Why does a bigger mind think more slowly?
Every part of a mind has to hear from the other parts. Signals cannot travel faster than light, so a mind that ticks together, like a chip with a clock, can only be as wide as the distance light covers in one tick.
Guess first A mind ticks a billion times a second and stays in step with itself. How wide can it be?
About 0.30 metres, the length of a school ruler. Light covers that in one billionth of a second. Make the mind wider and it can no longer agree with itself within a tick.
Now scale up. The Vigil's swarm is enormous, and for a thought spread across one zone of it, news needs about 7 minutes to get from one side to the other, and 50 to 200 seconds just to reach the zone from Vesper at its centre. A mind that big can be brilliant, but it has one synchronized thought in minutes. The page on big minds and slow minds does the sums.
Size trades storage capacity against coordination time. A compact mind can synchronize faster; a wide one can contain more storage and processors. Many residents of the Vigil choose to run slowly so that friends across the swarm can stay in step. Whether software minds have experiences like yours remains unresolved frontier. The light-speed limit applies to their communication under either interpretation.
There is also an upper limit on how fast anything can think for a given amount of energy, whatever it is built from. How fast can anything think? explains that limit, and Copy, merge, choose your clock looks at the copying and merging that makes the choice possible.