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Chapter 26: Problem 26

. Describe two different ways in which the cosmic microwave background is not isotropic.

Short Answer

Expert verified
The Cosmic Microwave Background (CMB) is not perfectly isotropic due to two main sources of anisotropy: 1) Dipole Anisotropy, which is a result of our motion relative to the CMB, and 2) Primary Anisotropies, slight temperature variations resulting from density fluctuations in the early universe, which eventually led to the formation of galaxies and large-scale structures.

Step by step solution

01

Dipole Anisotropy

The first significant anisotropy observed in the Cosmic Microwave Background is called Dipole Anisotropy. This is caused by our motion relative to the rest frame of the CMB. As the Earth moves towards a certain direction, the CMB photons in that direction appear slightly warmer due to the Doppler effect, while the photons from the opposite direction appear slightly cooler. This generates a pattern of hot and cold spots in the sky.
02

Primary Anisotropies

The second source of anisotropy is due to tiny fluctuations in the density of the early universe, visible today in the form of slight temperature variations in the CMB. The seeds of these variations are quantum fluctuations generated in the very early universe, which get stretched to macroscopic scales due to the expansion of the universe. Over time, denser regions attract more matter and become even denser, eventually leading to the formation of galaxies and large-scale structures.

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Most popular questions from this chapter

Describe how the expansion of the universe explains Hubble's law.

What does it mean to say that the universe is darkenergy-dominated? What happened when the universe changed from being matter-dominated to being darkenergy-dominated?

Explain the difference between a Doppler shift and a cosmological redshift.

Estimate the age of the universe for a Hubble constant of (a) \(50 \mathrm{~km} / \mathrm{s} / \mathrm{Mpc}\), (b) \(75 \mathrm{~km} / \mathrm{s} / \mathrm{Mpc}\), and (c) \(100 \mathrm{~km} / \mathrm{s} / \mathrm{Mpc}\). On the basis of your answers, explain how the ages of globular clusters could be used to place a limit on the maximum value of the Hubble constant.

Temperatures in the Early Universe. Access the Active Integrated Media Module "Blackbody Curves" in Chapter 26 of the Universe Web site or eBook. (a) Use the module to determine by trial and error the temperature at which a blackbody spectrum has its peak at a wavelength of \(1 \mu \mathrm{m}\). (b) At the time when the temperature of the cosmic background radiation was equal to the value you found in (a), was the universe matter-dominated or radiation- dominated? Explain your answer.
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