6 ms·

The path to detecting extraterrestrial life with astrophotonics

102 points by arbesman 3y ago

panki27 3y 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 3y 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. see also https://en.wikipedia.org/wiki/Doppler_spectroscopy https://en.wikipedia.org/wiki/Doppler_spectroscopy
  - panki27 3y ago
    Thank you! I was massively confused there for a second.
icapybara 3y 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 3y 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 3y ago
  And polarimetry!
- Nevermark 3y 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 3y ago
    Any advanced civilization will quickly lose interest in space exploration. Just a phase.
  - throwbadubadu 3y 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...
    - Nevermark 3y ago
      Life. Individuals compete. Resources have limits, and life quickly scales to them. 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. — Also - starlight is going unused on a galactic scale. Actively managing energy production will enable a larger, longer, and more efficient future.
- hammock 3y 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 3y ago
  Where in the scale of spectroscope and imaging would one put LIGO?
- mturmon 3y 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 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.)
jmyeet 3y 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 3y 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.
sprawld 3y 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.
- rnk 3y 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 3y 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.
- Shekelphile 3y 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.
ck2 3y 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_I_Phase_II/Solar_Gravity_Lens_Mission/ https://www.nasa.gov/directorates/spacetech/niac/2017_Phase_...
- hinkley 3y 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?
  - ck2 3y 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 https://en.wikipedia.org/wiki/Lagrange_point

102 points by arbesman 3y 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 3y 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. see also https://en.wikipedia.org/wiki/Doppler_spectroscopy https://en.wikipedia.org/wiki/Doppler_spectroscopy
- panki27 3y ago
  Thank you! I was massively confused there for a second.

icapybara 3y 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 3y 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 3y ago
And polarimetry!
Nevermark 3y 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 3y ago
  Any advanced civilization will quickly lose interest in space exploration. Just a phase.
- throwbadubadu 3y 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...
  - Nevermark 3y ago
    Life. Individuals compete. Resources have limits, and life quickly scales to them. 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. — Also - starlight is going unused on a galactic scale. Actively managing energy production will enable a larger, longer, and more efficient future.
hammock 3y 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 3y ago
Where in the scale of spectroscope and imaging would one put LIGO?
mturmon 3y 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 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.)

jmyeet 3y 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 3y 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.

sprawld 3y 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.

rnk 3y 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 3y 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.
Shekelphile 3y 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.

ck2 3y 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_I_Phase_II/Solar_Gravity_Lens_Mission/ https://www.nasa.gov/directorates/spacetech/niac/2017_Phase_...

hinkley 3y 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?
- ck2 3y 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 https://en.wikipedia.org/wiki/Lagrange_point