UNIX timestamps used to be a signed 32-bit integer with January 1st 1970 at 00:00:00 UTC as the start of epoch.
The maximum value of a signed 32-bit integer is 2147483647 and 2147483647 seconds after the start of Epoch is:
$ date -u -d @2147483647
Tue Jan 19 03:14:07 UTC 2038
We’re living in a time warp after all.