Big Bang Theory

Big Bang Theory

Introduction

• The Big Bang theory is a fundamental concept in cosmology that explains the origin and evolution of the universe.
• It is supported by various pieces of evidence, including redshift, the expansion of the universe, and the relationship between temperature and emitted radiation.

Redshift and Expansion

• Redshift is the phenomenon where light from distant galaxies appears to shift towards longer wavelengths, indicating they are moving away from us.
• The expansion of the universe, driven by dark energy, is responsible for this redshift.
• While redshift and expansion support the idea of a Big Bang, they do not provide direct evidence of the event itself.

Temperature and Emitted Radiation

• The relationship between temperature and emitted radiation is a crucial piece of evidence for the Big Bang theory.
• In everyday life, we observe that hot objects emit visible light, with colours ranging from red to blue as their temperature increases.
• Starlight can be analysed to determine the temperature of stars, usually measured in Kelvin (K), where 0 K is absolute zero (-273.15°C).

Kelvin Scale

• The Kelvin scale is similar to the Celsius scale, with temperature intervals of 1 K equal to 1°C.
• Absolute zero corresponds to 0 K, which is equivalent to -273.15°C.

Radiation Distribution

• The distribution of radiation emitted by an object at different temperatures can be graphed.
• The graph shows curves representing the radiation distribution for objects at various temperatures.

---

Big Bang Theory

Physics

Peak Intensity

• The dotted line on the graph represents the peak intensity of radiation, also known as radiation per unit surface.
• Objects at higher temperatures have shorter peak wavelengths in their spectra.
• Shorter wavelengths correspond to higher frequencies and bluer colours, indicating that hotter objects emit bluer light, while cooler objects emit redder light.

Hertzsprung-Russell Diagram

• The Hertzsprung-Russell (HR) diagram is a tool used in astronomy to plot the brightness of stars against their temperature.
• It helps classify stars and predict their evolutionary paths.

Significance

• The HR diagram is essential for understanding the life cycle of stars, including their potential to become red giants or black holes.
• The evidence from the relationship between temperature and emitted radiation supports the Big Bang theory by demonstrating how the universe's temperature has changed over time.

Summary

• The Big Bang theory explains the universe's origin and evolution.
• Evidence such as redshift, the expansion of the universe, and the relationship between temperature and emitted radiation supports this theory.
• Temperature and radiation data are crucial in understanding the universe's history and the life cycles of stars.