7 ms·

The bigger problem is that UTC (and TAI) is defined in a gravity well so it's not going to be very useful in the long run. GPS has to correct its clocks to kee

The bigger problem is that UTC (and TAI) is defined in a gravity well so it's not going to be very useful in the long run. GPS has to correct its clocks to keep track of what we slow Cesium/Rubidium down to on the surface, and Voyager's clock is going even faster. We clearly want an Earth-centric time standard for wall clocks and that is UTC. The Earth is not a precision time-piece so we will always have to adjust our wall clocks to its rotation. Realistically, we should probably be deriving a time standard where every day has a slightly different length and we record the timestamps of the beginning of each day relative to a universal monotonic clock in a log (with rollups to years, centuries, etc.) that we keep around as long as anyone cares exactly how many Cesium vibrations have happened since $whence. If we want to actually solve the problem then let's switch to an interstellar time standard in a rest frame relative to the CMBR as far outside of gravity wells as possible and make that the universal monotonically increasing standard. Then computers can run on that time standard and UTC and friends can be derivatives.

Enginerrrd 4y ago
I'm not sure it matters. To synchronize, you'll have to make corrections either way, and over sufficiently large scales, signal propagation delays are going to be quite large.
- benlivengood 4y ago
  Here my physics knowledge gets a little sketchy, but if we have an accurate clock broadcasting on a known frequency somewhere far away we should be able to at least measure the drift between it and a local clock to arbitrary precision. With ~zero drift we can measure the distance and relative velocity very accurately with round-trip timing and Doppler measurements, and from that measure the clock offset as accurately as we can measure the distance. I think, but could be wrong, that we'd always be measuring the spacetime interval, not the euclidean distance in space, but that is probably what we actually want once we start caring about relativistic timekeeping.
Denvercoder9 4y ago
> let's switch to an interstellar time standard in a rest frame relative to the CMBR as far outside of gravity wells as possible This won't work: since galaxies aren't static, and because the universe expands, the point with the highest gravitational potential ("as far outside of gravity wells as possible") will both move w.r.t. the CMBR and have a gravitional potential that changes over time.
- benlivengood 4y ago
  Maybe I'm making a bad assumption that intergalactic space is so flat that pretty much any region of it will do as a reference. Since we can't reach those regions yet we'd still be approximating it with our slower clocks, but it seems like it's at least feasible.
  - NineStarPoint 4y ago
    Galactic groups are gravitationally bound enough that they’ll stay together through the expansion of the universe. Would want to find an area that is particularly void of galactic influence maybe?
ncmncm 4y ago
Your proposal is to make the time Standard of billions of people not match what they experience, on behalf of a few space probes, none of which will use it.
- XorNot 4y ago
  Meta don't want leap seconds because leap seconds make distributed system cluster synchronization tricky, because that's the only case where an extra second here or there actually matters. Across all the devices in my house that have a clock in them, the time drift is a little over an hour and it doesn't make the slightest bit of difference to me: internet connected computers being the most accurate. Between individual computers, thanks to filesystem semantics, drifts of up to 2 seconds are expected and generally considered "identical" - it certainly doesn't matter for file sync applications. So either we want to build a time standard that can be transformed in a sensible way to all the others which are useful - in which case something which works for interstellar timekeeping would be a sensible step, given that relativistic issues crop up even in Earth orbit, or we're building a time system "for humans" in which case everything we have now is fine, and will by definition be messy because time and timezones change all the time.
  - nullc 4y ago
    That is absolutely not the only case where an extra second here or there matters. It's just for distributed systems the OTHER ways of dealing with the problems leapseconds create (e.g. using a local monotone clock) aren't available. But even where they are available leapseconds still create issues because they're extremely difficult to test and are often handled somewhat incorrectly. UTC without leapseconds would in no way be less "for humans". After 4000 years of drift the effect on the solar noon would be about the same as you get driving to the next state over.
    - XorNot 4y ago
      Except as I noted up thread we've already got "UTC without leap seconds" - it's UNIX epoch time which is defined to ignore leap seconds. Leap seconds are still seconds so even with GPS sync, if all you're doing is tracking 1000ms increments then we have a format already which doesn't have them.
a9h74j 4y ago
> let's switch to an interstellar time standard in a rest frame Timex(TM) Watches, now featuring Puslar(TM) Time.
nullc 4y ago
The TAI second is defined relative to a particular gravitational potential. Adapting to another known one is just a unit change. (if you don't know then nothing can help you). The difference between potential already need to get handled on earth. Esp. since the NIST labs in boulder are at about 5400 feet.

