It is a fascinating mind bender... the basics roughly follow this outline (from a great article at www.waitbutwhy.com):
1) Given the number of stars and the different types of stars, scientists estimate there might be 500 billion billion stars like our sun. That's right 500 billion billion which is quite a few.
2) With a few more calculations we could arrive at an estimated number of 100 billion billion earth-like planets. Given this crazy huge number and given the age of the universe there should be some civilizations advanced enough to communicate with us or at least be noticed by our scientists.
A type one civilization is one that has the power to harness the power of their own planet. We, the classification posits, are nearing this point. Humanity in its present state has achieved the ability to affect the whole planet. That is certain. We have destroyed vast forests, mined enormous quantities of minerals and oil. We have nearly depleted many of the world’s fisheries. We have built cities, damned rivers, and launched rockets and probes beyond the earth. We created and even used nuclear weapons that have the power to destroy the earth several times over. Yes my friends, our current technology allows us to affect and even destroy the entire earth and all of its ecosystems. We are pushing countless species to the brink of extinction and have already sent many others to the human engineered oblivion we seek to escape.
At our current state of development, we have a limited understanding of the cumulative effect of human population amplified by our technology on the systems of our planet. In today’s world, we are a great distance from creating methods to govern the outsized effects our species has on the planet. Even now, we all too easily dismiss the effect of individual action regarding our planet and even dismiss the actions of whole countries to try to alleviate some of the damage we are doing to our planet. We are nowhere near achieving coordinated action taken on behalf of all of humanity. We do not yet understand the intricacy and complexity of the systems of our planet. We have not developed enough to be able to protect and sustain them. Dare I say our species has failed to learn to love the earth enough to devote sufficient energy to nurturing our home.
Let us create an equation with the following notations:
Let N be the ability of the Holocene age earth to maintain its equilibrium in the face of shocks to its systems.
Let P be the population of man.
Let T be the technological level of human civilization.
Let p^T be the shock to earth’s system a given size human population can produce with a given level of civilization.
Let K be the knowledge of the cause and effects of the human produced shocks on the planet.
Let C be the ability to coordinate human action to control the effects of human produced shocks.
So the ability of the earth to maintain its equilibrium could be written as
∑ from the dawn of humanity to the present of N + KCPT -PT
We know that the current maximum value of PT is already greater than N. The human race can create a shock sufficiently great to overwhelm the ability of earth’s systems to self-correct. If the sum of the difference between our knowledgeable and coordinated action and the human induced negative shocks to the system become large enough to overwhelm the ability of the Holocene earth to maintain equilibrium we will destroy ourselves.
The great filter represents minimum achievement for science, psychology, spirituality, and politics to protect the future of humanity. It represents our physical ability to heal or atone for all of the damage we have done to our biosphere. Let's call this our particular human psycho/terrestrial filter.
Let's assume in the billions of years that the earth has been in existence our science's ability to "hear" or "see" alien life might, with optimism, cover the last 400 years (if we date it from the discovery of the first telescope in 1608). That is about 1 hundred thousandth of a percent of the time the earth has existed. I would call that a miniscule flash in the history of the earth. We have not had long to "hear" or "see".
The real question is: how long will this window remain open?
Will we have another 400 years to discover alien life or be contacted by it?
On our current course, I don't think we will have a100.
I believe we stand on the precipice of the great filter. It is a dangerous time. We have the ability and knowledge to destroy without the commensurate knowledge and ability to healt. As of right now, I think Agent Smith in the Matrix summed up our current conundrum -
Agent Smith: "I'd like to share a revelation that I've had during my time here. It came to me when I tried to classify your species and I realized that you're not actually mammals. Every mammal on this planet instinctively develops a natural equilibrium with the surrounding environment but you humans do not. You move to an area and you multiply and multiply until every natural resource is consumed and the only way you can survive is to spread to another area. There is another organism on this planet that follows the same pattern. Do you know what it is? A virus. Human beings are a disease, a cancer of this planet."
Are we a virus?
No, we are a form of life with a conscience and an ability to cooperate. How we develop these abilities will determine whether we pass beyond the psycho-terrestrial filter or find ourselves inhabiting a planet which can no longer bear our presence. Unfortunately, we know a virus isn't the only life capable of destruction. Humanity has shown a great proclivity for choosing destruction as a solution to almost any problem.
When we discover the means (likely a combination of political, psychological, spiritual, and technical) to create an equilibrium between our ability to harness and transform our planet and our ability to maintain its biosphere that discovery will be the greatest advance yet of humanity.
The knowledge of our earth and the ability to positively coordinate our actions will be the vehicle that will carry us beyond the psycho-terrestrial filter.
It will be the interplanetary dawn of which science fiction dreams and of which dystopian nightmares despair. This will be the light that allows us to see others in the universe and hear their voices.
Ite missa est.
Go it is the dismissal.