The Cosmic Connectome | Cosmos: Possible Worlds

[Horn honking] [Siren wailing] A city is like a brain. It develops from a small center and slowly grows and changes, leaving many old parts still functioning. New York can't afford to suspend its water supply or its transportation system while they're being replaced by something more efficient. Changes have to happen piecemeal.

And that's how it is for the brain. There is no way for evolution to rip out the ancient interior of the brain because of its imperfections and replace it with something of more modern manufacture. The brain and the city both must function continuously during the renovation. That's why our limbic system is surrounded by the cerebral cortex.

The old part is in charge of too many vital mechanisms for it to be replaced altogether. So it's sometimes counterproductive, but that's a necessary consequence of evolution. The city is a gift of the cerebral cortex. But the brain's language is not encoded in the DNA of genes because the vocabulary of life is too small.

Our brains need a language with 10,000 times as many words. The information content of the human brain expressed in bits is probably comparable to the total number of connections among the neurons, about 1,000 trillion bits. If all the contents of your brain were transcribed into written language, it would amount to vastly more books than are contained in the largest libraries on Earth.

The equivalent of more than 4 billion books are inside your head. The brain is a very big place in a very small space. It's written in those neurons pioneered by the undersea microbial mats. These are tiny electrochemical switching elements, typically a few hundredths of a millimeter across.

Each of us has 86 billion neurons, comparable to the number of stars in the Milky Way galaxy. The neurons and their parts, axons, dendrites, synapses, and the cell bodies themselves make up a network in the brain. Many neurons have thousands of connections with their neighbors.

Dendrites, those pathways sent out by neurons to connect with other neurons, extend these nerve cells to synapses until they create a full-blown network of consciousness. [Orchestral music] The neurochemistry of the brain is astonishingly busy, the circuitry of a machine more wonderful than any devised by humans. Your brain functions are due to those 100 trillion neural connections that make you, you.

Your deepest feelings of love and awe, those moments when we glimpse the grandeur of nature and all the elegant architecture of consciousness are made possible by those connections. This is the essence of emergence, tiny units of matter operating collectively to become something much more than themselves, to enable the cosmos to know itself.

But there is a vision of emergence that takes it even higher. Can we know the universe? And will it ever come to know us? [Dramatic music]