City lights could reveal E.T. civilization

Nov 03, 2011
If an alien civilization builds brightly-lit cities like those shown in this artist's conception, future generations of telescopes might allow us to detect them. This would offer a new method of searching for extraterrestrial intelligence elsewhere in our Galaxy. Credit: David A. Aguilar (CfA)

In the search for extraterrestrial intelligence, astronomers have hunted for radio signals and ultra-short laser pulses. In a new paper, Avi Loeb (Harvard-Smithsonian Center for Astrophysics) and Edwin Turner (Princeton University) suggest a new technique for finding aliens: look for their city lights.

"Looking for alien cities would be a long shot, but wouldn't require extra resources. And if we succeed, it would change our perception of our place in the universe," said Loeb.

As with other SETI methods, they rely on the assumption that aliens would use Earth-like technologies. This is reasonable because any intelligent life that evolved in the light from its nearest star is likely to have artificial illumination that switches on during the hours of darkness.

How easy would it be to spot a city on a ? Clearly, this light will have to be distinguished from the glare from the . Loeb and Turner suggest looking at the change in light from an as it moves around its star.

As the planet orbits, it goes through phases similar to those of the Moon. When it's in a dark phase, more artificial light from the night side would be visible from Earth than reflected light from the day side. So the total flux from a planet with city lighting will vary in a way that is measurably different from a planet that has no artificial lights.

Spotting this tiny signal would require of telescopes. However, the technique could be tested closer to home, using objects at the edge of our solar system.

Loeb and Turner calculate that today's best telescopes ought to be able to see the light generated by a Tokyo-sized metropolis at the distance of the - the region occupied by Pluto, Eris, and thousands of smaller icy bodies. So if there are any cities out there, we ought to be able to see them now. By looking, astronomers can hone the technique and be ready to apply it when the first Earth-sized worlds are found around distant stars in our galaxy.

"It's very unlikely that there are alien cities on the edge of our solar system, but the principle of science is to find a method to check," Turner said. "Before Galileo, it was conventional wisdom that heavier objects fall faster than light objects, but he tested the belief and found they actually fall at the same rate."

As our technology has moved from radio and TV broadcasts to cable and fiber optics, we have become less detectable to aliens. If the same is true of extraterrestrial civilizations, then artificial lights might be the best way to spot them from afar.

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Justin458161
4.6 / 5 (9) Nov 03, 2011
Interesting approach; nice article!
pauljpease
4.7 / 5 (9) Nov 03, 2011
Good idea. I also think that nuclear explosions would be easy to detect, as long as you happen to look at exactly the right moment.
Nerdyguy
2 / 5 (10) Nov 03, 2011
"Looking for alien cities would be a long shot, but wouldn't require extra resources."

FOLLOWED BY:

"Spotting this tiny signal would require future generations of telescopes. "

Since one could presume that future telescopes will have no shortage of astronomers standing in line to gain access to their capabilities, it seems dubious to characterize the need for new technology PLUS the need to divert resources away from other projects as not requiring "extra resources".

Many better uses for those funds, IMO.
Temple
3.8 / 5 (6) Nov 03, 2011
Optical light pollution is probably one of the least likely means of detecting an industrialized civilization.

Things like radio/light pollution from communication networks, artificial atmospheric pollution via spectroscopy, energy drive emissions, etc are all going to be far-far more easily detected than the potential waste light pollution of the equivalent of lightbulbs.
Isaacsname
4 / 5 (3) Nov 03, 2011
I would think we could also, given the right methods, find civilizations by looking for clouds of garbage and space debris, that would be a type similar to us, but a fairly advanced civilization might have figured out how to recapture and use every bit of space garbage, it'd be absent as a " interstellar biomarker ", for lack of better terms.

I'm curious how much light is refracted from debris around Earth, and whether it hepls or hinders anybody else being able to find us in the chaos ?

thales
4.5 / 5 (8) Nov 03, 2011
"It's very unlikely that there are alien cities on the edge of our solar system" Turner said.


