Finding aliens: Is there a ‘theory of everything’ for life?

The search for alien life is far too human-centric. Our flawed understanding of what life really is may be holding us back from important discoveries about the universe and ourselves.

SARA WALKER: We have, through science over the last 400 years, come to have a really deep understanding of the natural world. But so far that deep understanding doesn't include us. It's really important in an age when we're being faced with existential threats on a regular basis to understand our place in the cosmos. And I think unless we actually really address the question of 'What is life?' we're not really gonna understand ourselves in the context of the systems that we live in.

Because we don't know what life is, we don't know where in the universe to look for it. My biggest worry is that we might just completely miss discovering it because we actually don't really have an idea what we're looking for. And we're thinking about the definitions of life the wrong way.

I'm Sara Walker and I'm an astrobiologist. What that means is that I'm really interested in understanding if there's life elsewhere in the universe, but I'm also really interested in just understanding ourselves. And so most of my work is really focused on understanding the origin of life on Earth. To do that, my group is building ensembles of thousands of organisms and thousands of ecosystems and looking at properties of their chemistry.

NARRATOR: On Earth, we're surrounded by life, but we have no idea how common or rare living systems are in the universe. We have no idea how many different forms life can take, no notion of what limits there are to its size or the timescales it operates on. We might've encountered alien life already and not recognized it.

WALKER: There's this assumption that we make that because we are alive, we actually recognize life when we see it, or we understand what life is, and I think that's actually a really flawed viewpoint. For a long time, it was thought if we see oxygen in the atmosphere of an exoplanet, that is a sign of life, and we will be able to claim victory that we have discovered aliens. But as scientists thought about it a little bit more, it turns out you can make atmospheric oxygen pretty easily with simple models that don't even contain life. We really need a more general definition for life that doesn't depend on the specific chemistry that life on Earth uses but is more characteristic of what life is as a process that organizes chemistry and does all of the wonderful things that we associate with living matter.

So I, for example, have a very broad definition of life that includes things like technology. Part of the reason for that is if you found a phone on Mars, you might not think that you discovered life, but you certainly would think you discovered evidence of life. Because the likelihood of that phone being there is zero without a living process putting it there. Life is literally the physics of creativity. It's the creative process in the universe. It's not an individual in that process, it's the entire process of how does information originate in the universe, and how does it expand through space and time to construct all of the things that we associate with life?

NARRATOR: Most of the hazy definitions of life as we know it are flawed because they're built around a very small sample size of one—the one living biosphere that we've evolved within.

WALKER: So anything that our technology creates, or we create, or subsequent generations will create, will be a part of our life or an example of our biosphere. To really understand the possibilities for life, we have to discover a second example somewhere else, because unless we get some constraints on how likely life is, I don't think we're really gonna fully understand what life is.

NARRATOR: It's possible that our sample set will soon double as we explore our solar system, we could find evidence of life on Mars, Europa, or Enceladus. And there was recently some indication of phosphenes, potential biomarkers in the atmosphere of Venus. Some of these places are hostile to life as we know it, but they might be extremely welcoming to life as we don't yet know it.

WALKER: So what I'm most interested in is trying to understand whether there are universal laws that describe living things much the same as we have uncovered universal laws that describe gravitation. And if they're equally fundamental and intrinsic to the structure of the reality that we live in.

NARRATOR: By defining gravity, Sir Isaac Newton put us on a path towards mastering it. A path that helped us understand tides, the orbits of planets and comets, equinoxes, and eventually helped humans navigate our solar system. Having a definition of life will improve our chances of finding extraterrestrials and could open our eyes to a whole universe of possibilities we can not yet imagine.

WALKER: It's hard to imagine what it's gonna be like when we actually understand what we are, all the technology we have, doesn't include us in our understanding of the world. And then if you add that level of understanding us and the technology we create, then it's possible for humanity—and our technology—to get to the next level, whatever that is, that we can't even anticipate yet. So a lot of the sort of deep understanding that I'm after I think is critical for the longevity of life and to expand our reach in the universe, beyond our own planet. I think we take for granted how special we are. We are a very odd kind of system to exist. I just can't imagine that an understanding of us wouldn't radically reshape how we think about the universe that we live in.

  • What, should it exist, is the universal law that connects all living things? To even dream of answering that question, and to one day find alien life elsewhere in the cosmos, humans must first reconcile the fact that our definition of life is inadequate.
  • For astrobiologist Sara Walker, understanding the universe, its origin, and our place in it starts with a deep investigation into the chemistry of life. She argues that it is time to change our chemical perspective—detecting oxygen in an exoplanet's atmosphere is no longer sufficient enough evidence to suggest the presence of living organisms.
  • "Because we don't know what life is, we don't know where to look for it," Walker says, adding that an unclear or too narrow focus could result in missed discoveries. Gaining new insights into what life on Earth is could shift our quest to find alien life in the universe.