By its nature, antimatter is a tricky substance.
After all, whenever it comes into contact with normal matter the two mutually annihilate
and release massive amounts of energy.
Obviously, that property of antimatter is attractive to anyone wishing to generate power,
and that's led to much speculation in science fiction about the possibility of antimatter
drives.
There are a number of hypothetical ways to do this.
One is the anti-matter rocket, of which there are numerous theoretical designs for and would
work in principle.
And there are some concepts that are just pure science fiction, such as those featured
in the warp cores of Star Trek.
The viability questions of any of those ideas aside, they all share a fundamental problem,
that of creating sufficient quantities of anti-matter for realistic usage.
Whether that can be done is an open question.
We really don't know how practical using antimatter will be in the far future.
All we do know right now is that it's really difficult to manufacture, for us.
But maybe not for someone more advanced.
And there are also natural sources of antimatter, such as positrons, which opens up the possibility
for mining.
I admit that positron mining is a speculative stretch, but if you could figure out a way
to magnetically capture and contain positrons there is a massive natural spraying fountain
of the things near the center of the milky way, thought to be related to giant star formation,
though no one knows for sure.
For whatever reason the anti-matter fountain seems to currently be an obscure area of astronomy
since little has come out about it since the Compton Gamma Ray observatory discovered it
back in the 90's.
See my video in the end screen on this galactic anti-matter fountain and an article linked
below for more on the subject.
The point is, it may well be possible that advanced alien civilizations are already employing
antimatter propulsion in the galaxy, and if they are, the natural question to ask is can
we detect evidence of that from a distance?
Can anti-matter propulsion be a technosignature?
This gets into a tricky question within SETI.
The tendency is to assume that whatever you might detect in space, say it's a radio beacon,
would probably need to use massive amounts of energy.
This tends to skew things towards planets and star systems, where natural energy sources
are readily available, such as a star, so we look in those places predominantly.
This has more to do with our understanding of ourselves and how we do things rather than
alien civilizations, since we don't really know what those look like yet, we can only
speculate.
As a result, some energy sources such as black holes and neutron stars aren't well studied
for their potential uses that aliens might employ.
Yet they are obvious sources of energy.
But what of ships using anti-matter?
Would they produce characteristic emissions?
Such a thing might be located anywhere in the galaxy, even in the depths of deep space.
But what would you look for?
One possible technosignature related to anti-matter propulsion was put forth in a paper by Michael
Harris in 2002, link below.
He points out that anti-protons are rare in nature, we see them with cosmic rays created
at very high energies, i.e. hot anti-protons, but any "cool" ones created during the big
bang have probably long ago annihilated when coming into contact with normal matter.
At the same time, they can be created artificially in our labs, opening up the possibility of
an advanced civilization manufacturing them and using them for energy.
As a result, the annihilation of anti-protons should produce a characteristic gamma ray
signature that we should be able to detect and identify, and more if it is a spacecraft
moving at high speed it would exhibit doppler shifts that would be inexplicable without
an alien origin.
So if we did see that signature, it would either mean there's some crazy new physics
creating it that we don't understand, or perhaps more likely we've found evidence of an alien
civilization.
Harris details in the paper that he used data taken by an instrument on the Compton Gamma
Ray Observatory to search for just such a signature.
He admits that the equipment wasn't likely to find much unless it was close and that
future equipment would be better suited for looking for looking at a distance.
So, he found nothing, except one exception.
Now this is a case where the universe loves to play tricks and confound.
The source was a quasar, QSO 2206+650, as if quasars in general weren't mysterious enough.
The author notes that there were issues with the detection, and I have to add here that
quasars are extremely distant and when that light left there likely had not been enough
time elapsed in the universe for life to arise, and that all made the quasar a poor SETI candidate,
but a mystery nonetheless.
But there was one more strange thing, the author notes that the variable light curve
he expected to be produced by an alien ship's proton-anti-proton annihilation process was
present with the quasar.
It's very unlikely that is what that was, but it's one of those things that just makes
you scratch your head and go huh!
Thanks for listening!
I am futurist and science fiction author John Michael Godier and be sure to check out my
new book Supermind available in both e-book and paperback on Amazon 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.