Question

How does the field of cosmology fit into the larger picture of astronomy?

Explain the specific evidence for the Big Bang. Was there ever opposition to this idea in the astronomical community? If so, who was opposed to it and why?

Dark matter and dark energy have been proposed to explain two very different phenomena astronomers notice about the universe. What are the two phenomena and how do dark matter and dark energy help explain them?

Cosmologists have two words that explain the overall picture of the universe: homogeneity and isotropy. What do these terms imply?

Answer 1

1. Astronomy is Science of celestial objects and phenomena. Cosmology studies the origin, large structure and fate of universe. Hence field of Cosmology fit into the larger picture of Astronomy and we can say Cosmology is a branch of Astronomy.

2. Some of evidence of Big Bang are - (i) Expanding universe as observed by Hubble (ii) Cosmic microwave background (iii) Relative abundances of light elements produced by Big Bang.

Fred Hoyle opposed the idea of Big Bang. He came with new theory of the continuous creation of Universe. According to this the universe had existed for an infinite past time and would continue infinitely into the future.

3. Dark matter explain the phenomena of galaxy rotational curve. Rotational velocity of galaxy with distance from center must be decreases similar to our solar system (via Newtonian gravity) but this is not the case. Galaxy rotational curve is constant which shows there is some unknown mass which is responsible for this odd behavior. This unknown mass is named dark matter.

Dark energy explain the phenomena of expanding universe. For expansion there must be some source of expansion. This unknown source is dark energy.

4. Homogeneity means same at all location and isotropy means same in all direction. Both these are important in modern Cosmology which depend on assumption that, on large scale universe is homogeneous and isotropic.

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