The Great Debate
The Great Debate was an influential debate between the astronomers
Harlow Shapley and
Heber Curtis which concerned the nature of
spiral nebulae and the
size of the universe. The basic issue under debate was whether distant nebulae were relatively small and lay within our own
galaxy or whether they were large independent galaxies. The debate took place on
26 April 1920 in the Baird auditorium of the
Smithsonian Museum of Natural History. 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. Much of the lore of the Great Debate grew out of two papers published by Shapley and 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.
Shapley was arguing in favor of the
Milky Way as the entirety of the universe. He believed galaxies such as
Andromeda and the Spiral Nebulae were simply part of the Milky Way. He could back up this claim by citing relative sizes - if Andromeda and such were not part of the Milky Way, then the distance to it would range in the 10^8
light years - a span most
astronomers would not accept.
Adriaan Van Maanen was also providing evidence to Shapley's argument. Maanen was a well respected astronomer of the time who said he had observed Andromeda rotating. If Andromeda was in fact a distinct galaxy and could be observed to be rotating, there would clearly be a violation of the universal speed limit, the
speed of light.
Curtis on the other side contended that Andromeda and other such nebulae were separate galaxies, or "Island universes". He showed that there were more
novae in Andromeda that in the Milky Way. From this he could ask why there were more novae in one small section of the galaxy than the others. This led to supporting Andromeda as a separate galaxy with its own signature age and rate of novae occurrences. He also cited dark lanes present in other galaxies similar to the dust clouds found in our own galaxy and massive
doppler shifts found in other galaxies.
Curtis stated that if Van Maanen's observation of Andromeda rotating were correct, he himself would have been wrong about the scale of the universe and that the Milky Way would fully encompass it. It later became apparent that Van Maanen's observations were completely false - one can not actually see Andromeda rotate during normal
human lifespans. It is now known that the Milky Way is only one of hundreds of billions of galaxies in the
visible universe, proving Curtis the more accurate party in the debate.
There is also a group at
University of Newcastle in
England whose
forum, also entitled The Great Debate, discusses the modern picture of what it is to be human in the light of evolutionary and neuroscientific discoveries.
The Great Debate is also the fourth track off of progressive metal band
Dream Theater's sixth album,
Six Degrees of Inner Turbulence*
Universe*
Galaxy*
Andromeda Galaxy*
Milky Way*
Astronomy*[
1] - resources related to the debate at the
NASA website
