5 ms·

What you are describing is not just impractical, it is actually impossible. Someone linked to "falsehoods programmers believe about time" but I think maybe "fal

What you are describing is not just impractical, it is actually impossible. Someone linked to "falsehoods programmers believe about time" but I think maybe "falsehoods non-physicists believe about time" might be more apt. There is no such thing as a universal frame of reference is the somewhat depressing outcome of Einstein's theories.

Retric 3y ago
You can select a rest frame based on the velocity of all observable galaxies adjusted for the expansion of the universe and the impact of local sources of gravity. As far as we can tell any observer would come to similar conclusions about that reference frame would be. It’s just not a particularly useful reference.
- nyrikki 3y ago
  There is no objective concept of 'now' even at distance scales of Alpha Centauri with reasonable curvature and speeds. If you want to stick to special relativity, the Andromeda paradox will show the problem with simultaneity with distance, and Einstein's train thought experiment about trains will show the problem of simultaneity with high speed. The order of events, timing of events, and even causal structure of events are not fixed. Even the Conventional Celestial Reference System is only quasi-inertial, only inertial like over small periods of time. The incredible smoothness of the earth approximating a co-rotating frame with a high error tolerance is the only reason we can treat time as absolute on the surface of the Earth. But to derive the new definition of the Kilogram requires lots of corrections as do modern atomic clocks. Don't confuse the ability to choose a reference frame with the Newtonian concept of universal reference frames. When making measurements SR is a framework that allows you to pick any reference frame that is convenient, but the speed of causality(light) prevents the existence of a universal reference frame.
  - numpad0 3y ago
    I don’t get it, can’t you just set off neutron bomb every second on Earth and use it as a monotonic counter signal? Isn’t that like, speed of light or wavefront of event propagation in the universe isn’t consistent but unavoidably potato shaped - but if so, wouldn’t it be at least difficult to have multiple potatoes intersecting, or potato being shaped like Klein bottle? Self intersecting potato shaped space-time would be cool, though.
    - nyrikki 3y ago
      The problem is that they aren't 'potato shaped' rotations, they are better thought of as hyperbolic rotations. Simultaneous distant events in Lorentz transformations will all lay on a shared hyperbola not a distorted circle. Really this is beyond typical human intuition and requires math, but here is a quick minutephysics video that quickly demonstrates fairly well it without me typing out a bunch of math that no one wants anyway. https://youtu.be/SrNVsfkGW-0 https://youtu.be/SrNVsfkGW-0
    - whimsicalism 3y ago
      in short, no. not if you want hyperaccurate time keeping
  - Retric 3y ago
    > The order of events, timing of events, and even causal structure of events are not fixed. You can calculate observed order of events for any reference frame from any reference frame. Thus they are fixed once everyone agrees to using a given reference frame. It’s not much more complicated than seismic detectors recording the seismic waves from an earthquake at different times based on their location. Sure detector X see earthquakes in order A, B, C and detector Y sees them in order C, B, A they would both agree that detector Z should see them in order A, C, B based on it’s location, the timing of the events, and wave propitiation speeds. It only seems unintuitive because you aren’t used to accounting for such issues.
    - nyrikki 3y ago
      In SR, you have the spacetime interval, it is more complex in GR. For constant velocity motion in flat spacetime: Δτ^2Δs^2 = c^2Δt^2-Δx^2-Δy^2-Δz^2 The spacetime interval is invariant, but notice it is also a scaler that combines space and time, and note that time is multiplied by c^2. Also note Δt is the time as observed but an inertial observer that is present at both events. You have three types of intervals here represented by one scaler. Timelike: Δτ^2 > 0 Spacelike: Δτ^2 < 0 Lightlike: Δτ^2 = 0 In the case of Δτ^2 = 0, that is equivalent to an inertial observer that is present at both events at the same time. Which will seem to be simultaneous. Δτ and Δt are practically the same in situations we commonly experience and an assumption of constant velocity motion in flat spacetime is usually accurate enough. And will an assumption of constant velocity motion in flat spacetime, you can CHOOSE a Δτ that is 0. There is no universal reference frame where Δτ =0. More importantly your observations are of the past for distant observers, and don't have a universal concept of 'now' outside of the local case.
