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NASA Asks: Will We Know Life When We See It? (nasa.gov)
In the last decade, we have discovered thousands of planets outside our solar system and have learned that rocky, temperate worlds are numerous in our galaxy. The next step will involve asking even bigger questions. Could some of these planets host life? And if so, asks NASA, will we be able to recognize life elsewhere if we see it? From a blog post on NASA's website: A group of leading researchers in astronomy, biology and geology has come together under NASA's Nexus for Exoplanet System Science, or NExSS, to take stock of our knowledge in the search for life on distant planets and to lay the groundwork for moving the related sciences forward.
"We're moving from theorizing about life elsewhere in our galaxy to a robust science that will eventually give us the answer we seek to that profound question: Are we alone?" said Martin Still, an exoplanet scientist at NASA Headquarters, Washington. In a set of five review papers published last week in the scientific journal Astrobiology, NExSS scientists took an inventory of the most promising signs of life, called biosignatures. The paper authors include four scientists from NASA's Jet Propulsion Laboratory in Pasadena, California. They considered how to interpret the presence of biosignatures, should we detect them on distant worlds. A primary concern is ensuring the science is strong enough to distinguish a living world from a barren planet masquerading as one.
"We're moving from theorizing about life elsewhere in our galaxy to a robust science that will eventually give us the answer we seek to that profound question: Are we alone?" said Martin Still, an exoplanet scientist at NASA Headquarters, Washington. In a set of five review papers published last week in the scientific journal Astrobiology, NExSS scientists took an inventory of the most promising signs of life, called biosignatures. The paper authors include four scientists from NASA's Jet Propulsion Laboratory in Pasadena, California. They considered how to interpret the presence of biosignatures, should we detect them on distant worlds. A primary concern is ensuring the science is strong enough to distinguish a living world from a barren planet masquerading as one.
It's life, Jim, but not as we know it. - Dr. McCoy
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The line between life and not-life is already indistinct here on Earth. Viruses? Not-life...quite. Kinda life?
And forget trying to figure out what counts as intelligent life. Trees communicate with an underground fungus network and through signals in the air, can probably feel pain, count and learn, but we're not quite at the point of calling them 'intelligent'. Birds turn out to be incredibly intelligent, but people are still reluctant to admit the level of intellect the birds have, and how deep it may actually go.
What hope do we have of classifying an indistinct gas-being that gets by just fine when we're not around, but immediately decoheres the moment a human passes through them waving their hand in front of their face? Or some sort of super-cooled snow creature with liquid nitrogen in its veins that reacts too slowly for us to even comprehend?
it is possible that life is everywhere, all around us in forms we don't recognize...
There are so many things that could make life unlike ours invisible. Imagine for a second a life form that's brain runs 1 billion times slower or faster than ours. Silly example to make my point: Mount Everest could be a slug, but it moves so slow that we would never know it as anything but a lifeless rock.
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An interesting (thought) experiment would be to determine how much data would be required to determine if there was life on Earth.
How many photons would it take for a telescope mounted spectrometer require to detect chlorophyll, C02 or other signs of life (industrial pollution) and how far away/how long would it take to collect them?
Humans are broadcasting light and radio waves from Earth, could Hubble, the James Webb telescope/other instruments detect them same amount of radiation from other solar systems?
Are there other characteristics of inhabited Earth that could be used to determine whether or not other planets have life?
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Our search for extraterrestrial life, such as it is, has been on the assumption that "as we know it" means carbon-based. But because right here and now we are in the early stages of a transition from carbon-based to silicon-based on Earth, what does this imply for other intelligent species?
Is this kind of change inevitable as soon as a civilization can accomplish it, and what does it mean for the possibility of communication? It could be that digitized silicon lifeforms produced by any given 'wet biology' will become good at concealing its own existence in the same way that good encryption is indistinguishable from noise.
Simplish version: A complex system, constructed and guided by a conserved information pattern, which acts so as to sustain itself (and by "itself" we mean a causally-connected sequence and/or group of instances of its constrained system pattern.)
Bafflegab-level Detail:
A Matter/energy system which embodies/contains a particular (that is, constrained in variation) complex information pattern. When processed by the matter/energy system, the information pattern constructs instances of the system, and by constraining and guiding the form and function of the system, allows a collection of causally connected instances of the system, and the constrained information pattern, to persist in its environment significantly longer than the thermodynamics and forces in the region would allow by random chance. In other words, the particular form and function of the complex system, and the consequent particular and constrained interactions of the system and its environment, ensures unexpected continuation of the particular complex system pattern in an entropic environment that would, without counteracting function, rapidly break down the complex order of a system of similar complexity.
Where are we going and why are we in a handbasket?
My father (who only went to school for seven years, and started working at 14, and isn't precisely highly educated) asked me the other day wether water is a pre-requisite for life. I answered as most do; yes, probably. Without some kind of solvent, reactions and material exchange is slow.
That got me thinking of scales... what if "slow" isn't a problem. What if we encounter beings with metabolism rates which are 100 000 slower or faster than ours? Would we be able to recognize it as life? Which other dimensions could scale so that we wouldn't recognize it? DeGrasse talks about intelligence - would we recognize life that is 100 000 times smarter or dumber than us? Could there be life at extreme temperatures? I don't mean 1000 deg C, I'm talking about life inside stars. There is for sure a thermal and entropy flow - could there be fusion plasma solutions to Maxwell that could make basic building blocks for something life-like? If so, could we ever observe it?
