Fear of Physics Read Online Free PDF

degree temperature in the interior of the sun may seem very hot by terrestrial standards, it did not seem hot enough to allow for some new kind of
physics to intervene. In one of my favorite put-downs in science, Eddington urged all those who did not believe his claim to “go and find a hotter place!” As it turned out, Eddington was vindicated in the 1930s when the physicist Hans Bethe, whose name will reappear shortly, recognized that the newly discovered nuclear reactions that could be used to build a bomb on Earth could in fact power the sun, allowing it to survive for as long as 10 billion years in the form we now observe it. Bethe won the Nobel Prize for his calculations, which now form the basis of the Standard Solar Model.
    To return to the question of whether Standard Solar Model approximations would break down when trying to determine the age of the oldest stars, with several colleagues, I was able to reexamine the age estimates of globular clusters; and we were able to explicitly incorporate the amount of uncertainty that was introduced into the results by the approximations used to derive them and show that the oldest globular clusters in our galaxy could be as young as 12 billion years, but not much younger, thus suggesting that the apparent conflict between their age and the age of the universe was a real one.
    Partly motivated by this result, but also by other data that appeared to be inconsistent with a universe whose expansion was slowing, in 1995 a colleague from Chicago and I were driven to heretically (and perhaps also somewhat facetiously) suggest that perhaps the expansion of the universe was not slowing down but instead speeding up! This may sound implausible but in fact the exotic possibility of a repulsive form of gravity had in fact been proposed by Albert Einstein in 1916, shortly after he developed his general theory of relativity, to allow for a static universe—then thought to be the case—but was discarded when it was discovered that the universe was expanding. Moreover, our
suggestion was not as completely crazy as it may have sounded as it turns out that we now understand an extra “repulsive” form of gravity could naturally result if empty space possessed a new form of energy which, in the context of modern particle theory, is allowed.
    Remarkably, in 1998 two teams—using observations of the apparent brightness of supernovae in distant galaxies to trace the expansion rate of the universe over time—independently discovered that the expansion of the universe is accelerating! This experimental discovery completely changed our picture of the expanding universe, so that trying to understand the nature of this dark energy is perhaps the most important outstanding problem in cosmology. Most interesting from the point of view of the present discussion, however, is the fact that once one incorporates this fact into a determination of the age of the universe, one gets an age estimate of approximately 13–14 billion years, which is in perfect agreement with the age determination of the oldest stars in our galaxy.
    Thus, the simple approximation of stars as spheres has continued for over 200 years to lead us to discover new and profound aspects of the universe.
     
     
    The previous examples demonstrate the great discovery power made possible by approximation in physics, but they should not distract us from the more fundamental fact that without approximation, we can do almost nothing. With it, we can make predictions that can be tested. When the predictions are wrong, we can then focus on the different aspects of the approximations we make, and in so doing we have learned almost everything we now know about the universe. In the words of James Clerk
Maxwell, the most famous and successful theoretical physicist of the nineteenth century: “The chief merit of a theory is that it shall guide experiment, without impeding the progress of the true theory when it appears.” 2
    Sometimes physicists