
Concept explainers
Choose the best answer to each of the following. Explain your reasoning.
What is the current temperature of the universe?(a) absolute zero (b) a few degrees K (c) a few thousand degrees K

The current temperature of the universe.
Answer to Problem 1QQ
b. Few degrees K
Explanation of Solution
Introduction:
Some microwave photons are observed since the end of the era of nuclei travelling through the space. The cosmic microwave background consists of these microwave photons. The photon starts travelling when the neutral atom formed by joining the electrons with the nuclei. So, very few free electrons are available as constrains in the path of the photon. As a result, the maximum photons travelled in the space were unobstructed.
Option (b) is: Few degrees K
The Big Bang theory predicts that the cosmic microwave background would show a perfect thermal spectrum generated due to the heat of the universe. The universe was cooled to the temperature of about 3000 K when the cosmic wave background broke free. Originally, the spectrum shows peak at 1000 nm. The peak is observed at 1000 nm because the universe is expanded by a factor of 1000. Now the wavelength of the photon is extended 1000 times the original wavelength. So, the peak wavelength is expected to be about a millimeter which lies in the microwave portion of the spectrum and corresponds to a temperature of about 2.7 K.
So, option (b) is correct and (a) and (c) are incorrect.
Conclusion:
The temperature of the universe is few degrees above the absolute zero.
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