I personally find it amazing that everything we have made - every photograph, every book, every movie, and everything we will ever make can be given a unique 256 bit fingerprint that has a negligible chance of collision before the heat death of the universe.
an interesting comparison is 2^256 ~= 1e77 ~= 0.001 x the number of atoms in the universe. So in 256 bits we almost have enough combinations to assign every particle _there is_. Considering we've made considerably fewer works than there are particles, you could probably actually get pretty far along collision resistance by just assigning fingerprints randomly. Another way to look at that is UUIDs are only 128 bits (sqrt as many combinations, 1e38) and they're pretty resistant. Another amazement is that we can have a deterministic hashing function to select a fingerprint _based on the content_ in a way that preserves collision resistance.
For a similar thought experiment, consider the space of all 1920x1080 RGB images , which necessarily contains all films ever made or ever _could_ be made, screenshots of future stock prices (including all the wrong ones), and pictures of your great great great grandchildren (or not). Then figure that randomly sampling that space just gives white noise – suggesting our 'content' probably isn't a large fraction of the total space. :)
My ISP hands out IPv6 /48 subnets. The upside of this is that every customer of theirs gets enough IP addresses to give every grain of sand on the planet a couple.
Yes. Even with 128 bits (uuid), I like that the policy is simply to treat each one as universally unique without needing to check any system for collision
As Raymond Chen put it, if you're worrying about UUID collisions, you need to also worry about way more probably things, such as random memory bit flips.
