When people think of the scientific detection
of of evidence of alien life, a lot of people think of radio telescopes picking up signals
from huge beacons that pulse out prime numbers or some other unambiguous broadcast. And for a very long time, looking for that
was essentially the only game in town regarding the search for extraterrestrial intelligence. But recent improvements in technology have
opened up multiple new avenues for detecting alien life and civilizations independent of
radio, greatly improving our chances of actually picking something up. So here are ten ways we might potentially
detect alien life other than radio signals. Number 10. Altered Atmospheres It’s no secret that life dramatically affects
earth as a planet, from its geology to its atmospheric composition. But perhaps most markedly from a distance
is the oxygenation of the atmosphere through photosynthesis. Without the plants, our atmosphere would look
radically different, and we wouldn’t be here. But other gases being actively created by
life on this world also include methane, and, of course, carbon dioxide which you are exhaling
as you watch this video. This makes Earth’s atmosphere unusual. As we begin the detailed study of exoplanet
atmospheres as our instrumentation improves, it could be that we see a planet with a similarly
odd mix of gases. While natural processes can produce these
gases without life, when you see the right mix so to speak, such as with Earth, then
biology being the origin for that mix becomes the simplest explanation. But knowing what that life is really like
would be very difficult to determine other than perhaps being able to reasonably conclude
certain things, such as exoplant photosynthesis creating oxygen. But, there is also a chance that we might
see gases that are not likely to come from nature, but instead from technology. One of these are the CFC’s and if we detected
those in the spectrum of an exoplanet atmosphere, we would know there was a technological civilization
there, perhaps in the process of destroying their ozone layer. Also here is the possibility of an atmospheric
curve ball. We might also see exoplanets with very unlikely
atmospheric compositions suggesting that someone had terraformed those worlds and assembled
a custom atmosphere for whatever purpose they had in mind. Perhaps a machine civilization might get rid
of their old, reactive biological oxygen atmosphere entirely and replace it with an unnaturally
pure inert gas. Number Nine. City Lights Radio emissions aren’t the only type of
electromagnetic radiation that human civilization produces that alien scientists might see if
they were studying this planet looking for unambiguous signs of a civilization. Another would be our artificial lighting on
the night side of our world. With sufficiently sensitive equipment, our
city lights would stick out like a sore thumb in a spectrum as purely technological in nature. Likewise, it might be reasonable to expect
that aliens might also light up the dark sides of their world with similarly technological
lighting. This is not yet a feasible technosignature
for SETI to look for, our current instruments wouldn’t pick up earth’s lighting much
past our own Oort cloud, but future instruments might be able to perform such a search. One speculative variant however might be significantly
easier to spot. If an alien civilization decided to use the
light of their star to create daylight conditions on the dark side of their world using orbital
mirrors, that arrangement might currently be visible in a light curve as the planet
transits its star. Number 8. Alien Waste Heat One thing that’s thought to be likely for
any advancing civilization is that they will generate increasing amounts of heat as they
consume increasing amounts of energy. This is true of all alien technologies that
we can envision, whether it’s a Dyson swarm or an ecumenopolis planet. Waste heat thusly would be detectable to us
as infrared radiation. The problem with detecting these sorts of
emissions are that nature also produces lots and lots of infrared radiation. For example, young stars still surrounded
by protoplanetary disks radiate brightly in infrared as the material in orbit absorbs
solar energy and then reradiates it as heat. However, there are ways to distinguish natural
from artificially produced infrared, for example if one found a galaxy that emits lots of infrared,
but little or no visible light, then this would be a good indicator that a Kardashev
type III civilization has encased the galaxy’s stars inside Dyson spheres, if such a thing
is possible, and in fact searches for this have been made for this, though so far nothing
has been found. Number 7. Laser Emissions In addition to radio, SETI began some time
ago to look also for laser emissions emanating from star systems, known typically as optical
SETI. This makes sense, laser light is very recognizable
as technological in nature, and laser also happens to be really useful in communications. It’s also useful in things like space-based
