A couple of months ago, sky-watchers around the world got pretty darn excited when news broke about a mysterious radio signal that seemed to be emanating from a star called HD 164595.
HD 164595 is located some 94 light-years away from Earth, and that epic distance – together with the unexplained nature of the transmission – had people thinking: if this were contact from an alien civilisation, they'd need to have some pretty powerful technology to send a signal all that way.
The anomaly was later explained as a terrestrial disturbance caused by a Soviet satellite (bummer!), but what if it had been an alien signal? How advanced would they have to be to achieve such a feat?
As the video above from the Wall Street Journal explains, the most popular frame of reference for considering such a question is what's called the Kardashev scale, proposed by Soviet astrophysicist Nikolai Kardashev in 1964.
The scale, which is totally hypothetical, is useful because it gives us three different stages of progress – called Type I, Type II, and Type III civilisations – that measure how technologically advanced a society is.
This in turn affects how far they'd be able to send a transmission into space, if any aliens wanted to get in touch and say hi, for example.
That's because we're not yet technologically capable of harnessing all the potential energy generated by our own planet – reaping every last watt out of solar, thermal, volcanic, tectonic, and oceanic energy. We might be getting closer all the time, but we're not a Type I yet.
In fact, our energy production would need to be 100,000 times more powerful than Earth's current state for us to be a Type I.
With that kind of awesome capability, an advanced alien civilisation on a planet orbiting HD 164595 would be able to harness more than 1 trillion watts, to send a transmission at us across space.
Stepping things up a notch, a Type II civilisation would be even more powerful, having learned to not only harness the power of its planet, but also controlling the energy of its host star.
To do that, you'd need to build what's called a Dyson Sphere – a machine megastructure that encircles a star and somehow manages to captures all of its solar energy.
With that awesome amount of power, a hypothetical Type II civilisation on HD 164595 would be able to transmit a more powerful signal, simultaneously broadcasting in every direction from its planet – having harnessed something like 100 billion billion watts of power from its sci-fi solar panels.
But even that far-out prospect pales into comparison with the fearsome power capabilities of a Type III civilisation.
Here, our alien pals have managed to co-opt all the energy of their entire galaxy. Basically, we're talking installing Dyson Spheres on every star – which, in the case of the Milky Way, would mean an awful lot of solar panels.
What comes next? Well, Kardashev himself only listed three types of civilisations on his original scale, but that doesn't mean that scientists haven't dreamed up even more powerful hypothetical societies since the 1960s.
We'll let the video above explain more about those… but suffice to say, there comes a point when a civilisation would be so advanced, it's not a question of "Would they have the power to contact us?" so much as "Why would they even bother?"