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Chapter 26: Problem 5

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

Short Answer

Expert verified
The expansion of the universe explains Hubble's law as it indicates that galaxies are moving away from each other, and the farther away a galaxy is, the faster it's moving away. This is observed through the redshift of light from distant galaxies, confirming the notion of an expanding universe.

Step by step solution

01

Understanding Hubble's Law

Hubble's law, named after the American astronomer Edwin Hubble, states that the speed at which a galaxy is moving away from us is directly proportional to its distance from us. Mathematically, it can be expressed as \(v = H_0 \times D\), where \(v\) is the velocity of a galaxy moving away from us, \(H_0\) is Hubble's constant, and \(D\) is the distance of the galaxy from us.
02

Understanding Redshift

Redshift is a phenomenon where the spectral lines of light from distant galaxies shift towards longer wavelengths - the red end of the light spectrum. This happens because of the Doppler Effect. As galaxies move away from us, their light waves are stretched out, which makes them seem 'redshifted'.
03

Connecting Hubble's Law and Redshift to Universe Expansion

The redshift observed in the light from distant galaxies supports Hubble's law and, in turn, the notion of an expanding universe. Since the speed at which a galaxy is moving away from us is proportional to its distance, the farther a galaxy is, the faster it's moving away from us. Furthermore, the redshift of light from these moving galaxies is evidence of their motion away from us and subsequently suggestive of an expanding universe.

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Most popular questions from this chapter

If the universe continues to expand forever, what will eventually become of the cosmic background radiation?

How can we detect the presence of sound waves in the early universe? What do these sound waves tell us?

4 Calculate the mass density of radiation \(\left(\rho_{\mathrm{rad}}\right)\) in each of the following situations, and explain whether each situation is matter-dominated or radiation-dominated: (a) the photosphere of the Sun \(\left(T=5800 \mathrm{~K}, \rho_{\mathrm{m}}=3 \times 10^{-4} \mathrm{~kg} / \mathrm{m}^{3}\right) ;(\) b \()\) the center of the Sun \(\left(T=1.55 \times 10^{7} \mathrm{~K}, \rho_{\mathrm{m}}=1.6 \times 10^{5} \mathrm{~kg} / \mathrm{m}^{3}\right)\); (c) the solar corona \(\left(T=2 \times 10^{6} \mathrm{~K}, \rho_{\mathrm{m}}=5 \times 10^{-13} \mathrm{~kg} / \mathrm{m}^{3}\right)\).

Explain how redshift can be used as a measure of lookback time. In what ways is it superior to time measured in years?

How did the abundance of helium in the universe suggest the existence of the cosmic background radiation?
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