Why is the Sky Dark ... and Quiet?

In the middle of lunch in the summer of 1950, Enrico Fermi, a Nobel-winning physicist, blurted out the question “Where is everbody?” Fermi backed up his question with some quick calculations based on the size and age of the galaxy, the likelihood of Earth-like planets and some other factors. It seemed that Earth should have been visited many times by extraterrestrials and yet we apparently have not. So, where is everybody?

Events have occurred to make the Fermi Paradox more relevant over time. In Science:
1. 1961 — Frank Drake, the father of SETI, presented the Drake Equation which is used to estimate the number of technologically advanced civilizations in the galaxy.
2. 1975 — Michael Hart writes a paper that shows that the Fermi Paradox has scientific merit.
3. 1995 — Exoplanets are found, the Drake equation gets some information for one of its factors.

In TV and movies:
1. Star Trek — 1966-1968. Though far too optimistic regarding star travel, many elements have already come true (e.g. cell phones) and a large number of future astronomers are inspired.
2. ET — 1982. The movie ET adds that 2-letter “word” to the language.
3. Contact — 1997. The movie based on Carl Sagan’s book celebrates the spirit of SETI.

And in books:
1. Rare Earth — Ward and Brownlee (2000), this book pointed out the various things that make the Earth unique: large moon, well-placed Jupiter, plate tectonics, asteroids to kill dinosaurs, and centrally placed in a habitable zone. Just like the realtors tell you, “location, location, location”.
2. Life Everywhere: The Maverick Science of Astrobiology — David Darling (2002), an answer to Ward and Brownlee that covered the possibilities of life. It also directly challenged Ward and Brownlee’s motivation by noting the influence of a creationist on their writing.
3. Where is Everybody? — Stephen Webb (2002) attempts to exhaustively look at each possible answer to the paradox, 50 in all.

Another well-known astronomical paradox is Olbers’ Paradox (see Ephemeris, July 2006). Olbers asked, “where are they” but the “they” he referred to were simply stars. If the universe is infinite then, no matter which direction you look, you should see a star. So instead of “where are they”, Olbers’ question is usually stated “Why is the night sky dark?”.

Consider the possibility that the Fermi Paradox can be answered the same way as Olbers’ Paradox. There were assumptions implicit in the question “Why is the night sky dark?” One of these was that there are no major systematic motions in the Universe. Early in the 20th century, it was widely held that the universe was in a steady state. After Hubble demonstrated the universe is expanding, the steady state proponents saw this as a possible answer to Olbers’ Paradox: if there is a major systematic motion in the Universe, namely Hubble’s expansion, then some of Olbers’ assumptions are not correct. According to P.S. Wesson, this made some sense before the big-bang theory but not so after it. Wesson says that the expansion answer was “uncritically repeated in research work and … textbooks” because there was “no account of the relative importance of the expansion and finite-age factors”. So Wesson used a computer model to compare two possible answers to Olbers’ Paradox: expansion versus the finite age of the universe. Wesson ran the model with and without an expanding universe. The result in both cases was exactly what we see: a dark sky. But setting the rate of expansion to zero only made a slight difference.

The parallels to the Fermi Paradox is that some of the original assumptions are not correct but strong adherence to certain models may cause us to look for answers that won’t stand up to scientific scrutiny.Indeed, Olbers’ Paradox and the Fermi Paradox may have the same answer: particular phenomena, be it stellar light or evidence of extraterrestrial intelligence, takes a long time to arrive.

The modern answer to Olbers’ is that the universe is not infinite, at least, we can’t see stars that are infinitely far away. The universe appears to be about 14 billion years old so any stars that are more than 14 billion years away cannot be seen because the light from them hasn’t reached us yet.

There are a few assumptions in the Fermi Paradox that seem unsupported. Consider just this one: A colonizing civilization will spread geometrically; moving from one location to two others, then each of those will move to two others, and so on and it will simply continue to do so. Jared Diamond’s book “Collapse” shows how the Norse moved to Iceland, Greenland and Labrador and then retrenched. China destroyed its naval fleet rather than risk contamination from other cultures. American “Manifest Destiny” was stopped by the inhabitants north and south and by the Pacific Ocean in the west. So the answer to Fermi is the same as to Olbers, they/it aren’t here yet.

Beings as temporally limited as we are, would prefer an answer that didn’t require so much patience. But hope won’t trump science in the long run and control of the fourth dimension seems unlikely. Otherwise, we could ask “Where is everybody, the people from the future?”