Hubble Law stands as a cornerstone of modern cosmology, elegantly describing the observed expansion of the universe. Formulated by Edwin Hubble in the late 1920s, this law reveals a direct relationship between a galaxy’s distance from us and its recessional velocity. Simply put, the farther a galaxy is, the faster it appears to be moving away, a concept fundamental to our understanding of the cosmos’ dynamic nature.
The evidence for Hubble Law comes from the phenomenon of redshift. As light travels across the expanding universe, its wavelengths are stretched, shifting towards the red end of the electromagnetic spectrum. The amount of this redshift is directly proportional to the galaxy’s recessional velocity, a consequence of the Doppler effect applied to the vast distances of space. By meticulously measuring the redshifts of numerous galaxies, Hubble established his groundbreaking law.
Mathematically expressed as v=H0d, Hubble’s Law introduces the Hubble constant (H0), the proportionality factor between a galaxy’s velocity (v) and its distance (d). This constant represents the current rate of the universe’s expansion. While its precise value has been refined over time through increasingly sophisticated observations, the fundamental relationship it describes remains a crucial tool for estimating cosmic distances and the age of the universe.
Hubble’s Law provides compelling observational support for the Big Bang theory. The recession of galaxies implies that in the past, the universe was much smaller and denser, eventually converging to a single point from which the expansion began. The Hubble constant, therefore, is intrinsically linked to the age of the universe; its inverse provides a rough estimate of the time elapsed since the Big Bang, offering a cosmic timescale.
It’s important to note that Hubble’s Law primarily applies to the large-scale structure of the universe. Nearby galaxies within our Local Group exhibit peculiar velocities, movements influenced by local gravitational interactions that can deviate from the overall Hubble flow. However, for distant galaxies, the recessional velocity due to cosmic expansion far outweighs these local motions, making Hubble’s Law a reliable measure of their distance and the universe’s expansion.