Hubble's Law

Definition

Hubble's Law states that the recessional velocity of a galaxy is directly proportional to its distance from Earth, suggesting that the universe is expanding. This key concept in cosmology indicates that galaxies are moving away from us, and the farther they are, the faster they seem to be receding. This observation supports the Big Bang theory and provides a way to estimate the age and size of the universe.

5 Must Know Facts For Your Next Test

1. Hubble's Law is often expressed mathematically as $$v = H_0 imes d$$, where $$v$$ is the recessional velocity, $$d$$ is the distance, and $$H_0$$ is Hubble's constant.
2. Hubble's constant has been estimated at around 70 kilometers per second per megaparsec, meaning that for every megaparsec (about 3.26 million light-years) of distance, a galaxy recedes 70 km/s faster.
3. The discovery of Hubble's Law was made by Edwin Hubble in 1929 when he analyzed the light from various galaxies and noted their redshifts.
4. This law implies that if we reverse the expansion, all galaxies would converge to a single point, supporting the idea of a dynamic universe rather than a static one.
5. Hubble's Law not only provides insights into the rate of expansion but also allows astronomers to measure cosmic distances, which is essential for understanding the scale of the universe.

Review Questions

• How does Hubble's Law demonstrate the relationship between distance and velocity for galaxies?
  • Hubble's Law reveals that as galaxies get farther away from Earth, they move away faster. This relationship can be represented by the equation $$v = H_0 imes d$$, where $$v$$ is their recessional velocity and $$d$$ is their distance. This direct proportionality indicates an expanding universe and allows astronomers to estimate both the distances to faraway galaxies and their velocities.
• Discuss how Hubble's Law supports the Big Bang Theory and our understanding of cosmic evolution.
  • Hubble's Law provides strong evidence for the Big Bang Theory by showing that the universe is expanding. As galaxies move away from us, it suggests they were once closer together in a denser state. This expansion indicates that time began with the Big Bang, helping scientists understand how the universe has evolved over billions of years since that initial event.
• Evaluate the significance of redshift measurements in validating Hubble's Law and what implications this has for cosmology.
  • Redshift measurements are crucial in validating Hubble's Law as they provide empirical evidence for galaxy velocities. By observing how much light shifts toward red wavelengths, astronomers can determine how quickly a galaxy is receding. This data not only supports the expanding universe concept but also impacts cosmological models, influencing our understanding of dark energy and the fate of the universe.

Related terms

Redshift: The phenomenon where light from an object moving away from an observer shifts to longer wavelengths, making it appear redder; this is a crucial evidence for Hubble's Law.

Cosmological Constant: A term introduced by Einstein in his equations of general relativity that represents a constant energy density filling space homogeneously; it has implications for the expansion of the universe.

Big Bang Theory: The leading explanation for the origin of the universe, proposing that it began as a singularity and has been expanding ever since, which is supported by observations of Hubble's Law.