5 reasons why we can actually have a “physics of people”🟢

As you may already know, I am a researcher in a field which goes under many different names: sociophysics, social simulations, computational social science, etc. These are actually just different ways to say that “we want to study social systems in a similar fashion to physics.

However, several people react to these studies as they were something silly. After all, “how could you study people when people are so complex and unpredictable? People are not as simple as inert matter!

In this post, we will see why this approach it actually makes sense to work for a “physics of people”. Specifically, we will show things such as:

  • If you think the physical systems are simple and predictable, you clearly don’t know physics.
  • Definitely we won’t be able to predict everything (also physics is not able to do that) but this doesn’t mean we won’t be able to make some big progress.
  • We already have at least a couple of “physics of people,” so I it is totally possible to make it.


(1) You cannot predict everything

During a conference, I have seen a person showing some pretty interesting results on simulating and predicting how people walk in a train station. These types of studies can be used for many things. For example, to design paths in such a way that a running person will not bump into other people stopping the flow. Also, similar studies have been used to design more efficient emergency exits, thus avoiding people clogging the path and getting stuck (and so, losing their lives…)

However, at the end of the presentation, a person asked “can your model predict what will happen if a person in the crowd has a heart attack? How will the rest of the crowd react?” Since the answer was a “no, I cannot do that” the person who asked the question started speaking about how these models were limited and so, of no practical use.

Let’s apply this to physics!

To understand if this argumentation is correct, let’s try to apply it to the world of physics. Let’s suppose we are in the early years of 1700 and that a young philosopher has just discovered that she can predict the trajectory of a stone after it has been thrown (given its initial position and speed).

Now, let’s ask the young philosopher: “can you still make your predictions if a bird catches the stone mid-air? Or what happens if someone else throws another rock which hits our rock during the trajectory? Is your equation able to take all of this into account?”

Of course, the young philosopher cannot give a precise answer, therefore, we can conclude that this “mechanics” that she is blabbing about is going to be pretty much useless…

Back to the argument

What we just saw is that even physics cannot predict everything. Indeed, every kind of science always requires that the system will not have too many external disturbances.

Does this make these sciences useless? Well, we still managed to discover medicines to cure diseases, send a man to the moon, create amazing devices such as smartphones, etc. So I would say that even if a scientific field is limited, we can still use it to do some pretty amazing things.

(2) But people are so random…

… for example, if you ask someone how they feel, their answer may depend on their sentimental life, on the weather at that moment, or even on the food they eat at lunch that now is giving them a stomach ache!

This argument is true, but also misleading. For example, let me see if you can make some predictions even with very limited information. Where am I while writing this blog?

a) At my place, sitting in front of my PC

b) In the jungle, while walking to avoid mosquitos

c) In a volcano, because ninja tacos!

Option (c) may sound weird (or maybe I should say “random…”) but it is already showing us that maybe people are less random than what we may think.

Option (b) makes more sense, but we can still tell that it is a very uncommon option. Yes, it may happen, but the majority of people writing a blog would be in a situation similar to (a). Maybe just instead of being at their place, they may be in another place where they can sit quietly for some time (e.g. a train or a bar). However, even with no additional information, we can tell which situations are likely to happen and which, instead are not. If people were really random, we could not distinguish between option a, b or c.

Another funny thing is that I have seen this comment mostly coming from people working in psychology and sociology. But, if people were really random, then how could we have fields like these two? If people had no regularities to study, then what would be the purpose of these fields? Just saying that people are random? I hope not!

This tells us that yes, you cannot exactly predict or exactly guess people’s behaviour. But still, people have quite a lot of regularities that we can study and eventually use for modelling.

(3) Still, people are not that simple!

This argument comes often when someone takes a look at the models we are currently developing in fields such as agent-based modelling. In these models, people are massively simplified to follow some simple behavioural rules.

Is this wrong? Or maybe it is a good scientific approach?

Also physics simplifies a lot

Let’s get back to the example of predicting the trajectory of a stone. Do you know how people usually perform this calculation in physics? They approximate the stone as a point and the surrounding space as vacuum*. (we also have a good example of this approach from the Big Bang Theory!)

Probably some centuries ago people were complaining of this approximation saying: “how can you simplify stones that way? Each stone has a unique shape and it is made of different materials. This one, for example, contains tiny quartz fragments which make it so shiny and beautiful! Can you really simplify it as a point?”