So you're saying there's a chance. :D
droid001
5 / 5 (1) Nov 03, 2011
let's find any life whatsoever
Nerdyguy
2 / 5 (12) Nov 03, 2011
let's find any life whatsoever


To what end? I'd say at our level of evolution, our innate immaturity would make it better for them -- and probably safer for us -- if we remain strangers. Maybe our level of "social maturity" will grown in lockstep with our technology, but I'm not holding my breath.
JDAM
3.5 / 5 (6) Nov 03, 2011
So I guess we won't detect all those nocturnal aliens that have night vision. And are we going to scour all possible wavelengths, or just assume that aliens use sodium-vapour street lamps like ours?
Jonah
2 / 5 (4) Nov 03, 2011
But what if this civilization can see in the dark, or uses sonar to "see" and therefore doesn't need lights?
antialias_physorg
2.7 / 5 (6) Nov 03, 2011
This is reasonable because any intelligent life that evolved in the light from its nearest star is likely to have artificial illumination that switches on during the hours of darkness.

Is this so reasonable? Life can evolve in the deep (sea or underground) where illumination is not an issue but other senses come into play (magnetic/electric fields, infrared, sound, ... ). civilizations derived from such ancestors may not go for city lighting (or above-ground living) at all.

And how exactly are they going to distinguish city lighting from thunderstorms with lightning (or partly overcast planets where cloudcover changes albedo/infrared signature locally? (or a passing moon)

Nice idea, but I don't yet see how it can be made to work without giving mostly false positives.
Pyle
2.1 / 5 (7) Nov 03, 2011
Any radiation we saw coming from a planet is going to be heavily scrutinized. This paper seems like a publish or perish type. Not anything of real value. Sorry.
Somebody tell me why having said this out loud changes our future investigations in any way.
martinwolf
2.6 / 5 (5) Nov 03, 2011
perhaps they are advanced enough to keep their light where it is needed unlike we humans who are still sending so much of it away to the point that it takes a total power blackout for some individuals in large urban areas to see the stars for the first time in their lives...our civilization at this point knows how to convert resources into useful products including lighting but it shows how much we are wasting...perhaps other civilizations out there are more frugal and thoughtful as new technologies evolve perhaps not as focused on the exchange of money for product..perhaps kind to their environment as well as themselves...an interesting thought anyway and certainly worth persuing...gently though..:)
ROBTHEGOB
3 / 5 (8) Nov 03, 2011
I suggest that if we see any Golden Arches or Burger King signs, we nuke them as soon as possible.
canuckit
3 / 5 (2) Nov 03, 2011
This technique should also be able to clearly distinguish artificial light from swamp gas :)
tkn
3 / 5 (6) Nov 03, 2011
We achieved enormously glowing night sky on Earth just few decades ago. Even if an alien civilisation had achieved it a million years ago, In order to get their light, we are still limited to a radius of a million light year around us.
It seems more plausible to me though, that another "Earth like" planet might have been in evolution more or less parallel to us. Hence the chances of getting a signal from a very distant (billion light year or so) place, are bleak. IMO
Grizzled
3 / 5 (6) Nov 03, 2011
"Looking for alien cities would be a long shot, but wouldn't require extra resources."

FOLLOWED BY:

"Spotting this tiny signal would require future generations of telescopes. "

Since one could presume that future telescopes will have no shortage of astronomers standing in line to gain access to their capabilities, it seems dubious to characterize the need for new technology PLUS the need to divert resources away from other projects as not requiring "extra resources".

You forgot riding the coattails of other projects. This is pretty much what SETI@home dose today. Since Arecibo is looking at recording at some patch of sky, we can use it too. No need to build a new dedicated t/scope or even fight for time on existing one.

Same could be done here, since you are looking there anyway, might as well check for this too.
Birthmark
3 / 5 (5) Nov 03, 2011
If this planet is 100 light year away, it means that with these lights, we're still looking 100 years in the past, they could have killed themselves or nearly trying to reach stage I civilization. It would be cool though, and it is an interesting approach.
kaasinees
1 / 5 (3) Nov 03, 2011
Theres no way to reach them. We have many issues to solve, yet we create more like these.
ubavontuba
1.5 / 5 (8) Nov 04, 2011
Gee, if we're going to look for city lights on the night-side, why don't we also look for the glint of sunlight reflecting off shiny surfaces as well?

