Whats the difference between the strong and weak anthropic principle?


I read about it but i really don’t get it.

In: 1

I don’t think there are really universally agreed definitions – different authors have used these terms to mean slightly different things.

The anthropic principle is generally the idea that we shouldn’t be surprised if conditions in the universe – or at least our corner of it – seem especially suited for life, because if they weren’t suited for life then we wouldn’t be here to observe them.

The “strongest” versions of this argument say that universal physical constants were somehow constrained to take on certain values in order to make our existence possible. The “weakest” versions just say that we’re more likely to be in a part of the universe that is especially suited to life than one that is especially hostile to life.

Most people would agree with some weak form of the argument, but the stronger forms are more controversial. There are certain properties of the universe that seem like they are in a sweet spot that allows for complex structures (solar systems, chemicals, etc.) to develop, allowing for life. But it’s a bit hard to be completely sure what would have happened if the universe was a bit different, and we also have no way of knowing whether it *could* have been different or if there is some fundamental reason why it has to be the way it is.

Weak: we only think that the universe is fine tuned because it’s the one we are in; if the variables were different we wouldn’t exist to be questioning it. The universe is the way it is because if it wasn’t you wouldn’t exist to ask this.

Strong: the universe appears fine tuned because that tuning in some way promotes life capable of questioning it. You exist to ask this because the universe is the way it is.

The strong anthropic principle states that the universe must have the conditions necessary for life to exist, while the weak anthropic principle states that the universe is the way it is because we exist to observe it.