4 ms·

Nice! It made me realise that we currently live in a time that can never be accurately referenced outside the planet. So no software can ever truly define 202

Nice! It made me realise that we currently live in a time that can never be accurately referenced outside the planet. So no software can ever truly define 2024-07-11T00:00 on Pluto. It also makes me think that the Mass Relais in Mass Effects could actually also be atomic clocks forming this galactic time grid of reference, so in-game lore seems less implausible.

WorldMaker 2y ago
There are interesting theories about how to use constellations of Pulsars as galactic "atomic clocks". Pulsars are generally extremely predictable in their emissions and with a big enough constellation, you can do old fashioned triangulation to get relative distance between yourself and enough pulsars to sync to some sort of standard time based on synchronicities in pulsar timing. I've not yet seen a full proposed standard for such a thing, but it's also not far from how GPS itself works and how GPS forms its standardized time, which is synced to Earth based atomic clocks but includes more relativistic effects. Most cellphones actually use GPS time rather than "atomic time" today, because they need GPS services in general and also because cell towers use a variant of GPS time in their communications with cell devices for complicated three dimensional dances like tower to tower hand-offs. It's kind of neat how even "Earth time" at its most accurate involves relative effects and triangulation in some of our most used and trusted devices. (Even NTP sync of non-cellphones uses IP pings as an approximate for triangulation to try to reduce error in syncing a laptop or desktop to nearby atomic clock sources. Though at least today in most internet usage, the Internet Protocol is less impacted by relativistic effects.)
- zokier 2y ago
  > how GPS itself works and how GPS forms its standardized time, which is synced to Earth based atomic clocks but includes more relativistic effects While the GPS satellites internal clocks might operate on whatever timescale, it is important to note that the time signal that is broadcast through GPS is strictly fixed offset from TAI without any additional relativistic shifts. And TAI is defined to use the geoid as reference frame. That is to say that if you have a clock synchronized to GPS signal then it should tick exactly at same rate as TAI and UTC.
  - WorldMaker 2y ago
    A goal of GPS triangulation is to sync a local device's clock to TAI/UTC, but it is still a sync done with 3 to 5 (or sometimes more) satellites and math that isn't just Euclidean triangulation but needs to account for relativistic effects. At the scale of GPS and the relative velocity differences between a moving cellphone and moving satellites in orbit that is mostly just accounting for drifts on the order of microseconds, but GPS triangulation does need to account for those and does the relativistic math (on a device, in your hand!). It's an incredible mathematical achievement that the byproduct of triangulation of your position on Earth also syncs your clock extremely close to our best and strictest clocks. Some of that math is relativistic. Certainly not on the scale (velocity/time/distance) that most people think of when they hear relativistic but partly because something as incredible as GPS satellites orbiting in space is no longer science fiction but a mundane part of our day to day lives and devices. There are satellites broadcasting clock signals from space 24/7! With relativistic math our phones figure out where we are down to foot, nearly (sometimes more) and figure out a precise time for where we are! It's incredible and it is a wonderful thing to take advantage of. Relativistic time math happens every day now (sometimes a lot of times in a day) in our lives, and we don't need to think about it.
zokier 2y ago
The whole point of the paper is to show that we can model the time for various bodies to very high degree of accuracy.
- jiehong 2y ago
  Indeed! My point being that it’s gonna be true someday, just not yet.
pfdietz 2y ago
Or even on/in the planet. The Earth's core is about a year younger than the Earth's surface.

WorldMaker 2y ago

There are interesting theories about how to use constellations of Pulsars as galactic "atomic clocks". Pulsars are generally extremely predictable in their emissions and with a big enough constellation, you can do old fashioned triangulation to get relative distance between yourself and enough pulsars to sync to some sort of standard time based on synchronicities in pulsar timing. I've not yet seen a full proposed standard for such a thing, but it's also not far from how GPS itself works and how GPS forms its standardized time, which is synced to Earth based atomic clocks but includes more relativistic effects. Most cellphones actually use GPS time rather than "atomic time" today, because they need GPS services in general and also because cell towers use a variant of GPS time in their communications with cell devices for complicated three dimensional dances like tower to tower hand-offs. It's kind of neat how even "Earth time" at its most accurate involves relative effects and triangulation in some of our most used and trusted devices. (Even NTP sync of non-cellphones uses IP pings as an approximate for triangulation to try to reduce error in syncing a laptop or desktop to nearby atomic clock sources. Though at least today in most internet usage, the Internet Protocol is less impacted by relativistic effects.)

zokier 2y ago
> how GPS itself works and how GPS forms its standardized time, which is synced to Earth based atomic clocks but includes more relativistic effects While the GPS satellites internal clocks might operate on whatever timescale, it is important to note that the time signal that is broadcast through GPS is strictly fixed offset from TAI without any additional relativistic shifts. And TAI is defined to use the geoid as reference frame. That is to say that if you have a clock synchronized to GPS signal then it should tick exactly at same rate as TAI and UTC.
- WorldMaker 2y ago
  A goal of GPS triangulation is to sync a local device's clock to TAI/UTC, but it is still a sync done with 3 to 5 (or sometimes more) satellites and math that isn't just Euclidean triangulation but needs to account for relativistic effects. At the scale of GPS and the relative velocity differences between a moving cellphone and moving satellites in orbit that is mostly just accounting for drifts on the order of microseconds, but GPS triangulation does need to account for those and does the relativistic math (on a device, in your hand!). It's an incredible mathematical achievement that the byproduct of triangulation of your position on Earth also syncs your clock extremely close to our best and strictest clocks. Some of that math is relativistic. Certainly not on the scale (velocity/time/distance) that most people think of when they hear relativistic but partly because something as incredible as GPS satellites orbiting in space is no longer science fiction but a mundane part of our day to day lives and devices. There are satellites broadcasting clock signals from space 24/7! With relativistic math our phones figure out where we are down to foot, nearly (sometimes more) and figure out a precise time for where we are! It's incredible and it is a wonderful thing to take advantage of. Relativistic time math happens every day now (sometimes a lot of times in a day) in our lives, and we don't need to think about it.

zokier 2y ago

The whole point of the paper is to show that we can model the time for various bodies to very high degree of accuracy.

jiehong 2y ago
Indeed! My point being that it’s gonna be true someday, just not yet.

pfdietz 2y ago

Or even on/in the planet. The Earth's core is about a year younger than the Earth's surface.