The 100th anniversary of the ‘Great Debate’ of astronomy raises thoughts about the search for life in the universe.
On April 26, 1920, in a sample of astute public relations, the Smithsonian Museum of Natural History in Washington, DC hosted a debate between astronomers Harlow Shapley and Heber Curtis. The topic was the question of whether the ‘spiral nebulae’ were actually distant galaxies (implying a universe much more expansive than previously imagined) or simply a part of our own Milky Way (implying that this galactic realm was, in fact , the universe).
Regardless of the immediate value of this somewhat artificial discussion, it helped spread the publication of works by Shapley and Curtis and, in a way, became a model for bringing the nature of the scientific method (and argument) more into the public eye.
In fact, in 1995, the format was revived, again at the Smithsonian, for the first of a new generation of public debates. That one addressed the then unknown nature of gamma-ray bursts. I was fortunate to be seated in the audience, having recently arrived in the USA as a postdoctoral fellow at NASA and I was impressed by the pomp and fun of it all.
Now, 100 years after the first debate, Professor Robert Nemiroff and Astronomy Picture of the Day (APOD) gathered another debate. This time, the question is how to expect to get the first evidence of extraterrestrial life and, instead of having just two debaters, APOD staff asked an entire group of astronomers and astrobiologists to weigh. You can see all the fantastic reviews on here. For my part, I made a short 5 minute video, embedded below.
The essence of my opinion on the issue is that we must also ask whether we will recognize alien life when we see it. To try to unpack a little, I came up with the following diagram:
The basic idea is that there is always a tension between the ‘credibility’ of the data or a measure related to life elsewhere and how informative that data or measure is. For example, if I dig up a contorted organism on Mars that would be extremely credible as evidence for life elsewhere, however, it is certainly as informative as other evidence. Perhaps the contorted organism is actually the same material as life on Earth (due to the exchange of materials between planets), or it simply reinforces how ‘special’ our solar system is.
On the other hand, if I detect a strangely structured signal transmitted by another civilization, it can increase our credulity or ability to interpret (less credible), but it would be surprisingly informative if it is real (they live, think, build!).
You can judge for yourself by watching the video:
As for my opinion on the issue of the debate – my guess is that bio-signatures are what we will get first, but we may not find any hard evidence. Instead, we can accumulate evidence that ‘something is happening’ in different environments, a sign that life is ‘general’, even if the details remain elusive…
