If the Universe Is Teeming with Aliens... Where Is Everybody? by Stephen Webb

Author:Stephen Webb [Webb, Stephen]
Language: eng
Format: epub
ISBN: 9780387955018
Google: Kp6g79LuKWEC
Goodreads: 180506
Published: 0101-01-01T00:00:00+00:00

They Do Not Exist

FIGURE 44

The planetary

nebula NGC 7027. Objects like

this produce much of the

carbon we observe in the

Universe.

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 colo-149

Chapter 5

nize 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.

SOLUTION 33: PLANETARY SYSTEMS ARE RARE

A time will come when men will stretch out their eyes.

They should see planets like our Earth.

Christopher Wren, Inaugural Lecture as Professor of Astronomy, Gresham College Anthropic arguments are rather abstract. There have been many more tangible suggestions as to why ETCs might not exist. For example, perhaps there is no place for them to develop.

A common assumption is that complex life requires a planet — prefer-ably Earth-like — on which to originate and evolve. A technologically advanced species may one day decide to move away from planet dwelling, of course, but the evolutionary ancestors of those species must have began as planet dwellers. (Some SF writers have explored the possibility of life evolving in more exotic locales, including the surface of a neutron star and a gas ring around a neutron star.

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