The argument goes like this: the universe is so vast it contains millions of Earth-like planets, all with a temperature, water content, and geology suitable for Life; thus, the universe is undoubtedly teaming with Life beyond Earth.
Intelligent Life might be rare, but the occurrence of simple reproducing cells in the universe must surely be as common as jam on scones!
This is an assumption based on a false premise. We know life can exist. We know there are countless places in the universe that might be suitable for life. And that's about as far as most people get when they ponder this issue. They get stuck there - bamboozled by the enormity of space.
The Many Suitable Planets Fallacy
Yes, I agree there are millions of planets with conditions favourable for Life…but so what? "If you go outside and look up on a clear night, it's almost impossible to believe that we are alone," says Stephen Webb, Physicist and author of 'If the Universe Is Teeming with Aliens...Where Is Everybody?'
"There's something innate in this feeling that we cannot be alone,” says Webb. I admit to the same emotions. I like to think there is Life beyond Earth, but gut feelings can be misleading.
The enormity of the universe is beyond what the human mind can conceptualize, and dealing logically with enormity is not something humans handle well with intuition.
The vast number of habitable planets in the universe seems impressive. It leads many to think Life, and intelligent Life, beyond Earth must exist. "Ultimately, the argument they are putting forth is that there are, for the sake of argument, a trillion places that life could get going on, and that's a big number," Webb says. But he adds there's a problem with this logic: "We don't know in this context whether a trillion is a big number or not." Suppose there are a trillion-trillion planets suitable for Life. That's still next to meaningless if the probability of Life occurring on such planets is a trillion-trillion-trillion trillion to one. And it might be even less than that. We don’t know.
Counting the number of Earth-like planets in the universe and claiming that implies an abundance of Life is silly. Just as silly as counting the number of grains of sand on a volcanic beach and pretending that means natural forces will have moulded these grains into a wine glass.
An abundance of necessary ingredients to create something is not equivalent to sufficient conditions to make that thing.
Many volcanos contain the necessary ingredient to make a wine glass; silica. Furthermore, volcanos supply the required conditions of heat and a shaping force to spin silica into wine glasses. But would you argue wine glasses must be abundant throughout the universe because planetary volcanoes are plentiful?
I doubt it. And for all we know, the probability of Life occurring, on a suitable planet, might be far less than the probability of a volcano spitting out a wine glass! Of course, a wine glass is one-hundred per cent man-made and a very specific object, while naturally occurring Life may come in many forms. The analogy, however, demonstrates that the fallacy of believing something must be common on account of its ingredients being common. The Building blocks of Life are common in the Universe, and some amino acids form readily when their ingredients are mixed. It is, however, a leap of faith to extrapolate that Life, therefore, occurs readily.
Evolution is a slow process, building on itself from trial and error in slow and gradual steps. So, of course, Life need not have been spit out instantly, fully-formed, and functional. Instead, it would have started with simple, self-organizing molecules that somehow crossed the murky threshold and became living matter.
But as yet, we don’t know how that transition (abiogenesis) happened or where to draw the line on the spectrum of living and non-living matter. Nor do we know the likelihood of it happening.
The Right Ingredients
Just because the right ingredients and conditions exist to create something, it does not follow that something is likely to be created. The Bottom line is this, we do not know what the probability of Life arising is, even giving the right ingredients and conditions.
“We just don’t know if what happened on Earth was unique or, given the right conditions, Life starts easily.” - Oleg Abramov, Research Space Scientist at the USGS Astrogeology Science Center.
Granted, we need not know something with one-hundred pecent certainty to be confident it is true. For example, I’m sure humans will walk the earth in a thousand years from now, but I can’t give you the statistical likelihood of it, worked out scientifically to the last decimal point. I can only say, based on what I know, that it is more likely than not.
But this does not even hold when it comes to Life beyond Earth. We can’t say it’s more likely, or not. We don’t have sufficient knowledge to say either way. The probability of Life occurring, given the right conditions, might be so close to zero that Earth harbours the only Life in our universe.
Conversely, Life might also be common. We have no idea, and we can't draw insightful conclusions either way.
An Early Goal
One reasonable argument in favour of Life occurring readily is it seems Life on Earth kicked off early. It’s thought not long after it became possible for Life to generate on Earth, it did so. This suggests Life gets underway as soon as it can when the conditions are right. Or does it?
