What happens when you set your phone back to 1970

We know the internet brings out the worst in people. But this is pretty bad. Last week an ad surfaced claiming you could experience a retro theme and a “wild ride” with your iPhone simply by setting its date back to January 1, 1970. Don’t do it! This is a nasty trick exploiting a bug discovered last week on all 64-bit iPhones. Due to something called the Unix epoch, if you set your iPhone’s date back to 1/1/70 it will crash and never restart! Unix time is a method of measuring time used by computer programmers around the world. It eliminates complications of things like time zones and daylight savings by simply counting the number of seconds that have passed since the Unix epoch of–you guessed it–midnight of January 1, 1970 GMT. It’s also way easier to manipulate time this way. In Unix time, this Curio was published at 1455878700. If you’re reading it two hours later, then it is 1455885900 (7200 seconds later). The most recent bug–which Apple has just acknowledged but cannot fix until the next major iOS release–only affects the newest iPhones. These phones store all numbers in 64 bits instead of 32 bits. While only Apple knows for sure, the crash likely has to do with integer underflow. This results when you try to manipulate raw binary numbers smaller than zero. Think of it like an old-fashioned odometer on a car with only 3 miles on it. If you put the car into reverse for five miles, the odometer wouldn’t show -2. It would show 99,998. So if you set the phone’s time to 0 (1/1/1970) and then some app like your voicemail tries to subtract a few hours from that time, the phone would try to display a time that is 2^64 seconds later than 1/1/1970. That is a date so far in the future it is 20 times longer than the lifetime of our universe! If you want a fuller explanation, watch programmer Tom Scott explain integer underflows and the 1/1/1970 bug in more detail below. Bueller!



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