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This chapter focuses on the informative fossils left from a time when the universe was very different from now, dense and hot enough to produce the light elements and the sea of thermal radiation that nearly uniformly fills space. It begins by reviewing the behavior of a sea of microwave radiation in an expanding universe. The chapter then considers how George Gamow and his colleagues, Ralph Alpher and Robert Herman, hit on the main elements of the hot big bang cosmology, including the sea of microwave radiation and the large helium abundance, but failed to capture the interest of the community. It assesses how it came to be seen that the abundance of helium is much larger than expected from production in stars but is readily understood as the result of thermonuclear reactions in the hot big bang cosmology. This attracted little attention prior to the recognition of a second fossil: the sea of microwave radiation. The chapter concludes with the steps to a persuasive measurement of the primeval abundance of deuterium and the implied baryon mass density.

This chapter introduces the standard cosmological model and explains basic general relativity, Robertson–Walker metric (geodesic motion, redshift, Hubble's law, angular diameter-redshift relation, and particle horizon), dynamics of expansion, matter-dominated Universe, radiation-dominated Universe, curvature-dominated Universe, vacuum-dominated Universe, thermodynamics of the early Universe, entropy, decoupling, and cosmic microwave background radiation.

This chapter considers the thermodynamics of electromagnetic radiation. It begins by discussing spectral energy density, Kirchoff's law, radiation pressure, and the statistical mechanics of the photon gas, respectively. It then goes on to cover the statistical mechanics of the photon gas and black-body distribution. The final sections concern the thermal radiation that exists in the Universe as a remnant of the hot big bang and the effect of thermal radiation on the behaviour of atoms, and hence the operation of the laser.

Physical hazards involve the release of energy in various forms: 1) noise, the most common and widespread physical hazard, can be continuous noise or impulse that can cause damage to the ear or deafness. 2) Vibration, either whole-body vibration or segmental vibration, which occurs when a particular body part is affected by vibrations from tools. 3) Pressure above or below atmospheric pressure in the workers' surroundings is associated with health risks in certain occupations, such as undersea diving and aviation. Conditions in the workplace may expose the worker to unusually high or low pressures. Examples are decompression sickness and high altitude sickness. 4) Temperature extremes are found in many occupations. The human body regulates its own internal level of heat, or core temperature, within a broad range through a variety of mechanisms (including sweating) but cannot adjust to extreme variations outside that range or when the mechanisms of adaptation are not working. 5) Ionizing radiation, either electromagnetic ionizing radiation (gamma radiation), or particle radiation. The major concern with exposure to ionizing radiation is severe tissue damage at very high levels and a risk of cancer in the future at lesser levels. 6) Nonionizing radiation consists of electromagnetic radiation of longer wavelengths when the energy level is too low to ionize atoms but sufficient to cause physical changes in cells. Ultraviolet radiation is the most common form and causes sunburn and prolonged exposure over time causes cataracts and skin cancer. Keywords: physical hazards, noise, vibration, pressure, temperature extremes, ionizing radiation, nonionizing radiation, ultraviolet radiation, tissue damage, cancer

Cosmology aims to build a coherent unified description of the entire universe as a single system. This means not just the disposition of everything that exists at a particular time, but also how this current state came about, and how it will evolve into the future. This chapter describes in some detail how the Big Bang model of creation is constructed, and what is the evidence that favours it over the alternatives. The cosmological constant introduced by Albert Einstein is discussed, along with the cosmic microwave background radiation and its importance for the advancement of the Big Bang model. The interplay between theory and observation over almost a century of dedicated study, has established a ‘standard’ cosmological model dominated by dark energy and dark matter, with a tiny flavouring of the baryonic matter from which stars, planets, and human beings are made.

This chapter looks at the change in the state of empirical cosmology in the five years from 1998 to 2003, which was great enough to be termed a revolution. It was driven by the two great experimental advances. The first is the measurement of the relation between the redshift of the spectrum of an object and its brightness in the sky, given its luminosity: the cosmological redshift–magnitude relation. The second is the detailed mapping of the angular distribution of the cosmic microwave background (CMB) radiation. The two programs reached the precision needed for significant constraints on cosmological models at essentially the same time. Quick acceptance of their interpretation was driven by the impressive consistency of implications of these two quite different ways to look at the universe and, equally important, by the consistency with other lines of evidence gathered in the years of research before the revolution.