Why life is constrained to be about the sizes we see on Earth.
Could things be any different?
Progress in the theory of computation suggests that sentience and intelligence likely require quadrillions of primitive “circuit” elements. Given that our brains are composed of neurons, which are themselves, in essence, specialized cooperative single-cell organisms, we can conclude that biological computers need to be about the physical size of our own brains in order to exhibit the capabilities that we have.
We can imagine building neurons that are smaller than our own, in artificially intelligent systems. Electronic circuit elements, for example, are now substantially smaller than neurons. But they are also simpler in their behavior, and require a superstructure of support (energy, cooling, intercommunication) that takes up a substantial volume. It’s likely that the first true artificial intelligences will occupy volumes that are not so different from the size of our own bodies, despite being based on fundamentally different materials and architectures, again suggesting that there is something special about the meter scale.
If both our brains and our neurons were 10 times bigger, we’d have 10 times fewer thoughts during our lifetimes.
What about on the supersize end of the spectrum? William S. Burroughs, in his novel The Ticket That Exploded, imagined that beneath a planetary surface, lies “a vast mineral consciousness near absolute zero thinking in slow formations of crystal.” The astronomer Fred Hoyle wrote dramatically and convincingly of a sentient hyper-intelligent “Black Cloud,” comparable to Earth-sun distance. His idea presaged the concept of Dyson spheres, massive structures that completely surround a star and capture most of its energy. It is also supported by calculations that my colleague Fred Adams and I are performing, that indicate that the most effective information-processing structures in the current-day galaxy might be catalyzed within the sooty winds ejected by dying red giant stars. For a few tens of thousands of years, dust-shrouded red giants provide enough energy, a large enough entropy gradient, and enough raw material to potentially out-compute the biospheres of a billion Earth-like planets.
How big could life forms like these become? Interesting thoughts require not only a complex brain, but also sufficient time for formulation. The speed of neural transmissions is about 300 kilometers per hour, implying that the signal crossing time in a human brain is about 1 millisecond. A human lifetime, then, comprises 2 trillion message-crossing times (and each crossing time is effectively amplified by rich, massively parallelized computational structuring). If both our brains and our neurons were 10 times bigger, and our lifespans and neural signaling speeds were unchanged, we’d have 10 times fewer thoughts during our lifetimes…