Physics Lecture 11 - Big Bang & Steady State

Q1: What's the main difference between the Big Bang and Steady State theories?

A:

- Big Bang: Universe had a definite beginning, evolving and expanding.

- Steady State: Universe is eternal, expands with continuous creation of matter, no beginning/end.

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Q2: How do the theories differ in galaxy age distribution predictions?

A:

- Big Bang: Distant galaxies (seen earlier in time) should be younger.

- Steady State: Galaxies of all ages evenly spread throughout the universe.

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Q3: Which theory naturally predicts the Cosmic Microwave Background (CMB)?

A: The Big Bang predicts the CMB; Steady State does not naturally predict it.

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Q4: What is recombination, and when did it happen?

A: At about 300,000 years, the universe cooled to 3000K, allowing electrons and nuclei to combine into neutral atoms.

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Q5: Why did recombination make the universe transparent?

A: Before recombination, photons scattered off electrons (universe opaque). After atoms formed, photons traveled freely, making the universe transparent.

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Q6: How were elements heavier than helium formed?

A: Through stellar nucleosynthesis (fusion in stars), and supernovae (neutron capture for heavier elements beyond iron).

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Q7: How do stars form?

A: Interstellar hydrogen gas clouds collapse under gravity into protostars; fusion begins once the core reaches 10⁷ K.

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Q8: What determines a star's life cycle and eventual fate?

A: The star’s mass determines its life span and how it dies (low-mass: white dwarf; high-mass: supernova, neutron star/black hole).

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Q9: What's a protostar?

A: Early stage of star formation, hot collapsing gas cloud before nuclear fusion starts.

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Q10: What's a brown dwarf?

A: A "failed star," too low-mass (**<0.08 solar masses**) to initiate fusion.

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Q11: What's a red giant?

A: An aging star that expands after exhausting hydrogen in its core; starts fusing helium into heavier elements (like carbon).

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Q12: What's a white dwarf?

A: The leftover hot, dense core of a low-mass star after shedding outer layers.

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Q13: What happens in a supernova?

A: Massive star collapses when fusion stops at iron, causing an explosive rebound, creating heavy elements and possibly leaving a neutron star or black hole.

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Q14: What's a neutron star?

A: Extremely dense remnant of a supernova, consisting mostly of neutrons.

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Q15: What's a pulsar?

A: Rapidly spinning neutron star emitting beams of electromagnetic radiation, seen as regular pulses.

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Q16: How do supernovae show the universe’s expansion is accelerating?

A: Supernovae brightness vs. distance measurements indicate distant ones are dimmer than expected—implying acceleration in expansion.

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Q17: What is equilibrium radiation (blackbody radiation)?

A: Radiation emitted by an object in thermal equilibrium; the CMB is exactly this form of radiation.

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Q18: Who formulated stellar nucleosynthesis theory?

**A:** Fred Hoyle.

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Q19: Who first predicted the CMB (Cosmic Microwave Background)?

**A:** Ralph Alpher and Robert Herman (1948).

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Q20: Who first observed the CMB?

**A:** Arno Penzias and Robert Wilson (1967).

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Q21: Who proved the CMB is equilibrium radiation?

**A:** John Mather and George Smoot (COBE satellite, Nobel Prize 2006).