More Falsehoods Programmers Believe About Time (2012)

The article doesn't contain explanations, so I dug into a few especially surprising ones:

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> 7. Months have either 28, 29, 30, or 31 days.

Great Britain skipped from Sept 2, 1752 straight to Sept 14 when they switched from the Julian to the Gregorian calendar. Google "English calendar riots".

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> 15. Unix time is the number of seconds since Jan 1st 1970.

When flipping over to the next second, Unix time "rewinds" back a second (i.e. repeats the last one) for leap seconds. [1]

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> 73. Time passes at the same speed on top of a mountain and at the bottom of a valley.

This is from "time dilation", related to Einstein's General Relativity. In short, gravity warps spacetime.

Say you use a stopwatch to measure 1 Earth rotation (a "day"). For each extra km of altitude, the stopwatch will tell you it took ~10 extra nanoseconds to complete the trip around the Earth. [2]

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[1] https://en.wikipedia.org/wiki/Unix_time#Leap_seconds

[2] https://en.wikipedia.org/wiki/Time_dilation#Time_dilation_ca...

Related:

Falsehoods Programmers believe about Time - https://news.ycombinator.com/item?id=4128208 - Jun 2012 (213 comments)

Falsehoods Programmers Believe About Time (2012) - https://news.ycombinator.com/item?id=12675527 - Oct 2016 (154 comments)

Falsehoods programmers believe about time - https://news.ycombinator.com/item?id=32548085 - Aug 2022 (204 comments)

Falsehoods programmers believe about time and time zones - https://news.ycombinator.com/item?id=11515125 - Apr 2016 (80 comments)

I really wish that these lists included explanations for why they are incorrect, or at least links to resources accordingly.

All models are wrong.

Some are useful.

Determine what level of the model is useful for what you want to do.