There's no place like home.
One of the most thrilling events of my childhood happened on 20 July 1969.102 My father woke me to watch Neil Armstrong and Buzz Aldrin land on the Moon. I guess most people of my age felt the same awe when they saw Apollo 11 touch down. More than thirty years later, we lack the ready capability — and motivation — to repeat the venture. Since Gene Cernan shook the lunar dust from his boots in 1972, no one has set foot on the Moon, and there are no definite plans for anyone to do so. Some space enthusiasts continue to do valuable work on establishing the factors needed for a manned trip to Mars, but such a trip is unlikely to happen soon. An assumption shared by many, including myself, is that intelligent species like ours will inevitably expand into space — so why are we not out there? Perhaps the assumption is wrong. Perhaps an unfortunate mixture of apathy and economics means ETCs stay at home; maybe that is the sad solution to the Fermi paradox.
There is reason to hope the suspension of manned space exploration is simply a pause. As technology improves, the journey into space will become cheaper and happen more frequently. We already have seen the first space vacationist, Dennis Tito, and more will surely follow him.103 Indeed, the driving force behind manned space travel in the next few years may be tourism rather than science or high-tech industry.
In the longer run, there is a compelling reason why we should establish viable independent colonies on Mars or in O'Neill habitats: it would help ensure the survival of humanity should disaster strike Earth. In recent years we have come to understand what a dangerous world we inhabit. If a large meteor hit Earth we would be wiped out; if a super-volcano erupted, our technological civilization would crumble; climate change, whatever the cause, could destroy our way of life. Things have been peaceful here on Earth over the span of recorded human history, but our history corresponds to just 10 seconds of the Universal Year. Believing the world is calm because we have never seen it otherwise is like taking the attitude of a man who jumps off the top of a tall building and figures that, since 29 of the 30 floors have passed without incident, he is going to be okay.
In the even longer run, it makes sense to establish colonies around other stars in case something happens to the Sun. A coronal mass ejection only a few times more powerful than the most intense solar flare on record could cause us serious problems.104 Ultimately, if we survive long enough, we will see the Sun moving off the main sequence on its way to becoming a red giant — and that really would force us to move home. (Zuckerman has shown that if the Galaxy contains between 10 and 100 long-lived civilizations, then almost certainly at least one of them would have been forced to migrate due to the death of its star.105 If there are 100,000 such civilizations, then the Galaxy should have been completely colonized by civilizations whose home stars have evolved off the main sequence.)
Mankind has not exactly rushed headlong into space, but it is surely too early to say we will never attempt space travel. We have had the capacity to launch space vehicles for only a few decades; in the context of the Fermi paradox we have to think in terms of thousands or millions of years. And although it is probably fruitless to speculate upon the motives of putative extraterrestrials, there seems to be a universal logic to the establishment of off-world colonies. A species with all its eggs in one planetary basket risks becoming an omelette. Surely technologically advanced ETCs will move, however hesitantly, into space?
The idea that all ETCs stay at home seems (to me, at least) unlikely — unless there is a good reason why they should stay at home.
Human kind Cannot bear very much reality.
T. S. Eliot, "Burnt Norton," Four Quartets
On page 51 we considered Baxter's suggestion that we exist in a virtual reality; the Universe appears devoid of life because advanced ETCs have engineered our reality to make it appear that way. We can invert the plane tarium hypothesis to provide a less paranoid resolution to the Fermi paradox: maybe ETCs generate virtual realities for their own use. Maybe we do not hear from them because they stay at home and engage with an engineered reality more interesting and fulfilling than "real" reality.
It is easy to dream up scenarios in which an ETC might choose to disengage with the real world and instead inhabit a virtual one. For example, suppose their physicists discover a theory of everything, a goal our own physicists may be only a few decades from achieving. Suppose their biologists trace life back to its chemical origins and learn how to manipulate living material at the biochemical level. Their observational astronomers amass a wealth of data about the Universe, their theoreticians explain how the data fit their cosmological models, and their philosophers combine it all into a consilient theory of knowledge. In short, suppose they conclude that their science is finished. Furthermore, suppose the computing power available to this ETC is far in excess of our own: everything is wired, and their virtual reality simulations, which might feed in directly to their brains, provide satisfying sensory-rich experiences. Finally, what if such a civilization decided interstellar travel, although possible, is too difficult or costly to be worth the effort? Perhaps, under those circumstances, they would cease from exploration. They might instead investigate artificial realities.
We have no idea whether such a scenario is probable. For example, one could argue there will never be an end to the process of science; there will always be some new knowledge for a civilization to discover, new intellectual vistas to explore. But it is just as possible that the Universe obeys a small set of laws, and that the phenomena emerging from those laws are relatively small in number; in which case a long-lived technological society might eventually find that its science is essentially complete. (Although, of course, there is always art to consider as well as science.)
Similarly, one could argue that it is impossible to generate virtual realities as convincing as the reality we inhabit. Recall our discussion of the planetarium hypothesis, in which we considered the computing power required to generate a virtual reality sufficiently accurate to fool a civilization like our own. The computing demands were enormous, and the computing power required to fool an advanced civilization might be impossible to achieve. But the two cases are not equivalent. The computing power required to generate a virtual reality to satisfy knowing participants is much less than is required to fool mankind. In other words, the simulation designers could take shortcuts. There would be no need to calculate the trillions of interactions in a particle physics experiment; no need to simulate the outputs of protein-folding calculations; no need to present the results of gravitational microlensing observations. Their scientists would already have generated that knowledge in the "real" Universe. The simulation designers could thus instead concentrate upon generating satisfying and compelling simulations of objects and situations on the relatively restricted scale that intelligent beings (we believe) inhabit. This is not to say that the simulations need be restricted in imaginative scope: the situations to be simulated might be truly bizarre. But the participants of the virtual reality would not be "kicking the walls" of reality in the way that scientists and explorers do. All that is required is for the simulations to satisfy the participants. The requisite computing power is thus much less than is needed to create a full-scale Baxter planetarium.
My guess is that, if our own technology permitted it, a large fraction of humanity would prefer to live in a virtual reality. Already some people spend hours surfing the Net and prefer interaction with others to be mediated by computer. If simulations could provide us with a safe yet perfect sensory experience of walking on the surface of Mars, or hunting dinosaurs, or scoring the winning goal in a Cup Final, then I believe most of us would spend our time in those simulations. It would be infinitely better than TV — and consider how much time we waste on that.
The scenario of a stay-at-home surf-the-Net civilization seems to me to be an uncomfortably plausible future for mankind, but it does not alone solve the Fermi paradox. It is an example of a sociological condition that has to apply to every technological species for it to work. We may eventually prefer virtual reality, but why should couch-potatohood be a universal characteristic of intelligent species? Just as some of us prefer to interact with flesh-and-blood humans, so surely would at least some civilizations want to interact with others. Surely some ETCs would choose to explore, either directly or by probe.106 Or, if interstellar travel proves impossible, would they at least not try to communicate?
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