Sagan wrote or co-wrote about twenty books. Here are the best known, what each is about in our own words, and why it is worth reading. All are still under copyright, so look for them at a library.
Key idea
| Book | Year | What it is about |
|---|---|---|
| The Cosmic Connection | 1973 | Short essays on the planets, life in the universe and our place in it. |
| The Dragons of Eden | 1977 | How the human brain and intelligence evolved; it won the Pulitzer Prize in 1978 and introduced the Cosmic Calendar. |
| Broca's Brain | 1979 | Essays on science, scientists and claims at the edge of science. |
| Cosmos | 1980 | The book of the television series (see the previous topic). |
| Contact | 1985 | A novel about a scientist who receives a message from the stars; made into a film in 1997. |
| Pale Blue Dot | 1994 | Our future in space, named for the 1990 Voyager photo in which Earth is a tiny speck. |
| The Demon-Haunted World | 1995 | How to think clearly about claims, written with help from Ann Druyan; it includes his "baloney detection kit" of thinking tools. |
| Billions and Billions | 1997 | His last essays, published after his death. |
Borrow the book
The Demon-Haunted World by Carl Sagan is still under copyright, so we do not reproduce it. Find it at a library: Open Library or WorldCat. Also search for Pale Blue Dot and The Dragons of Eden.
Thinking tools, in our own words
In The Demon-Haunted World Sagan collects tools for checking a claim. Here are some of them, restated:
- Look for independent confirmation of the facts.
- Encourage debate among people who know the evidence.
- Don't trust a claim just because an important person makes it.
- Think of more than one explanation, and test each.
- Measure if you can: numbers help you tell explanations apart.
- Every link in a chain of argument must hold.
- Prefer the simpler explanation when two fit the facts equally well.
- Ask whether the claim could, in principle, be shown false.
He also made famous a short rule: extraordinary claims require extraordinary evidence. A surprising claim needs strong evidence before we accept it.
Worked example: The pale blue dot
- $6{,}000{,}000{,}000 \div 300{,}000 = 20{,}000$ seconds.
- $20{,}000 \div 3600 \approx 5.6$ hours.
Answer: About 5.6 hours.
Common mistake
Read more: Carl Sagan, Pale Blue Dot and The Demon-Haunted World.