Seriously, every time the sun rises against a shiny building, a moving beam of light is angularly reflected into space (think: searchlight). All we have to do is look for the flashes as the beams angle toward us.

Sternenfisch
1 / 5 (3) Nov 04, 2011
Well, what if those civilizations are consisting of violently expanding, somewhat intelligent fungi, or geometrically spreading crystals? Only a monkey-man civilization needs light in the spectrum we deem visible. Were we more of an eagle-civilization, we would rely on the infrared spectrum. Something that should be accounted for when looking for light signals.
Grizzled
2.3 / 5 (3) Nov 04, 2011
Gee, if we're going to look for city lights on the night-side, why don't we also look for the glint of sunlight reflecting off shiny surfaces as well?

Seriously,

You must be joking, right?

I'm too lazy to search for the link now but there was ALREADY news that they have detected exactly that - a gleam of starlight reflected from some liquid surface.

Granted, the planet wad quite a bit larger than Earth and the liquid was more suitable for the moons of Saturn (hydrocarbons), but the idea was tested and found working.
Grizzled
3 / 5 (6) Nov 04, 2011
Theres no way to reach them.

Hmmm, what if for hundreds or thousands years now they've been broadcasting the message: "You lazy sods, THIS is how you do FTL communications. Now switch channels and we'll talk".
Grizzled
2.3 / 5 (6) Nov 04, 2011
Another possibility in the same vein belongs (I think, if I remember right) to Arthur Clark who discussed the same possibility.

Imagine yourself as a late 19th to early 20th century radio enthusiast who somehow managed to pick up and decode a mesage sent aeons ago from a galaxy far, far away :-) What could be wrong with that?

Well, what if it goes like that: ... Ok kids, now that you've got enriched U235...
Vendicar_Decarian
4 / 5 (8) Nov 04, 2011
Once the catalog of potentially habitable planets is large enough, there will be pressure on the technological nations to launch an interferometer system most probably located at one of the Lagrangian points for the purpose of performing a reasonably detailed spectral analysis of the atmospheres of those planets.

Such a system will also allow for high resolution distance estimates based on simple and reliable parallax, as well a a precise measure of the planets size and shape.

Once the rough composition of the atmospheres of those planets are known those that can support intelligent life as we can imagine it will be targets of a range of other observations to find any additional evidence of life.

Those observations will necessarily include looking for the signatures of surface features that when identified will allow the rotational orientation and speed of the planet to be determined.

From this information and the measure of spectral line broadening the wind speed CONT...
Vendicar_Decarian
3.7 / 5 (9) Nov 04, 2011
the wind speed at various latitudes will be able to be determined.

Similarly by looking at variance in brightness of the daylit surface as the planet rotates, the rough shape of continents and oceans will be able to be computed, and on the dark side, the location and shape of bright areas - probably cities - will be able to be determined.

All of these observations will be possible with a high resolution orbiting interferometer.

As to cities, I doubt if any will be found using this technique for the machine inhabitence of the planet will not need street lights.
antialias_physorg
4.5 / 5 (8) Nov 04, 2011
It's pretty unlikely that we'll see city lights on other planets.

1) Given our own history: Having city lights at all is just a miniscule fraction of time in the planet's life-bearing existence (a few hundred years vs. several billion years). Catching that timeslice is unlikely in the extreme.