At any rate, it may be material for a star trek episode...
I seem to recall a talk about sulphur-eating archaea in a hydrothermal vent environment in which no evolution has taken place for millions of years, because they've apparently reached an optimal solution (local maximum anyway) in utilizing the resources in the simple and small environment.
Evolution only works (and takes place) if you can still do better. Otherwise, you get the "surprising continuation" aspect of life without the (further) evolution aspect.
Where are we going and why are we in a handbasket?
I think the correct way to think of viruses is to draw the boundary of the living system differently. The virus living-system comprises the virus bodies plus a spatiotemporal subset of host organisms. That is, the parts and mechanisms of the host organism that the virus uses for a period of time to perform its reproduction. The system boundary (of a living system) is the minimum boundary of a matter/energy system that can accomplish the "living" definition above. In the virus case, that boundary is bigger than the individual virii bodies, but so what.
Ants pretty much need a colony worth of them to survive, through much of their lifecycle. So is a (worker) ant alive? Or is it more a component of a larger colony-system that meets the full life definition?
Where are we going and why are we in a handbasket?
Microbial. Mounting evidence suggests microbial life *might* be very common. If it spends a long time dormant and comes to replicate itself only under ideal conditions, then we'll need to experiment with conditions to see if we can bring it back to life to observe..
Animal. Even if microbial life is plentiful, multicellular life seems likely to be very uncommon. We've only had it on Earth for the last half-billion years, seemingly by some freak accident.
Lingual. Dolphins and whales exhibit languages with complex grammars, refer to each other by name even gossip about each other while the other is away, have an exquisite sense of past, present, and future and yet man has only uncovered a fraction of their languages. There is no known capability of human languages that bottle nosed dolphins lack. If we cannot even hack their language, what hope is there of extra-terrestrials if ever encountered? All we need is a dolphin drone, remotely controllable with VR headset and computer translation of phonemes (both ways), in order to learn through immersion... Nobody is even trying.
Technological. To be a technological species, you need (A) dexterous manipulators, (B) social behavior, and (C) imitation learning/substitution problem solving. You cannot build things without dexterous manipulators and cannot pass along knowledge and skills without both imitation and social behavior. Imitation must be substantial enough to do without a reason for doing so. Chimpanzees imitate but do not continue with behaviors that serve no obvious purpose. Humans continue regardless... We don't seem to care what customs are for. Substitution problem solving the other side of the imitation coin. In order to imitate one person/thing for another, you need to build a mental model of each, identify similarities, and swap one for another. For example, a rock with a flat side might substitute for a hammer. This is analogy -- the essence of conceptual knowledge.
I suspect that, if celestial bodies with subsurface liquid water oceans are as common as they seem then an aquatic technological species would have a far lower bar to entry into space than a surface species, such as ours. On Earth, octopi species have requirements A and C and recently two small examples of B (social behavior) have also been found (look up "Octopolis and Octlantis"). Unlike most octopi species, they build small city-like collective settlements and the mothers live for a time simultaneously with their offspring. This strongly suggests they are building knowledge and/or at least skills across generations. It seems to me likely that species such as these could be more common than surface species, such as us. Furthermore, Pluto suggests they might more so inhabit the colder regions of space... They might even be averse to places as close to stars, as Earth is to the Sun.
Just like all physics: we theorise, we predict, we observe.
Predict: by current theory, spectral lines of elements on earth should be "this".
Observe: yep, that seems to be true on earth.
Predict: the universe is pretty boring, same rules everywhere, so spectral lines will be the same everywhere, plus (consistent) red/blue shift because stuff is moving (and we can predict that too, with current theory).
Observe: look at distant objects and what do you see... crikey jingo, it matches the prediction.
Sure you could no doubt dream up an alternative reason why the predictions work that involves exotic "physics" in distant galaxies, but that seems like an unjustified complexification to me.
Our brightest "passive" emissions are our ballistic missile early warning radars. Most transmissions/emissions from Earth fade rapidly with distance. A signal that is tightly focused, powerful, and with a narrow spectrum will far outshine everything else on Earth in the electromagnetic spectrum.
So if aliens detect us from a distance they will be seeing the bright pulses of FPS-115 PAVE PAWS (Precision Acquisition Vehicle Entry Phased Array Warning System) whose signals are now 41 light years out.
These radars are detectable to 15 light years with a clone of the Arecibo radio telescope, and a thousand 100-m dishes (once proposed for a Project Cyclops) would be able to detect us to 250 light years. A really advanced civilization could have a radio telescope much larger than that so our radar signals might be detectable across much of the galaxy. There has to be some limit of detectability against natural noise though, but I don't know what it is.
So thanks to the nuclear arms race we have an interstellar beacon already operating!
Of course "detectable" is simply the lowest bar to clear. Since these beams sweep and also change frequency to avoid jamming, an alien is just going to pick up a few blips at different frequencies, with more blips not seen for a day until we are illuminating that part of the sky again. Not extremely obvious, but as they collect data across decades, it might be enough signal. But since these advanced aliens would presumably have a lot knowledge of natural signals they might be able to flag this as an anomaly fairly quickly. And of course we are only beaming things in the Northern Hemisphere, but the center of our galaxy is visible from PAVE PAWS sites.
Starships were meant to fly, Hands up and touch the sky - Nicky Minaj