Tag: New Methods

Compared to the Cocconi and Morrison’s proposal to search for radio signals in the nearby stars. Dyson (1960) pointed out it was also useful to look at infrared signals at 10 microns radiated by his hypothesized Dyson sphere. He argued much more advanced civilizations would have built thin shells around their host stars to more efficiently harvest the energy of the host star.

He argued the Malthusian pressure would drive some of the advanced civilizations to build such a sphere to catch up with the exponential population growth. Additionally, he also argued that the such a sphere would have similar orbit size as the Earth and same temperature as well so that we could possibly detect it at the 10 microns which was also transparent to the Earth atmosphere.

I do not really understand how he concluded that the temperature of the sphere would be at the same temperature as the Earth. Would not the energy harvesting efficiency be much higher if the sphere was radiating at a much lower effective temperature. It seems to me that his conclusion about the temperature of the sphere came from our understanding of the Earth and it was 10 microns which was also transparent to the Earth atmosphere made him draw the conclusion that we should observe at 10 microns.

In the later reply letter, he clarified the idea of Dyson sphere to not being a solid sphere which was physically impossible to build but a swarm of objects traveling on independent orbits around their host star. He also admitted whether the alien civilizations obeyed the Malthusian principle or not was a question of taste. Finally, he argued that even if we did not find any aliens, the search for intense infrared signals could help us identify interesting astronomical objects.

In Dyson (1960), the beginnings of a new type of SETI is proposed that has significantly fewer behavioral and technological assumptions about ETI (Wright 2014). If ETI does exist and use a large amount of energy, they will likely be utilizing starlight as an easily accessible energy source and be indirectly converting it into IR radiation. The search for this IR radiation is proposed to complement the existing searches for communication.

Dyson argues that if exponential population and technology growth is sustained for a couple millennia, a civilization could use on the order of a Jupiter mass’s worth of material to construct a spherical shell around the Sun (using only 800 years worth of solar energy!). This is followed by the bold statement that “One should expect that, within a few thousand years of its entering the stage of industrial development, any intelligent species should be found occupying an artificial biosphere which completely surrounds its parent star.” Finally, he notes that the thermal emission of these shells will be in the IR range and that ground telescopes will be able to detect them through the atmosphere.

A popular idea that resulted from this paper was that of a Dyson sphere, a hypothetical megastructure that completely encloses a host star, capturing all of its energy. It is sometimes postulated that the sphere is not only used to capture energy, but to also serve as a space for habitation, where life can live on the inner surface of the sphere. If one was constructed with a radius of 1 AU around out Sun, there would be more livable space than half a billion Earths! There are several problems with this implementation, namely, there is no material we know of that could withstand thepressure imposed by the star’s gravity. Additionally, there would be no effective gravity imparted by the shell on anything in its interior, so there would be nothing holding anything to the interior surface and the shell could drift into the star over time.

The Dyson Sphere has remained a prevalent idea in popular culture to this day, with appearances in many forms of science fiction media (including the television show Star Trek: The Next Generation and the grand strategy videogame Stellaris)

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.

1. Has the definition of Type I always been the same over time?
2. Did we keep up with Kardashev’s energy growth rate predictions?
3. Whatever became of CTA-21 and CTA-102?

I’ll tackle these one at a time.

1. 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.
2. 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.
3. 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.

On November 16, 1974, the Arecibo radio telescope in Puerto Rico sent out a message to the stars (specifically those in M13, a cluster 25000ly away). This message, in binary, was the first emission from Earth with the intent of someone else receiving it. And here it is:

Isn’t that sexy? For those of you who can’t read binary and/or have no idea how to break this code (probably most everyone on this planet), the message is decoded into groups of 23 characters, leaving 73 groups. The authors explain that because these numbers are prime, this would clearly be the right way to interpret this. Personally, I would never get there. I wouldn’t think there to be any significance in the number of characters per line, or what have you. Once you know how many characters should go into each line, this looks a little bit more like something that could be interpreted:

This personally reminds me of Christmas sweaters, nonograms, or the early Atari games, but there is meaning to it. The first line indicates the numbers 1 through 10 in binary. Apparently the numbers 8, 9, and 10 are too large, so they are written differently? I’m not sure I really understand that even with a decent explanation from the authors, which makes me believe that anyone trying to decipher this would have an even more difficult time (I suppose they could just be remarkably more clever than I).

After these numbers, there is a “description of fundamental terrestrial biochemistry.” Although I can pretend to see the 1-10 numbers, I have no idea where they biochemistry stuff is (apparently lines 12-30). First comes the numbers 1, 6, 7, 8, and 15, indicated the elements H, C, N, O, and P. These elements are required for life as we know it (although some might argue the importance of other elements). After these numbers are chemical formulae of molecules or radicals (the paper doesn’t say which ones). Included in here are the structures of the molecules that make up DNA, in the structure of a double helix, and the number 4 billion to indicate the number of molecular pairs (adenine-thymine or guanine-cytosine) in DNA in a single chromosome.

Below all this is a representation of a human! We are bipedal with arms and a head. This comes with the number 14, indicated that the human is about 14 units tall. The units are (apparently obviously) the wavelength of the original transmission.

Below the human is a schematic of the solar system; the big blob is the Sun, then all nine [at the time] planets. The length of each bar is a semi- indication of the planetary size, and the third dot from the Sun is us! It is slightly placed out of plane, in an attempt to indicate that that planet is where humans reside. I would interpret it as the planet’s inclination, but that’s okay.

Below our solar system is a drawing of Arecibo. I would never guess this, but that’s what it is. This drawing is accompanied by the size of the telescope, my guess is with the hope that any response would take into consideration our limitations and make sure that we could actually hear them.

This message was put together by numerous people, and is quite creative to say the least. That being said, I am extremely doubtful that this message could be interpreted! For starters, the only way I could make heads or tales of it was from the picture directly, and that was after the whole 27-73 thing was implemented. But what if the receivers only caught part of the transmission? It took 169 seconds to send, so it is possible that only a minute or less would be received if the receiver was not pointed at Earth for the entirety of the message. With only part of the message, there is nothing to indicate where each line starts or how long it should be. In addition to all this, it would take a lot of brain power to decipher all of it. Sure, some of it could be understood without much time, but to get all of the message would take work and prior knowledge. This all assumes that whomever receives this thinks in a way similar to how we do, and what is to say that they way we think is normal? What’s to say that clearly it is logical that the first line is just numbers, and then straight from numbers we switch to chemistry?

I do wonder, assuming that the recipient of this deciphered it, what the odds are for misinterpretation, and what the consequences of this would be. It would certainly be amusing (to read about, not to experience), if the compounds were interpreted as a cry for help, and some lovely civilization prepared them all and brought them to us in quantities large enough for our population (4 billion at the time). What if they thought that each of our chromosomes needed these compounds for each of the 4 billion people? Imagine an entire fleet of interstellar (or intergalactic) ships coming to our rescue in 50,000 years with buckets and buckets full of thymine (I don’t think you can just store that in a bucket).

I also wonder if a group of humans could decipher this. If we just gave this message in binary (we could also just send it via radio, but I’m not sure that would be picked up) to a group of intelligent, multi-disciplinary people, would they be able to pull out all of this information? This seems like an important sanity check (to me) for any METI that we do end up sending out. If we humans can’t decipher our own messages, with the culture and knowledge that went into its making, then why would anyone else out there be able to decipher it?

With all this being said, I should note that the people who sent this message did not really expect it to be received or answered, that this was just a proof of concept of the current technological capabilities. So whether or not this message is received, understood, correctly interpreted, or responded to isn’t all that important.