We have never discovered extraterrestrial life. Why not? Something must be stopping life from getting sufficiently advanced. This something, mysterious as it is, has been called The Great Filter.
What is The Great Filter? It could be as banal a idea that intelligent life like ourselves is just a very rare thing. So many conditions have to be just so, that in fact it arises only once per trillion stars say. But more ominously, The Great Filter could be the inescapable tendency for intelligent civilizations to wipe themselves out.
As for the first possibility: We are finding a lot of planets orbiting stars already. Clearly there are many, many planets out there. Organic chemicals are quite common, we know from comets. Are planets like ours really that scarce? Admittedly they have to be watery, far from big clusters of stars and associated frequent gamma ray bursts, and in a system with some outer gas giants to shield them from collisions. But I doubt such conditions are all that rare.
So we're left with that sticky little second possibility: that civilizations invariably wipe themselves out before getting to the technological state to spread through the galaxy.
Sounds nutty that we can observe no little green men and conclude therefore that we are likely doomed to be wiped out soon. Yet there are 100 billion stars in our galaxy, and they have had billions of years of time to colonize the galaxy (or to build space probes called "Von Neuman Probes"). It would only take about 20 million years to reach every star in the galaxy, assuming probes could reach 1 percent of the speed of light. So little green colonists or Von Neuman Probes should have been here for billions of years. Yet they are not. Why not?
Well I think that recent events have provided us with a likely answer. The Great Filter is... climate change. Here is my reasoning.
Over the millions of years required to develop intelligent life, planets tend to accumulate carbon. This carbon gets sequestered in various places around the planet, such as gaseous carbon in cold places (methane trapped in permafrost, methane stores in the ocean floor) as well as liquid and solid forms, stored in warmer, more accessable places (oil fields, coal deposits). Such carbon is too easy a fuel source, and an intelligent civilization will invariably learn to burn the warmer sources of carbon, achieving rapid growth in population.
Every planet has a limit at which it will be overwhelmed with the greenhouse effect achieved from burning carbon (i.e. from CO2), to the point that a warming trend eventually releases the trapped gaseous carbon, sealing the planet's fate. It so happens that planets can hit the released carbon tipping point much sooner than they can learn to build intragalactic rockets or Von Neumann Probes. They hit the tipping point before they can develop technologies to reverse it (carbon sequestration). Even before they have time to convert to carbon neutral energy sources (wind, nuclear).
It turns out that our gaseous carbon tipping point will likely occur very soon, like within a decade, according to climate scientists who build predictive models. Our planet will likely be a very hostile place, mostly desert by the end of this century. One climatologist predicts Earth's population to be just 1 billion by 2099.
It's fashionable at this point in the discussion to put a positive spin on things and say we can solve our problems. I see no reason to do this. Positive spins just promote complacency and inaction. There is no reason for positive spin here. We can pretty much be certain that 6.76 billion Earthlings are not going to come together and stop burning fuels. We are not even going to come together and slow the rate at which we increase burning fuels any time soon. Carbon sequestration technologies are not going to happen on a large enough scale.
Our planet, like the 10 to the x ones before it, will wipe itself out due to climate change. And that will probably occur over just the next couple centuries. Even today's child is likely to experience major hardship or early demise because of this problem. Sorry folks.
That said, I do not believe in fatalism. I intend to do all I can to delay this. The more generations we can eek through our post-industrial Fools Paradise the better.
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3 comments:
I think I would expand this to dealing with the side effects of industrial civilization in general. 25 years ago, the great filter would have been nuclear annihilation. 25 years from now, it will be whatever issue is current at the time. Modern technology seems to have no end to things that could possibly destroy us. This will remain the case until such time as we figure out how to get all of our eggs out of one basket.
Note that in spite of the end of the cold war, we have not yet successfully avoided nuclear annihilation.
Jim,
It's a good point that the Great Filter in reality amounts to a bunch of different problems. Maybe you are correct. Let's say that a given intelligence has a 50% chance of avoiding nuclear annihilation. There might just be so many threats (plague, pestilence), each at 50% likelihood, that only the occasional galaxy fields a star that can survive to attain the required technology to make probes. My hypothesis is that those threats are real and do claim a number of civilizations. But no civilization can avoid the trap of climate change.
I don’t think you’ve got the science quite right regarding CO2. You’re confusing long and short term trends.
In the case of Earth, the long-term trend is for our planet to lose CO2, gradually locking it up for good in silicate rocks. The plants around now have to be more efficient at using CO2 than previous species, because there’s a lot less of it around now. During the Cambrian Explosion, CO2 levels were 18 times higher than today.
Regardless of what humans do about their fossil fuel consumption, scientists estimate that, within half a billion years, CO2 levels will have dropped too low to permit photosynthesis. At that point, all plants will die, followed by us.
Our long term problem is to:
1) find a way to raise the amount of CO2 in the atmosphere so that plants can continue to feed us and create oxygen, while we
2) find a way to lower the amount of CO2 in the atmosphere to compensate for a sun that’s gradually heating up.
Resolving the seemingly incompatible needs of the biosphere is the real “great filter”. I suspect all advanced civilisations eventually confront a version of it. Only a civilisation that can fully master geo-engineering - maybe including geo-relocation - will pass through it.
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