Since now we have hundreds of years of experience with physics, we know that “being shiny” is an optical property, which (usually) has practically no effect on the trajectory. Similarly, now we know that subjective properties (such as the beauty of an object) are completely separate from physical properties.

However, it took humanity thousands of years to figure this out. For example, alchemy books included praying in the steps for obtaining the right chemical reaction. Indeed, they often connected the chemical processes to the processes of someone’s soul.

Before getting the conclusions to this point, let me introduce you to the next one:

(4) Humans systems are so entangled!

This means, for example, that something that I have seen when I was 5 years old, may have an impact on my current decisions now. Furthermore, my decisions will impact the mood of the person next to me, which will then impact their lifestyle, etc. However, in physics, everything is independent… right? Or maybe not…

Actually, I am sorry to inform you, that also in physics everything is quite untangled (and I am not even referring to quantum entanglement). For example, the stone we have just thrown is entangled to the Moon! Yes. Indeed, the Moon has a gravitational field, pulling everything towards itself.

In most cases, this force is so weak that we can neglect it. But, even if we neglect it, the rock is still entangled with the Moon (and the rest of the universe). We just know that this effect is so small, that including this in our model will increase the complexity, without adding much to the precision. However, this is not always the case.

To show this a little better, let’s suppose we are playing a game where we have to throw our stone beyond a certain distance (if you want to spice things up, suppose this is part of the Squid Game and your life depends on this throw). Unfortunately, our throw was a little too weak, and our stone is going to land 0.2 mm before the distance; thus making us lose. However, if the Moon was in the right position, it will pull our stone enough to land beyond the threshold distance.


All of this is to say that also in physics things are also complex and entangled. However, we studied physical systems so much, that we can distinguish between effects to take into account for each problem.

For example, if we are studying colors, we know we will have to rely mostly on optical properties. If we are studying water pipes, we will look for fluid dynamics. Finally, if we are sending a man to the moon, we will have to take into account quite a lot of effects!

Unfortunately, our knowledge of social system is still very primitive. For example, we really don’t know if publicly insulting anti-vaxxers will, in the long run, increase or decrease the number of people getting a vaccine shot.

We do not even know what would be the main factors in such a process. For example, would be the aggressivity of the insult play a major role? Or any type of insult will produce very similar effects? Does it matter if the insults come from experts, institutions or common people? We really don’t know!

I think the major problem we are facing now is not about the entanglement of the system (which happens also in every other discipline). I think the major problem is that we still did not accumulate enough knowledge and methods in the social sciences to be able to address similar problems.

(5) We already have two “physics of people”

Yes, it may sound weird, but we have not one, but even 2 different “physics of people.”

The first one is a bit unpractical, but it is based on the fact that people are actually made of physical matter. Therefore, our body and brain can be studied and predicted using just physics.

At the moment this sounds like an absurdly complicated task (simulating human behaviour via simulating our entire body), however, we already have some projects moving in this direction, such as the Blue Brain Project.

The second physics of people is actually even more famous and it goes under the name of “economics. Yes, actually we already have a field that, exactly like physics, use equations for modelling people’s behaviour (specifically on the exchange goods).

So, probably, saying that we will never have a physics of people is actually quite wrong.

In conclusion

We have shown that our “physics of people” will not allow us to predict everything. Indeed, this goal is not achievable even in the hard sciences. Instead, what we want to achieve, is to find conditions in which people have fairly regular behaviour and see what happens when this is perturbed.

Studying how people behave under stress may help us design better emergency exits or buildings that will protect more people in case of a terrorist attack. Knowing how people will react to new technologies will help us design better products and communication campaigns, without producing distrust in people. Figuring out how people communicate and argue, may help us in designign social media that will help us grow as a society, instead of considering us as two opposite groups in an ideological war.

To do this, we will not need only knowledge, but also the development of new tools. For example, advancements in physics have made possible both by physical tools (e.g. telescope, atomic-force microscope…) and by theoretical tools (integrals, differential equations, Fourier transform…).

Definitely, all of this would be extremely hard and complex. Also, it will require decades or even centuries to develop to maturity. However, I don’t think this is a good excuse to just sit back and stop moving towards a better future.

Want to know more about Agent-Based modelling?

Check out this video!


*As mentioned later, the amount of features taken into account depends on the situation and required precision. For example, air friction usually may be neglected when throwing a stone, but not when throwing a feather. Furthermore, if we really need high precision, we cannot neglect friction even in the case of the stone.