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The Importance of the Anthropic Principle
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11874 |
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BOOK WORLD
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| Issue
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8 / 1987 |
3,263 Words |
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Sir Don N. Page
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One of the main goals of science is to discover and explain facts about our world. While a great variety of scientific explanations exist, most serve as descriptive models, constructed to encompass many phenomena. The simpler and yet more inclusive a model is, the better it is considered scientifically.
In the field of physics, the deepest and most unified explanations are generally mathematical models, for mathematics has proven to be an amazingly effective language for describing the world. Newton's laws of motion and their generalizations in special relativity (for velocities comparable to that of light) and in quantum mechanics (for sizes comparable to or smaller than atoms) describe in precise mathematical terms how objects move under the influence of known forces. The forces themselves are also described mathematically (e.g., Newton's laws of gravitation and Maxwell's equations of electromagnetism). One goal of physics is to unite the descriptions of the forces into a single "theory of everything" (TOE). Many physicists hope that this may be accomplished by a theory of what are called "superstrings."
Even a TOE, however, would not be a complete model or description of the universe. Roughly speaking, a TOE would enable a sufficiently intelligent being to calculate everything that happens within the universe at all times if he, she or it somehow knows what everything in the universe is like at one particular time, say at its beginning. (This is analogous to what you do on a much smaller scale when you foresee roughly how a ball will travel if you throw it with a certain speed and direction). But a TOE itself does not pin down what the universe is like at any one time, such as its beginning. A TOE would give a complete set of equations for how the universe can evolve, but these equations would have many solutions, one for each possible initial state of the universe at the beginning. As Thomas Gold of Cornell University has put it, "Things are as they are because they were as they were," but even a TOE would not answer the question of why things were as they were. A complete model of the universe must include a description of the initial conditions, as well as the TOE equations for its evolution.
As a guideline for selecting the initial conditions of our universe, as well as for choosing which TOE may be correct, the anthropic principle is gaining importance in physics and cosmology, although its true significance and applicability are controversial. Indeed, there are several versions of the anthropic principle defined in the introduction of Barrow and Tipler's book, The Anthropic Cosmological Principle appearing in this issue, each having varying degrees of acceptance. The least controversial is the weak anthropic principle (WAP), which says roughly that what we observe about the universe is restricted by the requirements of our existence as observers. A stronger bur more controversial version is the strong anthropic principle (SAP), which says that the universe must have the properties necessary for life to develop at some time within it. Barrow and Tipler put forward an even more speculative extension they call the final anthropic principle (FAP): Intelligence must develop within the universe and then never die out.
The weak anthropic principle as an explanation
It is hard to disagree with the WAP itself, for it basically states that we could not conceivably observe a universe with properties that do not
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