Caption: A diagram of the triple-alpha process.

Features:

1. The triple-alpha process in the diagram looks like a straightforward chain of binary nuclear reactions, but beryllium-8 is a highly unstable radioactive isotope (i.e., it is subject to spontaneous radioactive decay) with super-short half-life 6.7(17)*10**(-17) seconds, and so it was thought circa 1950 that the second nuclear reaction would almost never occur and that carbon in the universe could NOT be produced this way.

2. In 1953, Fred Hoyle (1915--2001) hypothesized the existence of a resonance reaction that enhanced the second nuclear reaction

         ⁸Be + ⁴He → ¹²C + γ

   which is exothermic with a release of 7.367 MeV of energy which is probably mostly in the emitted gamma ray (γ) (see Wikipedia: Triple-alpha process).

   This resonance reaction was discovered soon thereafter by experiment (see Wikipedia: Triple-alpha process: Discovery).

3. Fred Hoyle's hypothesis was an early explicit use of the anthropic principle in an extended sense: since carbon exists (and therefore we could exist), the relevant resonance reaction must exist.

   However, the term anthropic principle was coined later in 1973 (see Wikipedia: Anthropic principle: Origin), NOT by Fred Hoyle.

   Fred Hoyle's did coin the term Big Bang in a BBC radio program in 1949 (Wikipedia: Big Bang: Etymology).

4. Really the anthropic principle is just a generalization of the obvious conditional probability P(B|A) = 1 (i.e., the conditional probability of B given A is 1): A exists implies B exists. In the case of this figure, A is carbon and B is the triple-alpha process. Since P(B|A) = 1 and A exists, B must exist: i.e., the triple-alpha process exists even if you have never noticed it.