This article leaves so many unanswered questions, starting with the elephant in the room: how accurate is it? (Or how accurate do they expect it to be?)
It turns out that the current state of the art is 10^-15. Which immediately raises the second question: how do they measure this? 10^-15 is an error of roughly a nanosecond a year. GR causes that kind of time difference between your head and your feet when you stand up.
I haven't done the math, but I'm guessing that just standing next to a 10^-15 clock would have noticeable effects due to the effects of your gravitational field.
Also: why does thorium-229 in particular have such a low-energy atomic transition? That seems kind of random.
A decent frequency counter can resolve a frequency difference of 1E-15 in a few minutes of averaging. Modern GPS-based frequency comparisons (dual-band, post-processed using precise point positioning) are also accurate to the 1E-15 level with around one day of averaging. Note that these counters operate with radio frequencies. The best atomic clocks use optical transitions and are accurate to around 1E-18. In this case, one gains around 6 orders of magnitude in frequency resolution by translating the laser frequency into a radio frequency using an optical frequency comb. The accuracy of the relative frequency measurement is not limiting at all.
The gravitational redshift amounts to around 1E-16 (not 1E-15) when moving the earth one meter closer or further from your clock. You standing next to it is going to have absolutely no effect.
An increase, but those effects are noticed with traditional atomic clocks too. The simple act of moving them between biuldings results in detectable GR effects: time dilation from acceleration as someone pushes the cart. A more accurate measure of such things could yield a functional GR-based accelerometer/gyroscope.
This and the recent advances in clock precision. In the last few years cryogenic sapphire clocks have achieved short-term stability on the order of 10s of attoseconds.
lisper|1 year ago
I found the answer here:
https://en.wikipedia.org/wiki/Atomic_clock#Accuracy
It turns out that the current state of the art is 10^-15. Which immediately raises the second question: how do they measure this? 10^-15 is an error of roughly a nanosecond a year. GR causes that kind of time difference between your head and your feet when you stand up.
https://www.nist.gov/news-events/news/2010/09/nist-clock-exp...
I haven't done the math, but I'm guessing that just standing next to a 10^-15 clock would have noticeable effects due to the effects of your gravitational field.
Also: why does thorium-229 in particular have such a low-energy atomic transition? That seems kind of random.
Mind-boggling stuff.
fsh|1 year ago
The gravitational redshift amounts to around 1E-16 (not 1E-15) when moving the earth one meter closer or further from your clock. You standing next to it is going to have absolutely no effect.
sandworm101|1 year ago
topspin|1 year ago
This and the recent advances in clock precision. In the last few years cryogenic sapphire clocks have achieved short-term stability on the order of 10s of attoseconds.
pvg|1 year ago
jas39|1 year ago
unknown|1 year ago
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