Time Roundup
Yee-haw đ€
A couple of cool science/technology news items just dropped:
- Thereâs going to be a new time zone for the moon (and non-Earth places, generally)
- The Earth was going to need an unprecedented negative leap second, but weâre not (yet)
Coordinated Lunar Time (LTC)
Remember that list of Falsehoods Programmers Believe About Time? You know, that migraine-inducing laundry list of gotchas for anyone who needs to deal with something as exotic as time in an app? Well, itâs going to get a whole lot worse. Be sure to tack on something like âa second is not always the same length of time.â Any sentence beginning with âDue to general and special relativityâŠâ ought to make your blood run cold as a programmer.
But, and this is the nifty part, itâs cool to think about as a concept. If you were standing on the moon, in your moonboots, and looking at those sloppy Earthlings, youâd notice that each day they lose about 58.7 microseconds. It would seem that their clocks just run more slowly. Clearly not a huge difference, but if youâre a sciency type that can really amount to some mustard on your shirtâscientifically speaking.
Navigation is something thatâs notoriously sensitive to pesky old Einstein. In fact, if the ol âStein werenât accounted for in the GPS system circling Earth, the cumulative error would amount to around 10km per day. Part of this effort then is to come up with a system thatâs going to be robust for use outside of the range of terrestrial GPS.
Thereâs some other fun stuff in this report. It mentions one of my favorite time standards International Atomic Time (or TAI). This is the standard that behaves much more like the naieve âFalsehoods Programmers BelieveâŠâ list seeks to demolish. It just lets you have your delicious falsehoods. TAI works by averaging hundreds of atomic clocks. It differs from UTC by some whole number of leap seconds, because it doesnât have them (UTC does). Basically, Earth is a great place to live but not great at being a clock.
Negative Leap Second
Everyday experience with things that spin should give you a intuitive understanding things slow down. A top will start to wobble and then eventually tip over. The Earth isnât different. Itâs just really big and itâs where all my stuff is stored. People also happen to have some misguided sentimental attachment to the sun being out around noon. These two facts:
- people wanting certain times to correspond to stuff like the sun being roughly overhead
- the Earth slowly losing that property
âŠmeans that we have to play some funny games with how our clocks work. In the past it meant slowly adding something called a leap second. Like a leap day, but much shorter. And theyâve always been added; thereâs occasionally some minute at some time (often when we least expect it) that has 61 seconds rather than 60. Which is what you expect if you want a steadily marching metronome to keep up with a gradually slowing Earth.
But! For various theorized reasons Earth has actually been spinning more quickly of late. And in the reverse of the above reasoning, that would mean that eventually weâd need to remove a second from the clock to keep pace with a faster Earth. Nobodyâs quite sure what the full implications of this would be.
And this is where software comes into the picture. Generally weâd assume code like this:
t1 = now();
// do some stuff
t2 = now();
diff = t2 - t1;
would always yield a positive, or depending on the timer resolution, zero value. We might be surprised if it would be negative. And when software developers are surprised, we donât get angry, we just make bugs. Sorry, but Iâm not sure what this means for the upcoming surprise party that you were thinking of throwing for your software developer friend.
And in the final twist here, thereâs some extra slowing that we can attribute to climate change. And that extra slowing is counteracting the somewhat-mysterious acceleration, and thus staving off the need for a negative leap second. Which would be unpopular.
So⊠for various competing reasons it looks like weâre safe from the hypothetical scourge of the negative leap second for at least a little while longer. But, you know, watch this space.
Sources
- White House Cislunar Technology Strategy Memo (Office of Science and Technology)
- A global timekeeping problem postponed by global warming (Nature)
- Leap Second (Wikipedia)
- Real-World Relativity: The GPS Navigation System
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