2) Citylights are only evident in (above-ground) civilizations that:
a) Waste energy (expect city lights that are visible from space to be a thing of the past a hundred years from now)
b) have not begun to alter themselves biologically or technologically so that they aren't dependent on exterior light sources. Imagine if we bio-engineered ourselves to see infrared light. We wouldn't need any light sources ever again. Adding an IR receptor to our makeup - or modifying an existing one to be sensitive to IR - isn't much of a SciFi stretch.
Nor would be having a cheap implant in the eye that transforms IR radiation into visible light for the retina to interpret.
mauro48it
2 / 5 (1) Nov 04, 2011
At a minimum should occur if the incoming light has a residual modulation, much of the artificial lights on earth in this historical period have a residual modulation at 50, 60Hz or harmonics derived from the mains power or higher frequencies with special power.
These signals may be able to overcome the background noise.
Royale
1 / 5 (1) Nov 04, 2011
That's a cool thing you bring up anti. I wonder what it would 'look' like getting IR signals as well as visible light. Would the heat glow? Would colors near heat sources change? Would we be able to see new 'colors'?
Because remember IR monitors convert to B&W or visible color, but that's not necessarily what they'd 'look' like.
It would be probably be a few generations after the proposed genetic modifications before people could see both without disrupting brain functions to some extent...
Really neat idea though; something fun to think about...
antialias_physorg
4 / 5 (4) Nov 04, 2011
I wonder what it would 'look' like getting IR signals as well as visible light.

The brain knows nothing about fixed color ranges (when you and I talk about the 'blue' sky our internal representation of what 'blue' looks like may be entirely different - only the mapping of our representations to the common concept 'blue' is the same by convention and learning). I thik the brain - at least of a newborn child - would not need any adaptation at all to interpreting sensory information comprised of an artificially enhanced spectrum.

Just like hearing: Some hear sounds that are higher or lower than others. Do they therefore need special skills to hear ultra/infrasound? No.
Some already percieve a little bit further into the ultraviolet or infrared than others (noticing hues in indigo or deep reds/blacks that others don't). That range would simply be extended a bit further.

IR or UV are just names. There's no hard, qualitative difference to 'visible light'.
Royale
not rated yet Nov 04, 2011
Gotcha.
I know exactly what you mean, as I'm able to see the hertz in florescent lights 'flicker' when others cannot.
So do you think an individuals perception of 'colors' would extend alongside the added IR receptors? Or do you think it would be more benign like hue extensions to that individual?
antialias_physorg
3.7 / 5 (3) Nov 04, 2011
I'm not sure. Since I have only my own perceptional impressions to compare to I really don't know how an augmented spectrum would map in the brain of one accustomed to another spectrum.

Let me get back to you once I get that chip implanted in my eye...

But seriously: best to ask someone who has had the exprience (e.g. people deaf or blind from birth who have received a cohlea/retina implant). I'd imagine it would be smoething like that.
Rdavid
not rated yet Nov 04, 2011
A planet with two or more suns might not experience darkness and thus would have no need to create light.
Grizzled
1 / 5 (1) Nov 04, 2011
Good idea. I also think that nuclear explosions would be easy to detect, as long as you happen to look at exactly the right moment.

...and a full-out nuclear war would be even easier to spot. So, if you happen to look at exactly the right moment, you might know that there -used to be- a civilisation there.
Osiris1
1 / 5 (3) Nov 05, 2011
Our governments are waayyy ahead of you. They are 'mandating' the use of yellow and orange varicolor lights for city lights now so that our cities would take on the appearance of being lit by firelite. They KNOW somebody IS out there and are afraid. Trouble is all the years of white light are still traveling outward spherically from our planet before we made the change a couple of years ago. Other questions may be: Who told us to do it?; If not, What did we discover out in deep space..maybe with that 'secret' observatory on a mountaintop in Mexico that is pointed to deep space?; and ...Are we now working with any neighbors or 'new found friends' in our local group that may have a 'snit' with some 'other' more distant sentients? Do not for a minute, nay not for a second, think that we are 'unique'. God has many children among the stars....all His creations in whatever degree.
Isaacsname
3 / 5 (2) Nov 05, 2011
Gotcha.
I know exactly what you mean, as I'm able to see the hertz in florescent lights 'flicker' when others cannot.
So do you think an individuals perception of 'colors' would extend alongside the added IR receptors? Or do you think it would be more benign like hue extensions to that individual?


