If the Universe Is Teeming With Aliens ... WHERE IS EVERYBODY?: Fifty Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life by Stephen Webb

Author:Stephen Webb [Webb, Stephen]
Language: eng
Format: epub, mobi, azw3
Tags: Astronomy, Astrophysics, Biology, Cosmology, Evolution, Extraterrestrials, Nature, Physics, Science, UFOs
ISBN: 9780387955018
Google: Kp6g79LuKWEC
Amazon: 0387955011
Publisher: Copernicus
Published: 2002-10-03T11:00:00+00:00

FIGURE 44: The planetary nebula NGC 7027. Objects like this produce much of the carbon we observe in the Universe.

The main producers of cosmic carbon are planetary nebulae, which occur at the end of the red-giant phase of average-mass stars. Planetary nebulae shed their outer layers into the interstellar medium, and the material is recycled to form later generations of stars and planets. Since astronomers believe they know the historical rate of star formation (it was higher in the past than it is now, with a peak about 7 billion years ago) and they know the relevant details of stellar evolution, they can calculate the rate at which planetary nebulae formed in the past—and thus the rate of cosmic carbon production. According to Livio’s calculations, the rate of planetary nebula formation peaked a little less than 7 billion years ago. From this, he argues we might expect carbon-based life to have started when the Universe was about 6 billion years old. Since the time required for advanced ETCs to evolve is a significant fraction of a stellar lifetime, we would expect ETCs to develop only when the Universe was about 10 billion years old. If this is the case, then ETCs cannot be more than about 3 billion years older than us.

Livio’s conclusion has been proposed by others as a resolution of the Fermi paradox. They suggest life could have emerged only relatively recently on a cosmic scale. There are presently no ETCs capable of interstellar travel or communication because, like us, they have had insufficient time to develop. Perhaps in the future the Galaxy will be aswarm with interstellar commerce and travel and gossip. For now, though, all is silence.

But even if Livio’s conclusion is correct, and there are no ETCs more than 3 billion years in advance of us, I fail to see how it solves the Fermi paradox. An ETC that is 3 billion years older than us has had plenty of time to colonize the Galaxy; it has had plenty of time to announce its presence to the Universe. (In the Universal Year, ETCs could have reached our present level of technology at about October 1; they thus have 3 months to colonize the Galaxy—a process we can measure in hours on this scale. They have had time enough to get here.) Unless it can be shown that intelligence is only coming into existence now, and thus life on Earth is among the most advanced in the Galaxy, the arguments do not really address the main thrust of the paradox.

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