This morning over on Eric Kaplan’s excellent philosophy and humor blog, I commented on a post in which he speculates on our fear of death in relation to the possibility that duplicates of our consciousness might exist. In my response I did some math to calculate that possibility. Keep this in mind for when you need to feel special:
Human brains are composed of nerve cells called neurons. Connections between two neurons are called synapses. Like a city’s streets and intersections, neurons and synapses map out our brains. So we can define a “unique brain” — i.e. you, assuming you’re a materialist — as a unique layout of synapses.
Biologists estimate that the human brain contains about 100 billion (1011) neurons. Because each neuron can connect to many other neurons, the number of synapses in the brain is 100 trillion (1014). We can use a simple formula to calculate the number of possible combinations of synapses:
That works out to approximately 5 x 1032 possible brains.
Now let’s be unrealistically generous and say that human beings will survive until the Sun makes the Earth uninhabitable. That gives our species a lifespan of about 3 billion (3 x 109) years. To create 5 x 1032 different brains in 3 billion years would require making about 1023 new brains every year. To date, only 1011 humans have ever existed, and we’re only creating about 100 million (109) new people each year. In other words, if we want to make enough humans to create a duplicate brain before our species dies out, we’re working about 1000 times too slow.
There will never be another you.