Arsenic-Based Life

This week, NASA geobiologist Felisa Wolfe-Simon announced the discovery of arsenic-based microbes in Mono Lake in Yosemite National Park. This is a major scientific bombshell that is causing biologists to re-examine much of the conventional wisdom about what life is. All life, from the smallest bacteria to the largest redwood tree, was thought to be based on five elements: Carbon, hydrogen, oxygen, nitrogen, and phosphorus. These elements are crucial ingredients in life’s software – DNA and RNA molecules – as well as life’s fuel – ATP molecules. But now scientists have discovered organisms that use arsenic instead of phosphorus in their biochemistry, which was thought to be impossible. Most organisms are poisoned by arsenic because it is highly reactive, destroying the DNA and ATP found in living cells. But this new species of extremophile not only thrives in a lake with an arsenic concentration 700 times what the EPA deems safe, but actually manages to incorporate it into its DNA and ATP. This is more than just a strange new species with an interesting quirk; many of those are discovered every year. This is a radical redefinition of what “life” is.

Although these microbes appear to have evolved from more traditional forms of life, their mere existence opens up the possibility of a "shadow biosphere" on earth. All known living things have descended from a common ancestor, but what if organisms with other biochemistries are living right under our noses undetected? Might they provide evidence of a second genesis on earth? If life has developed twice, with two different biochemistries, it would prove that the evolution of life on earth was not just a one-in-a-trillion fluke, and would greatly increase the likelihood of life developing on any suitable world.

The discovery of arsenic-based life has important applications in the search for extraterrestrial life, which is where NASA comes in. For ages, scientists have pondered about the possibility of completely new types of life. A handful of astrobiologists (and a slew of science fiction writers) have speculated that extraterrestrial life might be too alien for us to even recognize as life. In fact, this is one possible explanation for Fermi's Paradox, which questions why we haven't already found life if it is commonplace in the universe. In light of this week's discovery, this explanation has become a lot more plausible. Perhaps DNA, reliance on water, and cells are just unique traits of life on earth, and we are barking up the wrong tree if we focus solely on finding them elsewhere.

Others have believed that “life as we know it” was the only type of life possible. This has been the dominant mindset of NASA for several decades, and is the basis of NASA’s search for life. NASA has concentrated its efforts on locating worlds similar to our own, where the conditions exist to permit the development of life as we know it. This generally means finding worlds with water on them, located in the “Goldilocks Zone” of their solar systems where they are neither too hot nor too cold to sustain life. This, of course, has been premised on the assumption that any extraterrestrial life is probably not too different from the life we know.

The discovery of arsenic-based life has cast doubt on this approach. If a new form of life can be found in Yosemite National Park, we can scarcely imagine how different extraterrestrial life must be. NASA’s obsessive search for earth-like planets may be overlooking a huge number of worlds where life may exist, in forms unknown to us earthlings. If it is possible for life to exist with a completely different biochemistry from our own, then it’s equally possible that it could thrive on worlds far different from our own, under conditions that have traditionally been regarded as hostile to life.

NASA will need to do a lot of soul-searching in light of this week’s discovery, and reevaluate how it determines if a world is potentially suitable for life. For the first time in history, a long-standing astrobiological question has been answered: Is “life as we know it” the only type of life possible? We now have our answer: It is not.

Are we living in a simulation?

Are we living in a simulated reality? Transhumanist philosopher Nick Bostrom thinks so. He puts forth the following argument. One of the following three statements must logically be true: 1) Advanced civilizations can never develop simulated realities; 2) No advanced civilization would ever choose to develop simulated realities; or 3) Our own reality is almost certainly simulated.

There are a few circumstances in which Statement #1 could theoretically be true. Perhaps there are no other advanced civilizations in the universe. Perhaps advanced civilizations exist, but simulations are simply impossible. Or perhaps they are possible, but beyond the technological capacity of any species. I think Statement #1 is the least plausible of the three. As I mentioned in a previous blog post, even extremely pessimistic interpretations of the Drake Equation should have yielded at least one other advanced civilization somewhere in our universe. The technological barriers to creating a simulation seem very small. We already have rudimentary virtual reality technology, and there is no fundamental reason why we shouldn’t be able to create all-encompassing simulations within a few decades. Since we’re nearly able to create them already, it seems unlikely that there are no other civilizations in the entire universe that are a few mere decades ahead of us.

