The path to detecting extraterrestrial life with astrophotonics
arxiv.org
arxiv.org
I think the paper’s title is a bit sensationalist (a callout to extraterrestrial life in an optics paper? Really?) but it’s basically talking about how these devices can help improve spectroscopy and imaging, which are the only two tools astronomers have.
Once a civilization began harvesting the energy of a few star systems, it would have a good chance of colonizing their whole galaxy in a blink of an eye.
(100 thousand years, plus or minus an order of magnitude, as compared to universe time in billions of years.)
So we would be much more likely to see totally colonized galaxies, rather than partially colonized.
I would be curious about which instruments would detect infra-red galaxies, I.e. galaxy sized objects where all starlight was put to use, with only infra-red light as waste.
And would that be an object that would stand out if a major telescope came across it, or require specific initiative to search and find?
And speaking of optics, is there any reason to suspect an efficient civilization would leak lower frequency light than infra-red?
But what's the motivation to do that, so that the collapse is bigger? Beyond just because it could also many good reasons not to do that...
Life harnessing new resources is the most constructive way to compete.
Creatures that expand, expand exponentially.
Creatures that don’t, collapse exponentially.
It takes a minuscule percentage of a population to be expanders, for the whole population to quickly become expanders.
It would take an exceptional explanation to explain why creatures that could expand, don’t.
An exceptional explanation on par with explaining how a balloon could be popped in a vacuum, but the compressed air inside somehow remained in place instead of dispersing.
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Also - starlight is going unused on a galactic scale. Actively managing energy production will enable a larger, longer, and more efficient future.
1/1,000, 1/1,000,000 ... it doesn't matter how small the fraction is to start.
Affluence in humans vastly increases consumption. By several orders of magnitude. Billionaires enjoy jets, yachts, and build companies that use vast resources to accomplish new things.
AI isn't going to be concerned about human lifetimes. 20 years to the nearest star for a laser sail ship smaller than a human takes physics we have now. For nano tech that would be a massive ship.
If you want a teleological argument, here is one: Life expands by colonizing and adapting to new environments and inventing new capabilities. Then expanding and adapting over and over again in response to each wave of change. Life expanding across the galaxy will produce beauty and complexity we can't imagine.
We will be sending entire civilizations of nanobots, or at least small artificial organisms.
At 5% of the speed of light, including travel, reproduction & relaunches, a civilization like that at the center of the galaxy will reach the rim in 100,000 years.
At the nano level time effective massively expands. Activity at that scale operates with speeds many magnitudes faster than gargantuan Ent-like beings like us, can easily imagine. :)
It isn’t a journey suitable for humans, and our position here is changing rapidly decade to decade. The galaxy was never going to belong to humans, but hopefully our progeny.
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Then there is hope from physicists, that harnessing stellar level energy will allow faster than light warp travel. That would let beings cross the vast spaces between galaxies.
Not at all depending on the timeframe you want to talk about in.
For example, one way to travel around the galaxy is to find some other object with a very fast orbit and colonize it. Then as it goes along you throw off seed ships. This is the whole idea behind 'von neumann probes'. Massive numbers of things working in parallel can get a lot of work done.
But were you saying "get started on this in 1000 years" instead of finish in 1000 years?
And for the laymen like me, "optical systems that involve waveguide structures" is a fancy term for fiber optics (and related systems).
The National Academies Decadal Survey for Astrophysics ("Astro2020") recommended that NASA study an ~6m aperture telescope that would be capable of direct-imaging of exoplanets, and obtaining spectra of these exoplanets sufficient to detect atmospheric constituents that are associated with life. The nominal name for the telescope is HWO - Habitable Worlds Observatory.
So this is very much an object of legitimate study, tech development, prototyping, etc. NASA's program for doing this is called GOMAP (https://science.nasa.gov/astrophysics/programs/gomap). The motivation being to consider novel approaches now, before the architecture is settled.
Detection and spectral characterization require excellent resolution and suppression of direct light from the host star, while preserving light from the planet.
The people on the author list are working on novel photonics-based approaches to do this.
As one example that I know about, and that your remark hints at, photonics approaches capture and manipulate amplitude and phase. There are photonic components that can achieve (in principle) any transfer function (filter), not just ones that can be implemented in glass. Doing this can help greatly to suppress starlight.
(I work in the area.)
2) 1000s of years where we're pretty sure that oxygen rich planet has life, but can't get there and have to concede it might be just a flaw in our theory of planet formation.
