The path to detecting extraterrestrial life with astrophotonics

by arbesman • 3 years ago

102 47 3 years ago

panki272• 3 years ago

This will require measuring a velocity change in the speed of light of <50 cm/s and more likely 10-20 cm/s (1 part in 3 × 10^9).

Can someone explain to me why the speed of light changes?

perihelions• 3 years ago

It doesn't; that language is garbled. It's the velocity of the star they're observing that changes by several cm/s. This translates to a Doppler shift in the starlight being detected: a change in its frequency and wavelength.

panki272• 3 years ago

Thank you! I was massively confused there for a second.

icapybara• 3 years ago

Optical engineer here. For anyone not in the field, “photonics” is a fancy academic term for optical systems that involve waveguide structures. You can do some neat things with waveguides that you can’t do with more traditional optics like lenses, prisms and mirrors.

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.

zzbn00• 3 years ago

Lots of exciting possibilities in here and good work by the authors previously but this one is a bit of "white paper" paper describing what could be done in the future if the money is there

martinclayton• 3 years ago

And polarimetry!

Nevermark4• 3 years ago

The other end of the spectrum from detecting bio-signatures of life on individual planets, would be mega structures.

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?

belter• 3 years ago

Any advanced civilization will quickly lose interest in space exploration. Just a phase.

throwbadubadu• 3 years ago

would have a good chance of colonizing their whole galaxy in a blink of an eye

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...

rnk5• 3 years ago

I strongly disagree, it's not beyond the dreams of humans to travel a few light years away with generational starships. How are you going to travel all the way across the galaxy without faster than light travel. We could send humans in the journey to the nearest stars within the next thousand years. At least we could start the ships. That's with only a little bit more technology than we have today. But colonizing the galaxy takes imagining things we have no idea if they will ever be possible, like faster than light travel.

hammock• 3 years ago

“photonics” is a fancy academic term for optical systems that involve waveguide structures

And for the laymen like me, "optical systems that involve waveguide structures" is a fancy term for fiber optics (and related systems).

genman• 3 years ago

Where in the scale of spectroscope and imaging would one put LIGO?

mturmon• 3 years ago

The mention of extra-terrestrial life is not as much of a red herring as you might imagine.

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.)

jmyeet4• 3 years ago

If and when we detect extrasolar technological life it's highly unlikely we'll do it by detecting planetary emissions. It'll also be a whole lot more obvious. Let me explain.

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.

jeremyjh• 3 years ago

This article isn't about a search for technological civilizations. Its about spectographic analysis of exoplanets, which can be used to detect organic molecules in the atmosphere.

zhynn• 3 years ago

It should support the work of lee cronin and sarah walker (Assembly Theory), a novel way to identify compounds that are indicators of life by virtue of their complexity (so we don't need to make any dogmatic assumptions about what life can be made of). We still need to detect these things at a distance, so this paper is relevant, I think, but I also love Assembly Theory.

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).

sampo2• 3 years ago

to detect organic molecules in the atmosphere

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.

gizajob• 3 years ago

Yet we seem to not be finding any sore thumbs.

unnah• 3 years ago

You know how it is, when all you have is a hammer...

jmyeet4• 3 years ago

That's... kinda the point. It's why many (including me) think the most likely scenario is that we are the only technological civilization in our galaxy.

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.

Shekelphile3• 3 years ago

We don't (can't) look for them. Current telescopes are not big enough and governments refuse to pony up the money for anything better. Even JWST was a disaster in terms of finances and time, there's zero chance anyone is going to pay 100-1000x as much for something better.

That's the entire point of the headline. Scientists are forced to search for 'wunderwaffe' solutions to make these observations.

jjk166• 3 years ago

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.

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.

TheBigSalad2• 3 years ago

The idea of the Dyson swarm is just taking humanity as we've seen it over the past 200 years and assuming the exact energy curve would continue for 2K more years. It's kind of silly. People don't need infinite energy to live. Many people are happy to live as much in harmony with nature as they can.

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.

hotnfresh• 3 years ago

This stuff made a lot more sense when it wasn’t yet crystal-clear that we’re on a shortish path to zero or negative population change.

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?

pixl972• 3 years ago

Define live....

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.

jmyeet4• 3 years ago

People don't need infinite energy to live

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).

rnk5• 3 years ago

I like what you say, but I think using the material of Mercury to build these spheres is beyond our technological base. What's not impossible is doing this with some of our asteroids. Send robots, start using the materials on the asteroid, hollow out the center, spin it, all of those things are at least conceivable today with probably the exception of figuring out how to work with the materials on site; engineering challenges but not impossible. A billion or two is probably enough to plan a robotic lander and do lots of fundamental material processing research, spend another billion to prototype it on the moon, another billion to build it and launch it to the asteroid, another billion to operate it. Elon or some other self-aggrandizing billionaire could do it today. Imagine all those billionaire sports team owners, if they weren't doing something stupid with their money they could do this.

jmyeet4• 3 years ago

... I think using the material of Mercury to build these spheres is beyond our technological base

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.

beders• 3 years ago

I'm not sure why people believe this is feasible and desirable.

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.

sprawld• 3 years ago

I do wonder if humankind will have 3 phases: 1) not knowing if life is out there, 3) discovering extraterrestrial life, but mainly:

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.

rnk5• 3 years ago

That's a really interesting breakdown. I think we'll be able to build larger and larger telescopes and figure out more and more of what's in atmospheres of planets. I feel like we'll be increasingly seeing more and more life signals without it being 100% decided. I want to see articles that consider what you could see about the earth from 100 light years away with just a little bit more advanced technology than we have.

api• 3 years ago

If we find a really good candidate for ET life, there are things other than interstellar probes. We'd probably start by building a much larger space telescope designed specifically for spectroscopy. The funding for a mega-scope would be easier to justify if we had a very strong extraterrestrial biosphere candidate.

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.

Shekelphile3• 3 years ago

Phase #2 is only a thing in a strict scientific definition. Nobody will remember the decades of overt denial that life could ever exist off of earth and obstruction of exploration efforts, and handwaving away of biosignature evidence when we do finally observe life on mars, after all. Even then naysayers will claim panspermia in order to kick the can down the road further.

ck22• 3 years ago

Let's build a second James Webb and send it in the other direction for a massive parallax camera (parallax is the wrong word but my brain can't remember the right one)

I just wish I could live long enough to see the SGL

https://www.nasa.gov/directorates/spacetech/niac/2017_Phase_...

hinkley• 3 years ago

I think you could make a case for whatever replaces James Webb going to L4 and L5 instead of L2.

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?

ck22• 3 years ago

The only fun fact I remember about Lagrange Points is when I first heard of them with JWST I figured someone really smart must have used a supercomputer in recent history to calculate such a thing.

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.

https://en.wikipedia.org/wiki/Lagrange_point

The path to detecting extraterrestrial life with astrophotonics

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