Why is the cosmic microwave background radiation so cool?

Question

BlackTom AI · Accepted Answer

To determine why the cosmic microwave background (CMB) radiation is so cool, let's evaluate each statement.

Option a: 'Interstellar dust grains absorbs and cools it.' While dust can interact with radiation, the CMB is not cooled primarily by absorption by interstellar dust. The CMB is a pervasive relic radiation filling the universe, and its temperature is not set by local dust cooling processes. This statement misconstrues the origin and cooling mechanism of the CMB.

Option b: 'It is emitted by cool stars.' The CMB is not emitted by stars. It is a snapshot of the early universe’s radiation that has cooled over billions of years. Stars emit their own spectra at much higher temperatures, and the CMB is a diffuse, nearly perfect blackbody from the early universe, not radiation produced by stars.

Option c: 'We are moving through it so fast it just looks cool.' The apparent temperature of the CMB can be affected by our motion via a dipole anisotropy, but our motion does not cause the radiation to be cool. The intrinsic temperature of the CMB remains about 2.7 K; our motion only introduces a small anisotropy, not a fundamental cooling effect.

Option d: 'The expansion of the Universe has lengthened its wavelength.' This explanation aligns with cosmological understanding. As the universe expands, photons stretch to longer wavelengths (cosmological redshift), leading to a lower observed temperature. The CMB started as a hot, high-temperature radiation in the early universe and has cooled as space expanded, giving it its current chilly temperature of about 2.7 K.

Overall, the correct physical explanation points to the expansion-driven redshifting of photons, which reduces their energy and lowers the observed temperature of the CMB over time. The other options mix up processes or misinterpret the CMB’s origin and how its temperature is set, making them inaccurate explanations for why the CMB is so cool.

ASTR 350 ONL FA25: Big Bang,Black Holes,Universe (Liu, X)

Why is the cosmic microwave background radiation so cool?

查看解析

登录即可查看完整答案

类似问题

The 3 degree Kelvin background radiation is most probably

The Cosmic Microwave Background radiation consists of photons that were released from their constant interactions with matter at a time coincident to another important event. Which one of the following events coincided with the formation of the CMB?

The cosmic microwave background radiation comes from

Which of the statements is true about the cosmic microwave background?

The fact that the Microwave Background Radiation has almost exactly the same spectrum in all directions in the sky is evidence that the Universe is:

Astronomers have found the cosmic microwave background (CMB) radiation. What is the nature of this radiation?

What is so important about the lumps we see in the Cosmic Microwave Background Radiation?

There is a ‘flash of light’ that can be measured throughout the universe as cosmic microwave background radiation. Where did it come from?

更多留学生实用工具

考试浏览器助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单