What the Drake equation has worked out is if that’s true (most species last an average of 150 years after the development of advanced technology before nuking themselves back into the stone age), then there are probably about 150 technologically advanced civilizations in the Milky Way at any given time.

A true staple of science fiction is the idea that our Galaxy is teeming with intelligent life, and that for one intelligent species, a monumental moment in their history is establishing contact with another intelligent species elsewhere in the Galaxy.The Drake Equation is an attempt by astronomer Frank Drake to try to determine about how many intelligent alien civilizations are likely to exist at any given time within the Milky Way. Without going into the mathematical details (which are interesting), you can work out that the number of intelligent civilizations is roughly equal to the amount of time an average civilization is willing and able to communicate with its neighbors in the universe. This has profound implications on the practicality of civilizations really being able to communicate with each other.For example, a common fear is that we are developing our technology too quickly, and we may not be that far off from destroying ourselves with our own technology. We developed radio technology (a great way of establishing communication with other civilizations) at around the same time we developed nuclear bombs. Ever since we developed nuclear weapons, it’s been an open question of “how long can we go before nuclear war breaks out and destroys our civilization?”A pessimistic approach is to say “not very long:” we’ll be lucky not to nuke ourselves back into the stone age within 100-200 years of developing nukes (let’s call it 150 years as an average). Of course, once we do so, we won’t really be in a position to be communicating with anyone “out there,” will we? And what if we are pretty typical as a species – that most species do something to destroy their own technological civilization within about 150 years of gaining the technology to communicate with aliens.What the Drake equation has worked out is if that’s true (most species last an average of 150 years after the development of advanced technology before nuking themselves back into the stone age), then there are probably about 150 technologically advanced civilizations in the Milky Way at any given time.So what? Well, if you treat the Milky Way as a flat disk, it has a surface area of about 8,000,000,000 square light years. If there are 150 civilizations (at any given time), that means each one would have about 8,000,000,000 / 150 = 53,000,000 square light years of “living space.” in our galaxy. If you imagine that “living space” as a big circle centered around the homeworld, you can estimate the “range” of this living space (the radius) by following this formula:Divide by 3: 53,000,000 / 3 = 17,700,000 (about).Then take the square root: Using my calculator, I figure out the square root of 17,700,000 is about 4,200 light years. Now double that (to turn radius into diameter): 8,400 light years.So if the average life span of a technological civilization is 150 years, the average distance between civilizations in the Milky Way would be 8,400 light years.Now, I want you to remember that a radio signal travels at the speed of light, and also remember what you learned about the idea of “lookback time” in Chapter 1.A civilization that is only going to last 150 years is 8,400 light years away from its nearest neighbor in space (that could communicate with it). And that is what I want you to discuss:1. Why is this a serious problem when it comes to civilizations being able to communicate with each other?2. About how long does the average life span of a civilization have to be in order to solve the problem implied by that first question?This may actually explain why we haven’t made contact with another civilization. Consider this: the Milky Way is 12 billion years old, but a civilization that has been around for only 100,000 years (at least) – a TINY fraction of that 12 billion years – should have had plenty of time to send a signal from one end of the Galaxy to the other – and therefore should have been detected by any civilization anywhere else in the Galaxy. Yet we’ve never detected any trace of another alien civilization. This problem of where are all the aliens? is called Fermi’s Paradox.3. How does your answer to questions 1 and 2 give a possible explanation for Fermi’s Paradox?