GK
THE UNIVERSE
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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The expansion of the Universe has cooled the radiation and stretched its wavelengths
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Dense clouds of dust have blocked most of it.
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The cosmological constant has “squashed” its wavelengths and cooled it.
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Hydrogen atoms have condensed on it and chilled it.
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Detailed explanation-1: -As the universe expanded, the light was stretched into longer and less energetic wavelengths. By the time the light reaches us, 14 billion years later, we observe it as low-energy microwaves at a frigid 2.7 K (-450° F). This is why CMB is so cold now. The expansion of space cools down the CMB .
Detailed explanation-2: -Cooler, clearer Universe The relic of that ‘first light’ is the CMB. Since the time when that radiation was released, the Universe has expanded, becoming at the same time cooler and cooler. The cosmic background has been affected by the same process: it has expanded and cooled down.
Detailed explanation-3: -And during that time the void itself grows larger and deeper as the universe evolves. That means that when the light entered the supervoid, the void was smaller than when the light exited. This difference saps energy from the radiation, causing it to cool and redshift more than the average for the rest of the CMB.
Detailed explanation-4: -Why is the cosmic microwave background (CMB) so cold if the early universe was so hot? The expansion of the universe has redshifted those photons to an effectively cooler temperature.