The universe is expanding. In four billion years, Andromeda will collide with the Milky Way. There are hundreds of billions of stars in our galaxy and most of them have planets. The Earth revolves around the Sun once roughly every 365 days. The Moon revolves around the earth once every 28 days and is moving away from us. Modern humans are descendants of primates. Over 14,000 years ago, we invented war. The climate is warming. The human population will reach 10 billion around 2050. The gap between rich and poor is growing. The human body sways to the rhythm of a 24-hour clock. Cell division is controlled by proteins called cyclins. Life on Earth began about 4 billion years ago when molecules that could replicate themselves emerged in the primordial ooze. Molecules are made of atoms and atoms are made of particles that are really organizations of energy. Energy is always conserved in a physical system. In the beginning all the energy in the universe was contained in a single point.* One more thing: there is water on the Moon.

How do we know these things? That depends on what you mean but  the short answer is “science”. As a culture, we know these things because of a collective process of inquiry; as individuals, we learn them in school. That is, some of us discovered these things and taught them to others, who taught them to others, and then, perhaps, to us. Some of us don’t know these things, but we know them. Almost anyone can learn them, too, i.e., become knowledgeable about them. Given ordinary intelligence, sufficient curiosity, some time and a good book or teacher, a human being can understand these things at a level that we’d consider “knowledge”. But how do we know? What did we do to acquire this knowledge? What are we doing when we know them?

This question fascinates me. It has many different answers, but I’m after a very practical one. I want to understand the practices by which we come to know things, both collectively and individually. Obviously, I want to know (!) how the collective and individual practices intersect. Ultimately, I believe that only things that can be known by individuals can be known at all. But that does not mean that there aren’t things that it “takes a village” to discover. It’s hard to imagine the discovery of water on the Moon by anything less than a coordinated effort. But once the discovery has been made, the knowledge is available to each one of us. This is very important to me, and I don’t think the point is trivial. When I look at what passes for knowledge these days, especially on social media, it sometimes seems to me that people believe things without assuming that anyone–any one person–knows them. They defer not to one expert or another but to an anonymous, undifferentiated, collective “expertise.”

Naturally, they don’t themselves claim to know what they believe either. They merely assert that “we know” or “it is known”. This saves them the trouble of defending their beliefs, and I think we let them, and ourselves, get away with this at our peril. No one is responsible for knowing everything, but we should assume that if anything is known it can be known by “little old me” too, perhaps in a simplified form, or at some level of generality, but, even if I would never have thought of it myself, or stumbled on it in my own experience, I can understand any knowable thing well enough to know it too. I want this to be a norm of “educated” people.

In that case, then, I want to suggest that we know things mainly through experience and conversation–broadly understood to include writing. Indeed, almost everything we know comes to us through conversation with others, through discourse with other knowledgeable people. We listen to them and read what they have to say. We question them and add thoughts of our own. We help each other sharpen our points and discard our errors. If we don’t participate in this process we don’t really know anything. It is not enough to look into a telescope or read a history book. We have to make sense of what we see or read there in collaboration with others. Once I’ve understood something well enough to hold my own in a conversation about it with other knowledgeable people, I, too, can claim to be knowledgeable. Until then, I’m still learning.

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*Update, 24.04.20: It has come to my attention that this may be a myth about the Big Bang.