3. Earth, No Ordinary Rock (3) |
What are the Odds of Other Habitable Planets?
You’ve probably heard about of
SETI[4]
(Search For Extraterrestrial
Intelligence), an institute that searches for intelligent life
in the universe using huge radio-telescopes. These are designed to
listen and zoom into any radio signal that might come from a
particular area in space. If that signal is more than random noise,
that would show that the signal must have originated from an
advanced extraterrestrial civilization (as occurred in the movie Contact). Obviously nothing has been detected, and millions upon
millions of dollars have been spent. This sparked a former senator
to say: “The millions spent
on the search for intelligent life in the universe are better spent
on the search for intelligent life here in
The founder of SETI – Radio Astronomer Dr. Frank Drake, devised an equation in 1961 to calculate the number of advanced civilizations in the Milky Way galaxy able to communicate with radio signals. It's idea is to allow for calculation of what are the odds of other habitable planets. This well known equation – the Drake Equation – is still used to get an educated estimate for the number of habitable planets with civilizations in the universe:
N = N0 x fp x ne x fl x fi x fc x fL
In this formula, the multiplication of N0 (the total number of stars) by various fractions, gives the total number of civilizations. The fractions in the original Drake Equation are:
fp = fraction of stars with planetary systems
ne = number of planets in a star’s habitable zone
fl = fraction of habitable planets where life does arise
fi = fraction of those planets on which intelligent beings also evolve
fc = fraction of those planets on which sufficient communication technology arises
fL = fraction of the average planetary lifetime when there is an advanced civilization
All fractions are between 0 and 1, and obviously estimated close to 0, therefore the resulting number of habitable planet with civilizations N is much smaller than the original number of stars – N0.
We have already mentioned that in the days of Drake and Sagan (1960-1990), calculations made by applying the Drake equation were in the order of magnitude of one million advanced civilizations (N) in the Milky Way alone. Advancing knowledge of factors required for life has forced the Drake equations to be modified to incorporate the new data. And the results are now very different.
In Rare Earth[6] Ward and Brownlee add a number of fractions to their own version of the Drake Equation, which they call the Rare Earth Equation. The fractions added include: fraction of metal-rich planets, fraction of stars in a galactic habitable zone, fraction of planets with a large moon, fraction of solar systems with Jupiter-sized planets and a fraction of planets with a critically low number of mass extinction events. They do not attempt to exactly calculate N but conclude that: “To us, the signal is so strong that even at this time, it appears that earth indeed may be extraordinarily rare.”
In The Privileged Planet[7] Gonzalez and Richards take the Drake Equation to the next level and formulate the Revised Drake Equation. They enhance the equation to include a total of 20 different fractions, allowing for critical factors like: enough oxygen and low carbon dioxide concentrations in a planet’s atmosphere, right mass range, proper concentration of sulfur in the planet core, presence of the right sized moon and right planetary rotation, right amount of water in the planet crust, steady plate tectonic cycling, low number of large impacts and more. Discussing and estimating some of these, the authors conclude the discovery of even a single new civilization (habitable planet) in the Milky Way galaxy is extremely unlikely.
Fermi’s Paradox[8]
In 1950, Nobel laureate and physicist Enrico Fermi (1901-1954) asked his colleagues:
“If there are
extraterrestrials, where are they?”
He reasoned that if there were indeed many other intelligent civilizations in our galaxy, some surely would be further developed than us. These advanced civilizations would also explore or even colonize the universe. In time, say perhaps a million years, the blink of an eye on galactic timescales, they would have reached the rest of the galaxy or sent self-replicating robots. They would surely target habitable planets such as earth.
In our galaxy, that could be 12 billion years old, there is no trace of such colonization, either now or in the past. The conclusion: They are not here because they do not exist.
So, what are the odds of other habitable planets? In The Creator and the Cosmos[9] Hugh Ross advances the concept of the Drake Equation to include a total of 128 identified factors for habitable planets. He also has calculated a probability estimate for each particular factor to be within an acceptable range to support life. Combining all probabilities (and compensating for dependencies) Ross calculates a probability for occurrence of all 128 factors to be a chance of 10-166. So even with a total number of planets in the range of 1022, the chance is less than 1 in 10144 (one in one thousand trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion) that any such planet in the entire universe exists! This chance is so small, it is beyond the comprehension of a human mind! In any other context results such as these would infer an absolute impossibility.
How Big is Small?
Numbers like 1022 planets and chances of 1 in 10144 are beyond our comprehension. We can write the numbers and count the zeroes, but they do not mean much. And as always with chances, it is so easy to say: “there’s still a chance – so give it enough time and it will happen….”
Therefore we need an illustration to understand these chances better:
● Imagine the total
land surface of the
● Also imagine one silver dollar. A silver dollar is about the size of a square inch.
● Now cover all the
land surface of the
● And start adding new layers of silver dollars to cover the surface again and again until a height is reached of 10 miles everywhere.
● Now all the land
surface of the
● Next, imagine a single silver dollar marked with an X placed at random in this mass.
● Finally, blindfold a volunteer, drop him anywhere, send him to wander about until he chooses a point to dig into the 10-mile high pile, and grab only one coin.
● The chance of that person picking the silver dollar with the X is about 1 in 1025!
● Therefore, a change of 1 in 10144 is like repeating this experiment six times in a row, and each time selecting the X marked silver dollar – a virtual impossibility.
Next: (4) Exhibit #4: Designed for Discovery
[4] The SETI institute, founded in 1984 – www.SETI.org.
[5] SETI is now no longer funded by federal money.
[6] Peter D. Ward and Donald Brownlee , Rare Earth (2000), chapter 12: Assessing the Odds.
[7] Guillermo Gonzales and Jay W. Richards, The Privileged Planet (2004), Appendix A: The Revised Drake Equation.
[8] Guillermo Gonzales and Jay W. Richards, The Privileged Planet (2004), pages 276-278.
[9] Hugh Ross , The Creator and the Cosmos (2001 revised edition), chapter 16: Earth: a Place for Life. See also Hugh Ross in Why I am a Christian, edited by Norman L. Geisler and Paul K Hoffman (2001).