The discovery of an alien life form would be the discovery of the century, with profound scientific and philosophical implications. Within the next 50 years, there’s a serious chance that we’ll make this discovery, not by finding life on a distant planet or indeed by such aliens visiting us on Earth, but by creating a new form of life ourselves. This will be the logical conclusion of using the emerging tools of nanotechnology to develop a bottom-up version of synthetic biology. Instead of rearranging and redesigning the existing components of “normal” biology, as currently popular visions of synthetic biology propose, scientists would synthesize entirely novel systems.

So what would it take to make a synthetic life-form that was truly alien? As we learn more about cell biology, we can see that it is intricate and marvelous, but in no sense miraculous—it’s based on machinery that operates on principles consistent with the way we know physical laws to work on the nanoscale. We are already seeing crude examples of synthetic nanostructures and devices that use some of the design principles of biology. Researchers are designing molecules that can self-assemble to make structures such as molecular “bags” that resemble cell membranes, pores that open and close to let molecules in and out of these enclosures, and molecules that “recognize” other molecules and respond by changing shape. It’s quite possible to conceive of these components being improved and integrated into systems. One could, for example, imagine a protocell, with pores controlling the flow of molecules into and out of it, containing a network of molecules and machines that together added up to a metabolism, taking in energy and chemicals from the environment, and using them to make the components needed for the system to maintain itself, grow, and perhaps reproduce.

Creating artificial life would be a breathtaking piece of science, but would it have any practical use? The selling point of today’s most popular visions of synthetic biology is that they will permit us to do difficult chemical transformations in much more effective ways—making hydrogen from sunlight and water, for example, or making complex molecules for pharmaceutical uses. Conventional life, however, including the modifications proposed by synthetic biology, operates only in a restricted range of environments; one could imagine making a type of life that operated in quite different environments—at high temperatures, in liquid metals, for example—and would open up entirely different types of chemistry. But such utilitarian considerations pale in comparison with what would be implied more broadly if we made a technology that literally had a life of its own.

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