What are the odds that there is life on other planets in the universe?
Carl Sagan and other smart thinkers in the 1960’s created quite a stir with their calculations and predictions of finding extra-terrestrial life in the universe. The subject has been the subject of many movies, television shows and books since then.
Of course, we have not found life in the years following those grand projections, not that five intervening decades of searching is very significant in the vast sea of time. Still, the prospect of finding extraterrestrial life in the universe seems no closer, maybe further off, than when Sagan spoke those words.
Should we be surprised? Is it really “just science”?
The calculations are known as the Drake Equation. There are about 400 billion stars in the Milky Way. There are about 100 billion stars with planets in the Milky Way. If each star with planets has about ten (10) planets (like ours does), there are about a trillion planets in the Milky Way. If we assume there are two planets suitable for life in each system, then about 200 billion planets are suitable for life. Notice these are all assumptions. (See Carl Sagan – Cosmos – Drake Equation)
The assumptions continue with an assertion that half the planets suitable for life actually give rise to life. Carl Sagan then concludes there are about “100 billion inhabited worlds” (see here). Carl Sagan assumes that one percent of inhabitable planets produce a technological civilization. That would be one billion planets. Based on the relatively short period of time in which we have had the ability to engage in radio communication, he reasons that maybe only ten (10) planets in the Milky Way may be capable of communicating with us.
Notice how many assumptions are made in this calculation. He was simply plugging in numbers (albeit not without some reasonable basis). He was assuming all kinds of things, not the least of which is that life simply appears where it can possibly survive (life occurs from “molecules that are readily made, they spontaneously self-assemble” (see here)).
Extrapolating conservatively out from the Drake Equation (on the Milky Way) to the entire universe and all of the galaxies, there are about 500 billion sun-like stars and about 100 billion Earth-like planets. That is 100 Earth-like planets for every grain of sand on Earth! From these assumption, “[m]oving forward, we have no choice but to get completely speculative.” If only 1% of those Earth-like planets develop life and 1% of those planets develop intelligent life, that would yield 10 million Earth-like planets with intelligent life. If we extrapolate back to the Milky Way, that would be equivalent to 100,000 intelligent civilizations in our galaxy!
This all sounds promising, and quite exciting! But then there is the rest of the story – the “Fermi Paradox” (see here):
“If we’re right that there are 100,000 or more intelligent civilizations in our galaxy, and even a fraction of them are sending out radio waves or laser beams or other modes of attempting to contact others, shouldn’t SETI’s satellite array pick up all kinds of signals?
But it hasn’t. Not one. Ever”
Consider that our Sun and Earth are rather young in the Universe. There are other systems that are over 3 billion years older than us! You would assume that civilizations on those planets in systems billions of years older than ours would be colonizing the Milky Way be now. So where is everybody??? That is the Fermi Paradox.
Ironically (or candidly), some people in the scientific community have called the prediction of other life forms in the Universe a “belief” rather than science. (See Ignoring 500 Billion Galaxies: Mathematics vs. Common Sense in the dailygalaxy.com “the state of knowledge measures a ‘personal belief’”.) In another article posted on the dailygalaxy.com, Extraterrestrial Life Common in the Universe – Wishful Thinking?, the author references Princeton researchers for the conclusion that an expectation of life forming from bacteria to sentient beings “might be based more on optimism than scientific evidence.” Far from finding further proof of Carl Sagan’s predictions in the 1960’s, scholars in the 21st Century are finding more evidence that the Earth is a “cosmic aberration” than one of many millions of life factories in the universe.
Even more interesting to me than all of this is the admission of Princeton astrophysical sciences professor, Edwin Turner, that the early predictions of the probability of other life in the Universe seem now more based on a “belief” (assumptions) than on science:
“If scientists start out assuming that the chances of life existing on another planet as it does on Earth are large, then their results will be presented in a way that supports that likelihood,” Turner said. “Our work is not a judgment, but an analysis of existing data that suggests the debate about the existence of life on other planets is framed largely by the prior assumptions of the participants.”
To be fair to “Science”, there are explanations for the apparent lack of intelligent life on other planets. The Great Filter theory is that there are some stages in the evolutionary process that are particularly difficult for life to get beyond. In that case, scientists have speculated that there are three possibilities: 1) we are either very rare to have emerged on the other side of this Great Filter (Rare Earth Hypothesis); 2) we are the first to emerge past the Great Filter; or 3) we are screwed (we have not come to the Great Filter, and when we do it will likely mean our demise).
