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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

#31

Post by bawolff »

nitwit005 wrote: post #29
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.

I don't know how other cultures viewed time, but i think there is a big difference between being able to make a clock and running your life by a clock. Modern industrialized society is very regimented - work starts at an exact time, ends at an exact time, lunch is exactly an hour, etc. I suspect such notions would be much less useful in a non-industrial society.

Re: MIT physicists improve the precision of atomic clocks

#32

Post by DannyBee »

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 use fairly precise time but that's because I control high speed machinery remotely. The synchronization is the important part (the actual time doesn't matter). At 1200 inches per minute, being a millisecond off will put a noticeable notch in a piece.

Ptp and careful hardware configuration keeps things synced to within nanoseconds

Re: MIT physicists improve the precision of atomic clocks

#33

Post by nitwit005 »

bawolff wrote: post #31
nitwit005 wrote: post #29

Earlier quoted context omitted.

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.

I don't know how other cultures viewed time, but i think there is a big difference between being able to make a clock and running your life by a clock. Modern industrialized society is very regimented - work starts at an exact time, ends at an exact time, lunch is exactly an hour, etc. I suspect such notions would be much less useful in a non-industrial society.

The utility of an idea is not the idea itself.

Re: MIT physicists improve the precision of atomic clocks

#34

Post by programjames »

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…

And paper money is a Chinese invention. Doesn't mean it's worthwhile to spend two weeks in an anthropology class talking about how much awesomer they are.

Re: MIT physicists improve the precision of atomic clocks

#35

Post by jacquesm »

crispyambulance wrote: post #20

They mention a "quantum noise limit", that must be the ultimate precision that is physically possible, right? What is this ultimate precision? I imagine that at some point, even the most modest relative motion at ordinary velocities would introduce measurable time dilation at fine enough clock precision.

Not just time dilation, at those scales time apparently can flow backwards for a bit!

https://arxiv.org/abs/2409.03680

Re: MIT physicists improve the precision of atomic clocks

#36

Post by DannyBee »

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…

Intel Ethernet pps input pin works much much better for this. See how the open timecard mini folks do it. Easy to get sub microsecond even on cheap embedded. Most m.2 of Intel chipsets expose it (for example) as well.

Re: MIT physicists improve the precision of atomic clocks

#37

Post by fsh »

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…

This is true, but atomic clocks are about a million times more accurate than any other measurement device. For all pratical purposes, they are never the limiting factor.

Re: MIT physicists improve the precision of atomic clocks

#38

Post by fsh »

crispyambulance wrote: post #20

They mention a "quantum noise limit", that must be the ultimate precision that is physically possible, right? What is this ultimate precision? I imagine that at some point, even the most modest relative motion at ordinary velocities would introduce measurable time dilation at fine enough clock precision.

Yes, there is a limit called "quantum projection noise" that determines how much frequency stability one can achieve with a single-atom clock [1]. With N independent atoms, this limit gets smaller by 1/sqrt(N), but with N entangled atoms one can achieve a 1/N scaling. This is the ultimate limit (Heisenberg limit).

[1] https://journals.aps.org/pra/abstract/10.1103/PhysRevA.47.35...

Re: MIT physicists improve the precision of atomic clocks

#39

Post by KeplerBoy »

themafia wrote: post #23
KeplerBoy wrote: post #10

Earlier quoted context omitted.

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.

Sure, I was specifically talking about computer system clocks. Also with an oscillator _absolute_ time offset doesn't matter, unless you want to synchronize the phase of distributed oscillators and then things quickly get non-trivial again.

Re: MIT physicists improve the precision of atomic clocks

#40

Post by stephen_g »

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…

If your board’s SOC has a general purpose timer (GPT) then you can often have it count cycles of a hardware clock and store the value every interrupt pulse from a GPIO. I designed a GPS disciplined oscillator like this where we had an ADC generate a tuning voltage for a 100 MHz OCXO (which was a reference clock for microwave converters) which we divided down to 10 kHz and fed into the GPT, along with the 1pps from a GPS module, and the control loop would try to adjust it until we got 10K clock cycles for every pulse. This kind of synchronisation gets very accurate over a few minutes.

Even just triggering an GPT from an GPS PPS input counting cycles of an internal clock you could use a GPT to work out the error in the clock, and you only need to query it once a second.

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