Chapter 9’s analysis of the orbits of test particles and light rays in the Schwarzschild geometry identified four effects of general relativity that can be tested in the solar system: the gravitational redshift, the deflection of light by the Sun, the precession of the perihelion of a planetary orbit, and the time delay of light. This list does not exhaust the tests that can be carried out in the solar system, but describes some of the more important ones. Experiments that measure these effects confirm the predictions of general relativity in the solar system to a typical accuracy of a fraction of 1 percent. The discussion in this chapter is not a review of the experimental situation in general relativity either in the past or at the time of writing. Instead, it presents a discussion of representative experiments that are currently among the most accurate, but are not necessarily the most accurate.

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WTO law provides for detailed rules with respect to dumping and subsidisation – two specific trade practices commonly considered to be unfair. The following sections will briefly examine the WTO rules concerning these trade practices.

The Schwarzschild geometry that underlies much of the physics in previous chapters is exactly spherically symmetric. It is an excellent approximation to the geometry outside a nonrotating star, and is the exact geometry outside a nonrotating black hole. However, no body in nature is exactly nonrotating. The Sun, for example, is rotating at the equator with a period of approximately 27 days, and it is not exactly spherically symmetric, but is slightly squashed along the rotation axis (it is less than 1 part in 100,000 longer than a diameter along the rotation axis). The small value of that difference is why the Schwarzschild geometry is an excellent approximation to the curved spacetime geometry outside the Sun. The curved spacetimes produced by rotating bodies have a richer and more complex structure than the Schwarzschild geometry. This chapter explores one simple example of a gravitomagnetic effect – the dragging of inertial frames by a slowly rotating body.

We will trace out some parts of the path that led Einstein to a new theory of gravity that is, unlike Newtonian gravity, consistent with the principle of relativity. The result will be general relativity, a theory that is qualitatively different from Newtonian gravity. In general relativity, gravitational phenomena arise not from forces and fields, but from the curvature of four-dimensional spacetime. The starting point for these considerations is the equality of gravitational and inertial mass, one of the most accurately tested principles in all physics. This leads to Einstein’s equivalence principle, the idea that there is no experiment that can distinguish a uniform acceleration from a uniform gravitational field – the two are fully equivalent.

Which of the four-parameter family of Friedman–Robertson–Walker (FRW) cosmological models best fits our universe and why? This chapter addresses these two central questions for observation and theory in cosmology. Of the four parameters that define an FRW model, only two are determined by observations so far: the Hubble constant; and the ratio of energy density in radiation to the critical density. To determine the others, the spacetime geometry of the universe must be measured on large scales through a study of how matter moves through it. We describe two illustrative ways of doing that – one based on observations of distant supernovae, and the other on observations of the cosmic background radiation. Remarkably, the best cosmological parameter values are consistent with the universe being spatially flat – right on the borderline between positive and negative spatial curvature.

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