Hubble's Law and the Expanding Universe
Edwin Hubble · 1929
"Distant galaxies are receding from us at speeds proportional to their distance — the first hard observational evidence that the universe itself is expanding, which run backward in time implies it began from a single point."
In 1929, using the 100-inch telescope at Mount Wilson, Hubble measured something nobody had confirmed before: the farther away a galaxy is, the faster it's flying away from us. Run that expansion backward, and everything converges.
Hubble plotted the redshift (a Doppler-like stretching of light toward red wavelengths, indicating motion away from the observer) of dozens of galaxies against their estimated distances and found a striking linear relationship — velocity equals a constant (now called the Hubble constant) times distance. This wasn't predicted by intuition; static-universe models were the default assumption at the time, including one Einstein had built a 'cosmological constant' fudge factor into specifically to avoid an expanding universe. Hubble's data forced the opposite conclusion: space itself is stretching, carrying galaxies apart. Extrapolated backward, an expanding universe implies a moment when all matter and energy were compressed into an extremely hot, dense state — the observational seed of Big Bang cosmology, though the theory itself would be built out by others over the following decades.
What did Hubble's 1929 redshift-distance data show, and why did it matter for cosmology?
Read more about the topic
The explanation above is written with AI assistance. These are the originals — go to them to check it.
- A Relation between Distance and Radial Velocity among Extra-Galactic NebulaeProceedings of the National Academy of Sciences, 1929
The Uncertainty Principle
"There is a fundamental limit to how precisely you can simultaneously know a particle's position and momentum — not because of instrument error, but because of the underlying nature of reality at the quantum scale."