      - Retric 3y ago
        You just completely missed my point. GR and curved space time again isn’t an issue as long as everyone knows what space time looks like. Mission Control on earth, a moon base, and mars would all experiencing time at a different rate and those rates would vary based on the orbits of each body. However assuming we needed extreme precision, such as telescope interferometry, people can pick one of them arbitrarily or perhaps due to politics some arbitrary 4th option. Whatever their choice everyone’s timelines based on that choice end up being absolutely identical. The math simply works without any ambiguity. So because there’s an obvious choice based on the actual universe we live in, ie maximum amount of time since the Big Bang, then in theory trillions of civilizations across many different galaxies might all use the exact same reference even if no particle experienced it. Edit: Well not exactly the same there’s uncertainty for such calculations but effectively the same.
- tshaddox 3y ago
  This sort of clock wouldn't be very useful for, say, baking bread for the correct amount of time in an accelerating frame of reference, right?
Out_of_Characte 3y ago
I dont think the GP is asking for a universal reference frame in the same way physics describes it. I think he's asking for a universal programmatic reference frame to describe the offsets that sattelites and lunar stations have. Even though time runs faster on sattelites, and the signal delay differs based on position. Because the vectors of sattelites and the moon is constant, as well as the moons gravity, you could calculate what those offsets should be and synchronise clocks anyway. To put it another way, you normalise the clock drift and the delay, whats left over is the same clock drift you'll need to account for when you have a quartz clock in your computer and a time server that runs an atomic clock. The point being, clock drift can become a huge issue unless you define a specification that allows any equipment to sync up with any other clock in Time And Relative Dimensions In Space.
- jzemeocala 3y ago
  Nice Dr. WHO reference
- whimsicalism 3y ago
  if the sequencing of events is not even consistent between the reference points, what offsets would possible make sense?
  - 317070 3y ago
    You can always say, "I observed event A at time X from position Y" Relativity doesn't make time-keeping impossible. It just requires more clarity. UTC was implemented after Einstein passed away.
dpedu 3y ago
Why can't Earth time be the universal frame of reference, and everywhere else use a factor of earth time? This article describes the rate difference already, why can't we use that?
- andrewla 3y ago
  For the moon that potentially works because we're close enough to the moon that the drift is dominated by local gravitation rather than relative motion. But for any other context, say Mars, the problem is that the clock drift will be non-uniform. An hour on Earth (as measured by a precise clock on Earth) vs an hour on Mars as measured by a precise clock on Mars) will not be a fixed ratio, but will depend on relative position and velocities at the time that you start measuring the hour.
  - dpedu 3y ago
    Aren't those relative positions and velocities predictable enough? I believe NASA regularly makes predictions somewhat like this, such as when specific large asteroids are predicted to come near earth.
    - ianburrell 3y ago
      Sure, just like the relativistic effects of GPS clocks on Earth are predictable. But it makes clock keeping on Mars much more complicated, always making corrections. The corrections are always changing and syncing time is hard because the motions are always changing. Simplest solution is to use local atomic clocks. And then calculate Earth time when needed. All for zero benefit because the Earth is variable number of minutes from Mars so there will always be variation. Mars day is different from Earth have to calculate Earth time anyway.
      - Izkata 3y ago
        > Simplest solution is to use local atomic clocks. And then calculate Earth time when needed. Which is exactly what OP was suggesting, everyone else went off on a tangent.
willvarfar 3y ago
(a bit late, but anyway, ... I wasn't suggesting we should have a true universal time, I was suggesting that we rename the mislabelled universal coordinated time that we already have to something else... :) )
Wissenschafter 3y ago
How is it depressing? Relativity of simultaneity implies the universe is basically a giant crystal, future and past both actually exist. They almost have to for relativity of simultaneity to be the way it is. That means everything happening is happening forever, all at once. I guess if you live a shitty existence, then its infinitely shittier, but if not, its infinitely meh. Guess it depends on how you look at it.

