“Why” is the only question which bothers people enough to have an entire letter of the alphabet named after it.
– Douglas Adams
“Why?”, a question that if asked and answered a sufficient number of times, leads to the fundamentals of nature. It is the question at the heart of science—in fact, science is the process of answering it. Science is the exploration of causality, and for some, it is a view on life and what we ought to do with it.
Perhaps we can understand the limits of science before discovering them. For example, we can ask ourselves about the limits to the question “why?”. There are two conceptual boundaries to this question: absence of cause and infinite causality. Think about both for long enough and you'll be unable to choose the more absurd of the two. Here, I'll look into both, starting with absence of cause.
Most people believe in the existence of a cause that does not have a cause of its own, often called God. There is a distasteful implication to causelessness: if the first link in the chain of causality exists without reason, the whole chain exists without reason. Another sort of absence of cause is where nothing exists, including causes. However, we know that our consciousness (at least one thing) exists, so we can move on to more interesting things like infinite causality.
Infinite causality is the question “why?” endlessly, creating a sort of chain or web of causality. I invite you to ponder the concept. Now perhaps the chain makes a loop, but then what causes the loop to exist? The chain has no end if everything has a cause.
It takes effort to grasp the concept of inifinity. We do not experience infinity in our everyday lives, and therefore, it's intrinsically non-intuitive. Similarly to analogies for concepts in quantum mechanics, analogies for infinity are simplistic. Truly understanding is difficult and potentially impossible, but we can at least make an effort to grasp its implications.
What if causality was infinite? What would that mean for science? Well, if the purpose of science is to discover the unknown, but discovery is unlimited, science becomes an act of satisfying desires rather than the pursuit of a concrete, attainable goal. In other words, science becomes a journey with no destination. This doesn't mean that science isn't worthwhile; rather, it's something to keep in mind when thinking about science. If causality was infinite, the physicists working on grand theories of everything would in fact be working on, and always would be working on, grand theories of not-quite-everything.
So we're left with the two concepts: infinite causality and finite causality. Either we can't know the reason for our existence or we exist for no reason. It sounds depressing, but of course, conclusions like this should never be taken too seriously. As Nicolaus Copernicus put it, “To know that we know what we know, and to know that we do not know what we do not know, that is true knowledge.”