I would think custom contact lenses with polarizable lenses will be available in the next 10-20 years. As long as they convey/convert images to colors the eye can still tell the difference between, ( opponent-color process ) It wouldn't matter, right ? We could potentially have an infinite range of types of vision, especially with all these high-falootin' metamaterials that are going to be popping up..
KapeKelly
1 / 5 (4) Nov 05, 2011
shucks, guys: we already have been doing this with our own moon, detecting the luminosities for over 400 yeras when they were first documented and observed by our worlds' best astronomers yet our own governments lie to us. Of course it is likely that nearly every planet in our solar system, including our own moon has advance life forms and beings living on it. Mars is the most likely after our moon, with many subterranean dwellings. Obama won't go back to the moon and scrubbed all efforts to that end because he KNOWS the MOON is occupied already. It's a satellite, and our country nuked it. Gee we are rotten neighbors and should be annihilated from existence. We are bullies and thugs if judged by our leaders actions. Perhaps it is our leaders who should be annihilated.
antialias_physorg
3 / 5 (2) Nov 05, 2011
They are 'mandating' the use of yellow and orange varicolor lights for city lights now so that our cities would take on the appearance of being lit by firelite.

You are aware that fire burns at different colors depending on the chemical mix in the subtance being burned and the atmosphere involved? even if the theory weren't top-level loony: no color choice would disguise anything as it's not the color of lights but the patterns that would be the give-away.
hush1
1 / 5 (1) Nov 05, 2011
I really don't know how an augmented spectrum would map in the brain of one accustomed to another spectrum. - AP


If you had these color (for UV/IR) eye receptors at birth, your brain and mind organizes these same way as visible light.

Red is red. Blue is blue. For everybody. The senses are 'standardized'. The resolution for the senses are 'standardized' as well. The 'differences' for red, blue, and all other impressions of the senses comes from the unique 'mappings' all input undergoes upon reaching the unique neuronal pathways in the brain. Not only is everyone's pathways different, if theoretical possible, two people possessing an identical pathway is no guarantee that the two identical pathways can ever experience the same identical input at the same time and place.

This is why 'adaptive optics and sound' find acceptance - we want to experience difference planets first with and from the perspectives are own senses has adapted to here on earth.
Grizzled
5 / 5 (1) Nov 05, 2011
as it's not the color of lights but the patterns that would be the give-away.

Actually, the color could be a give-away too. Not all spectra are created equal. If you look at the dark side of an Earth-like world and see a signficant number of Volt Arc flares (for ex.) you would be justified in wondering what's going on even if those flares don't form a clear pattern.
hush1
3 / 5 (4) Nov 05, 2011
What is the purpose of justifying wonder? Or curiosity?
Au-Pu
1.7 / 5 (6) Nov 06, 2011
This assumes that other civilisations would also use radiant light sources.
Quite an assumption.
Arrogant as well, assuming that other life forms must follow our course and have the same needs and solutions.
But it is worth a try, though I would't be holding my breath in anticipation.
MSRGeekGirl
5 / 5 (3) Nov 07, 2011
There's nothing arrogant about starting a search based on factors we know are in use by an advancing intelligent civilization: Us!

In our search for intelligent life in the Universe, *we* count as an example of what we're looking for. There's no question that intelligent life exists. We're here! We know it happened once, and in the vastness of Space and Time we may very well find evidence of other civilizations, either living or dead.

In starting any search though, it helps to have some idea of what to look for. Since we have concrete examples of the kinds of energies and signals that an intelligent civilization puts out, those are very sound points from which to begin looking. As we search, we may find other examples of those signals, or we may stumble across telltales that we've never even thought of. Anything we find out there expands our search string, so to speak, and improves the chances of locating someone else out there in the dark.
antialias_physorg
2.2 / 5 (6) Nov 07, 2011
There's nothing arrogant about starting a search based on factors we know are in use by an advancing intelligent civilization: Us!

Until we find out who or what else is out there I'd be very careful on the use of the word 'advanced' in that sentence.

That we should search for ET is certainly a good idea (it always pays to be aware of your environment - either for further knowledge or simply to be on the safe side).

