Interviewer: George Dvorsky of Gizmodo
Interviewee: Co-author Dr. Craig A. Tovey
Transcript:
We accidentally kept the videocamera running for an hour after the tower had been completely built. Not wanting to throw away this data, but not wanting to waste an hour staring at the same thing, we watched it at 10x speed. At that speed, the ant movement looked completely different. At real speed, you see a bunch of ants scurrying about in different directions on the surface of the tower of apparently stationary ants. At 10x, the ants on the surface move so fast they are a blur. Through the blur, you can see that the entire tower is slowly sinking. The ants in the tower are all holding on to each other. Those grips don't change but the whole thing is sinking. You know how you can see the motion of a waterfall through the mist of the water vapor around it? The blur of the surface ants was like that mist. The only difference is that the ants sink much slower than the water in a waterfall. Even at 10x the sinking is slow. It is impossible to see the sinking at regular speed.
We were led to it because we wanted incontrovertible evidence that the tower was sinking. We talked to an experts at Lawrence Livermore labs and other places. They told us that the technology did not exist to track individual particles in the interior of a three dimensional object, at the time and size scales of the ants, without killing the ants. But when we talked to the expert here at Tech, Physics professor Dan Goldman, he told us that a postdoctoral researcher in his laboratory had just developed novel technology that ought to work. She (Daria Monaenkova) worked with us to get the right amount of radioactive iodine that could be detected but took a long time (a couple of days) to be seriously toxic. Dan generously let Daria and us use his laboratory space and equipment. I should emphasize that this research was the first to use Daria's novel techniques. She is a co-author, of course. As an aside, just fyi, many professors in Goldman's position would have refused the use of their laboratory equipment.
You have asked two great questions.
Overall structure: The sinking is actually necessary to the overall structure! Remember, the ants are decentralized. There is no one in charge of the others. And they can't "see" the overall shape of the tower or what is happening outside their immediate vicinity. So, the ants at the top have no way of knowing that the tower building is complete. They keep trying to build it higher. But there aren't enough ants below to support a higher tower. A higher tower would force the individual ants below to bear too much weight. (That is why the more ants, the higher the tower they build). So the tower gets physically unstable. The ants at the bottom layer of the tower leave and the rest of the tower sinks to fill in the missing space.
The intent of the ants: We have to be careful not to anthropomorphize. How they behave is one question; why they behave that way is another. We biologists look for a reason an observed behavior would have been selected for as the organism evolved. I can offer some speculations, but nothing firm. It might be that ants in the tower get tired, and it is beneficial for them to take turns being on the surface rather than the interior. If so, the sinking behavior would be beneficial. I have observed, for example, fish who school in rivers, swimming upstream. They do what a team of bicycle riders do: they take turns being at the front of the school, taking the brunt of the current. Then the peel off and go to the back of the school. On the other hand, it might be that if the ants could somehow "know" that the tower had reached its maximum stable height, and they all stopped moving, that they would expend significantly less energy, which would be better for the colony. If the latter is true, we have to wonder why they "waste" energy. One possible explanation is that the ant raft is far more important to the survival of the ant colony than is the tower. The raft, after all, keeps the ants from drowning for a period of several weeks. Since, as we show in our paper, the individual ants behave the same way when building the tower as when building the raft, it could well be a good tradeoff from an evolutionary point of view to build a good energy-efficient raft and an inefficient tower than vice-versa.
We've just discovered this stuff, so there are no implemented real-world applications now. The most likely applications are for decentralized control of large numbers of small robots. Very little is known so far about how to get a fleet of robots to cluster together into a 3-dimensional structure. In search-and-rescue applications and in exploration applications, this can be necessary. If a fleet of robots in a collapsed building needs to travel upwards, they might have to form a tower if the surface is too steep for them to climb individually. Similarly, robots exploring irregular terrain may need to cluster 3-dimensionally to traverse obstacles. This study shows that very simple rules of individual movement can produce a useful structure.
The other reason we are excited about possible applications is that the ants are forming a structure quite different from the ant raft, despite their individual behaviors being consistent. This shows how a simple individual-level control program can produce very different group-level outcomes depending on the specifics of the environment.
It adds to the store of human knowledge. I wish the sentence above were a sufficient answer. Some elaboration:
1) The only thing that provably distinguishes humans from all other living organisms on our planet is our vast accumulation of knowledge, of information that is not transmitted genetically. Thus science is the most human activity of all.
2) No one can predict the impact a scientific discovery will ultimately have on technology, the economy, and society. Scientists are principally motivated by curiosity, not by potential societal impact. Yet without the unbridled curiosity of scientists, the technological luxuries people take for granted would not exist. When Faraday and Henry discovered electromagnetic inductance, they were not trying to bring lighting and electric-powered machinery to people around the globe. When Leeuwenhoek trained his lenses on a drop of water and discovered micro-organisms, he wasn't trying to save a billion lives from horrible diseases, nor did he know he had initiated a medical revolution. He was curious.
On a much, much smaller scale, I was involved in research on honey bee behavior that ultimately led to an improvement in web services. I did the honey bee foraging behavior research with colleagues about 27 years ago. About 15 years later, by pure serendipity, I and a doctoral student discovered that imitating the honey bee behavior made web-hosting services 5 to 25 percent more efficient. Last year we received a Golden Goose award for this work. I assure you that none of us, when we were studying the honey bee foraging, thought it was going to have significant impact on a tens-of-billions-of-dollars per year industry.
I am attaching a book review from Science, earlier this year, about the value of research.
Also, in case you are interested, here is a link to the Golden Goose awards.
https://www.goldengooseaward.org/awardees/honey-bee-algorithm