Exercises: The origin of the Universe

Explain what the Big Bang theory consists of and state approximately how long ago the origin of the Universe occurred.

Name two lines of evidence supporting the Big Bang theory and briefly explain each one.

Look at the timeline of the Universe (not to scale): the letters A, B, C and D mark four events — Big Bang, formation of the Sun, formation of the Earth, and appearance of life — without indicating which is which. Identify which event corresponds to each letter, order them from oldest to most recent, and state approximately how long ago each one occurred.

Hubble observed that the light from distant galaxies shifts towards the red. Explain what redshift is and what conclusion about the Universe can be deduced from this observation.

Describe the main stages of the formation of the Solar System from a nebula: collapse of the cloud of gas and dust, formation of the Sun at the centre, and the protoplanetary disc.

What is cosmic microwave background radiation? Explain why its detection is considered key evidence for the Big Bang.

A classmate claims: "Since from Earth we observe that almost all galaxies are moving away from us in every direction, the Milky Way must occupy the exact physical centre of the universe where the Big Bang occurred."

1. a) Use the analogy of the surface of an inflating balloon with dots drawn on it to refute their claim: deduce what an astronomer located in any of the other galaxies would observe.
2. b) Identify an important limitation of this analogy: explain why placing the Big Bang in the "hollow inner centre" of the balloon is a conceptual error about the expansion of space.

Science communicator Carl Sagan popularized the phrase "we are made of starstuff." Analyze the origin of the atoms in your body based on these data: hydrogen represents about $62\,\%$ of the total atoms, oxygen $24\,\%$, carbon $12\,\%$, and iron $0,001\,\%$ (essential in hemoglobin to transport oxygen).

1. a) Justify why carbon, oxygen, and iron had to form inside or during the death of earlier stars and not during the Big Bang.
2. b) Deduce why it was impossible for rocky planets with life like ours to exist around first-generation stars (Population III, formed shortly after the Big Bang consisting solely of hydrogen and helium).

In the "cosmic calendar," the $13\,800$ million years of the universe are condensed into a single year of 365 days (January 1st at 00:00 h is the Big Bang and December 31st at 24:00 h is the present moment).

1. a) Calculate approximately on what date (month and day) the Earth formed ($4\,600$ million years ago) and at approximately what date and time the human genus (Homo, about $2,8$ million years ago) appeared. Show your calculations.
2. b) In light of these results, refute the anthropocentric argument that the universe exists with the main purpose of harboring the human species, comparing the fraction of time occupied by our existence with that of the cosmos.