MIT physicists improve the precision of atomic clocks • Hacker News Board

Re: MIT physicists improve the precision of atomic clocks

#41

Post by stephen_g » Sat, Oct 18, 2025, 1:05 PM UTC

stephen_g wrote: post #40

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…

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…

Sorry that should be “had a DAC generate the turning voltage”, not ADC!

Re: MIT physicists improve the precision of atomic clocks

#42

Post by amy_petrik » Sat, Oct 18, 2025, 1:27 PM UTC

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…

> where do we actually hit diminishing returns with clock precision?

ah yes - that would be Planck's second which can be derived from Planck's constant and the speed of light

Re: MIT physicists improve the precision of atomic clocks

#43

Post by themafia » Sat, Oct 18, 2025, 7:36 PM UTC

KeplerBoy wrote: post #39

themafia wrote: post #23

Earlier quoted context omitted.

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.

> the phase of distributed oscillators

What do you imagine the clock in your computer is made out of?