(Starts With A Bang!) – Ethan Siegel:
On April 26, 1920 — more than a full century ago — the most famous debate in the history of astronomy was held: simply known as The Great Debate. Two well-respected astronomers, Harlow Shapley and Heber Curtis, took on the important question of what, exactly, those spiral “nebulae” in the night sky actually were. The two lines of thought were as follows:
- These are proto-stars, in the process of becoming stars and even Solar Systems, located within our own galaxy, which is much larger in size and extent than typically thought.
- These are their own galaxies, or “island Universes,” located at distances so great that they must be outside of the Milky Way entirely.
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What did decide matters was the subsequent observations of Edwin Hubble, which involved finding and identifying not only novae in these spiral nebulae, but a particular type of variable star: Cepheids. From these Cepheid variables, we could actually compute a distance to these nebulae, and found them to be on the order of millions of light-years away, placing them far outside the Milky Way. The debate was settled not by superior arguments, but by new, superior evidence. That 1923 finding, a full century old this year, was what truly answered this burning scientific question. …
The most important rule in any scientific debate is this: it doesn’t matter who wins the debate. It doesn’t matter who makes the better argument; it doesn’t matter who convinces more people; it doesn’t matter who votes with you. When it comes to science, the very ideals of democracy are completely irrelevant.
What matters is that, scientifically, you identify the key points of evidence that could definitively settle the contentious issues, and then you do your best to go out and find that evidence. Once that evidence is in your hands, you follow it wherever it leads. …
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