which of the following statements about the microwave background is not true?

1. [1 pts] which of the following statements about the microwave background is not true?

a. it has a temperature of about 3 kelvin

b. it is produced primarily by hot stars

c. it is the remnant of the radiation in the big bang

d. except for effects due to the Earth's own motion, it is virtually the same in all directions

I think it is C or D. Am I close?

Please any help would be great! Thanks!

1 Answer

  • 8 years ago
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    It is difficult to give you "the" correct answer that is sought in your test because, depending on the observer's frame of reference, all four could be wrong.

    If you are allowed to change the observer's frame of reference, then three of the four could be made to be "correct".

    as far as anyone can tell, the radiation was caused by the liberation of all the "trapped" light of the universe, at the moment the universe became transparent. This happened when electrons could finally orbit protons. Before that, the universe was too hot and electrons kept being knocked off their orbits by the energy quanta which were still too strong; the hotter universe was opaque (not transparent).

    At the moment when it did happen, the temperature of the Universe was between 3000 K and 4000 K. Because of the expansion of space that has taken place since the event, all the photons involved have been expanded (to longer wavelengths) so that the radiation appears to us AS IF it were cooler. A lot cooler.

    Because it took place everywhere in the universe, at the same time and with light being liberated in all directions simultaneously, you expect the radiation to appear the same in all directions (but there are extremely tiny differences).

    Because the gas (mostly hydrogen, with some helium) was extremely hot at (and before) that moment, gravity was unable to form any collapsing nuclei. Stars were impossible before that moment. Stars came well after that moment.

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