Giancoli is a very popular college physics text. This is a quote from the 4th edition for Scientists and Engineers. It occurs in the last section, on the last pages of the last chapter:
The questions raised by cosmology are difficult and profound, and may seem removed from everyday “reality.” We can always say, “the Sun is shining, it’s going to burn for an unimaginably long time, all is well.” Nonetheless, the questions of cosmology are deep ones that fascinate the human intellect. One aspect that is especially intriguing is this: calculations on the formation and evolution of the universe have been performed that deliberately varied the values–just slightly–of certain fundamental physical constants. The result? A universe in which life as we know it could not exist. [For example, if the difference in mass between a proton and a neutron were zero, or less than the mass of the electron, 0.511MeV/c2, there would be no atoms: electrons would be captured by protons never to be freed again.] Such results have contributed to a philosophical idea called the Anthropic principle, which says that if the universe were even a little different than it is, we could not be here. We physicists are trying to find out if there are some undiscovered fundamental laws that determined those conditions that allowed us to exist. A poet might say that the universe is exquisitely tuned, almost as if to accommodate us.
What an amazing way to end a physic’s textbook!
