Wednesday, December 24, 2008

Astronomical energy density is key to becoming an interstellar species

I've been thinking recently about the actual energy costs of our consumer culture. The energy argument for most of what we do is concerned primarily with economies of scale. The idea is that by increasing the number of a given good we decrease its unit cost. My first question is: how are we measuring cost? Monetary cost? That doesn't seem very objective. How about total energy cost? And I do mean the whole process, not just some arbitrary human-defined subset of the process, like the cost of a cheeseburger being computed as just the cost to grill it.

What if we address the actual energy cost in say, producing, shipping, and cooking a domestic chicken and then dealing with the refuse in our conventional way. I suspect that the actual energy cost for just maturing the chicken is significant. If we compared it to the way in which a chicken lives in a state of nature when there are no humans to guide the process we would find that the energy gap is enormous. An ecology is pretty damn efficient in terms of energy use. Everything is useful to the ecosystem, and nothing goes to waste. For human use, the chicken would be a far lower energy cost if I were a hunter-gatherer and had hunted, killed, cooked, and eaten the bird myself. Our process doesn't achieve any efficiencies above this. In all likelihood, our process is abysmally inefficient when compared to an ecology. Our economies of scale just decrease this substantial difference.

So what is it about our methods that allow them to be successful? If the energy costs are so much greater, how are we able to accomplish anything? The answer is obvious. We inject our abundant energy resources into our manufacturing and production processes to speed things up. Currently that energy is primarily in the form of petroleum. Petroleum has a far higher energy density than the solar collected by living plants. We speed up a process by adding gobs and gobs of energy to it. This allows us to make tremendous progress in respect to human goals whereas ecosystems change at a leisurely pace, slow but incredibly efficient. Left alone (and free from catastrophic disaster) earth's ecosystems would far outlive any existing human system. But the processes by which biological systems evolve are as slow as they are efficient. If we didn't bootstrap ourselves using available energy we wouldn't have been able to do the things that we have done. Abundant and cheap energy enables human innovation.

So, we are burning through our low-density energy resources at a frenetic pace, a pace which quickens each year. We are on an asymptote of energy usage (and an asymptote of innovation). The possible failure modes of such meteoric increases can be seen in examples posed by nature (earthquakes, floods, hurricanes, volcanoes), or by the catastrophic failures of human systems (dam failure, exploding circuits, overpopulation and disease). The possible failure modes of unchecked growth are just as abysmal as our inefficiencies. My prediction is that we must, nonetheless, continue to ride the asymptote. And that if we peak in energy usage and roll-off or alternatively stabilize, then we will either crash and die off quickly, or live alone and sequestered to our dinky little speck of the galaxy. The reasons are manifold.

Clearly we can become much more efficient in doing what we do. If we approached ecological efficiencies and we stopped finding new ways to use energy, human energy usage would stabilize. If at the same time human populations were to stabilize, we would probably begin decreasing our overall energy usage. This sounds like exactly what we should be doing, decreasing our energy dependence by increasing efficiencies and stabilizing our populations. The problem is not the efficiency gains or the possibility of sustainable energy use. These are both good. The problem is that such a scenario makes no stipulation that we a) find new ways to use energy, and b) find new energy sources.

If we fail to do these two things then we will fail to leave this solar system. Period. If we fail to ever leave the solar system, this is a terminal species failure. The sun dies and then we die. Interstellar travel is necessary and the sooner we embark, the better. Low-density energy sources won't cut it, but they currently fuel our technological endeavors. These endeavors must become ever more fantastic or we risk the slow death of a species stranded on a lonely planet far from the nearest interstellar pub.

The energy cost of interstellar space travel is quite literally, astronomical. I suppose if we don't care how fast a colony reaches their destination then the energy required at first appears quite minimal. But this presupposes that a) it would be acceptable to take tens of thousands of years of travel time, and b) that somehow such a ship will sustain life in the void between solar systems for such an incredible duration. There is a great novel by Robert Heinlein that explores the likely failure of such a slow moving ship (Children of the Sky). The results would look something like Mad Max but where everybody is insane (even the law enforcers), the Manual of Astrophysics is treated as a book of analogical gospel, and the ship IS the universe.

So the scenario of low-energy interstellar travel is not a likely one. At the other extreme, we would prefer to reach another habitable star system with a portion of a human lifespan. Even if we choose one of our nearest stellar neighbors (Alpha Centauri), this means we would need to reach speeds approaching 10% of the speed of light giving us a travel time of around 50 years. The energy required for such a feat for even a very small craft is quite large. The Voyager I spacecraft left the solar system traveling at about 38,000 mph, putting it at Alpha Centauri distance in only 80,000 years. Clearly we have to move much, much faster to achieve speeds necessary to be successful in interstellar travel. 40 years would be nice. We would need to achieve (and decelerate from) speeds of 134,120,000 mph and provide 40 years of energy to sustain the lives of several hundred people. Achieving the speeds necessary is the easier part of the problem.

Clearly, we need some fantastic, astronomically-dense energy sources in order to travel unreasonable distances. Nuclear fission or fusion might work. The energy densities are orders of magnitude greater than those of chemical reactions (including the chemical rockets we currently use for extraterrestrial travel). We will require some very smart engineering to use these energy sources safely over a long journey. But right down here on the ground we will need to have already developed these technologies for widespread use. This means that we must continue to innovate and to find new and ever more fantastic uses for energy. It means that we must continue to increase our demand for energy by orders of magnitude and fuel this innovation. We need to ride the asymptote or we won't ever be able to leave. We must find and use new energy sources and technologies terrestrially to fill the very large energy-gap between us and any expectation of interstellar space travel.

Conservationism is still necessary. Efficiency is absolutely necessary, and becomes even more necessary as energy densities and power generation capabilities increase and we get closer to our technological goals. We must enable our species to use energy at an ever increasing pace. If our energy usage were to taper off now, we wouldn't likely ever have the ability to create the energy technologies necessary for interstellar travel. Such a decrease in energy usage would be an indicator that we had failed, terminally. I hope this won't happen. I think that unless catastrophe strikes (asteroid impact, thermonuclear war, bird flu kills too many people, zombies eat all of my neighbors), we will continue along our asymptotic energy consumption curve. I don't think the alternative is a viable option. We have to.



This indicates that we shouldn't be concerned so much with how much energy we use. Energy use is good, really, so much as it drives innovation and isn't just due to stupid human engineering deficiencies. It is also impossible to proceed if we are using low-energy-density bio-fuels. High-energy physics experimentation requires significant fractions of our current energy production. Future experiments will require larger energy resources still. Current power sources won't cut it. We need to replace petroleum, coal, and similar bio-fuels as soon as possible. For the future, they are useless. For now, they pollute and contaminate and prevent forward progress by maintaining energy scarcity and maintaining high energy costs. That energy costs have recently increased is a sign of our current failures. We are continuing to innovate, but our energy sources are not keeping pace. They are slowing us down. If this continues over many decades, it will be our first indicator of a potentially terminal species failure.

If we don't make major breakthroughs in astronomically high energy density technologies or we choose to curtail the research necessary to do so because we continually find new petroleum reserves or continue to invade unfortunate petroleum rich nations (or planets) ... it will take us an astronomically long time to innovate ourselves off of the planet and out of the solar system. If this happens, we will be here a very long time, all the while continually screwing up the efficient clockwork of Earth's ecosystems.


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