But the search for 'city lights' is as misguided as the search for extraterrestrial signals using radio waves. Neither takes into account that what we call 'the height of development' is not the end point by a long shot (nor does it take into account the realities of space and the variabilities of objects therein).

That we have an example (us) does not mean every other speciemen will conform to our mould - given different environments (which we can be certain of) we should expect quite the opposite.
Guy_Underbridge
1.8 / 5 (6) Nov 07, 2011
There's nothing arrogant about starting a search based on factors we know are in use by an advancing intelligent civilization: Us!


Got to agree with AP.. 'Advanced' is a pretty relative term, and 'intellegent' is awfully generous when referring to 'Us'.
Guy_Underbridge
1 / 5 (1) Nov 07, 2011
As with other SETI methods, they rely on the assumption that aliens would use Earth-like technologies.


In other words, let's not just look for unicorns, but let's look for flying, blue unicorns named Gertrude.
thematrix606
1 / 5 (2) Nov 08, 2011
Question: how long have we had light we can spot from space? 100 years or less? How long before we no longer need it? I.e. have implants in eyes which just adjust the brightness wherever you go. 100 years or less? Around there I suppose, probably much less.

Why must we always assume that any civilization will either use light, or radio frequency, or any other technology we use?

Even if they had used it for a 100 years, how hard would it be to detect that looking at the age of the universe x the amount of planets to check?
antialias_physorg
1 / 5 (2) Nov 08, 2011
Even if they had used it for a 100 years, how hard would it be to detect

Signals we have inadvertently been sending out (TV broadcasts and whatnot) are not detectable, even with theoreticaly optimal receivers that can detect and amplify individual photons, beyond 2 light years out.

So unless someone is pointing a really bright beacon straight at us for a really long time - we'll not detect anything by simply listening.
(we're talking in the range of the power output of a small sun. And why would they single out Earth? )

If we follow the argument that others are like us then it could also very well be that everybody is listening and no one is sending.
After all: listening is a lot easier and safer. If you start sending you never know who might catch the signal and how they will react to it.
Oysteroid
2.2 / 5 (10) Nov 08, 2011
e
This is reasonable because any intelligent life that evolved in the light from its nearest star is likely to have artificial illumination that switches on during the hours of darkness.

Is this so reasonable? Life can evolve in the deep (sea or underground) where illumination is not an issue but other senses come into play (magnetic/electric fields, infrared, sound, ... ). civilizations derived from such ancestors may not go for city lighting (or above-ground living) at all.


Life sure can evolve in such places but civilisation? Not in our sense of the word. Deep sea dwellers (just for starters) will have great dfficulty inventing open fire even. Without it, it's hard to imagine them building civilisation like ours.

If they got something completely different, different enough to not even use fire...well, we probably won't recognise it even if we met it face to face.

Same for your other objections - yes, of course, some civs could be harder to spot than others.
Oysteroid
2.1 / 5 (11) Nov 08, 2011
Cont.: But, if you accept the premise that both life and intelligence are more or less common throughout the Universe, it stands to reason that at least some would follow the same or similar path.

That's the ones they are looking for with that project.
sstritt
1 / 5 (1) Nov 09, 2011
At a minimum should occur if the incoming light has a residual modulation, much of the artificial lights on earth in this historical period have a residual modulation at 50, 60Hz or harmonics derived from the mains power or higher frequencies with special power.
These signals may be able to overcome the background noise.

This would only be detectable if all the lights on the planet were in sync- ie on the same power grid, assuming they have something like a grid. It does seem to me though, that deliberately syncing the light output of the planet would allow another way of transmitting a message!
Seeker2
1 / 5 (1) Dec 05, 2011
What is the purpose of justifying wonder? Or curiosity?

or purpose?
Seeker2
1 / 5 (1) Dec 05, 2011
MSRGeekGirl: ...There's no question that intelligent life exists.

Well ok.
Seeker2
1 / 5 (1) Dec 05, 2011
There being, I would say, a difference between intelligence and thinking power.

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