It turns out that intentionally telling the universe that your civilization exists might
not be that easy.
You could set up radio beacons that repeat and send out mathematical signals at the hydrogen
line that would be unambiguous and tell anyone else that might be listening with a radio
telescope that they are not alone.
But to do it, you need energy and energy is expensive.
While this does not preclude any civilizations from setting up just such a beacon, we have
yet to detect one.
And if we take ourselves as an example, we've really only sent out a few signals, mostly
unintentional radar, that would be easily detectable at long distance and even then,
most of those did not repeat, missing SETI's main criteria for a verifiable signal.
Whether you agree or disagree with proactively trying to contact alien species, it's clear
that to do so in a meaningful, sustained way would be unlikely because it simply costs
to much to do it.
And, even if you do, it's a serious long shot.
But there are cheaper ways than radio.
If your intention is to merely tell others that there is indeed other intelligent life
in the universe one way to do that would be to simply suspend baffles in front of your
star that block the light in an unnatural way.
Just put up a geometric baffle, or a series of baffles that would appear to anyone looking
with a Kepler-type telescope as distinctive, regular dips in your star's light curve.
Now, Kepler never saw any such thing.
And even a potential candidate for this, the day 792 dip in the Boyajian's star's light
curve, does not quite fit the profile of what something like this would look like.
And, to add to that, there are engineering questions about building baffles that large,
whether it would be a monolithic object or an arranged cloud of smaller objects and given
that large structures, even very thin ones, require lots of matter to construct.
But what happens if you create something that blocks a star's light like a baffle for reasons
other than announcing yourself to the universe?
A new paper by Eric Gaidos of the University of Hawaii proposes just such a thing and a
method for detecting them, link in the description below.
Planets orbiting stars similar to our sun have a problem.
As stars like the sun age, they grow more luminous and become hotter.
That pushes the star's habitability zone further out and planets similar to earth experience
runaway greenhouse effects as their liquid water evaporates.
Water vapor is a good greenhouse gas, and the hotter it gets on that planet, the more
water will evaporate.
Water is a molecule of hydrogen and oxygen, and the radiation from the star will break
that molecule up and the hydrogen will escape the atmosphere entirely.
Eventually, that planet becomes uninhabitable and waterless.
This process, unless someone intervenes, is inevitable for our own planet.
A common misconception about earth is that it still has 4.5 billion years to live and
that life on earth is safe until then.
But that's not the case.
While the planet will remain for 4.5 billion more years, and might even survive longer
as a scorched cinder orbiting the sun in its red giant phase, life on it has far less time.
Climate science is highly complicated and that's led to a lot of estimates of just when
this process will begin for earth.
It could happen as soon as 600 million years from now, or take as long as 1.5 billion years.
But if we're still around in those days, there are several things we can do about the brightening
of the sun.
One of them is a surprisingly simple idea: block some of the sun's light with a baffle
to cool things down.
The paper details that any civilization in such a position and having built a starshade
should be detectable using our current equipment or at least the upcoming James Webb Space
Telescope as the planet and starshade pass in front of their star and block the light.
They might also use such a starshade to moderate their climate, or even reflect their star's
light to areas of the planet in darkness perhaps to improve agriculture if they have it or
something like it.
Baffles and starshades are interesting because they would be more easily detected than many
of the other signatures of alien life.
And, unlike other methods in SETI there is a higher chance of accidentally stumbling
across these during routine astronomy, such as what happened with Kepler and Boyajian's
star and its weirdness.
After this paper, we now know what to look for regarding starshades, so add their detection
to the growing list of ways we might soon detect an alien civilization.
Thanks for listening!
I am futurist and science fiction author John Michael Godier currently with a new book in
the works, it's called Supermind and a 5000 word excerpt is up at Amazon Kindle Scout
for only four more days, link in the description below, check it out and if you like it give
it a nomination!
And be sure to check out my other 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.