In a recent article for Nautilus, Harvard physicist and cosmologist Lisa Randall speculates about what she calls “dark matter life.” Since dark matter is thought to constitute 85 percent of the mass in the universe, is it reasonable to imagine some kind of life based on this mysterious substance? Dark matter does not seem to interact with the stuff we are made of, but it might interact with itself, or at least some fraction of it might. If it does, what kinds of structures could it build? Could any of those structures constitute “life?”
Unfortunately, if dark matter life does exist, Randall says it would be incredibly difficult to detect. It would interact only very weakly with familiar matter, most likely by gravitational force, which is the weakest of all nature’s forces. In principle, it could exist right under our noses here on Earth, and we wouldn’t see it.
The idea of dark matter life, of course, is highly speculative. But the concept of a type of biology unknown to us, coexisting but not interacting with the familiar life on our planet, has been suggested previously by Carol Cleland and Shelley Copley. They proposed that a second type of life may exist on Earth that originated independently to form a “shadow biosphere” that is different biochemically from our own. Paul Davies and colleagues later elaborated on how such a shadow biosphere could be detected.
So far, we have not found any life on Earth with a significantly different biochemistry. All known terrestrial life shares the same chemical building blocks, and life has been incredibly successful at inhabiting all the places it possibly can. Is this because the life that appeared first on our planet was the best adapted? If different types of life originated early in Earth’s history, perhaps our type outcompeted all other variations.
Or do other types of life exist on our planet that we just haven’t found yet? If such a shadow biosphere does exist, maybe it’s in obscure ecological niches, like deep in the crustal rocks or at ocean floor vents. If so, that would explain why we haven’t detected it. The methods we use to search for and analyze life on our planet, mostly via DNA sequencing and culturing, are aimed specifically at our type of life. It is not difficult to imagine that we could overlook life of a different kind, even if it existed right here.
Indeed, it makes some sense to look for “alien” life on Earth before looking on extraterrestrial worlds. But it’s difficult to search for something when we don’t know exactly what to look for, whether it’s dark matter biology or a shadow biosphere.
As always, we need to stay open-minded. We live in a vast universe, and our minds would likely be completely boggled if we truly understood all the diversity of forms and functions that life can exhibit.