What is the anthropic principle?
In: Physics
It’s a certain type of answer for “why” questions about science and nature.
Imagine a very clever fish is asking “Why is my world made of water?”
One answer to that question is: “because if it weren’t, there would be no fishes to observe it and ask why.”
Of course, us more sophisticated humans, with our science and our telescopes, we know that the whole world *isn’t* made of water. Places with liquid water, which are hospitable to marine life, are actually very rare in the universe.
But if Fred the fish(I just named him that)’s mind is blown by what an amazingly lucky coincidence it is that there’s water right *here*, right where he needs it, then the anthropic principle still helps us explain that coincidence away. “If it weren’t here, you wouldn’t be either. If the water were someplace else, then you (or somebody a little bit *like* you) would be there instead, asking the same questions about *that* place.”
So if our minds are blown about some bigger coincidences like: “how amazing that all our universal constants are perfectly tuned to allow the existence of matter and atoms and stuff at all!” then maybe the anthropic principle has an answer too. Our universe could be just one of many, like part of a multiverse. If it is, then the “neighbouring” universes which are not hospitable to life, are uninhabited. There’s no one there to take note of the fact that that universe was a dud, and add it to the dataset.
It’s the principle that experimental observations happen in universes capable of supporting human life (or more generally, intelligent life), since without that no experiment would occur in the first place.
One example: concluding that planets should have an atmosphere with oxygen, because that’s all humans notice. Of course, this is disproven if humans send probes to Venus or Mars.
Or another: why is this universe three-dimensional spatially, with specific values for the gravitational constant and fine structure constant and other parameters, when slightly adjusting any of that would mean the universe would be a very different place? Well, in those universes, there wouldn’t be intelligent lifeforms to study the universe because those lifeforms couldn’t evolve on planets that form around stars.
There are some people who say that the physics of the universe is very finely tuned. That if gravity was a little bit weaker or stronger, stars wouldn’t burn the same way, or if other forces or physical constants were slightly different planets and life as we know it would be impossible. That our universe is an extremely unlikely set of coincidences, that all need to come off in order for humanity to exist. It’s like winning the lottery dozens of times in a row. And the question arises: if this universe is so unlikely, did Someone intervene to make it happen? Is there a creator?
The anthropic principle is a possible answer to this. It says that of course we live in a universe perfectly tuned for life. If it wasn’t perfectly tuned for life, we wouldn’t *be* here to ask that question. There are no humans living in universes entirely full of black holes due to ultra strong gravity asking “why is this universe so impossible for humans to live in?” because they don’t live there.
Prior answers are correct. However, someone, I believe Hawking, spelled out that there are two anthropic principles: The strong and the weak.
The Weak Anthropic Principle points out that we can only ask “why is the universe like this” in a universe that allows us to exist.
The Strong Anthropic Principle says that in fact, no universe without questioning intelligence can exist, because really our perception of the universe is the only thing that makes it real (!)
I’m certain someone could explain that better… maybe when you turn 6.
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