World-renowned astrophysicist Stephen Hawking, and Buzz Aldrin, the second man to walk on the moon, are united by a common belief. They are members of an influential group of scientists and visionaries who believe that the long-term future of the human race lies in space, and that we need to grow beyond the confines of our home planet in order to ensure our long-term survival. The logic behind this viewpoint is that sooner or later the Earth will inevitably endure another planetary catastrophe, such as the asteroid collision that lead to the extinction of the dinosaurs some 65 million years ago. Failing that, they believe we have a pretty good chance of accomplishing our own extinction through mismanagement of the planet.
While these arguments are compelling, future space travel would require a number of major technological advances to be made. The fact is that we are uniquely adapted to living here on Earth. Our bodies have evolved to cope with the unique environmental conditions which exist here, and very likely only here, in the universe. It is unlikely that any potentially habitable planet we could find would have the same concentration of oxygen in its atmosphere, the same gravitational pull, the same seasonal patterns, or any one of the millions of other factors which we never think about, but which uniquely characterize our home planet. Although many of us now lead lives completely isolated from nature, our survival is still dependent on the physical processes which drive the Earth system.
The Earth is unique in our solar system in that it provides the conditions which enable complex life to flourish. While scientists hold out the possibility that microbial life could exist on Mars, or perhaps on Saturn’s moon Titan, it is highly unlikely that complex multi-cellular organisms will be found anywhere else in our solar system. Contrast this with the Earth, where life is everywhere. Even physically hostile regions such as Antarctica and the Sahara support life in surprisingly large concentrations. Space is a vacuum, in which astronauts are totally dependent on life support, and where the smallest problem can be life threatening. The distances are also unfathomable. For example, Proxima Centauri, the next-closest star after our sun, is more than four light years away.
Given the current state of our technology, it is unlikely we will be venturing far into space this coming century. However over this same time period we will face tremendous challenges here on Earth. For our species to survive into the 22nd century, we will need to find ways to mitigate the worst effects of climate change, solve a host of related environmental problems, and stabilize our population. This will need to happen within the lifetime of many people who are alive today. Achieving such a transformation requires that we turn away from unsustainable growth-based models of resource use, and transition to a steady-state economy.
Type I, II, and III civilizations
It is useful to look at where our current civilization stands in terms of theoretical models of planetary development. In 1964 the soviet astrophysicist Nicolai Kardashev developed a method for classifying the level of development of theoretical planetary civilizations. The so-called Kardashev scale recognizes three levels of advanced civilization, which are classified according to their energy usage. Type I civilizations are able to harvest all the energy falling on the planet from their local sun. Type II civilizations are able to gather all the energy provided by the entire star, whereas Type III civilizations would be able to utilize the energy resources of their entire galaxy. As to where we fit into this model; the theoretical physicist Michio Kaku believes we are currently at a level of about 0.7 and are on the way to transitioning into a full level I civilization within the next 100 – 200 years, if we survive that long.
The Kardashev scale suggests that our energy requirements will continue to increase indefinitely as our civilization develops. However, as we saw above, the future of humanity depends on us being able to stabilize our numbers and live sustainably on the Earth. This implies that our energy consumption will inevitably reach a peak sometime in the next century, and flatten out thereafter. Planetary limits dictate that this must be so. Our civilization simply cannot advance fast enough to allow to us to perfect space travel before we run up against the limits imposed by nature.
The reason for the contradiction is that the Kardachev scale is based on the idea of exponential growth. It is exactly the same logic that current economic theory is based on, except that in this case energy usage is used as a proxy for the level of development of a civilization. However, it is inevitable that our current growth economy must ultimately transition into a steady-state economy if we are to survive in the long term. This does not imply that our society will stop developing, nor that we will be confined to Earth in the future; it simply means that the advance of our civilization will not require the consumption of exponentially increasing amounts of energy, as Kardashev suggested.
For many years now people have wondered whether we are alone in the universe. Researchers from the SETI (search for extraterrestrial intelligence) Institute have scanned the skies for signs of intelligent life and have so far seen no conclusive evidence of other civilizations. Two explanations are commonly suggested for this. The first is that we really are alone; that in all the countless billions of planetary systems within our galaxy, and in all the billions of galaxies, no other species has reached our level of development. The second explanation is that when civilizations reach a certain level of development, they inevitably end up destroying themselves.
There is however a third possibility, which is to assume that as civilizations advance they must inevitably bump up against the physical limits imposed by their home planet, as we ourselves are now doing. At this stage of their development it is highly unlikely that they will have perfected space travel. Therefore in order for their civilization to endure, they would have no choice but to learn to live sustainably within the limits imposed by the planet. With stable populations, and a well-managed planet, there would simply not be the pressure for such a civilization to continually expand, thereby consuming an ever-increasing supply of new resources.
Such civilizations would still face challenges. However over time it is likely they would develop any technology they would need to protect their home planet from external threats. They would very likely develop space travel, but its primary use would be for research purposes, rather than to drive an exponentially expanding wave of colonization through the galaxy. The idea of a hostile alien civilization strip-mining the resources of the galaxy is a science fiction staple. However it is a perception which is derived largely from the assumption that economies must continually grow and consume ever-more resources in order to survive. It therefore says more about the perceptions and biases of our times than it does about the development of civilizations.
If we consider the alternative hypothesis that any civilization destined to survive in the long term would have evolved to a steady-state economy long before they perfected space travel, then it is quite possible that there could be millions of such civilizations scattered through the universe, each quietly going about their own business. This is probably the best option for a long-term sustainable future for the human race. It is a future which most likely will include space travel, but not one in which space travel is a prerequisite for our survival.