Measured edge to edge, the universe as we know it stretches some 93 billion light-years across. That unfathomable expanse contains 2 trillion galaxies, each shining with millions of stars and dotted with more planets than you can imagine. Given all that real estate, it seems unlikely we're alone. Yet in all of human history, we've found nothing to suggest otherwise.
Scientists who have spent their careers searching for any sign of an otherworldly civilization concede it’s possible we’ve got the cosmos to ourselves. Still, they highly doubt that’s the case. “To say this is the only place where there’s any intelligence is hubris of a very high order,” says astrophysicist Seth Shostak of the SETI Institute. (The acronym stands for “search for extraterrestrial intelligence.”) Statistically speaking, there are too many locations where life could thrive for humanity to be an anomaly.
Astronomer Frank Drake suggested as much in 1961. He posited that the number of technologically advanced civilizations in our galaxy would be the product of seven variables. They include the number of stars throughout the Milky Way, how many of those bright, burning gas balls illuminate planets, and what percentage of those worlds could support life. His eponymous equation was a thought exercise meant to start a discussion among colleagues, but it has helped frame the topic in the years since he wrote it.
Many of Drake's variables are speculative, making his math little more than conjecture. But astronomers now know for certain that exoplanets, many of which could harbor life, form throughout the Milky Way like dust bunnies under your couch. In the past two decades, researchers have confirmed the existence of more than 4,000 planets in our galaxy, a finding that suggests the cosmos all but brims with them. Astrophysicist Christopher Conselice of the University of Nottingham puts the number at 100 quintillion. That's a one with 20 zeros. Some think there may be far more than that.
What kind of school subjects do you have at school today?
How many school subjects do you have at school today?
What is your favorite subject at school?
What is the name of your German teacher?
How do you find your math teacher?
How does Dominik find his English teacher?
How many lessons did you have yesterday?
How many lessons did you have last Friday?
How long is the big break?
When do you have lunch today?
Do you have geography in middle school, or did you only have geography in elementary school?
Were you in the classroom yesterday?
How are your English lessons?
When do you come back home from school?
Do you have lessons on Saturday?
Where have you been on Sunday?
How was your first day at school?
How is your vocabulary in English?
Is your vocabulary more extensive in English than in German?
42-42(2/7)
42-12
30
There are 30 options with no chocolate.
keq = [SO3]^2
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[SO2]^2[O2]
Products over reactants and coefficients as exponents
