In the Dark

I was so busy at the weekend that although I had the date in my diary I forgot to write a post on 26th April, which was the centenary of the Great Debate that took place on 26th April 1920 at the Smithsonian Museum of Natural History.

The principal protagonists on the US debate were astronomers Harlow Shapley and Heber Curtis. It concerned the nature of so-called spiral nebulae (such as the Andromeda Nebula M31 shown above) and the size of the Universe.

Shapley argued the case that distant nebulae were relatively small and lay within the outskirts of Earth’s home galaxy, while Curtis held that they were in fact independent galaxies, implying that they were exceedingly large and distant.

The two scientists first presented independent technical papers about “The Scale of the Universe” during the day and then took part in a joint discussion that evening. Two papers outlining their opposing positions were subsequently published by Shapley and by Curtis in the May 1921 issue of the Bulletin of the National Research Council. The published papers each included counter arguments to the position advocated by the other scientist at the 1920 meeting.

Many at the time felt that Shapley had won the debate, interpretating the Milky Way as the entire Universe rather than just one of many galaxies. The spiral nebulae were relatively nearby, possibly solar systems in the process of formation.

A key piece of evidence in favour of the Shapley argument was provided by Adriaan van Maanen, who claimed to have measured the rotation a spiral nebula which implied the object had to be nearby. Van Maanen’s measurements were later shown to be incorrect. Moreover, within a decade, Edwin Hubble and others had established that the spiral nebulae are in fact large and enormously distant; they galaxies like our own Milky Way.

Two things struck me about this story. One is that it illustrates that its not unusual for a majority scientists to be wrong about something. Debates like this are really not very good for settling scientific arguments. In the end it the data count far more than opinions.

The second is that it is remarkable to think that just a century ago we knew so little about the Universe. Our modern view of the Universe may well turn out to be wrong in some important respects but I still think we can say we know more now than we did then!

I’m reminded of this quote:

We have not succeeded in answering all our problems. The answers we have found only serve to raise a whole set of new questions. In some ways we feel we are as confused as ever, but we believe we are confused on a higher level and about more important things.