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The prospect of the existence of extraterrestrial life has both fascinated and bewildered mankind throughout history. Scientists have long been searching for signs of life on other planets based on the qualities that approximate life on Earth, such as the existence of water. But what if we’ve missed the mark by limiting our definition of “life” only to what is familiar?
It’s possible that we have already encountered extraterrestrial life but we’re not able to recognize it because we were relying on our limited notion of what life is to begin with. As we continue to seek out life which exists outside of our biosphere, we need to get creative and imagine the unimaginable.
By redefining the unique attributes of life itself, as well as how it emerges and thrives, we can not only conduct better-informed searches for alien life, but in the process we can learn more about the nature of our own lives and chart our fate in the future.

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 going to 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. 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 time scales it operates on. We might have encountered alien life already and not recognized it.

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.

WALKER: 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. 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 set of one, the one living biosphere that we've evolved within.

WALKER: So, anything that our technology creates or we create or our 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 going to 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, Enceladus. There was recently some indication of phosphines, 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 cannot yet imagine.

WALKER: It’s hard to imagine what it's going to 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.