Thursday Throughput: Great Debate Edition
[ThTh1] In 1920, the nature of the universe was still not settled. We knew that our Sun was one of many stars within our galaxy. But we didn’t quite know what our galaxy was nor did we understand the nature of the so-called “spiral nebulae” — swirled clouds of light like M31 pictured above.
One view was that the Galaxy was the Universe and that the spiral nebulae were new stars being formed from clouds of gas. There were theories that a collapsing gas cloud could form long spiral structures as it congealed into a star. The other view was that the spiral nebulae were “island universes” — galaxies like our own. Only they had to be incredibly far away — hundreds of thousands or even millions of light years. This was such an unimaginably vast scale, that the former view tended to hold sway.1
On April 26, 1920 — one hundred years ago this week — two astronomers had a debate on this subject at the Museum of Natural History. Heber Curtis of the University of Virginia and Harlow Shapley of Mt. Wilson faced off to present their respective cases for the nature of the spiral nebulae.
Shapley took the view that the Milky Way comprised the entire universe. He presented a number of arguments: if M31 really were so far away, it would be much bigger than the Milky Way; the novae within M31 were extremely bright, sometimes outshining the entire galaxy, which was inconceivable. But the most important was that Adriaan van Maanen had observed another spiral nebulae — the Pinwheel Galaxy — and measured its rotation. If the Pinwheel were really hundreds of thousands of light years away, Van Maanen’s measurements meant it was rotating faster than the speed of light, which Einstein had recently proved was impossible.
Curtis, for his part, pointed out while the novae in Andromeda were really bright, there were also a lot of them (relatively speaking), more than anywhere else in the sky. It didn’t make sense for one part of the Galaxy to have so any novae compared to the rest of space; but it would make sense if that nebula was actually a vast collection of stars comparable to the rest of the visible universe. He also noted that Andromeda had dust lanes similar to what was seen in the Milky Way. He finally argued that Van Maanen’s measurement was in error, being too precise to be believed.
In the end, Shapley won the debate. But history would vindicate Curtis. It turned out that van Maanen had erred in his measurements, failing to account for the effects of distortion on the reference stars he was using as his reference points for the Pinwheel Galaxy2. But it was Edwin Hubble who provided the real proof. Using the Cepheid variables discovered by Henrietta Swan Leavitt, he measured the distance to Andromeda and showed it was indeed hundreds of thousands (later revised to millions) of light years away. It was also found that there were two types of novae and the brighter of them — supernovae — could indeed outshine an entire galaxy. And we eventually discovered that both the Milky Way and Andromeda were much larger than we’d thought.
The Great Debate is one of my favorite subjects in Into Astronomy because it illustrates the scientific method so beautifully. Shapley was wrong. But he won the debate because the evidence was on his side. It was only when new techniques and new evidence emerged that we discovered the error that had led him astray. I even memed it once:
So now I've memed the Curtis-Shapley debate. It has the advantage that Curtis won the debate but was ultimately wrong. pic.twitter.com/fCTRWaEWp7
— SecondSkonnanEmpireComputer (@Hal_RTFLC) April 5, 2018
The beauty of science is not that it always gets the right answers. It’s that we are constantly testing our theories to make sure they still work. And so even if you’re wrong — as Shapley was — you will eventually figure it out. It is a grinding, humiliating and inefficient way of figuring out the universe. But it’s better than anything else we’ve tried.
I also like to tell my students that the story of astronomy — one that now spans thousands of years — is the story of us discovering how increasingly small we are in the whole of creation. The Greeks expanded the Universe from just the Earth to the Solar System. Kepler expanded it to many light years with thousands of distant suns like our own. Hubble expanded it to millions of light years by measuring the distances to the nearest galaxies. And then he expanded it to billions of light years by discovering the expansion of the Universe. Our understanding of the universe now stretches out to as far as light will allow — some 92 billion light years. But maybe we’ll one day find the evidence that our universe is even more vast. Or is one of many universes.
The story of astronomy is far from over. But this week we can remember one of the most important chapters.
[ThTh2] Speaking of Hubble and the telescope that bears his name … I mentioned the 30th anniversary. Here is the image they released to celebrate.
#Hubble30 For its 30th anniversary, Hubble presents a colorful scene nicknamed the "Cosmic Reef." These two nebulas, NGC 2014 in red & NGC 2020 in blue, are part of a vast star-forming region in a nearby galaxy & are illuminated by young, massive stars: https://t.co/tWW42JAu3w pic.twitter.com/rdmCUS9ZMH
— Hubble (@NASAHubble) April 24, 2020
[ThTh3] This week, a video circulated from two urgent care doctors claiming that the COVID crisis is massively overblown. The indispensable Orac dispatches them with ease. Their argument is that since 6% of the people who came into their clinic tested positive for COVID, that must mean that 6% of the population is infected and therefore the fatality rate is 0.02%, a fraction of that for the flu.
This is jaw-droppingly stupid. People come into a clinic because … they’re sick. They specifically came into this urgent care clinic because it advertised that it could do COVID testing. So unless they were abducting random people off the street to test them for Coronavirus, their sample is not representative. More to the point, if you take the number of people who have already died3, a 0.02% CFR would imply that of NYC’s 8 million people, 60 million have been infected. Of the 60 million people in Italy, 135 million have been infected.
It’s hard to believe something this obviously stupid would get such play. But .. that’s the Age of Humbug for you.
[ThTh4] The technology used in farming is astonishing. This looks like a setup we might use to run a spacecraft.
Here’s what I’m doing inside the cab!! pic.twitter.com/IKnbwbEi0d
— Ag of The World (@AGofTheWorld) April 22, 2020
[ThTh5] The Pentagon has declassified and released UFO footage. I’m not terrifically impressed that these are aliens or anything. But it is interesting footage and I can’t wait to see it explained.
[ThTh6] Even if we act on global warming, many of the world’s reefs will still be in danger. But there may be some hope on that front.
[ThTh7] A great look at the amazing but deeply flawed Space Shuttle program.
[ThTh8] One of the early triumphs of the Theory of Relativity was that it explained changes in Mercury’s orbit. Mercury’s orbit precesses, meaning the orientation of its orbit moves around the Sun, making it more like a spirograph drawing than an ellipse. Well, we just measured that precession again — for a star zooming around a 4 million solar mass black hole at nearly 8000 kilometers per second.
[ThTh9] In theory, the idea of using the Sun as a giant lens to take high-resolution pictures of an exoplanet would work. I suspect the technical hurdles will prove insurmountable. But I’d love to see it happen.
- The island universe theory — and the name for it — was the work not of an astronomer but of a philosopher: Immanuel Kant.
- In the end, I have to sympathize with poor van Maanen, a great astronomer who is mostly remembered for these days for making a bad measurement.
- And recent analysis indicates we’re undercounting by as much as 60%