And that's the part that Google Spanner gets around with Atomic clocks and GPS clocks.

Just the concept of using time for the logical clock is sketchy. It's not monotonically increasing, it drifts, it can go decrease, etc... Curious what their cross host/region ordering and consistency looks like.

"An atomic clock is not that expensive." -- http://research.google.com/archive/spanner.html

Indeed. A GPS clock accurate to 50ns is around $25 on eBay.

Especially since there are 24 circling the earth that send out time continuously.