This week, I wanted to talk about Kardashev (1964) because I naturally started doing a lot of follow-up as I read. The famous idea that was first proposed in this paper was the classification of civilizations by the amount of energy they consume, as summarized below:
Type I: Earth-level, consuming 4 * 10^19 erg/s
Type II: Full-star usage (a la Dyson spheres), consuming 4 * 10^33 erg/s
Type III: Full-galaxy usage, consuming 4 * 10^44 erg/s
I had three questions that popped up over the course of reading the paper.
- Has the definition of Type I always been the same over time?
- Did we keep up with Kardashev’s energy growth rate predictions?
- Whatever became of CTA-21 and CTA-102?
I’ll tackle these one at a time.
- In my memory, when I’ve heard about the Kardashev scale before, humanity was said to be at a Kardashev 0.7 or so, which is a pretty long way from a Kardashev I (because the scale is not linear). The argument that I read (I believe in the book Physics of the Impossible by Michio Kaku*) is that a Kardashev I civilization uses an amount of energy equal to the amount of starlight falling on the planet’s surface. A quick glance at the Wikipedia page confirms that interpretation. But, as I mentioned above, Kardashev defined it as being the amount of power that Earth was using in 1964, at the time the paper was written. So when did the flip in definition happen? Turns out this shift was the fault of the ever-present Carl Sagan. His standardization of the scale with a logarithmic power formula allows values other than I, II, and III and allows a more generalizable formulation (versus Kardavshev’s Earth-centric standards). It’s amazing to me that a redefinition happening a decade after the original paper has caught hold so strongly.
- Since it has been over 50 years since this paper was written, I was curious to see if we had kept up to Kardashev’s proposed growth rate of 3-4% a year, starting at 4 * 10^19 erg/s. After a long 10 minutes of trying to figure out why my simple exponential growth rate equations were wrong (ergs/second not ergs/year, past-Me), I got an answer of ~6.5 * 10^27 to ~1.3 * 10^28 erg using his values (using 3% and 4% growth respectively). The actual current value is 3.9 * 10^27 erg, so while Kardashev’s predictions were optimistic by a factor of 2-3, they weren’t really that far off. That’s honestly pretty impressive, at least to me (perhaps an economist would say that this is an easy problem, but it isn’t quite intuitive to me). Will it continue at this rate, or will we level off in some logistic-like function? That’s the question, isn’t it? But at least so far, we’re on track with Kardashev’s prediction.
- After some research on CTA-21 and CTA-102, it looks like (predictably) they were both false alarms. CTA-102, according to a quick Wikipedia, is identified as a very-variable quasar with extremely luminous “blazar states”. This is a great example of how objects of interest to SETI (at least in the context of artifact SETI) are going to invariably be interesting to the rest of astronomy, and should be valued for that reason. Meanwhile, both objects had an entire article in the NYT written on them by none other than Isaac Asimov. A quick scan on Google Scholar suggests that it too is just a quasar, though a less extreme example than CTA-102.
*This book was my “eureka” moment about wanting to be a physicist/astronomer. I picked it up on a whim when my seventh grade book club got to go to the local book store for a mini-field trip. After finishing it, I decided that I wanted to go into physics, and I haven’t looked back since.