On August 6, 1967, a student named Jocelyn Bell (later Jocelyn Bell Burnell) discovered a strange radio signal coming from space. It was a series of pulses, evenly spaced with about 1.337 seconds between each pulse. Her supervisor initially thought it was some sort of radio interference. But this possibility was ruled out. The signal was jokingly designated LGM-1 for little green men one.
The designation of the signal as coming from little green men was not entirely serious. But the possibility that this was a radio signal from an alien race was certainly being considered. The reason is that the signal exhibited specified complexity. A pulsating pattern has a very short description. But the probability of the pattern arising out of random noise is very small. That was why the researchers immediately rejected the idea that it was simply random noise and opened the possibility that it was small green aliens.
Chance and Necessity
But why did the researchers not jump entirely to the alien hypothesis? Before adopting such an explanation, they would want to do something else: rule out all possible chance hypotheses. They could not initially give a naturalistic chance and necessity explanation of the signal, but they had not compellingly ruled out the possibility of such an explanation, either.
Bell went on to find other pulsing radio signals coming from different parts of the sky. She deemed that this killed the little green men hypothesis. One strange radio signal might well be an extraterrestrial civilization. Two, and soon more, suggested an unknown natural phenomenon. Shortly after the announcement of the discovery of these signals, a hypothesis was suggested: they were rotating neutron stars. They would become known as pulsars, a shorthand for pulsing star.
A Negative Result
We have then an example of the application of a design inference, ending up in a negative result. The signal did exhibit specified complexity according to the initial random noise hypothesis. However, when other hypotheses were explored, it was determined that another explanation was correct.
What if no explanation for the signal had been found? Likely, many would be convinced that these pulsars were signals being emitted by distant technologically advanced alien civilizations. If we were confident that we had eliminated the possibility of a natural explanation for such signals, we would adopt the remaining possibility, inferring the existence of intelligent alien life.
That is not what happened in this case. But it illustrates an important point: evidence for intelligent extraterrestrial life is being evaluated based on the logic of the design inference as defended by intelligent design.