Large Number Coincidences and the Anthropic Principle in Cosmology
Brandon Carter · 1974
"Several of the universe's fundamental physical constants appear implausibly fine-tuned for the emergence of life — but this isn't necessarily evidence of design, because any universe where observers exist to notice the constants will, by definition, have constants compatible with observers existing."
Carter's paper, presented in 1973 and published in 1974, formalized an observation physicists had noticed informally: numbers like the strength of gravity relative to electromagnetism, or the precise ratios governing stellar formation, sit in an extremely narrow range — if they were even slightly different, stars, chemistry, or stable planets, and therefore anyone around to measure them, likely couldn't exist. Carter's key move was pointing out a subtle selection effect: we should expect to find ourselves in a universe compatible with our own existence, no matter how statistically rare such a universe is among all possible ones, simply because we couldn't be observing it otherwise.
Carter distinguished a 'weak' version — among possible times and places, we should expect to find ourselves in one compatible with observers existing, an observational selection effect, not a metaphysical claim — from a 'strong' version — the universe's constants must be such as to admit observers at some stage, a much bolder claim closer to teleology. The weak version is now widely accepted as basic statistical reasoning; the strong version remains genuinely contested, with critics arguing it risks becoming an unfalsifiable way to explain away any fine-tuning, and defenders arguing it's a legitimate response once you accept something like a multiverse of many universes with varying constants.
What is the core insight of the (weak) anthropic principle?
Read more about the topic
The explanation above is written with AI assistance. These are the originals — go to them to check it.
- Republication of: Large number coincidences and the anthropic principle in cosmologyGeneral Relativity and Gravitation (Springer)
- Fine-TuningStanford Encyclopedia of Philosophy
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