Enginerrrd 4y ago

I'm not sure it matters. To synchronize, you'll have to make corrections either way, and over sufficiently large scales, signal propagation delays are going to be quite large.

benlivengood 4y ago
Here my physics knowledge gets a little sketchy, but if we have an accurate clock broadcasting on a known frequency somewhere far away we should be able to at least measure the drift between it and a local clock to arbitrary precision. With ~zero drift we can measure the distance and relative velocity very accurately with round-trip timing and Doppler measurements, and from that measure the clock offset as accurately as we can measure the distance. I think, but could be wrong, that we'd always be measuring the spacetime interval, not the euclidean distance in space, but that is probably what we actually want once we start caring about relativistic timekeeping.

Denvercoder9 4y ago

> let's switch to an interstellar time standard in a rest frame relative to the CMBR as far outside of gravity wells as possible This won't work: since galaxies aren't static, and because the universe expands, the point with the highest gravitational potential ("as far outside of gravity wells as possible") will both move w.r.t. the CMBR and have a gravitional potential that changes over time.

benlivengood 4y ago
Maybe I'm making a bad assumption that intergalactic space is so flat that pretty much any region of it will do as a reference. Since we can't reach those regions yet we'd still be approximating it with our slower clocks, but it seems like it's at least feasible.
- NineStarPoint 4y ago
  Galactic groups are gravitationally bound enough that they’ll stay together through the expansion of the universe. Would want to find an area that is particularly void of galactic influence maybe?

ncmncm 4y ago

Your proposal is to make the time Standard of billions of people not match what they experience, on behalf of a few space probes, none of which will use it.

XorNot 4y ago
Meta don't want leap seconds because leap seconds make distributed system cluster synchronization tricky, because that's the only case where an extra second here or there actually matters. Across all the devices in my house that have a clock in them, the time drift is a little over an hour and it doesn't make the slightest bit of difference to me: internet connected computers being the most accurate. Between individual computers, thanks to filesystem semantics, drifts of up to 2 seconds are expected and generally considered "identical" - it certainly doesn't matter for file sync applications. So either we want to build a time standard that can be transformed in a sensible way to all the others which are useful - in which case something which works for interstellar timekeeping would be a sensible step, given that relativistic issues crop up even in Earth orbit, or we're building a time system "for humans" in which case everything we have now is fine, and will by definition be messy because time and timezones change all the time.
- nullc 4y ago
  That is absolutely not the only case where an extra second here or there matters. It's just for distributed systems the OTHER ways of dealing with the problems leapseconds create (e.g. using a local monotone clock) aren't available. But even where they are available leapseconds still create issues because they're extremely difficult to test and are often handled somewhat incorrectly. UTC without leapseconds would in no way be less "for humans". After 4000 years of drift the effect on the solar noon would be about the same as you get driving to the next state over.
  - XorNot 4y ago
    Except as I noted up thread we've already got "UTC without leap seconds" - it's UNIX epoch time which is defined to ignore leap seconds. Leap seconds are still seconds so even with GPS sync, if all you're doing is tracking 1000ms increments then we have a format already which doesn't have them.

a9h74j 4y ago

> let's switch to an interstellar time standard in a rest frame Timex(TM) Watches, now featuring Puslar(TM) Time.

nullc 4y ago

The TAI second is defined relative to a particular gravitational potential. Adapting to another known one is just a unit change. (if you don't know then nothing can help you). The difference between potential already need to get handled on earth. Esp. since the NIST labs in boulder are at about 5400 feet.