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Chapter 26: Problem 19

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

Short Answer

Expert verified
The abundance of helium in the universe supports the Big Bang theory. The same theory that predicts the formation and proportions of helium also predicted the existence of the Cosmic Microwave Background (CMB), the afterglow of the Big Bang, thus suggesting the existence of the cosmic background radiation.

Step by step solution

01

Understand the composition of the universe

The universe is made up mainly of hydrogen and helium. These are by far the most abundant elements, with helium making up about 25% of the observable universe's elemental mass.
02

Link to the Big Bang theory

According to the Big Bang theory, the early universe was extremely hot and dense. During the first few minutes, nuclear reactions could took place which resulted in nucleosynthesis of light elements. This 'primordial nucleosynthesis' stage ended after about 20 minutes. It is during this period that much of the helium in the universe was created.
03

Prediction of the Cosmic Microwave Background

The Big Bang theory also predicted the existence of the Cosmic Microwave Background (CMB). The CMB is a form of radiation that fills the universe and can be detected in all directions. This radiation is considered to be the afterglow of the Big Bang.
04

Connect helium abundance with CMB

The quantity of helium and its isotopes in the universe provide strong evidence supporting the Big Bang theory. The same theory that predicts these proportions is also the theory that led scientists to hypothesize and later discover the CMB.

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Most popular questions from this chapter

If a photon from the cosmic microwave background had wavelength \(\lambda_{0}\) when it was emitted at redshift \(z\), its wavelength today is \(\lambda=\lambda_{0} /(1+z)\). (a) Let \(T\) be the symbol for the temperature of the cosmic microwave background today. Explain why the radiation temperature was \(T_{0}=T(1+z)\) at redshift \(z\). (b) What was the radiation temperature at \(z=1\) ? (c) At what redshift was the radiation temperature equal to \(293 \mathrm{~K}\) (a typical room temperature)?

What is meant by "the observable universe"?

Before the discovery of the cosmic microwave background, it seemed possible that we might be living in a "steady-state universe" with overall properties that do not change with time. The steady-state model, like the Big Bang model, assumes an expanding universe, but does not assume a "creation event." Instead, matter is assumed to be created continuously everywhere in space to ensure that the average density of the universe remains constant. Search the World Wide Web for information about the steady-state theory. Explain why the existence of the cosmic microwave background was a fatal blow to the steady- state theory.

(a) Explain why the radius of the observable universe is continually increasing. (b) Although the universe is \(13.7\) billion years old, the observable universe includes objects that are more than \(13.7\) billion light- years away from Earth. Explain why.

What is a cosmological constant? Why did Einstein introduce it into cosmology?
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