Retric 3y ago

You can select a rest frame based on the velocity of all observable galaxies adjusted for the expansion of the universe and the impact of local sources of gravity. As far as we can tell any observer would come to similar conclusions about that reference frame would be. It’s just not a particularly useful reference.

nyrikki 3y ago
There is no objective concept of 'now' even at distance scales of Alpha Centauri with reasonable curvature and speeds. If you want to stick to special relativity, the Andromeda paradox will show the problem with simultaneity with distance, and Einstein's train thought experiment about trains will show the problem of simultaneity with high speed. The order of events, timing of events, and even causal structure of events are not fixed. Even the Conventional Celestial Reference System is only quasi-inertial, only inertial like over small periods of time. The incredible smoothness of the earth approximating a co-rotating frame with a high error tolerance is the only reason we can treat time as absolute on the surface of the Earth. But to derive the new definition of the Kilogram requires lots of corrections as do modern atomic clocks. Don't confuse the ability to choose a reference frame with the Newtonian concept of universal reference frames. When making measurements SR is a framework that allows you to pick any reference frame that is convenient, but the speed of causality(light) prevents the existence of a universal reference frame.
- numpad0 3y ago
  I don’t get it, can’t you just set off neutron bomb every second on Earth and use it as a monotonic counter signal? Isn’t that like, speed of light or wavefront of event propagation in the universe isn’t consistent but unavoidably potato shaped - but if so, wouldn’t it be at least difficult to have multiple potatoes intersecting, or potato being shaped like Klein bottle? Self intersecting potato shaped space-time would be cool, though.
  - nyrikki 3y ago
    The problem is that they aren't 'potato shaped' rotations, they are better thought of as hyperbolic rotations. Simultaneous distant events in Lorentz transformations will all lay on a shared hyperbola not a distorted circle. Really this is beyond typical human intuition and requires math, but here is a quick minutephysics video that quickly demonstrates fairly well it without me typing out a bunch of math that no one wants anyway. https://youtu.be/SrNVsfkGW-0 https://youtu.be/SrNVsfkGW-0
  - whimsicalism 3y ago
    in short, no. not if you want hyperaccurate time keeping
- Retric 3y ago
  > The order of events, timing of events, and even causal structure of events are not fixed. You can calculate observed order of events for any reference frame from any reference frame. Thus they are fixed once everyone agrees to using a given reference frame. It’s not much more complicated than seismic detectors recording the seismic waves from an earthquake at different times based on their location. Sure detector X see earthquakes in order A, B, C and detector Y sees them in order C, B, A they would both agree that detector Z should see them in order A, C, B based on it’s location, the timing of the events, and wave propitiation speeds. It only seems unintuitive because you aren’t used to accounting for such issues.
  - nyrikki 3y ago
    In SR, you have the spacetime interval, it is more complex in GR. For constant velocity motion in flat spacetime: Δτ^2Δs^2 = c^2Δt^2-Δx^2-Δy^2-Δz^2 The spacetime interval is invariant, but notice it is also a scaler that combines space and time, and note that time is multiplied by c^2. Also note Δt is the time as observed but an inertial observer that is present at both events. You have three types of intervals here represented by one scaler. Timelike: Δτ^2 > 0 Spacelike: Δτ^2 < 0 Lightlike: Δτ^2 = 0 In the case of Δτ^2 = 0, that is equivalent to an inertial observer that is present at both events at the same time. Which will seem to be simultaneous. Δτ and Δt are practically the same in situations we commonly experience and an assumption of constant velocity motion in flat spacetime is usually accurate enough. And will an assumption of constant velocity motion in flat spacetime, you can CHOOSE a Δτ that is 0. There is no universal reference frame where Δτ =0. More importantly your observations are of the past for distant observers, and don't have a universal concept of 'now' outside of the local case.
    - Retric 3y ago
      You just completely missed my point. GR and curved space time again isn’t an issue as long as everyone knows what space time looks like. Mission Control on earth, a moon base, and mars would all experiencing time at a different rate and those rates would vary based on the orbits of each body. However assuming we needed extreme precision, such as telescope interferometry, people can pick one of them arbitrarily or perhaps due to politics some arbitrary 4th option. Whatever their choice everyone’s timelines based on that choice end up being absolutely identical. The math simply works without any ambiguity. So because there’s an obvious choice based on the actual universe we live in, ie maximum amount of time since the Big Bang, then in theory trillions of civilizations across many different galaxies might all use the exact same reference even if no particle experienced it. Edit: Well not exactly the same there’s uncertainty for such calculations but effectively the same.
tshaddox 3y ago
This sort of clock wouldn't be very useful for, say, baking bread for the correct amount of time in an accelerating frame of reference, right?

