The possibility of strange forms of alien life seems to have just got a whole lot closer to home. Astrobiologists from Arizona State University, Florida, UC Boulder, NASA, Harvard and Australia have recently theorized about a “shadow biosphere” – a biosphere within a biosphere where alternative biochemistry may be thriving in a way that we haven’t yet thought to examine. Such “weird life” may have had, for hundreds of millions of years, their own ecologies right here in our own backyard. Indeed, like Dark Energy and neutrinos, “weird life” may be all around us even now, only in a non-obvious way. Some astrobiologists are now suggesting that “weird life” is just as likely to be found here on Earth as it is in the Martian regolith, the seas of Europa , or certainly the complex bio-hadronistry on the surface of a neutron star.
I have included a link to their full article here: Davies_etal_Astrobio2009.pdf
Now, while I think that shadow organisms and shadow biospheres are certainly cool enough to blog about, please allow me to take the logical next step by citing yet another intriguing astrobiology paper that came out of the Santa Fe Institute. Published nearly a decade ago in an astrobiology related Nature commentary article titled, “Where are the dolphins?” scientists Jack Cohen and Ian Stewart realized (and showed mathematically that it’s already happening here on Earth) that as a civilization advances they begin to use the available electromagnetic spectrum for communication more fully and efficiently until ultimately their radiative emissions are indistinguishable from blackbody radiation. In other words, when we look out into space with telescopes to search for signs of alien life (SETI for example) we will likely mistake it for being just a regular old hot rock! So either three things must be true to find life through a telescope: 1. The civilization is at a very precise moment in its development,2. The civilization wants to be found and so sets aside some broadcast space for a message, 3. We know their decompression algorithm and what frequency band to apply it to.
It’s this last possibility that relates to the shadow biosphere in a philosophical sense. Unless we know how to interpret the signs of such life, we may not be able to distinguish it from the natural background.
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5 Comments
You’re assuming the entropy of the “shadow-biological” signature would be similar to the entropy of a radiated signal. There’s an incentive to compress powered signals (efficiency). There doesn’t seem to be a similar evolutionary pressure; certainly this planet’s biosphere has not rewarded compression. Nucleic acids are not optimal binary encodings, the atmosphere has been dramatically altered by respiration, etc.
Thank you for this excellent point, it really got me thinking. First off though, ‘shadow life’ as expressed in the Davies paper, while certainly ‘weird’ would likely be easily identified as life once observed, it’s just that it’ll be made of different chirality molecules, or different sets of amino acids, things like that.
That said, I don’t agree that evolution doesn’t reward compression. Examples immediately come to mind – sunflower seed packing, micro-capillary water transport in plants, maximal environmental quantum efficiency of photon absorption by chlorophyll , slime mold mimicking of Tokyo rail network efficiency .
Would such pressure toward efficiency lead naturally to camouflage as amazing as the blackbody spectrum? I am having trouble thinking of why not. Visual appearance is communicated though the electromagnetic spectrum. This of course applies not just to a “powered spectrum” but also to the more common reflected one that most animals utilize. So what is the relationship between efficiency and camouflage? Forgetting spectra for a moment…morphological maximum information packing, for example holographic kinoforms , appears like white noise without the knowledge of how to decompress it. Some life is just so obvious that we miss it!
Thank You
You’re right that evolution at least sometimes favors compression. But only in a balance with all the other selection pressures. I suspect that all biospheres would be extremely “leaky” in terms of emitting signals, because the amount of diversity needed to “use up” all the energy in a system would be staggering. Tropical rain forests and coral reefs are wildly diverse and famous for absorbing large amounts of the energy that is in them (the thin soil of the rain forest, the efficiency with which reefs clean suspended organic matter) but are still very easily detectable by other ways (chemically, electromagnetically, etc.). Can you imagine a biosphere that was so efficient at consuming energy that it appeared as white noise? (Fun to imagine, but I’d submit unlikely.)
I think that the problem with shadow-biology (which seems to me intuitively VERY possible) is not that we wouldn’t be able to detect its signature, but that the range of things that might signal a shadow-biosphere is very large.
(On your point about “camouflage vs. efficiency,” it’s interesting to ponder the polar bear, whose hollow fur appears white, both camouflaging and insulating it. Although I doubt that any Arctic prey can see in infrared, the insulating benefit of the fur coincidentally camouflages the bear in IR, hiding that “signal” from scientists in some “All living objects emit large amounts of heat” shadow biosphere.)
I have often wondered why we only see one tree of life on Earth. If in over 4 billion years, there has only been one genesis of life on Earth, this means that a genesis of life is very very rare, perhaps 1 in billions of a chance, or that the Earth was seeded by microbes that already existed and had a genesis from somewhere else in the Galaxy. Because it has been shown that life existed on Earth 3 and half billion years ago, I tend to think Earth was probably seeded by microbes hitching a ride on impact residue from another genesis source. This is a huge mystery and one I am deeply interested in, I hope we can come closer in my lifetime to understanding this further.
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