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MIT physicists improve the precision of atomic clocks

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Re: MIT physicists improve the precision of atomic clocks

#21

Post by technothrasher »

at-fates-hands wrote: post #5

When I was in anthropology, many of the cultures I studied had very vague concepts of time (sunrise/sunset, passage of stars and constellations, different seasons). One of my professors spent two weeks about how time was a Western construct and how people want to go to such great lengths to have such precise measurement of it. The very lengthy discussion around the concept was fascinating to me as a 23 year old colle…

> how time was a Western construct

Japan had a whole fancy temporal hour system before Western contact. It was more complicated than our modern framework, as it was based on the time between sunrise and sunset and so the length of the hours had to be adjusted about every two weeks. But they certainly thought quite a bit about it, so I'm not sure how it could be claimed to not be a concept there at the time.

Re: MIT physicists improve the precision of atomic clocks

#22

Post by themafia »

at-fates-hands wrote: post #5

When I was in anthropology, many of the cultures I studied had very vague concepts of time (sunrise/sunset, passage of stars and constellations, different seasons). One of my professors spent two weeks about how time was a Western construct and how people want to go to such great lengths to have such precise measurement of it. The very lengthy discussion around the concept was fascinating to me as a 23 year old colle…

We've been using sundials since antiquity. What was your professor even talking about?

Re: MIT physicists improve the precision of atomic clocks

#23

Post by themafia »

KeplerBoy wrote: post #10
ram_rar wrote: post #2

I’ve spent a decent chunk of my career wrestling with time sync — NTP/PTP, GPS, timezones, all that fun stuff. For real world network time infrastructure, where do we actually hit diminishing returns with clock precision? Like, at what point does making clocks more precise stop helping in practice? Asking partly out of curiosity, I have been toying with a future pet project ideas around portable atomic clocks, just t…

I guess very few systems have better absolute time than a few microseconds. Those systems are probably exclusively found in HFT and experimental physics. This past week I tried synchronizing the time of an embedded Linux board with a GPS PPS signal via GPIO. Turns out the kernel interrupt handler already delays the edge by 20 us compared to busy polling the state of the pin. Stuff then gets hard to measure at sub mic…

10 MHz reference oscillators that are GPS locked are quite common. They're very useful in RF contexts where they're quite easy to find.

Re: MIT physicists improve the precision of atomic clocks

#24

Post by MengerSponge »

pyuser583 wrote: post #17
ram_rar wrote: post #2

I’ve spent a decent chunk of my career wrestling with time sync — NTP/PTP, GPS, timezones, all that fun stuff. For real world network time infrastructure, where do we actually hit diminishing returns with clock precision? Like, at what point does making clocks more precise stop helping in practice? Asking partly out of curiosity, I have been toying with a future pet project ideas around portable atomic clocks, just t…

My understanding is that precise measurement of time is the basis of all other measurements: space, mass, etc. They are all defined by some unit of time. So increasing time precision increases potential precision in other measurements. Including of course information - often defined by the presence or absence of some alterable within a specific time. We invent new uses for things once we have them. A fun thought expe…

> were perfectly in sync

They couldn't stay synced. There's a measurable frequency shift from a few cm of height difference after all. Making a pair of clocks that are always perfectly in sync with each other is a major step towards Le Guin's ansible!

For other readers' info, clock stability is crucial for long-term precision measurements, with a "goodness" measured by a system's Allan variance: https://en.wikipedia.org/wiki/Allan_variance

Re: MIT physicists improve the precision of atomic clocks

#25

Post by 3eb7988a1663 »

technothrasher wrote: post #21
at-fates-hands wrote: post #5

When I was in anthropology, many of the cultures I studied had very vague concepts of time (sunrise/sunset, passage of stars and constellations, different seasons). One of my professors spent two weeks about how time was a Western construct and how people want to go to such great lengths to have such precise measurement of it. The very lengthy discussion around the concept was fascinating to me as a 23 year old colle…

> how time was a Western construct Japan had a whole fancy temporal hour system before Western contact. It was more complicated than our modern framework, as it was based on the time between sunrise and sunset and so the length of the hours had to be adjusted about every two weeks. But they certainly thought quite a bit about it, so I'm not sure how it could be claimed to not be a concept there at the time.

