The European: There is a famous movie scene in “The Matrix” where one character stares at data and can see the people behind the codes. How much does data tell you?
Leskovic: Oh, data tells you a lot. You just have to listen to it.

The European: You have looked at a lot of codified data in social networks. What has been the most surprising discovery?
Leskovic: Good question. On many occasions, when you go into data, you do it with some intuition. Most of the times you have to change this intuition because the data tells you that had a wrong metaphor in your mind. The surprising events, however, are when you find something and you get a bit scared, scared in the sense that you discover something very different from what the scientific community has been thinking so far. Then you ask yourself if you have a bug. On one occasion we found that when a network becomes bigger and bigger its degree of separation begins to shrink – you are connected to others through a smaller number of intermediate steps. You have a network that grows but a degree of separation that decreases. Isn’t it very counterintuitive to have an object that grows but gets smaller?

The European: So you generate answers by just looking at data?
Leskovic: Yes, in this case it was an empirical fact. It was unclear what was going on and then we found out by looking at it. We were scared at first but then discovered the background.

The European: From the viewpoint of philosophy of science, can you find out anything about the human being by only looking at data? Is the truth rooted in codes?
Leskovic: Isn’t this the whole premise of science and natural sciences in particular, this materialistic view? You want to observe and quantify phenomena. You goal is to identify new facts and their causes. The important thing is that you are able to repeat the thing.

I am not a philosopher but from an empirical point of view, the truth is the thing that always repeats itself. It is something that anyone can repeat over and over again and it always happens the same way. If you think of what we have on the web and social media, the truth is what people are saying. Think of crowdsourcing for instance. If you ask how good a restaurant is online and receive answers from the internet community, that is the truth.

The European: You explained how you are able to identify the most vulnerable spots of any given network. What is the political dimension of this observation?
Leskovic: Any kind of science can be used for the good or the bad. The same is true for networks and computer sciences. This is why the American Defense Department is so interested in our research.

The European: Does the American Defense Department fund your research?
Leskovic: Yes, they fund a lot. But their angle has changed. Until a few of years ago, they were interested in understanding terrorist networks. After 9/11 it was all about understanding their structures. It was about knowing where they are keeping nodes and connections, and how you can efficiently disrupt them. This is how they thought about it until recently – but when they talk about network research today, they want to understand population dynamics, How can we understand the uprisings in the Middle East? How can we facilitate the new social media? At least in the mindset of those funding agencies it went from “how do we destroy networks?” to “how do we know that the truth comes out?” People are able to organize themselves.

The European: You argue that a sufficient data set would enable us to predict forty percent of your Facebook friends. Isn’t human behavior somewhat more irrational?
Leskovic: Of course on certain occasions people are irrational. But in large populations the regularity of our behavior is huge.

If you think about your movement patterns or sleeping habits, all this has very well defined the periodicities. In networks there are lots of good signals for your behavior and preferences. If you are similar to people, you follow them. The more friends you have in common, the more likely you are to meet that person. There are various simple intuitions that allow you to make these statements. We are not predicting that you will meet a particular person at a friend’s party, maybe you already know him. We are only saying: for some reason, these are the likely links. You have to differentiate between correlation and causality.

The European: Imagine you lived twenty years ago and did not have any of this technology. What would you be doing?
Leskovic: I would still be using computation to solve interesting problems. This is what I am excited about. The most amazing machine that humanity built is the abstract computer where at the bottom it is just zeros and ones and at the top it is pure abstraction. We gave meaning to zeros and ones. Every use of modern computers builds upon this idea, it is fundamental for most things that we do today.

The European: Is there any special myth that you want to solve?
Leskovic: Yes, there is this one thing I would like know, although it is kind of silly. People say that bad news spread very quickly. I would like to measure why bad news spread so much faster.

The European: What is your intuition?
Leskovic: I don’t know. First we need to clearly define what we mean by bad news and speed. So it’s still a long way but I can see the horizon.

The interview was recorded at the DLD Conference 2012 as part of the media partnership between DLD and The European.