There are also some literally far-out proposals to place a space telescope way out beyond the orbit of Pluto and use gravitational lensing from the Sun as a giant objective lens. It wouldn't make sense for a general purpose scope but could make sense if the exact orbit and timing were selected to observe a specific object. Difficult but probably not as hard as interstellar flight.
Can someone explain to me why the speed of light changes?
I just wish I could live long enough to see the SGL
https://www.nasa.gov/directorates/spacetech/niac/2017_Phase_...
They put JW at the L2 point. I don't think L1 would make a good astronomical location (we put Sun monitoring satellites there, which is probably a good idea), and L3 wouldn't be able to transmit to earth because there's a big ball of fusion in the way.
L4 and L5 have the advantage of being stable. No reaction mass needed for orbital correction. I'm not sure how much reaction mass you need for the orbital corrections versus going to L2. Anyone know?
Nope. Someone in freaking -1750- figured them out (okay 1770 it was furthered)
No electricity, telescopes primitive at only 100 years old, barely grasping the idea of a solar system and they are doing that level math by hand.
The future of humanity is likely to be in orbitals. With existing materials these are likely to be 2-3 miles in diameter and 10-20 miles in length, producing EArth-like gravity by simply spinning. You then cover the surface with solar panels. If graphene ever becomes viable as a mega-engineering material, you can scale these up 100x+ larger. Why? Lots of advantages:
1. You can produce this with existing materials. No magic theorized materials are required;
2. No magical new technology is required. Even something like nuclear fusion power generation, which I'm not yet convinced will ever be commercially viable, isn't required;
3. Spin gravity is identical to normal gravity. Earthlike gravity means we don't have to worry about our ability to live in microgravity or even low-G (eg Moon, Mars);
4. You can largely be shielded from cosmic radiation with water tanks beneath your feet;
5. You get to harness the full output of the Sun for energy. For reference, only about one billionth of the energy of the Sun hits Earth. This is a Dyson Swarm;
6. This is incredibly efficient in creating living space per unit mass. Roughly 1% of Mercury's mass is enough to create a Dyson Swarm with billions of times of the living area of Earth.
So, by looking for technological signatures from exoplanet atmospheres we're essentially hoping to find the ~1000 year window where there are detectable signals and we're not looking for a Dyson Swarm instead. SETI has the same problem with a much smaller window.
So why is this much easier to detect? Because of thermodynamics. You absorb a star's light output and you heat up in anything less than perfect energy efficiency (which is impossible). The only way to dispose of heat in space is to radiate it away. Technically you could eject mass but then you have to replace that mass. And the frequency of the radiated heat is determined by the temperature of the radiating object. For any reasonable temperature, that's in the IR range.
The Sun is less than a million miles in diameter. If we were looking for a Dyson Swarm around a star like our Sun, we'd see an object that was more than 200 million miles across (ie the cloud of orbitals) that is producing much of that energy as infrared. It would stick out like a sore thumb.
They have a new preprint that argues that Assembly theory can explain and quantify selection and evolution in complex systems: https://arxiv.org/abs/2206.02279 (I think that it is one of the more under-appreciated papers out there).
You don't really need to detect organic molecules. If anyone detected 21% oxygen (O2, inorganic) in Earth's atmosphere, they sure knew something was going on. Lifeless planets like Venus, Mars, have atmospheres that are close to chemical equilibrium. And Earth's atmosphere is far from equilibrium, free oxygen it much too reactive and wouldn't exist without photosynthesis continuously producing it.
Our understanding of astrochemestry is still limited enough, that we cannot say with confidence that a given signature requires a biotic process to produce.
It will always be possible to find a new extreme edge case to deny far easier and more common processes that leave around biosignatures, it's the exact same rhetoric used to handwave away the methane in the martian atmosphere.
There are lots of natural objections to this statement (eg civilizations that "hide") and a lot of these has gone into these explanations for the Fermi Paradox. It can be shown that such a structure has massive benefits, the biggest of which is energy (which is our ultimate limiting factor). If there's 1 other civilization in our galaxy then we can't really guess what they'll do. If there are 1000 civilizatiions then what are the chances that none of them go this route, given if there's even one there's a reasonable chance we could detect it? It starts to stretch credulity.
That's the entire point of the headline. Scientists are forced to search for 'wunderwaffe' solutions to make these observations.