Another group of explanations assume that life “out there” exists, but there are reasons we have not heard from them. Maybe aliens already visited us and found no one home (before intelligent life emerged). Maybe we are in a rural area of the galaxy, and others have not discovered us yet. Maybe others do not care about us and are happy where they are. Maybe we have not found others because one super intelligent group wipes out all others they encounter (and fortunately for us, they have not found us yet). Maybe our technology is too primitive to make contact. Maybe we are receiving communication, but our government(s) is hiding it from us. Maybe others are simply observing us (Zoo Hypothesis). Maybe others are all around us, but we are too primitive to communicate with them.
You can read all about the Fermi Paradox and other explanations for it here, but something is missing in all of this great thinking, much of which is the stuff of science fiction.
It is clear that science, like logic, is highly dependent on the premises we begin with. (See End of Reason: Leap of Faith) That science can be influenced (or driven) by assumptions that may be false is a sobering thought – at least it should be a sobering thought. The Fermi Paradox strongly suggests that Carl Sagan’s assumptions were “optimistic” if not simply wrong. Not even under consideration in this discussion is the assumption that evolution can lead to sentient life.
The only thing we can say with certainty is that life occurred on Earth on the conditions which existed on Earth. We can say that there is evidence that evolution has occurred within species. Let us be honest here; we cannot say with certainty that evolution is what caused life to emerge or that evolution caused non-sentient organisms to change into sentient, intelligent life (if, indeed, one emerged from the other).
What I am getting at, of course, is the assumption that “all this” happened without design. We can safely say that intelligent life exists on the Earth under the conditions that exist, which are ideal for such life. We really cannot conclude with any certainty anything else, including how it was that life came to be in the first place. The conclusions we reach are all based on assumptions that we cannot duplicate, that we have never found to be duplicated anywhere else.
The line of reasoning that is causing scholars at Princeton and elsewhere to wonder whether the Earth is simply a cosmic aberration rather than one of many life-sustaining environments in the Universe should give those same scholars pause to rethink other assumptions from which other more fundamental conclusions are drawn –like whether evolution can account for sentient life. The main point made by these researchers is that we cannot use the example of one planet to extrapolate a prediction of life on other planets because it is too small a sample (one in fact) from which to make a solid prediction.
The same is true with evolution. Just because life exists on Earth, and life has evolved (to some extent), does not mean that evolution caused life or that evolution caused simple, non-sentient life to become intelligent life. There is no other example of life from which we may compare our world to another world to determine if the same patterns exist – we have only assumed that is how it works.
The odds seemed great in the 1960’s that other intelligent life existed in the Universe and that we should be able to find it. The odds do not look very good today. Taking many things into account today that were not considered as part of the equation then, such as over 200 known parameters necessary for a planet to support life, which all must exist at the same time and perfectly coincide, the odds of intelligent life existing on another planet in the Universe are approaching zero. “The odds against life in the universe are simply astonishing.” (Science Increasingly Makes the Case for God – by Eric Mataxas in the Wall Street Journal)
Metaxas points out that the unlikelihood of all of the requirements coming together in perfect harmony to allow life to exist on Earth is nothing compared to the fine tuning that allows the Universe even to exist!
“For example, astrophysicists now know that the values of the four fundamental forces—gravity, the electromagnetic force, and the “strong” and “weak” nuclear forces—were determined less than one millionth of a second after the big bang. Alter any one value and the universe could not exist. For instance, if the ratio between the nuclear strong force and the electromagnetic force had been off by the tiniest fraction of the tiniest fraction—by even one part in 100,000,000,000,000,000—then no stars could have ever formed at all. Feel free to gulp.”
And it gets worse:
“Multiply that single parameter by all the other necessary conditions, and the odds against the universe existing are so heart-stoppingly astronomical that the notion that it all “just happened” defies common sense. It would be like tossing a coin and having it come up heads 10 quintillion times in a row. Really?”
At what point do these astonishingly infinitesimal odds for a materialist explanation of life, even on this planet, begin to suggest intelligent design as a possible explanation? I also wonder how much personal belief and assumption goes into science that we do not examine or talk about. At some point, saying that “it is just science” is just not being honest.