Again, we really can’t say. It might mean that, or early Life might have been a fluke on Earth. Drawing statistical conclusions from a sample of ‘one’ (the Earth) is problematic.
We’d need to have evidence for Life kicking-off early on more than one occasion to draw any meaningful conclusions.
Put it this way, if you saw only one soccer game, and it so happened the striker put the ball in the net in the first thirty seconds, could you safely conclude goals are typically scored in the first minute of all soccer games? We have observed Life in the most inhospitable places on Earth. Some people believe this indicates Life might therefore exist throughout the inhospitable regions of the Universe. Maybe, maybe not.
The evolutionary process of living organisms evolving to survive in challenging environments is a very different proposition to non-life transitioning into Life in such environments. It would, however, be fair to say that extra-terrestrial Life may take on forms that we can't even imagine and thrive in a diverse spectrum of environments that do not even exist on Earth. And of course, any organism that thrives in a particular environment isn’t actually living in an inhospitable environment, as far as it is concerned!
For certain, we can say that Life occurred at least once in the universe, on Earth. It's therefore logical to conclude it could develop elsewhere - but it's not logical to assume it has. Life on Earth does not imply Life exists elsewhere - it merely implies it might. It makes it possible, not probable.
Believing Life is common in the universe is not dissimilar to a belief in God. It's a Faith-based impulse.
It's fun to note how scientists are often extraordinarily unscientific when it comes to this topic.
Many are so keen for there to be Life beyond Earth that they convince themselves that Life is likely on account of planet numbers. This is a flawed argument when ignoring the question of, what is the probability of Life occurring, given the right conditions?
On this question, we have almost no idea. Many people just assume it's high, without basis, which is unscientific.
Drake tells us Nothing!
In discussions on this topic, the Drake Equation is frequently resurrected by folk keen to tint their arguments with a bit of seemingly impressive maths - as if it somehow gives credibility to the belief that Life beyond Earth is likely. If you were grappling in your scientific kit-bag for this mathematical estimate of extra-terrestrial life, think again.
Firstly, the Drake Equation is meant to estimate the number of communicating civilizations in our galaxy.
That’s vastly different to solving the question of the probability of Life existing beyond earth. Life can be a single cell and very different to the communicating civilizations that the Drake Equation addresses.
Secondly, we don’t know all the correct numbers to plug into the Drake Equation to produce an accurate estimate anyhow.
So the Drake Equation is meaningless here. It is the equivalent of saying, “Here’s an irrelevant equation that proves nothing, and I don’t know what data to feed into it, but I present it as evidence all the same.” That’s a bit like a religious, faith-based argument. Astrophysicist, Frank Drake, came up with his equation in 1961. The thought behind it was to assign a number to various terms to calculate the number of intelligent, communicative civilizations that might exist beyond Earth.
But as Astronomy Magazine wrote, "The problem with these terms, though, is that we don't know what number to assign them."
Researchers at the University of Oxford tied to get around this problem. They used a wide range of numbers for each term in the equation.
"The probability distributions that resulted surprised even them," reported Astronomy. "Humans, they found, are likely to be alone in the observable universe."
But of course, the range of numbers the Oxford Univerity used in their calculation might still be way off the mark.
Using The Rare Earth Equation, it was calculated that Earth-like, conducive to life circumstances, occur amongst planets with a frequency of no more than 10 to the power of minus ten, and it could plausibly be as small as 10 to the power of minus twelve.
Conversely, David Kipping from Columbia University found in his calculations, using a statistical method called Bayesian inference, that intelligent life may be common beyond Earth. However, reporting on this, Peter Dockrill writes, "Of course, a lot of this conjecture is based around a particular assumption: that it makes sense for life (and intelligent life) to exist elsewhere, given the mind-boggling number of habitable worlds estimated to exist out there in the cosmos. Given that excess of exoplanets – and given how we emerged here on Earth – then surely other life-forms will similarly spring up on other orbs too, right?
Well, maybe not. At least, we don't yet have any real data to know one way or the other."
Unfortunately, none of these equations and calculations gets us far. Ed Turner, an astronomer at Princeton University, recently formulated yet another equation, one that addresses the likelihood of Life occurring. But he admits to not knowing what numbers to plug into it, and thus he says, "It's not an answer; it's a new tool for trying to think about the issues involved." And that's the only manner in which these equations assist us. As Turner puts it, they act to "divide our ignorance into different factors."
