With no audio amplification in the auditorium, Curtis’ ability to project his voice gave him an undeniable advantage. The 19-page paper Shapley presented focused mainly on the scale of the Milky Way, while Curtis’ type-written slides emphasized spiral nebulae as island universes.
“The two authors really talked around each other and were in some sense not even talking about the same thing,” says Mulchaey. “I suspect that Shapley’s concentration on the Milky Way also did not help his case, since everyone else was there to debate the island universes. This, combined with his underwhelming speaking abilities, probably led to Curtis being declared the winner, irrespective of the actual evidence.”
The results did no great harm to either scientist’s career, though; Shapley won the directorship of Harvard College Observatory, while Curtis took the helm of Allegheny Observatory.
Later that decade, Edwin Hubble’s measurements of Cepheid variable stars proved that Andromeda did indeed lie outside the Milky Way, forever changing our understanding of the scale of the universe.
“The distance measurement to Andromeda was the most significant game changer since the work of Copernicus/Galileo,” asserts Mulchaey. “Hubble effectively discovered the universe. It’s hard to do much better.”
A century after the Great Debate
Nowadays, there are far fewer opinion-polarizing debates in astronomy. “I suspect this is more a reflection on how modern astronomical research works,” explains Mulchaey. “Back in 1920, most individuals worked alone and communication about new results or observations was fairly slow.
“These days, we all work in collaborations where ideas can be easily shared,” he says. “We can hear about new observations or results almost as they happen, as opposed to having to wait until a new scientific paper is completed. Because many papers have multiple authors, there is also a lot of extensive discussion going on before a paper is even written.”
However, Mulchaey identified four modern-day astronomical unknowns with a wide range of possible explanations — dark matter, fast radio bursts, the fate of the universe, and extraterrestrial life. However, he remains unconvinced that they will be solved anytime soon.
“We’ve had the dark matter problem for decades now,” he says. “If you asked me back in 1990, I would have told you we will have an answer by 2020. The fact that we don’t suggests to me that we might be fundamentally missing something.”
And although a dark matter particle could be detected tomorrow and the search for life on Mars and in exoplanetary atmospheres continues, Mulchaey is pessimistic of a near-term breakthrough in these realms.
Fast radio bursts, though? We have a reasonable chance to figure those out in the not-too-distant future.