Unfortunately large objects emitting a lot of total energy in infrared don't stick out like a sore thumb. It's very difficult to distinguish a Dyson swarm from a Dyson swarm sized ball of Dyson swarm temperature gas and dust, which is a reasonably commonplace phenomenon. Indeed for one of the simpler construction methods, a dyson swarm may essentially be a big ball of dust where each mote is a solar energy collector. Further, over long time scales without active maintenance you'd expect dyson swarms to break down into literal clouds of gas and dust. While dyson swarm candidates might be good places to focus other SETI experiments like radio telescopes, it's unlikely that the thermal signature of the swarm alone would ever be unambiguously artificial.
This whole line of thinking is short sighted. For example "No magic theorized materials are required;" but we literally WILL have 'magic' materials in the future. Of course we can't predict the things we don't have yet, but assuming we'd just move in some linear line from where we are is probably unlikely.
Why build and pay for a complex life support system in space when… I’m living on a really big and really good one for free? It doesn’t seem like we’re going to run out of space for people, so why expend resources making mediocre space environments for people to live on, except for certain narrow purposes?
[edit] I think the problem becomes obvious if one considers colonizing the oceans with big ships and floating platforms. We haven’t really done it, and it’s hard to imagine why we would—it’s just so much more expensive and less convenient than living on land. Space is like that, except all the bad parts are even worse. What do we have on the oceans? Resource-gathering operations, shipping, exploration ships. I don’t see why space would see more colonization than the oceans have (which is nearly zero, mostly temporary purpose-specific habitation and movement across it to land)
I’d include Mars and such as places much worse and more expensive to colonize than the oceans. I don’t see it happening any time soon—why would it?
Dinosaurs lived for 100+ million years on Earth, then boom, extraterrestrial events extincted them. As an intelligent species (somewhere above dinosaur/ape intelligence) eventually you discover that planets and stars are unstable. You are not living in harmony with nature. Nature is just temporarily not killing you. Now you've further pushed the question to "Does an intelligent species accept its eventual planetary extinction".
It doesn't matter what many do. For example with bacteria it only takes a single cell to make a single change to become the dominant form of that species in some number of generations if it gives them a evolutionary advantage.
Our current rate of energy consumption is unsustainable. This is a problem no matter how you want to live (unless you want the entire civilization to go primitive). This is a problem.
> This whole line of thinking is short sighted.
That's a strange assertion. It's a really long term solution, like billions of years long.
As for your magic materials, I hate this kind of argument. It's really just hand-waving "we don't know what we don't know". But we do know physics and we know we need energy. That energy has to come from somewhere. We can't just make it up from nothing. So far the only viable long-term energy options we have are solar power and nuclear power (particularly fusion). There are some far future options like antimatter and using black holes but these don't actually solve the energy problem. They just make really great batteries (eg to have antimatter you have to make it and that takes energy).
This is presently true. My point is that it's a conservative estimate to say we'll be capable of it within the next 1000 years. Our biggest issue currently is the high cost of getting payloads into LEO. For Apollo and the Space Shuttle that cost was ~$50,000/kg. Factoring in reusability it's now estimated to be $1000/kg or less. There are paths to get this much lower (eg <$10/kg).
Mercury has specific issues and advantages. The biggest advantages are access to energy, high orbital velocity and no atmosphere. A thin atmosphere like on Mars is the worst of both worlds. It really just makes landing difficult and creates dust storms to cover your equipment in dust.
The high orbital velocity of Mercury is both an advantage and a disadvantage. It makes it really difficult to get there, which is why there have been relatively few missions there, but once you are there, it means the delta-V of getting anywhere else in the Solar System is quite low, whether that be finished products or just raw materials.
Mercury is metal rich but probably lacks elements like oxygen for, say, smelting steel (and, of course, living). The long day/night cycle is an issue too.
My point in relating the mass requirement to Mercury is because, even though 1% of Mercury is still a lot of mass, it would still leave Mercury relatively intact. It's also metal-rich.
I had another vision, informed from science fiction. It was that we could send relatively small machines (self replicating using local materials on the asteroid) and they could do everything we want after we figure out the replicating w local materials part. And because we only need to send a small starter robot it doesn't use that much energy.
What do you think of that? I mean we could do the same with materials to process them on Mercury.
There's no resources up there. Where do you get the water from? Where do you get the materials from?
Unless you have a close, cheap source to replace and replenish, this is a pipe dream.