[...] how to reason when you suspect that your evidence is biased by “observation selection effects”—that is, evidence that has been filtered by the precondition that there be some suitably positioned observer to “have” the evidence. This conundrum—sometimes alluded to as “the anthropic principle,” “self-locating belief,” or “indexical information”—turns out to be a surprisingly perplexing and intellectually stimulating challenge, one abounding with important implications for many areas in science and philosophy.
There are the philosophical thought experiments and paradoxes: the Doomsday Argument; Sleeping Beauty; the Presumptuous Philosopher; Adam & Eve; the Absent-Minded Driver; the Shooting Room.
And there are the applications in contemporary science: cosmology (“How many universes are there?”, “Why does the universe appear fine-tuned for life?”); evolutionary theory (“How improbable was the evolution of intelligent life on our planet?”); the problem of time’s arrow (“Can it be given a thermodynamic explanation?”); quantum physics (“How can the many-worlds theory be tested?”); game-theory problems with imperfect recall (“How to model them?”); even traffic analysis (“Why is the ‘next lane’ faster?”).
In physics and cosmology, the anthropic principle is the philosophical argument that observations of the physical Universe must be compatible with the conscious life that observes it. Some proponents of the argument reason that it explains why the Universe has the age and the fundamental physical constants necessary to accommodate conscious life. As a result, they believe that the fact that the Universe’s fundamental constants are within the narrow range thought to allow life is not remarkable.
The Strong Anthropic principle as explained by Barrow and Tipler (see Variants) states that this is all the case because conscious life, in some sense, needed to exist. Critics argue in favor of a Weak Anthropic principle, which states that the universe’s fine tuning amounts to selection bias; in an infinite universe, some worlds might evolve conscious life. Douglas Adams used the metaphor of a living puddle examining its own shape, since, to those living creatures, the universe may appear to fit them perfectly (in fact, they simply fit the universe perfectly).
UDASSA (A framework for anthropic reasoning due to Wei Dai.)
UDASSA is a philosophical “theory of everything” (TOE). It provides a framework to understand the universe and our place within it. Basically it can be summed up very simply as: Universal Distribution (UD) plus ASSA (absolute self selection assumption).
To make progress in cosmology we really need to understand the fundamental issue of how to compare different theories and work out the posterior credences of different models in the light of what we know and observe.
The Anthropic Principle
References and Resources
A Primer on the Anthropic Principle
Anthropic principle (Wikipedia)
A summary of some popular anthropic reasoning principles.
Recommended papers
Anthropic principles agree on bigger future filters (PDF) (The honours thesis of Katja Grace.)
UDASSA (A framework for anthropic reasoning due to Wei Dai.)
Comparing cosmological theories
Articles Tagged ‘anthropic’ - Less Wrong (Open Problems: The Anthropic Trilemma)
The Great Filter