Are we alone in the universe?

What makes this fascinating

• The Fermi paradox — The galaxy is old and vast, with billions of Earth-like worlds. So where is everybody? The silence is itself a puzzle.

• The Drake equation — A famous attempt to estimate how many civilizations we could contact — but nearly every term in it is still wildly uncertain.

• Sniffing alien air — Telescopes like JWST are beginning to read exoplanet atmospheres for biosignatures — gases that life might produce.

Frequently asked questions

Is there alien life?

Unknown. No extraterrestrial life has been confirmed, but with billions of potentially habitable planets many scientists think microbial life could be common. Intelligent life is far more uncertain.

What is the Fermi paradox?

It is the tension between the high apparent likelihood of alien civilizations and the complete absence of evidence for them — captured by Enrico Fermi's question, 'Where is everybody?'

What is the Drake equation?

A 1961 formula by Frank Drake that estimates the number of communicating civilizations in our galaxy by multiplying factors such as star formation rate, the fraction of stars with planets, and how long civilizations last. Most of its terms are still poorly known.

More summits in Earth & Cosmos

• Predicting earthquakes

  Can the moment a fault will slip ever be forecast — or is the Earth fundamentally unpredictable?

• Tipping points in the climate system

  Where are the thresholds past which change becomes abrupt and irreversible?

• Earth's magnetic field

  A churning ocean of molten iron shields all life from space. How does it work — and why does it flip?

• The origin of the Moon

  A Mars-sized world struck the young Earth — maybe. We still can't fully explain our own Moon.