What is Hubble's Law?
Hubble's Law is a fundamental principle in cosmology that describes the observed relationship between a galaxy's distance from Earth and its recessional velocity. It states that galaxies are moving away from us at a speed directly proportional to their distance. This means the farther a galaxy is, the faster it appears to be receding, indicating a uniformly expanding universe.
Key Principles and Observational Evidence
The law is mathematically expressed as v = H₀d, where 'v' is the recessional velocity of a galaxy, 'd' is its proper distance from the observer, and 'H₀' is the Hubble constant. This constant represents the rate of the universe's expansion. The primary evidence for Hubble's Law comes from observing the redshift of light from distant galaxies, which occurs when light waves are stretched as the source moves away, shifting their spectrum towards the red end.
Practical Application: Measuring Cosmic Distances
Hubble's Law provides a crucial method for estimating distances to remote galaxies, which are too far for other distance measurement techniques. By observing a galaxy's redshift, astronomers can determine its recessional velocity. Using the known value of the Hubble constant, they can then calculate the galaxy's distance, effectively mapping the vast scales of the universe. This has been instrumental in building our cosmic distance ladder.
Importance in Modern Cosmology
Hubble's Law is a cornerstone of modern cosmology, offering compelling evidence for the Big Bang theory. The observed expansion implies that the universe originated from a hot, dense state and has been expanding ever since. It allows scientists to estimate the age of the universe and continues to be vital for understanding cosmic evolution, the distribution of matter, and the ultimate fate of the universe.