Where does my computer the time from?

Tony Finch has a delightful blog post trying to answer a relatively simple question - where does my computer get the time from? The answer is an NTP server, but where does the NTP server get its time from? GPS probably. Okay, well where does GPS get its time from? Schriever Space Force Base in Colorado! And where does Schriever Space Force Base in Colorado get its time from? The US Naval Observatory Alternate Master Clock on base. But that master clock gets the time from the US Naval Observatory in Washington DC that uses atomic clocks. You think we're done now? Oh no, there's still more links in this chain that would be rude of me to fully go into here and deprive the author of some well deserved website traffic.