Hubble-Lemaître law

Definition

The Hubble-Lemaître law is a fundamental principle in cosmology that describes the relationship between the recessional velocity of galaxies and their distance from the observer. It states that the recessional velocity of a galaxy is proportional to its distance from the observer, indicating that the universe is expanding.

5 Must Know Facts For Your Next Test

1. The Hubble-Lemaître law was independently discovered by the astronomers Edwin Hubble and Georges Lemaître in the 1920s.
2. The law states that the recessional velocity ($v$) of a galaxy is proportional to its distance ($d$) from the observer, with the constant of proportionality known as the Hubble constant ($H_0$), expressed as $v = H_0 d$.
3. The Hubble constant has been measured with increasing precision over the years, with the latest estimates falling in the range of $67-74$ km/s/Mpc.
4. The Hubble-Lemaître law provides strong evidence for the expansion of the universe, as predicted by the Big Bang theory, and is a cornerstone of modern cosmology.
5. The Doppler shift of light from distant galaxies is the primary observational evidence used to measure the recessional velocities and confirm the Hubble-Lemaître law.

Review Questions

• Explain how the Hubble-Lemaître law is related to the Doppler effect.
  • The Hubble-Lemaître law is directly linked to the Doppler effect, which is the observed change in the frequency or wavelength of a wave due to the relative motion between the source and the observer. In the context of the Hubble-Lemaître law, the Doppler shift of light from distant galaxies is used to measure their recessional velocities, which are then found to be proportional to their distances from the observer. This relationship between the recessional velocity and distance, as described by the Hubble-Lemaître law, provides strong evidence for the expansion of the universe.
• Describe how the Hubble-Lemaître law is used to establish the extragalactic distance scale.
  • The Hubble-Lemaître law is a crucial component in the establishment of the extragalactic distance scale, which is the system used to measure the distances to galaxies and other objects outside our own Milky Way galaxy. By observing the Doppler shift of light from distant galaxies and using the Hubble-Lemaître law to relate their recessional velocities to their distances, astronomers can calibrate a distance scale that extends far beyond the boundaries of our own galaxy. This extragalactic distance scale is fundamental for understanding the large-scale structure and evolution of the universe, as well as for testing and refining cosmological models based on the expansion of the universe.
• Analyze how the Hubble-Lemaître law supports the concept of an expanding universe.
  • The Hubble-Lemaître law provides strong observational evidence in support of the expanding universe model, which is a cornerstone of modern cosmology. By demonstrating that the recessional velocities of galaxies are proportional to their distances, the Hubble-Lemaître law suggests that the universe is continuously expanding, with galaxies moving away from each other. This observation is a key prediction of the Big Bang theory, which posits that the universe originated from a hot, dense state and has been expanding ever since. The Hubble-Lemaître law, along with other cosmological observations, such as the cosmic microwave background radiation, has been instrumental in establishing the Big Bang theory as the prevailing model for the origin and evolution of the universe.

Related terms

Doppler Effect:

The Doppler effect is the change in the observed frequency or wavelength of a wave due to the relative motion between the source and the observer. It is the underlying principle that allows the Hubble-Lemaître law to be observed.

Extragalactic Distance Scale: The extragalactic distance scale is a system used to measure the distances to galaxies and other objects outside our own Milky Way galaxy, which is crucial for understanding the Hubble-Lemaître law and the expansion of the universe.

Expanding Universe: The expanding universe is the observed phenomenon that the universe is continuously expanding, with galaxies and other celestial bodies moving away from each other. The Hubble-Lemaître law is a key piece of evidence supporting the expanding universe model.