It was the loudest and longest signal the observatory ever recorded. He circled the data and wrote “Wow!” next to it, thus the name the Wow! signal. He brought it to the attention of the other observatory staff and they were amazed as well. After investigating, there is still no explanation or repeated signal after all these years. This just goes to show that IF (and that is a really big if) it was a communication from another life form, we apparently don’t meet the intelligence criteria on their version of the Drake equation.
  2. Fermi paradox. This theory is named after Enrico Fermi. Talking with his friends, he decided that if there were beings in the galaxy that had the technology and initiative, they could have easily colonized the galaxy during the time since its creation. He asked, “Where is everybody?” A lot of people support his argument. There aren’t any extraterrestrial beings here because there are none.
  3. Rare Earth Hypothesis. This theory has its own equation(the Rare Earth equation) to rival the Drake equation. Essentially, the theory believes that complex, multi-cellular life is rare. It suggests there has to be very special circumstances for intelligent life to evolve. In addition to the Drake identified variables, other variables address factors such as metal-rich stars, galactic zone, complex metazoans, planet lifetime, large moon, large outer planets, extinctions, and more. I won’t pretend to know about this and you can follow the link in the resources to learn more.
  4. Copernican principle/Mediocrity principle. Remember learning about Copernicus? He is the mathematician and astronomer who declared that the Sun was the center of the Universe and not the Earth. This theory takes its name from him. It basically uses the rules of statistics and the laws of nature to look at the likelihood of something occurring. Everyone used to believe that humans and Earth was the center of everything, literally. Then the cold and cruel reality hit home, we aren’t special. Earth isn’t special. Our solar system isn’t special. We are all just following the laws of the universe. If we aren’t special, then there must be others just like us in the galaxy that aren’t special either.
  5. Seager equation. This equation doesn’t dispute the Drake equation, it is simply another way of looking at the issue of life on other planets. The equation looks at the chances of detecting any kind of extraterrestrial life by their biosignature gases. Using spectroscopic imaging, scientists can look at the light and determine what gases are present. If the gases identified don’t really seem to fit, there is a reason for it. That reason could possibly be life. This is a practical approach because scientists can realistically pursue gathering data using today’s technology.


Where does that leave us?

Obviously, there are some variables in the Drake equation that scientists don’t have any answers or even any data on which to make an educated guess. Our technology or understanding of the galaxy needs to catch up with our questioning minds.

How can we even begin to address such enormous questions, especially when we have such little data to go on? You break it down into smaller, more manageable questions. Then you may have to break those questions down again.

The great thing about the equation is really the question or rather questions that it raises. It starts the conversation. It also grounds the discussions to data and facts. Even if they are currently unknown it can tell us where science needs to go. This is what inspires the great scientists of tomorrow.



Are we alone?

So, what do you think? Have you ever spent much time seriously considering life outside of our planet. If you really get into the space stuff like I do, I would encourage you to participate in Zooniverse. You can participate in scientific study from the comfort of your own phone or computer for only minutes at a time. Learn about it by reading my article Have some time? Volunteer online.

Have you come up with any opinions on life in our galaxy or even beyond? What were your results for N in the online calculators? What are your thoughts on how to approach the search for intelligent life outside of Earth?

Let me know in the poll and comments!


10 Facts about the Milky Way at

A New Equation Reveals Our Exact Odds of Finding Alien Life at

Calculating The Odds of Intelligent Alien Life (video) at

Drake Equation Calculator at

Here’s How Many Intelligent Alien Civilizations Might Live In Our Galaxy at

How Science Figured out the Age of the Earth at

Interactive calculator for Drake Equation at

Nearly All Sun-Like Stars Have Planetary Systems at

NASA exoplanet archive at

Neil deGrasse Tyson On Life On Other Planets! at

The Chance of Finding Aliens at

The Drake Equation at

The Drake Equation: 50 Years of Giving Direction to the Scientific Search for Life Beyond Earth at

The Mediocrity Principle at

The “Rare Earth” Hypothesis at

The Search for Life in the Universe at NASA

What is the Golden Record? at NASA

What is the Wow! signal at

Wikipedia contributors. “Drake equation.” Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 2 Jun. 2015. Web. 8 Jun. 2015.