Hubble & The Age of the Universe | Physics for GCSE/IGCSE - Year 11 PDF Download

Hubble Constant Calculations

• In 1929, Edwin Hubble demonstrated the expanding nature of the universe by scrutinizing the absorption line spectra emitted by galaxies.
• Through his meticulous observations, Hubble detected a consistent shift of light towards the red end of the spectrum, indicating a crucial phenomenon.
• This shift, known as the Doppler effect, serves as compelling evidence that galaxies are moving away from our vantage point on Earth.

Understanding Hubble's Discovery

• By examining absorption line spectra from distant galaxies, Hubble noted a consistent shift towards the red end of the spectrum.
• This shift, known as the Doppler effect, indicated that galaxies were moving away from Earth.

Implications of Redshifted Light

• Hubble observed that more distant galaxies exhibited greater redshift compared to nearer ones, suggesting faster movement away from us.
• This finding implies that objects farther from Earth are receding at higher velocities than those closer to us.

Hubble's Law

• Hubble's law explains the relationship between the recessional velocity of a galaxy and its distance from Earth.
• Hubble's law can be mathematically expressed as:
  
• Where,
  • Hubble Constant (H₀): Represents the rate at which the universe is expanding.
  • Recessional Velocity (v): Speed at which an object moves away from an observer.
  • Distance (d): Measure of how far the object is from Earth.
• The Hubble Constant is defined as the ratio of a galaxy's speed moving away from Earth to its distance from Earth.
• It helps us comprehend the expansion rate of the universe.
• The Hubble constant's accepted value is H₀ = 2.2 x 10^-18 per second.

Age of the Universe

• Hubble's Law, which highlights that the further a star is from Earth, the faster it moves away from us, plays a pivotal role.
  
• This law can be rearranged to demonstrate the relationship.
  
• Hubble's law indicates that the farther a star is from Earth, the faster it moves away from us.
  
• The gradient of the graph can help us determine the Age of the Universe. When the distance is zero, it signifies all matter in the Universe was concentrated at a single point, the singularity during the Big Bang moment.
  • When the distance reaches zero, it signifies that all matter in the Universe was condensed into a single point, marking the singularity during the Big Bang.
  • This singularity denotes the moment when the Universe originated from an infinitely small, dense, and hot state.
• The gradient, measured in units per second (similar to the Hubble Constant), can be transformed into seconds by taking the reciprocal.
  • By taking the reciprocal, the units will become seconds
  • By reciprocating the gradient, we obtain a time value indicating the expansion period of the Universe.
• Astronomers utilize a specific formula involving the gradient to approximate the Universe's age, estimating it to be around 13.7 billion years.