The Unexpected Measure that Makes the Modern World Tick

↓↓↓ More info and sources below ↓↓↓

All of modern society relies upon a seemingly simple but surprisingly complex unit of measurement: the second. But knowing exactly what a “second” is is more complicated than you might think!

Thank you to the following for helpful discussions and research for this episode:
Geoff Chester - U.S. Naval Observatory
Judah Levine - National Institute of Standards and Technology
Jeffrey Sherman - National Institute of Standards and Technology
Elizabeth Donley - National Institute of Standards and Technology

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[besmart]

I really enjoyed making this video. I had the TIME of my life 😏On second thought that was a bad joke.

[Ekevoo]

I still remember in high school a teacher going okay let's talk about the basics. Distance: unit, definition, uses. Time: unit, definition ("there is no definition. time is time. moving on…"), uses.

[rickintexas]

We are so fortunate to live in a world where all of this information is taken for granted. I remember as a kid in the 70s you could call the local bank and get an automated machine telling you the time of day precise to a minute. That is what we would use to set our watches. If our watches were precise to within 5 minutes, well that was good enough.

[zetsumeinaito]

Speaking of leap seconds, I thought it fascinating that there was a leap second for the earthquake that caused the Fukajima power plant to fail. It made THAT much of a difference.

[LordTelperion]

Fun fact, while the Romans would measure time during the day using sundials, to keep time during the night or when it was cloudy (or during Senate meetings) they also used "water clocks" which operated by dripping water out of a vessel at a regular rate to measure the passage of time.

[flamencoprof]

I wondered about this in 2014 and these were my findings: -
Network Time Protocol (NTP) is a networking protocol for clock synchronization between computer systems over packet-switched, variable-latency data networks. In operation since before 1985, NTP is one of the oldest Internet protocols in use.
It is amazing that although the internal clock on my laptop runs at 1.50 GHz, i.e. chops time into of a second, it can't keep accurate time over a few hours. Proper NTP can tolerate and correct a PC's clock that is out by up to +/- 43 seconds a day.
Wikipedia NTP page:
"Future versions of NTP may extend the time representation to 128 bits: 64 bits for the second and 64 bits for the fractional-second.
The current NTPv4 format has support for Era Number and Era Offset, that when used properly should aid fixing date rollover issues. According to Mills, "the 64 bit value for the fraction is enough to resolve the amount of time it takes a photon to pass an electron at the speed of light. The 64 bit second value is enough to provide unambiguous time representation until the universe goes dim."

Then in 2015/11/1 I found: -
The latest in atomic clocks would neither gain nor lose one second in some 15 billion years—roughly the age of the universe.
(One second in 15 billion years is 1 part in 1000, 000, 000 x 15 x 365.25 x 24 x 60 x 60 = 473, 364, 000, 000, 000, 000 = 4.73 x 10^17)
Now, after taking in the almost incomprehensible accuracy this represents, one could be forgiven for thinking "Yes, but who needs clocks that accurate? What could they possibly be used for?"
Well, it turns out that they can be made useful by studying what makes them INACCURATE. Once you have this steady pulse, gravity, magnetic fields, electrical fields, force, motion, temperature and other things can introduce tiny but measurable variations, such measurements becoming a proxy for measuring the actual gravity or force etc.
For example, as Einstein predicted, a gravitational field causes time to pass more and more slowly as gravity increases. A clock which is higher is further from Earth, experiences less gravity, and thus runs faster. The new clock is sensitive enough to detect the time shift caused by a rise of only two centimeters! It can thus serve as an extremely accurate measure of height for mapping, and of gravity variations caused by the earth's composition and shape. (Note that gravity's effect on time is NOT relevant to GPS satellites)
 
A reader interested in a fuller description of the intricacies involved and the influences which must be accounted for to achieve this accuracy should click here for the article "About time: New record for atomic clock accuracy", April 21, 2015 at phys.org.

[MonkeySimius]

Fun fact:. The US is on the metric system. It is the official measurement system. The imperial system is also the official measurement system. We officially use both. Which is to say, being intentionally pedantic, your graphic pointing to the US saying "not metric" is wrong.

In fact measurements like "feet" are officially defined as conversions from metric units.

[lara_xy]

I truly love how this channel makes learning fun and give me answers to both questions I have always wanted to know the answer to, and questions I never asked myself until watching a video.

[SuicV]

I would really like to know more about the candela. All throughout my graduation in Engineering I never had to use it, and it sure doesn't look like you can't express it in function of the other base units (just at face value). So yeah, feels like a bit of a mystery

[TheOriginalFaxon]

I just want to point out that the US does actually legally rely on the metric system at this point. The only reason you still see Imperial used was because they didn't want to force all our industrialized manufacturing capacity to completely retool (which would have set the US back decades at the time), but that was over a century ago, and while we actually still use some of those same machines in production of stuff today, modern machinery for manufacturing has been universal for a long time, basically since we started making everything using CnC operated machines. Even decades old CnC lathes can be used in both imperial and metric. Imperial as it currently stands today is effectively considered an extension of the metric system, because all the base units we use to define what imperial is today, are based on metric measurements.

[jadonbelezos]

i love how this video makes such a good point about how we take knowing what time it is for granted.

[Beryllahawk]

I still remember the first time I ever heard about cesium-atom clocks. Great little book about naked-eye astronomy, and the author went on to discuss tachyons and all sorts of other nifty ideas and science that depend on time. He didn't get into THIS though! (Not mad about it, either, that was a fabulous book and I still own it 30 years later.)
I love that the guy said "I used to think one second was "one Mississippi"..." That made me laugh a lot, especially because I recently had a discussion with an old friend about whether "one Mississippi" is more accurate than "one Hippopotamus." I have very fun friends, heh.

[reddcube]

Every unix user know time starts at 1 January 1970

[SherilRKirshenbaum]

Love this video Joe!

Thanks for the shout out and sending folks our way. As you know, we’re all big fans of Be Smart! 💫

[tomsko]

0:06 - He published a 638 page ESSAY?? I'm not looking to be pedantic here, but no. No no no. Essays are 1-10 pages MAX and are written late Sunday night, right before they are due. What John Wilkins wrote was a manifesto or a book with no plot.

[ShubhGG]

"i cannot tell you what time is, but i can tell you exactly what time it is"
- Geoff 2022

[mwm]

“The Absolute Unit” was my nickname in college.

[bitsofgeek]

It would be fascinating if you could manage to get a chat in with David L. Mills, the inventor of Network Time Protocol and probably the most underrated contributor to technological progress over the last 40 years.

[nerd_alert]

Your guys' videos are always so fun and educational (obviously)! 😆
I can't wait until my son is old enough so he can watch and understand, instead of just randomly skipping the videos I'm watching.

[nHans]

The metric units (or more specifically, SI) are *_not_* a realization of John Wilkins' idea of _"A standard and universal system of measurement based on the natural world."_ Those would be the *_Planck Units._* A video for another day, perhaps?