Hubble-Lemaître Law

Definition

The Hubble-Lemaître Law states that the recessional velocity of galaxies is directly proportional to their distance from Earth, indicating that the universe is expanding. This fundamental relationship was first established by Edwin Hubble and Georges Lemaître in the 20th century and provides crucial evidence for the Big Bang theory.

5 Must Know Facts For Your Next Test

1. The Hubble-Lemaître Law is often expressed mathematically as $$v = H_0 imes d$$, where $$v$$ is the recessional velocity, $$H_0$$ is the Hubble constant, and $$d$$ is the distance to the galaxy.
2. The law supports the idea that the universe has been expanding since the Big Bang, providing a framework for understanding cosmic evolution.
3. Measurements of distant galaxies' velocities and distances allow astronomers to estimate the Hubble constant, which currently has a value around 70 km/s/Mpc.
4. Hubble's observations in the 1920s transformed our understanding of galaxies from individual entities to components of a larger, dynamic universe.
5. The Hubble-Lemaître Law leads to implications for the fate of the universe, as the rate of expansion influences theories about its ultimate destiny.

Review Questions

• How does the Hubble-Lemaître Law demonstrate the relationship between a galaxy's distance and its recessional velocity?
  • The Hubble-Lemaître Law shows that as the distance of a galaxy increases, so does its recessional velocity. This relationship can be mathematically represented by the formula $$v = H_0 imes d$$. The observation that more distant galaxies recede faster supports the conclusion that space itself is expanding, leading to an ever-increasing distance between cosmic structures.
• Discuss how observations related to the Hubble-Lemaître Law contributed to our understanding of cosmic evolution and structure formation.
  • Observations supporting the Hubble-Lemaître Law led astronomers to conclude that the universe began in a hot, dense state known as the Big Bang. As galaxies move apart, their light undergoes cosmological redshift, which offers insight into both their distances and velocities. This expansion indicates that structures in the universe are not static but dynamic, influencing how galaxies form and evolve over time.
• Evaluate how the Hubble-Lemaître Law intersects with modern cosmological theories and what it implies about the future of our universe.
  • The Hubble-Lemaître Law is central to modern cosmology as it lays the groundwork for understanding how galaxies interact and evolve within an expanding universe. Current theories suggest that if this expansion continues at an accelerating rate, influenced by dark energy, it may lead to scenarios such as the 'Big Freeze,' where galaxies drift far apart over trillions of years. Thus, this law not only explains current observations but also shapes predictions about cosmic fate.

Related terms

Cosmological Redshift: The phenomenon where light from distant galaxies is shifted to longer wavelengths due to the expansion of the universe, leading to a redder appearance.

Expansion of the Universe: The observation that galaxies are moving away from each other, suggesting that the fabric of space itself is stretching over time.

Distance Modulus: A way to express the distance of an astronomical object in terms of its apparent and absolute magnitudes, which helps in determining distances in cosmology.