propulsion, scientific measurement and may other areas. Once again, if we find this sort of thing
useful, a technological alien civilization might also, so it’s at least worthwhile
to search for evidence of alien laser communications. The problem with laser SETI however is that
it’s very directional meaning that the laser would have to be pointed at us, either intentionally
as a beacon, or accidentally as in a detection of alien internal communications, or leakage
from a light sail, or some other purpose that happens to be pulsed or emitted in such a
way that it can be detected and verified. You’d be right if you were to say that it’s
a long shot that we would detect intentional alien laser emissions. In order to point a laser at earth and start
sending pulsed communications the alien civilization would have to know that we’re here. They might do this if they suspected that
earth might be inhabited, and our atmospheric composition has given away life’s existence
here for some time, but it’s unlikely that anyone could know about our civilization much
further out than about 80 light-years, and even then, our own emissions to date would
be very hard to detect. In short, if they don’t know about us, they
probably wouldn’t put the energy into a laser beacon to contact us. But say they did. Just such a detection would be far less ambiguous
than what’s possible with radio. The reason for this is that radio is plagued
by two issues, one is the abundance of natural radio that lots of things in the universe
emit, if you turn a radio telescope towards space you will hear bizarre, difficult to
explain signals. But you can’t say they are of alien origin
unless they are absolutely unambiguous. All you can say is that you saw a weird signal,
as is the case for the Wow! signal. The other issue is our own radio interference
which complicates things further. We produce a ton of radio emissions and it’s
not always easy telling difference between a signal coming from afar, or one originating
from earth. With laser, these concerns are less of a problem. Number 6. Alien Artifacts This one is an outright trope within science
fiction. Over the decades many stories have been written
about humans finding some kind of alien artifact. These include Clarke and Kubrick’s monolith,
the various Prothean artifacts from Mass Effect, and my own personal favorite, the 20 million
year old ship frozen in the arctic ice from John W. Campbell’s novella “Who Goes There?”
the film adaptation of which was John Carpenter’s “The Thing”. But in reality, it actually is plausible that
at some point we may run into some kind of alien artifact in our solar system. This could take many forms, and in fact if
we did find one, it may not be what we expect. Instead of a monolith or Von Neumann probe,
it could simply come in the form of an asteroid that, at some point in the distant past, had
been mined by aliens passing through leaving it mysteriously exhausted of certain materials. Another might be an accidental artifact, perhaps
a dead probe sent out by aliens for scientific exploration that just happened to enter the
solar system just as some of our probes, such as Voyager II, might some day, millions of
years from now, pass through someone else’s star system long after they ceased their original
mission and stopped functioning. Another possibility is seeing artifacts from
a distance, perhaps the remains of a space-faring civilization might be detected through infra-red
emissions, such as a dyson swarm, but with no evidence that the civilization is still
active. And, of course, there’s always the possibility
of an intentional artifact, a kind of self-replicating or repairing Rosetta stone sent out by a civilization
wishing to announce its presence to others by planting physical messages in all star
systems in the galaxy that seem suitable to eventually develop life. Number Five. Satellites and Orbital Rainbow Telescopes These two concepts are relative newcomers
to the field of technosignatures. The first is that extensive geostationary
alien satellite networks might be visible in light-curves as they transit across the
face of their star. Satellites should be distinguishable from
natural ring systems by their overall geometry as satellites would form more of a belt rather
than a disc as natural ring systems typically do. The other possibility here is an orbital telescope. This one has not yet been well fleshed out
but the idea of such a thing was put forth by Marco Quadrelli and colleagues at JPL,
link below. Known as orbiting rainbows, the idea was to
create an extremely large telescope in space by using the optical properties of particulate
matter spread out over a large distance, much like droplets of water bend light to form
rainbows. While this is in itself an interesting idea
for us to do here on earth, a way to build true mega-telescopes straightforwardly, alien
telescopes could also be feasibly built and ,if so, such a structure might be visible