Statement #2 involves speculation into the motives of other civilizations, of which we can’t possibly know anything. However, we do know about our own civilization and what motivates us. If humans develop this technology within a few decades, we will almost certainly make use of it, creating thousands upon thousands of simulations for entertainment or research. Therefore it seems very likely to me that Statement #2 is false.

This leaves Statement #3. If we have concluded that Statements #1 and #2 are false, Bostrom reasons that Statement #3 must be true. Why? Because there will be an enormous number of simulated realities. The probability that we find ourselves in the one parent universe, as opposed to one of the many simulations, must be vanishingly small.

The Simulation Hypothesis fascinates me, because it is one of the few rationales for the existence of some form of a god which I, an agnostic, do not think is easily refutable. Let’s examine the common rebuttals of the simulation hypothesis to see how much merit they hold.

Some have questioned the assumption that there is one parent universe and many simulations. If there are many parent universes and many simulated universes, critics reason, then the probability that we are in a simulation would not necessarily be quite so high. But I disagree. What are the implications of many parent universes capable of sustaining life and technology? Presumably EACH of them would be running many simulations, and thus it would not affect the probability of our being in a simulation much at all.

The most serious problem I see with the Simulation Hypothesis is that it has no empirical basis, and falls apart under the scrutiny of Ockham’s Razor. There is absolutely no conclusive evidence that we are living in a simulation. There may be a few teasing clues (e.g. the quantum world behaves suspiciously differently when we aren’t watching), but nothing substantive. However, I can see no obvious flaw in the logic of the Simulation Hypothesis. This leads back to an old philosophical debate between empiricists and rationalists: Can we determine reality through sound logic, without empirical evidence? I tentatively plant my flag on the side of the rationalists. Scientists frequently adopt a rationalist mindset when interpreting the Drake Equation or formulating string theory (despite absolutely no evidence for extraterrestrials or strings), but switch over to empiricist mode for topics like philosophy or theology. This seems to be a product of cultural bias. In my view, while we should always seek out evidence wherever possible, sound logic is often a sufficient (if inferior) substitute.

At the end of the day, I tend to lean toward the conclusion that Bostrom is correct: We are probably in a simulation. What do you think? Let me know if/where you think the logic of the Simulation Hypothesis is flawed, or any other examples of clues that would suggest a simulated reality.

Resolving Fermi's Paradox

If intelligent life exists elsewhere in the universe, where is everyone? Enrico Fermi’s 1950 question has elicited many theories in the sixty years since. If advanced life was as commonplace as Frank Drake or Carl Sagan believed, it seems unlikely that not a single extraterrestrial civilization would have made itself known to us.

Some, like futurist Ray Kurzweil, believe that this means that we are alone in the universe: the product of a series of astronomically unlikely occurrences. Kurzweil reasons that any advanced civilization would use all the matter of its own planet for computing, then radiate outward from their home world. The fact that no one seems to have done this already is supposedly evidence that we are alone.

I think this is a remarkably anthropocentric view of the universe. Both Fermi’s Paradox and Kurzweil’s reasoning employ the same faulty assumption that extraterrestrial life would act the same way that humans might. How can we possibly guess the goals of an extraterrestrial civilization when we don’t even know how our own civilization will act in the future? Why should we assume that extraterrestrials will be expansionists, desiring to conquer (or even communicate with) the rest of the universe? This is a remarkably human trait to project onto other potential civilizations. It’s entirely possible that extraterrestrial life does exist, but is simply not interested in interacting with us, content with not venturing far from their home worlds. Any civilization capable of interstellar travel or communication will almost certainly have access to anything it wants at home, and perhaps would have no particular reason to be interested in a pale blue dot populated by bipedal apes.

There is another, darker explanation for the lack of contact with extraterrestrials. If advanced civilizations tend to eliminate any inferior civilizations with which they come in contact, then we will have no evidence of them until immediately before our extinction, if at all. The fact that we have not yet been eliminated, then, simply means that no other advanced civilizations are aware of our presence yet. We can employ the Anthropic Principle here: We would not be here to speculate about Fermi’s Paradox if we had been discovered by another civilization.

These are the explanations for Fermi’s Paradox which seem the most plausible to me. The least plausible explanation is the one Kurzweil suggests: That we are alone. Even if advanced life developed in only one in a billion solar systems, there would be trillions of civilizations in the vastness of our universe. Finding them, however, may be much more difficult. Perhaps a truly intelligent civilization would leave no evidence of its existence at all.