What is emergence? What does “emergent” mean?

The word “emerging” is often used colloquially to mean something like “giving rise to” or “becoming apparent”. But emerging, emergent, and emergence are also technical terms. So, today I want to explain what physicists mean by emergence, which is also the way that the expression is often, but not always, used by philosophers.



Emergent broadly speaking refers to novel types of behavior in systems with many interacting constituents. A good example is the “La ola” wave that you sometimes see in the audience of sporting events. It’s not something you can do alone. It only becomes possible because of the interaction between people and their neighbors.

Indeed, something very similar happens in many condensed-matter systems, where the interactions between atomic constituents gives rise to certain types of collective behavior. These can be waves, like with la ola. The simplest example of this are sound waves. Sound waves are really just a simple, collective description for atoms in a gas that move periodically and so create a propagating mode.

But we know that in quantum mechanics waves are also particles and the other way round. This is why in condensed matter systems one can have “quasi-particles” which behave like particles – with quantum properties and wave-behavior and all that – but are actually a collective that moves together. Quasi-particles are emergent from the interactions of many fundamental particles.

And this is really the most relevant property of emergence. Something is emergent if it comes about from the collective behavior of many constituents of a system, be that people or atoms. If something is emergent, it does not even make sense to speak about it for individual elements of the system.

There are a lot of quantities in physics which are emergent. Think for example of conductivity. Conductivity is the ability of a system to transport currents from one end to another. It’s a property of materials. But it does not make sense to speak of the conductivity of a single electron. It’s the same for viscosity, elasticity, even something as seemingly simple as the color of a material. Color is not a property you find if you take apart a painting into elementary particles. It comes from the band structure of molecules. It’s an emergent property.

You will find that philosophers discuss two types of emergence, that is “strong emergence” and “weak emergence”. What I just talked about is “weak emergence”. Weak emergence means that the emergent property can be derived from the properties the system’s constituents and the interactions between the constituents. An electron or a quark may not have a conductivity, but in principle you can calculate how they form atoms, and molecules, and metals, and then the conductivity is a consequence of this.

In physics the only type of emergence we have is weak emergence. With strong emergence philosophers refer to the hypothetical possibility that a system with many constituents displays a novel behavior which cannot be derived from the properties and the interactions of the constituents. While this is logically possible, there is not a single known example for this in the real world.

The best analogy I can think of are photographic mosaics, that are photos made up of smaller photos. If I gave you all the individual photos and their properties you’d have no idea what the “emergent” picture will be. However, this example is hardly a natural phenomenon. To make a photographic mosaic, you start with the emergent image you want to get and then look for photos that will fit. In other words, the “strong emergence” which you have here works only thanks to an “intelligent designer” who had a masterplan.

The problem with strong emergence is not only that we have no scientific theory for it, it’s worse. Strong emergence is incompatible with what we already know about the laws of nature. That’s because if you think that strong emergence can really happen, then this necessarily implies that there will be objects in this world whose behavior is in conflict with the standard model of particle physics. If that wasn’t so, then really it wouldn’t be strong emergence.

A lot of people seem to think that consciousness or free will should be strongly emergent, but there is absolutely no reason to think that this is the case. For all we currently know, consciousness is weakly emergent, as any other collective phenomenon in large systems.