Abstract
This article is the first in a continuing series of general interest papers on the applications of microwaves in areas of science and technology that might not be evident to the casual observer. What better topic to start the series than an introduction to the most pervasive microwave field in the universe: the cosmic microwave background (CMB). The prediction, discovery, and importance of the CMB from a microwave engineering perspective are reviewed and discussed.
Highlights
If one were to measure the spectral radiance (Watts per meter squared per steradian per hertz) versus wavelength in any arbitrary direction/location in interstellar or intergalactic space where there is no obvious source of localized energy, the resulting plot would match that of a black body obeying Planck’sLaw with a temperature of 2.72548 ± 0.0057 K [1], [2]: B (f,T) = 2h f 3 c2 × eh f /kT −1, where h is Planck’s constant, k is Boltzmann’s constant, c is the velocity of light, T is the temperature and f is the frequency
We end with current experimental programs to refine cosmic microwave background (CMB) measurements so as to bring out extremely small anisotropies and answer even more detailed questions about the nascent, present, and predicted future structure and evolution of the universe
EARLY PREDICTIONS OF THE CMB The initial concept of the CMB is intimately tied to the idea of a universe that began with a “bang” – we think of it more as a smooth expansion
Summary
If one were to measure the spectral radiance (Watts per meter squared per steradian per hertz) versus wavelength in any arbitrary direction/location in interstellar or intergalactic space where there is no obvious source of localized energy (planet, star, dust cloud, galaxy, or any of the other more intriguing interstellar or galactic objects), the resulting plot would match that of a black body (perfect thermal emitter) obeying Planck’s. Where h is Planck’s constant, k is Boltzmann’s constant, c is the velocity of light, T is the temperature and f is the frequency The peak of this energy emission plot occurs at a frequency of 160 GHz, wavelength of 1.875 mm (Figure 1). This microwave, or more appropriately millimeter-wave energy, is everywhere in our current universe. It is the unseen and unfelt backdrop to all other coherent or incoherent energy sources we experience (light, heat, radio waves, etc.) and represents a lower limit to what we would measure if we were able to sense this thermal background directly. We end with current experimental programs to refine CMB measurements so as to bring out extremely small anisotropies and answer even more detailed questions about the nascent, present, and predicted future structure and evolution of the universe
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