The Drake equation In 1961 astronomer Frank Drake developed an equation to try to estimate the number of extraterrestrial civilizations in our galaxy that might be able to communicate with us via radio transmissions. Now largely accepted by the scientific community, the Drake equation has helped spur efforts by radio astronomers to search for extraterrestrial intelligence.

Here is the equation:

NC=N⋅fp⋅ne⋅fl⋅fi⋅fc⋅fL

OK, it looks a little messy, but here’s what it means:

So, how many ETs are out there? That depends; values chosen for the many factors in the equation depend on ever-evolving scientific knowledge and one’s personal guesses. But now, some questions.

1. What quantity is calculated by the first product, N⋅fp?

2. What quantity is calculated by the product, N⋅fp⋅ne⋅fl?

3. What probability is calculated by the product fl⋅fi?

4. Which of the factors in the formula are conditional probabilities? Restate each in a way that makes the condition clear.

Transcribed Image Text:

Factor N fp ne fl fi fc fL Nc What It Represents Number of stars in the Milky Way Galaxy Probability that a star has planets Number of planets in a solar system capable of sustaining earth-type life Probability that life develops on a planet with a suitable environment Probability that life evolves intelligence Probability that intelligent life develops radio communication Fraction of the planet's life for which the civilization survives Number of extraterrestrial civilizations in our galaxy with which we could communicate Possible Value 200-400 billion 20%-50% 1? 2? 1%-100% 50%? 10%-20% 11,000,000? ?