The Drake Equation
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By Andy Kaiser
Article ID: 1317
I’m about to prove to you that aliens exist. I’m talking space aliens. Whether they’re the traditional Little Green Men, bug-eyed monsters, or something incomprehensible to the human mind, they exist, they’re intelligent, and they’re trying to find us.
I’m going to prove this to you by using the most powerful tool on Earth: mathematics. Ready? Here we go:
The number of stars in the Milky Way galaxy
Our planet Earth resides comfortably in the Milky Way galaxy, a pinwheel-shaped collection of at least 200 billion stars. You know how our sun is just ONE star? Give it 200 billion friends. That’s 200,000,000,000. At the time of this writing, this is roughly thirty times the number of humans living right now on this planet. Personally, I can’t even visualize a number that high. Again, that’s why we’re using math – even if we can’t see it or fathom it, we can represent it and come up with meaningful answers.
So, we have 200 billion stars. We know this number fluctuates – new stars form and die. Astronomers think that the birth rate of stars in the Milky Way galaxy is roughly one star per year.
The percentage of stars that have planets
Next, let’s look at all those stars. How many have planets around them? They’re hard to see, but we’re sniffing them out. NASA and the Jet Propulsion Laboratory tell us we’ve so far found hundreds of “extrasolar planets”. As of April 2009, the count was at 344. Some astronomers think at least fifty percent of all stars have planets! We’ll be more conservative. Let’s cut the ratio in half, and estimate twenty-five percent of all stars have a planet.
The number of “Goldilocks planets” per star
Now look at the planets spinning around all those stars. Of those planets, how many (per star) are capable of sustaining life? Such habitable places are sometimes humorously called “Goldilocks planets”, meaning that conditions for life (as we know it) are not too cold, not too hot, but just right.
In our own solar system, we have an idea of this number. Earth is such a planet. As we explore further, we may find that other places in our solar system are also “just right”. Or say you have a solar system with a Venus-like planet, where the greenhouse effect has escalated beyond control and turned the planet into an acidic-raining wasteland which is hot enough to melt lead. Take that hellish planet and move it away from the sun. Get it out far enough and you’ll find a sweet spot, where the planet is warm enough (thanks to the greenhouse effect), but not so hot it kills everything on the surface.
There are endless possibilities and plenty of conjecture as to the number of habitable planets per star. For now, let’s use the number as dictated by our only example, ourselves: let’s assume that of the stars which have planets, one planet is capable of supporting life in some form.
The fraction of planets where life evolves
This leads us to a conversation about life itself: on planets capable of sustaining life, what are the chances that life exists? Some biologists think that if life can exist somewhere, it will. Their opinion is bolstered by so-called “extremophiles” – Earth-based life that has adapted to some truly nasty conditions. Extremophiles can exist without sunlight, or under massive pressure, or bombarded by amounts of radiation that would make The Incredible Hulk blush. With evidence here on our planet, this is why many suggest that if life can exist somewhere, it will. Others say that getting to that point – the point where life begins – is very difficult. We know it’s possible, of course, because I’m writing this and you, my fellow human, are reading it. But let’s err on the side of caution. Let’s say that on life-capable planets, only one percent of those will harbor living beings.
The fraction of life evolving into intelligent life
So we’ve got a lot of stars. They have a lot of planets. Some of those planets are capable of supporting life, and some of those actually have life. Our next question is: is that life intelligent? Yes, the discovery of any form of life outside Earth would be world-changing, but remember, we’re talking about aliens. The things that you see in movies where they sneak up on people before revealing themselves to be evil killers. Or cute, huggable geniuses. Or both.
This is another contention point: some people think that if you have life, intelligence will evolve as a survival trait. Some disagree, and say that intelligence isn’t needed in order to survive. Let’s just take a guess here, and assume that if life occurs, there is a fifty percent chance it will become intelligent.
