There are eight planets in the social system. They used to be nine. But in 2006, one of them ceased to be a planet. So now there’s only eight planets left. To truly understand what happened, we must understand the difference between physical reality and social reality. This case of the missing planet also happens to be a perfect example for explaining the difference between these layers of reality.

You see, humanity has had a lot of impact on planet Earth. We have built cities, roads and canals all over the place. Rearranged the biosphere and changed the climate. Our physical constructions, such as buildings, are also social constructions in many ways, being products of civilization. Thus, physical reality and social reality are intertwined.

While our impact on Earth has been great, we have made only minimal impact on The Moon and on the planet Mars. A flag here, a robot there. Some footprints and tracks. So far, we have had no impact at all on any other planet or similar. Not in this solar system, and not beyond the solar system either.

Thus, the fact that Pluto used to be a planet but isn’t a planet any more… it has nothing to do with humans affecting Pluto itself. It is not Pluto that has changed, only our perception of it. The thing is this: Those things we call “planets” are not socially constructed. Not only are they a part of physical reality, but they are a part that is too far out of our reach to interact with social reality at all. However, the very concept of “planet” is a social construction. All concepts are socially constructed. They are more or less arbitrary, and they are changing over time.

When astronomers made the distinction between planets and stars, only a few planets were known. These were the largest and closest planets, because these were the ones easiest for us to observe. Pluto was the by far smallest of the planets. Later on, asteroids were discovered, but Pluto was too big to be considered an asteroid. So it remained a planet. But then it was discovered that asteroids like Ceres was actually on the same kind of size as Pluto. A choice had to be made. A choice between constantly adding new planets to our vision of the solar system, while having a hard time drawing the line between planet and asteroid. Therefore, in 2006, a new category was created: Dwarf-planets! Pluto, Ceres and three others were exiled to this category. Thus the number of planets in the solar system was reduced to eight.

When this kind of choice is made, it is not a matter of right versus wrong. Pluto is not a planet. This is true by definition, because Pluto does not fit our definition of what a planet is. Pluto used to be a planet, and this was also true by definition. Because Pluto did fit the definition we used to have of what a planet is. The question is not whether the definitions are right or wrong, but to what extent they are reasonable.

Astronomers didn’t discover that Pluto is not a planet, they decided it. But they did make this decision based on the discoveries they made, and this decision was a very reasonable decision to make.

Back in 2006, one of my friends took the decision very badly. It brought her to despair, crying because Pluto wasn’t a planet anymore. Not that she cared about Pluto, her problem was that the universe didn’t make sense to her anymore. If we can’t even trust that the number of planets in our very solar system is correct, what can we trust? She didn’t understand that there was never a truth to trust or distrust. It wasn’t the planets that had changed. Only our conceptualization of them.

Categories and other concepts do not exist in physical reality. They are social constructs: They are things that we human beings make up as we go along. We create and reinforce our categories individually in internal realities, as well collectively in social realities. If we fail to understand that concepts exist only in our minds and in our cultures, we will not be able to understand ourselves and each other. Furthermore, we won’t be able to understand physical reality either.

The universe is vast, and it exists independently of us. It is not socially constructed. Our understanding of this universe, however, is always socially constructed. How tempting it is to believe that our minds and culture shapes the universe around us. To believe that is the universe that is a small part of us, rather than we who are a small part of the universe.

The truth, however is that human perceptions of reality are always limited and subjective. They can be better or worse, especially when it comes to understanding the universe as well as understanding ourselves and each other. While constructs are ultimately arbitrary, they are NOT all equally valid. Some constructs promotes prejudices or misperceptions, while others promote more valid understanding. What we need to do is to always strive towards better perspectives and more reasonable concepts. Not delude ourselves into thinking that our current perspectives and concepts hold ultimate truth.