Rank these times based on the wavelength of the peak intensity of the cosmic background radiation at those times, from shortest to longest. (Hint: consider how the temperature of the universe or the cosmic background radiation changed with time.)
A) Today, 1 million years after the Big Bang, 100 million years after the Big Bang
B) Today, 100 million years after the Big Bang, 1 million years after the Big Bang
C) 1 million years after the Big Bang, 100 million years after the Big Bang, today
D) 100 million years after the Big Bang, 1 million years after the Big Bang, today

Question

Quizplus · Accepted Answer

The wavelength of the peak intensity of the cosmic background radiation is inversely proportional to the temperature of the universe. As the universe expands, it cools down, and the temperature decreases. Therefore, the peak intensity wavelength increases with time. Thus, the oldest the period is, the longer the wavelength is.

From the options given, it is clear that today is the modern period, and the wavelength is the longest. The temperature of the universe was the highest just after the Big Bang, which was approximately 13.8 billion years ago. As time progressed, the temperature dropped. Therefore, 1 million years after the Big Bang was warmer than 100 million years after the Big Bang. Thus, the wavelengths are shorter.

Option D is the best choice because it is arranged from the shortest wavelength to the longest wavelength. Thus, the correct order is 100 million years after the Big Bang, 1 million years after the Big Bang, and today.

Rank These Times Based on the Wavelength of the Peak