When our Solar System formed about 4.5 billion years ago,...

Name: Problem 2, Chapter 80: Pathways to Astronomy
Uploaded: 2020-07-22T16:11:28-08:00
Duration: 55 s
Channel: Sarah Mccrumb
Description: When our Solar System formed about 4.5 billion years ago, approximately what would the temperature of the CMB radiation have been? Would the structure in the CMB have looked the same as today? Explain your answer.

When our Solar System formed about 4.5 billion years ago, approximately what would the temperature of the CMB radiation have been? Would the structure in the CMB have looked the same as today? Explain your answer.

Key Concepts

Cosmic Microwave Background (CMB)

The CMB is the relic radiation from the early universe, specifically from the time of recombination when the universe cooled enough for protons and electrons to combine and emit freely streaming photons. It serves as a snapshot of the state of the universe at that epoch and is a crucial observational pillar supporting the Big Bang model.

Cosmic Expansion and Redshift

As the universe expands, the wavelength of photons lengthens, a process known as redshift, which in turn lowers their energy and temperature. The temperature of the CMB is related to the redshift parameter by the relation T ? (1+z), meaning that in the past, when the universe was smaller, the CMB was correspondingly hotter than it is today.

Recombination and the Last Scattering Surface

The epoch of recombination marks the time when the universe had cooled enough for electrons and protons to form neutral atoms, allowing photons to decouple from matter and travel freely. The radiation released at that time now appears as the CMB, with its initial temperature fluctuations largely preserved.

Angular Scale of CMB Anisotropies

While the intrinsic pattern of temperature fluctuations imprinted on the CMB at the time of last scattering remains unchanged, the apparent angular scale of these anisotropies depends on the geometry and expansion of the universe. Observers at different cosmic times, such as 4.5 billion years ago, would perceive these fluctuations at different angular sizes due to the evolving distance scales in an expanding universe.

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