The fraction of intelligent life trying to communicate
Next we have communication. What fraction of that intelligent life will actively try to communicate with other intelligent races? What fraction has the capability and, more importantly, the desire? Because this is as nebulous as the previous estimate, let’s use the same fifty percent value.
How long does a communicating civilization live
We’re almost done. We’ve got one variable left. It’s an important one: how long does an intelligent civilization live?
Because we humans are the only example we know of, let’s look at ourselves: The sun and Earth in their present forms will be around for another ten billion years. But the human race might just destroy itself with nuclear war, bioweapons, or some other self-inflicted suicide. What about a solar flare or meteorite impact? How long can the human race survive? With Earth as our only home, we are in a very vulnerable position. If we manage to explore outside of Earth and begin colonization of our solar system and beyond, the human race could live a very long time. At the risk of depressing my audience, let’s assume the human race – and any intelligent race such as ours – will last 100,000 years before it’s completely obliterated from existence.
The proof that aliens exist
There. I did it. I proved aliens exist, that there are many, many intelligent races in our galaxy, and that they’re trying to communicate with us.
What, you don’t follow?
The previous thousand words are nothing more than a big math equation. Here’s the short form of everything I just said:
The Milky Way galaxy creates one new star per year. 25% of all stars have planets. 1 planet per star is capable of supporting life. 1% of those planets have life. 50% of those evolve intelligent life. 50% of those civilizations are trying to communicate with other beings outside their home planet. Such races live at least 100,000 years.
If we do the math and run this equation, we get a number. That number will tell us how many races (besides us humans) exist in our galaxy. That number is 65.There are 65 other civilizations covering the Milky Way, all of them wondering why we aren’t answering our galactic phone.
The Drake Equation
I really wish it were that easy. It’s not. While the numbers above may sound reasonable, while the math involved makes perfect sense, while the number “65″ even seems low for a galaxy with two hundred billion stars, I’ll share with you an uncomfortable secret: None of this proves anything.
This whole exercise was an example of plugging in values to The Drake Equation. The Drake Equation is a formula created by astrophysicist and astronomer Frank Drake in 1960. Frank Drake is also the guy who created the SETI program, the formalized search for extra-terrestrial life.
To paraphrase Neil Armstrong: The Drake Equation is an important step for man, but one giant leap of faith for mankind.
Drake, however, didn’t intend for this equation to specifically predict a certain number of intelligent races. The way I used the equation in this article is a popular and fun way to use it – but that’s not how it was intended. The Drake Equation enables us to understand the many factors enabling (and preventing) life on other worlds.
Use this tool to play with values and results in the Drake Equation.
When someone uses the Drake Equation to supposedly “prove” the existence of alien life, there are a number of flaws with that claim:
1) Some values in the equation are directly observable, like the number of stars in our galaxy and the number of planets orbiting other stars. But other values are completely unknown, like the chances of life emerging on a “Goldilocks planet”, and the chances of that life evolving intelligence. The Drake Equation has too many unknown values to produce a meaningful result.
2) We only have one example of intelligent life: us. Therefore, we know for sure that a correctly-formulated Drake Equation will give us a value of at least one! But besides those funny, fragile, bipedal occupants of the third planet from the sun, we have no other examples in which to base our guesses. Are we unique or not? Do intelligent races have a long lifespan, or does advanced technology bring about inevitable extinction? Without any other examples, and being such a young race, we just don’t have enough information. At least, not yet.
Drake formulated his famous equation to define and analyze the factors responsible for intelligent life. This allows us to research those individual factors, and study how they affect us and the chances of other life. This gives us a better understanding of life on Earth, and will eventually help us get out of our celestial sandbox and really start exploring.
The Drake Equation is indeed important. But realize what it’s intended to do. It’s not meant to predict or prove anything. It’s not supposed to impart hidden knowledge. It was designed to help discuss the possibility of life on other worlds, and to better define our lives in this incredible planet, galaxy and universe.
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