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

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

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

Option 1: 'From the earliest formed stars' — This is incorrect. The CMB is not light from individual stars or their radiation; stars formed long after the CMB's origin and their light would be absorbed or redshifted by later cosmic history. The CMB is a relic signal from an earlier epoch, not from stellar radiation as such.

Option 2: 'From an original explosion referred to as the ‘big bang’' — This is a common simplified description, but it’s not precise enough to identify the physical origin of the CMB. The Big Bang describes the overall origin of the universe, but the CMB specifically arises from the era of recombination when the universe became transparent. Saying it comes from a Big Bang explosion misses the key process of photon decoupling.

Option 3: 'From the transparency which resulted when plasma condensed into neutral atoms' — This statement captures the essential physics. In the early universe, photons were constantly scattered by free electrons in a hot plasma. When electrons combined with protons to form neutral hydrogen (recombination), the Universe became optically transparent and photons could travel freely. Those photons are the CMB we observe today, redshifted to microwave wavelengths.

Option 4: 'From the release of energy as the early universe cooled' — While cooling of the universe accompanies many processes, the CMB specifically corresponds to when photons last scattered off matter during recombination, not a generic release of energy from cooling. This description omits the critical detail of photon decoupling and the resulting propagation of photons through a now transparent medium.

Summary of key idea: The cosmic microwave background is the afterglow of the early universe when a hot plasma became neutral and transparent, allowing photons to travel freely. The remaining options either attribute the CMB to later stellar sources, overly broad Big Bang terminology, or a general cooling narrative without pinpointing the photon decoupling event.

My LMS Subjects Quiz Topic 1: The Big Bang

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

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