Expanding universe
Also called: Hubble's law · Topic: Origin and Evolution of the Earth and the Solar System · NCERT: Class 11, Ch 2 "The Origin and Evolution of the Earth"
Meaning
The expanding universe is the finding that galaxies are moving away from one another. They are not flying through space. Instead, the space between them is growing. Edwin Hubble gave the evidence in the 1920s. NCERT dates it to 1920, and his law linking speed and distance came in 1929. It showed that the farther away a galaxy is, the faster it moves away. The expansion is now speeding up, and scientists put this down to dark energy.
Example
Light from distant galaxies reaches us stretched towards the red end of the spectrum. This "redshift" shows that the galaxies are moving away. Hubble measured it at Mount Wilson Observatory in California, USA.
Don't confuse with
- Balloon analogy: dots on a blown-up balloon get bigger as it swells, but real galaxies do not swell. Only the space between galaxies grows.
- Hubble's law: this is the rule that a galaxy's speed away from us grows with its distance. It is one piece of evidence for the expanding universe, not a second name for the whole idea.