How would the variable hours be used? Presumably access to the timekeeping was limited, so who even was aware of the difference so that they could modify their life to accommodate it?

Re: MIT physicists improve the precision of atomic clocks

#26

Post by cma »

TrueDuality wrote: post #16
ram_rar wrote: post #2

I’ve spent a decent chunk of my career wrestling with time sync — NTP/PTP, GPS, timezones, all that fun stuff. For real world network time infrastructure, where do we actually hit diminishing returns with clock precision? Like, at what point does making clocks more precise stop helping in practice? Asking partly out of curiosity, I have been toying with a future pet project ideas around portable atomic clocks, just t…

Another commenter mentioned that this is needed for consistently ordering events, to which I'd add: The consistent ordering of events is important when you're working with more than one system. An un-synchronized clock can handle this fine with a single system, it only matters when you're trying to reconcile events with another system. This is also a scale problem, when you receive one event per-second a granularity…

Google Spanner paper has interesting stuff along these lines, heavily relied on atomic clocks

Re: MIT physicists improve the precision of atomic clocks

#27

Post by jcelerier »

nomel wrote: post #18
ram_rar wrote: post #2

I’ve spent a decent chunk of my career wrestling with time sync — NTP/PTP, GPS, timezones, all that fun stuff. For real world network time infrastructure, where do we actually hit diminishing returns with clock precision? Like, at what point does making clocks more precise stop helping in practice? Asking partly out of curiosity, I have been toying with a future pet project ideas around portable atomic clocks, just t…

For network stuff, high security and test/measurement networked systems use precision time protocol [1], which adds hardware timestamps as the packets exit the interface. This can resolve down to a couple nanoseconds for 10G [2], but can get down to picosecond. The "Grandmaster" clock uses GPS/atomic clocks. For test and measurement, it's used for more boring synchronization of processes/whatever. For high security,…

and that precision is really important. For instance, when working with networked audio, which usually has a temporal resolution of packets that can be between 100us and 10ms (so abysmally slow in computer-time), non-PTP network cards are basically unusable.

Re: MIT physicists improve the precision of atomic clocks

#28

Post by 1970-01-01 »

at-fates-hands wrote: post #5

When I was in anthropology, many of the cultures I studied had very vague concepts of time (sunrise/sunset, passage of stars and constellations, different seasons). One of my professors spent two weeks about how time was a Western construct and how people want to go to such great lengths to have such precise measurement of it. The very lengthy discussion around the concept was fascinating to me as a 23 year old colle…

It wasn't even a daily utilized concept in the West until trains were chugging their way to various stations. Farmers didn't need to know the exact minute the cows came home.

Re: MIT physicists improve the precision of atomic clocks

#29

Post by nitwit005 »

at-fates-hands wrote: post #5

When I was in anthropology, many of the cultures I studied had very vague concepts of time (sunrise/sunset, passage of stars and constellations, different seasons). One of my professors spent two weeks about how time was a Western construct and how people want to go to such great lengths to have such precise measurement of it. The very lengthy discussion around the concept was fascinating to me as a 23 year old colle…

Your professor was just wrong if they claimed time was a Western construct. Calendars, sundials, and other time keeping devices were created independently around the world.

All you need to create a clock is realize that your oil lamp consumes its fuel in a somewhat consistent interval, or a similar observation for the time it takes drips of water to fill a cup. People figured it out.

Re: MIT physicists improve the precision of atomic clocks

#30

Post by bawolff »

at-fates-hands wrote: post #5

When I was in anthropology, many of the cultures I studied had very vague concepts of time (sunrise/sunset, passage of stars and constellations, different seasons). One of my professors spent two weeks about how time was a Western construct and how people want to go to such great lengths to have such precise measurement of it. The very lengthy discussion around the concept was fascinating to me as a 23 year old colle…

I don't think its fair to say that atomic clocks represent a western cultural value. After all, they are extremely niche. Physicists care but the average "westerner" does not.
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