in the light-curves of stars with exoplanets, though it might ultimately prove to be difficult
to distinguish from ordinary dust. Number Four. Arnold Louvers Perhaps the biggest problem with announcing
your presence to the rest of the universe is that while there are many of the methods
for doing so, particularly radio, most would be very energy intensive, which is made particularly
unattractive when you have no idea if you’ll ever get a response to your signal. But what of more passive ways to announce
your existence? What of methods that are useful in more ways
than just saying hello? In 2005, astronomer Luc Arnold suggested in
a paper, link below, a way of sending a message simply by having an unnaturally shaped object
transit in front of a star. Any civilizations studying stellar astronomy
might then see the weird geometric dip in light caused the transit of a shaped solid
object, such as a set of louvers, that would not likely exist in nature. Then that civilization would know that what
they were seeing in the light curve was of alien origin. The beauty of this approach is that such a
megastructure in orbit of a star could be dual use, such as being both a visual beacon
to other civilizations but also a massive orbital habitat or energy collector. The aliens then could have their exocake and
eat it too. Number 3. Unlikely Movement One thing that can virtually be said for sure
is that the universe changes and presents situations where it might be advantageous,
or even critical, for a civilization to move their own planet, or even their own star. Hypothetical technologies to do this range
from gravitationally migrating planets using asteroid passes over very long periods of
time, something we may well do with earth long term to avoid the effects of the eventual
swelling of the sun into a red giant. Eventually, through this method very unnatural
looking star systems could be designed, or over millions of years of astronomical observation,
a planet might be spotted that is being migrated to a different orbit unnaturally. Or even a star might be seen moving. Enormous shkadov thrusters might be spotted
in light curves, where partial dyson spheres are built nearby to stars to allow them to
thrust themselves into different areas of the galaxy. Number Two. Star Tickling One of the biggest issues with radio SETI
is that if you really want to tell the universe in general that you exist you must essentially
beam out very powerful omnidirectional, or nearly so, signals for a very long period
of time to have any hope of success. In other words, it would be among the most
expensive things an alien civilization could do. But there is an alternative. There are objects in this universe that already
do all of the above and if you could tweak them into somehow behaving unnaturally, then
you’ve got yourself a more economical beacon. Of particular interest here are the variable
stars. The idea is that if you could bombard a cepheid
variable star with neutrinos, you might be able to make it pulse unnaturally, perhaps
pulsing out prime numbers or some other mathematical message that shouldn’t occur in nature. The beauty of this approach is that, while
fairly cheap to set up, it’s also fairly easy to spot. A lot of data has been taken by astronomers
on variable stars over the years, and much more will come, meaning that to search for
such signals one would merely need to look through data already being taken anyway for
variable star study. Number One. The Unknown Signal Ultimately, nothing says that we currently
possess the technology to even intercept an alien communication at all. Maybe they use none of the above methods,
and, simply put, we don’t know everything about the universe and essentially nothing
about advanced alien civilizations. We do not yet have a full understanding of
our universe and can only guess about the technologies it allows. Because of this, within SETI there are hypothetical
ideas of signals that highly advanced alien civilizations might produce that we can’t
intercept yet, such as using neutrinos or gravity to communicate, if that’s even possible. As a result, the galaxy could be teeming alien
communications that we simply do not have the science and tech yet to be able to receive,
and some day if we do come upon technologies like that we might just find that the universe
is indeed full of intelligent alien life, we merely just didn’t know how to see them. Thanks for listening! I am futurist and science fiction author John
Michael Godier currently reminding the interested that I’ll be on Open Space with Fraser Cain
over on his channel later today at 5 pm Pacific, 8 PM Eastern where we’ll take questions
and talk about space, science fiction, or whatever you want. Literally. I’ll talk about Exomusks, toast, or octopus
intelligence, or just about anything if prodded. See you there and be sure to check out my
books at your favorite online book retailer and subscribe to my channel for regular, in-depth
explorations into the interesting, weird and unknown aspects of this amazing universe in
which we live.