What are the Odds?
What do scientists say about the odds of Life getting started? Opinions range from highly likely, to highly unlikely, with each camp citing either data or lack of data to support their claims.
We can take our pick of opinions and select quotations to support whatever position we wish to argue.
But with nothing verified either way and debate still circulating among scientists, the only safe conclusion we can draw, for now, is science is unable to provide a satisfactory answer.
To arrive at an accurate probability, we need a far better understanding of how Life occurs than we currently have. Unfortunately, as NASA puts it, "We don't know how readily life begins, whether it's common or rare."
David Kipping, an assistant professor in Columbia's Department of Astronomy, places the likelihood of Life beyond Earth as very high. He uses a statistical technique he describes as "Akin to betting odds".
He says his analysis, "Can't provide certainties or guarantees, only statistical probabilities based on what happened here on Earth."
The problem here is, we don't know if what happened on Earth was a one-off freak or a typical outcome.
As Space.com says of the likelihood of abiogenesis, "To get a grip on that probability, humanity would have to encounter another instance of life's emergence beyond our own for comparison."
The summary in Kippligs work reads, "Despite knowing when life first appeared on Earth, scientists still do not understand how life occurred, which has important implications for the likelihood of finding life elsewhere in the universe." We have discovered organic compounds on meteorites. More than fifteen amino acids, some basic components of Life, were noted on one that landed in Australia.
The building blocks of Life are indeed common beyond Earth. That increases the probability of there being extraterrestrial Life. It is, however, an increase from an unknown level to another unknown level. Concluding it is an increase into the realms of Life being likely, beyond Earth, is a leap of faith.
In 1996, a group of scientists announced they’d found bacterial fossils on a meteorite fragment from Antarctica. At the time, there was no known abiotic (non-biological) process that could explain the microscopic formations on this two-kilogram lump of Martian rock. It was so extraordinary that Bill Clinton held a special press conference to announce the discovery.
Since then, geologists have explained how physical forces may have produced the formations without biological intervention. So do we have compelling evidence of Life here? No. Hans Amundsen runs the Mars analogue project AMASE (Arctic Mars Analogue Svalbard Expedition). When interviewed on the significance of the alleged bacterial fossils, he said, “If you can explain your observations with purely physical, abiotic processes, then you can’t use it to argue that you have found life outside Earth.”
Given favourable conditions for the emergence of Life, and a vast number of trials over enormous amounts of time, surely Life is assured?
It's a popular argument, but the problem here is, we don't know how many trials and how much time is required for Life to be likely to occur.
It might be minimal. Conversely, it might be far beyond what the universe is yet to supply, making Life on Earth a one-off freak.
From our limited human perspective, it certainly feels as if fourteen billion years and at least that many planets ought to be ample scope for Life to get going all over the place.
Compared to our brief experience of several decades, billions of years seems like it must surely be long enough for everything that can happen to happen. It's common sense.
Well, no. We have to be careful not to project our brief human perspective onto the enormity of time and space; to conclude it's so big, it must be big enough for all arrangement types of matter to be readily produced. It might be, it might not be.
Unfortunately, we don't know if the age of the universe, along with the planet numbers in existence, is enough to tip the balance in favor of Life or not.
"We have no way of estimating the odds," says Astrobiologist Paul Davis. "It may be one in a trillion trillion, it's easy to imagine that, in which case, Earth life may be unique in the observable universe…We simply can't say."
When you find out, let me know!
Claiming there is no Life beyond Earth would be a 'faith based' argument, too, equal to claiming there is Life beyond Earth. They are essentially the same; claims with almost nothing to back them up.
We just don't know, and we don't even know enough to say what is probable or improbable here.
"Because nobody knows how non-life transitioned to Life on Earth, it is impossible to estimate the odds of it springing forth elsewhere in the universe." - Astrobiologist, Paul Davies.
Life on Earth might be a complete fluke. It might be so improbable that it has not arisen anywhere else in the universe, beyond Earth. Conversely, Life might be common throughout the cosmos.
The point is, we don't know, and we can't conclude anything. Isn't that wonderful!