Physical Science

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Evidence of Big Bang Theory

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1. 1. The universe is expanding

2. 2. The universe is getting cooler

3. 3. The abundance of hydrogen and helium in space.

4. 4. The Cosmic Microwave Background radiation present everywhere.

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Formation of Light Elements

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(Big Bang Nucleosynthesis)

• Conditions: The universe was extremely hot and dense, filled with protons, neutrons, and electrons.

• Process: As the universe expanded and cooled, nuclear reactions fused these particles into the first atomic nuclei.

• - Light elements are those formed during Big Bang nucleosynthesis (the first few minutes after the Big Bang). These include hydrogen (75%), helium, and small amounts of lithium and beryllium.

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Nucleosynthesis

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It is the process of creating new atomic nuclei from pre-existing nuclei.

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The presence of matter in the universe.

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There are more light elements than heavy elements. Observations and the Big Bang Theory show that the universe is made up mostly of light elements (hydrogen ~75% and helium ~25%), with trace amounts of lithium and beryllium.

• Heavy elements (like carbon, oxygen, iron, etc.) were formed much later inside stars through stellar nucleosynthesis and make up only a small fraction of the universe’s matter.

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Cosmic Microwave Background supports Big Bang Theory.

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• The Cosmic Microwave Background Radiation (CMBR) is the faint glow of radiation left over from the early universe, discovered in 1965 by Penzias and Wilson.

• It is essentially the "afterglow" of the Big Bang, showing that the universe was once extremely hot and dense, and has since cooled as it expanded, thus it supports the idea that the universe used to be hotter.

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Formation of Iron

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• Iron is formed inside massive stars during the final stages of stellar nucleosynthesis.

• Fusion reactions in stars build heavier nuclei step by step

• (hydrogen → helium → carbon → oxygen → silicon → iron).

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Formation of Heavy Elements

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• Heavier elements up to iron are formed by nuclear fusion inside stars.

• Beyond iron, elements are formed during supernova explosions (via neutron capture).

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Formation of Element

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• When three helium nuclei (alpha particles) fuse together in stars, the process is called the triple-alpha process.

• This reaction produces carbon (C), which is a crucial building block for life.

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Stages of Low mass star

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Low-mass stars (like our Sun) go through these stages:

1. Protostar → The star forms from collapsing gas and dust.

2. Main sequence → The star fuses hydrogen into helium in its core.

3. Red giant → After hydrogen runs out, the star expands and cools.

4. White dwarf → The final stage after shedding outer layers.

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Stages of Medium-mass stars

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Medium-mass stars (like our Sun) follow this life cycle:

1. Protostar → forms from collapsing gas and dust.

2. Main sequence → fuses hydrogen into helium.

3. Red giant → expands after hydrogen runs out.

4. Planetary nebula → outer layers are shed.

5. White dwarf → the remaining hot core, final stage of a medium-mass star.