Science Puzzle
The Fermi Silence
The Milky Way galaxy contains about 400 billion stars, is roughly 13 billion years old, and astronomers estimate it contains billions of planets in the habitable zones of their stars. The physics that produced life on Earth is the same physics everywhere in the universe.
Given all of that, where is everybody? Why have we detected no signals, no visitors, and no evidence of any other civilisation?
The Answer
This is the Fermi Paradox, named after physicist Enrico Fermi, who asked exactly this question. The silence is genuinely puzzling and nobody has a universally accepted answer.
Proposed explanations fall into a few broad families. Perhaps intelligent life is extraordinarily rare even if simple life is common (the Rare Earth hypothesis). Perhaps civilisations destroy themselves before reaching interstellar communication (the Great Filter hypothesis, which raises the uncomfortable question of whether the filter is behind us or ahead of us). Perhaps signals exist but we lack the technology to recognise them. Perhaps interstellar communication is simply too energetically expensive for any civilisation to maintain. Or perhaps everyone is listening but nobody is transmitting.
The Fermi Paradox is valuable not because it has an answer but because it forces precise thinking about probability, timescales, and what assumptions we are hiding inside words like "inevitable" and "common".
The principle: The Fermi Paradox. The apparent contradiction between the high probability of extraterrestrial civilisations and the complete absence of evidence forces precise reasoning about probability, timescales, and hidden assumptions.