What a Unix Timestamp Is (and Why It Starts in 1970)
A Unix timestamp is the number of seconds that have elapsed since midnight UTC on January 1, 1970 — a reference point known as the Unix epoch — chosen by the early designers of Unix as a convenient, arbitrary zero point around the time the system itself was being developed, and it has remained the standard reference point ever since simply because so much software was built around that original choice.
This single, simple definition is why Unix timestamps are used so pervasively across programming, logs, and databases.
Why a single incrementing number is so useful
Representing a point in time as one plain number, rather than a formatted calendar date, makes comparing, sorting, and doing arithmetic on dates trivial for a computer — subtracting two timestamps directly gives the number of seconds between them, without needing to parse a formatted date string first.
Why the epoch itself doesn't matter much beyond convention
The exact starting date is fundamentally arbitrary — what matters is that everyone's software agrees on the same reference point, so a timestamp means the same instant in every system that uses it. 1970 stuck simply because that's the convention the early Unix systems adopted and it was never worth changing industry-wide afterward.