100 years ago, an unprecedented scientific revolution occurred.
Individual stars were measured in galaxies outside the Milky Way.
By combining measured distances with observed recession speed, we determined the Universe was expanding.
But was the Universe truly evolving, like the Big Bang predicts?
Perhaps it was dynamic but unchanging: cosmically indistinguishable at different times.
The Universe could obey the perfect cosmological principle: identical in all locations and throughout time.
Only a small, constant amount of spontaneous matter creation would be required.
Galaxies and stars of all ages should be found everywhere, universally.
The expansion rate and density shouldn’t change over cosmic time.
And the only cosmic backgrounds would arise from reflected starlight and heated dust.
The evidence, beginning in the 1950s and 60s, quickly demolished the idea.
Distant galaxies are younger, bluer, lower in mass, and less morphologically (shape) evolved.
The density of objects, measured by mass and galaxy counts, increases with distance.
The expansion rate evolves with time: the “Hubble constant” isn’t really a constant.
And a cosmic background exists, with a spectrum incompatible with reflected starlight or heated dust.
The Universe really does change with time, supporting the Big Bang and ruling out the Steady State model.
Mostly Mute Monday tells an astronomical story in visuals, images, and no more than 200 words. Talk less; smile more.