Living Without Atomic Clocks
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Living Without Atomic Clocks
1–10 of 52 posts
Re: Living Without Atomic Clocks
#2I don't understand why 7ms is considered a good bound for atomic clocks?
Hafele and Keating Experiment: "During October, 1971, four cesium atomic beam clocks were flown on regularly scheduled commercial jet flights around the world twice, once eastward and once westward, to test Einstein's theory of relativity with macroscopic clocks. From the actual flight paths of each trip, the theory predicted that the flying clocks, compared with reference clocks at the U.S. Naval Observatory, should have lost 40+/-23 nanoseconds during the eastward trip and should have gained 275+/-21 nanoseconds during the westward trip ... Relative to the atomic time scale of the U.S. Naval Observatory, the flying clocks lost 59+/-10 nanoseconds during the eastward trip and gained 273+/-7 nanosecond during the westward trip, where the errors are the corresponding standard deviations. These results provide an unambiguous empirical resolution of the famous clock "paradox" with macroscopic clocks."
So if we are loosing nano seconds per day, couldn't we fly clocks around the datacenters and resync every month. 7ms seems beatable and not a terrible operational overhead for a fast globally consistent database.
Re: Living Without Atomic Clocks
#3I don't understand why 7ms is considered a good bound for atomic clocks? Hafele and Keating Experiment: "During October, 1971, four cesium atomic beam clocks were flown on regularly scheduled commercial jet flights around the world twice, once eastward and once westward, to test Einstein's theory of relativity with macroscopic clocks. From the actual flight paths of each trip, the theory predicted that the flying clo…
Maybe they've mixed up ms and µs? Their claim of "between 100ms and 250ms" for NTP also seems way too high.
Re: Living Without Atomic Clocks
#4I don't understand why 7ms is considered a good bound for atomic clocks? Hafele and Keating Experiment: "During October, 1971, four cesium atomic beam clocks were flown on regularly scheduled commercial jet flights around the world twice, once eastward and once westward, to test Einstein's theory of relativity with macroscopic clocks. From the actual flight paths of each trip, the theory predicted that the flying clo…
Something I never understood. If velocity (?) affects time, wouldn't time operate a different speed at different parts of the universe / solar system?
Re: Living Without Atomic Clocks
#5I don't understand why 7ms is considered a good bound for atomic clocks? Hafele and Keating Experiment: "During October, 1971, four cesium atomic beam clocks were flown on regularly scheduled commercial jet flights around the world twice, once eastward and once westward, to test Einstein's theory of relativity with macroscopic clocks. From the actual flight paths of each trip, the theory predicted that the flying clo…
Something I never understood. If velocity (?) affects time, wouldn't time operate a different speed at different parts of the universe / solar system?
Both velocity and gravity (distance from the nearest planet/star) affect time.
It does, but the difference is negligible unless we're talking about the surface of a neutron star.
Re: Living Without Atomic Clocks
#6I don't understand why 7ms is considered a good bound for atomic clocks? Hafele and Keating Experiment: "During October, 1971, four cesium atomic beam clocks were flown on regularly scheduled commercial jet flights around the world twice, once eastward and once westward, to test Einstein's theory of relativity with macroscopic clocks. From the actual flight paths of each trip, the theory predicted that the flying clo…
Something I never understood. If velocity (?) affects time, wouldn't time operate a different speed at different parts of the universe / solar system?
I am not a physicist but I believe the answer is yes as time is affected by acceleration.
Re: Living Without Atomic Clocks
#7I don't understand why 7ms is considered a good bound for atomic clocks? Hafele and Keating Experiment: "During October, 1971, four cesium atomic beam clocks were flown on regularly scheduled commercial jet flights around the world twice, once eastward and once westward, to test Einstein's theory of relativity with macroscopic clocks. From the actual flight paths of each trip, the theory predicted that the flying clo…
Something I never understood. If velocity (?) affects time, wouldn't time operate a different speed at different parts of the universe / solar system?
The movie Interstellar does a decent job demonstrating this (well the gravity piece anyway with the proximity to black holes).
I also think satellite clocks have to take time relativity it into account (both due to distance from earth's gravity and their speed).
Randall Munroe has a pretty entertaining write up that does a decent job giving a high level overview in pretty easy to understand terms: http://www.newyorker.com/tech/elements/the-space-doctors-big...
Re: Living Without Atomic Clocks
#8I don't understand why 7ms is considered a good bound for atomic clocks? Hafele and Keating Experiment: "During October, 1971, four cesium atomic beam clocks were flown on regularly scheduled commercial jet flights around the world twice, once eastward and once westward, to test Einstein's theory of relativity with macroscopic clocks. From the actual flight paths of each trip, the theory predicted that the flying clo…
The 7ms bound is on the machines that do the actual work, not the ones with access to special clock hardware.
Re: Living Without Atomic Clocks
#9I don't understand why 7ms is considered a good bound for atomic clocks? Hafele and Keating Experiment: "During October, 1971, four cesium atomic beam clocks were flown on regularly scheduled commercial jet flights around the world twice, once eastward and once westward, to test Einstein's theory of relativity with macroscopic clocks. From the actual flight paths of each trip, the theory predicted that the flying clo…
Maybe they've mixed up ms and µs? Their claim of "between 100ms and 250ms" for NTP also seems way too high.
It likely has more to do with network latency than with any fundamental physical limitation of the system.
Re: Living Without Atomic Clocks
#10I don't understand why 7ms is considered a good bound for atomic clocks? Hafele and Keating Experiment: "During October, 1971, four cesium atomic beam clocks were flown on regularly scheduled commercial jet flights around the world twice, once eastward and once westward, to test Einstein's theory of relativity with macroscopic clocks. From the actual flight paths of each trip, the theory predicted that the flying clo…
Something I never understood. If velocity (?) affects time, wouldn't time operate a different speed at different parts of the universe / solar system?
I always thought it would be an interesting physics exam question to ask: "If a clock were landed on Halley's comet, and retrieved on its next orbit, what would be the expected difference in time relative to an earth bound clock?" It's tricky because all orbiting bodies experience a range of velocities as they orbit their star. But I gather Halley's comet has a particularly eccentric orbit (0.9) with a rapid perihelion of around 70km/sec, an aphelion of about 1km/sec, and about 75 years for a single orbit (ΔT' = ΔT / sqrt(1 - (v²/c²)))