Out_of_Characte 3y ago

I dont think the GP is asking for a universal reference frame in the same way physics describes it. I think he's asking for a universal programmatic reference frame to describe the offsets that sattelites and lunar stations have. Even though time runs faster on sattelites, and the signal delay differs based on position. Because the vectors of sattelites and the moon is constant, as well as the moons gravity, you could calculate what those offsets should be and synchronise clocks anyway. To put it another way, you normalise the clock drift and the delay, whats left over is the same clock drift you'll need to account for when you have a quartz clock in your computer and a time server that runs an atomic clock. The point being, clock drift can become a huge issue unless you define a specification that allows any equipment to sync up with any other clock in Time And Relative Dimensions In Space.

jzemeocala 3y ago
Nice Dr. WHO reference
whimsicalism 3y ago
if the sequencing of events is not even consistent between the reference points, what offsets would possible make sense?
- 317070 3y ago
  You can always say, "I observed event A at time X from position Y" Relativity doesn't make time-keeping impossible. It just requires more clarity. UTC was implemented after Einstein passed away.

dpedu 3y ago

Why can't Earth time be the universal frame of reference, and everywhere else use a factor of earth time? This article describes the rate difference already, why can't we use that?

andrewla 3y ago
For the moon that potentially works because we're close enough to the moon that the drift is dominated by local gravitation rather than relative motion. But for any other context, say Mars, the problem is that the clock drift will be non-uniform. An hour on Earth (as measured by a precise clock on Earth) vs an hour on Mars as measured by a precise clock on Mars) will not be a fixed ratio, but will depend on relative position and velocities at the time that you start measuring the hour.
- dpedu 3y ago
  Aren't those relative positions and velocities predictable enough? I believe NASA regularly makes predictions somewhat like this, such as when specific large asteroids are predicted to come near earth.
  - ianburrell 3y ago
    Sure, just like the relativistic effects of GPS clocks on Earth are predictable. But it makes clock keeping on Mars much more complicated, always making corrections. The corrections are always changing and syncing time is hard because the motions are always changing. Simplest solution is to use local atomic clocks. And then calculate Earth time when needed. All for zero benefit because the Earth is variable number of minutes from Mars so there will always be variation. Mars day is different from Earth have to calculate Earth time anyway.
    - Izkata 3y ago
      > Simplest solution is to use local atomic clocks. And then calculate Earth time when needed. Which is exactly what OP was suggesting, everyone else went off on a tangent.

willvarfar 3y ago

(a bit late, but anyway, ... I wasn't suggesting we should have a true universal time, I was suggesting that we rename the mislabelled universal coordinated time that we already have to something else... :) )

Wissenschafter 3y ago

How is it depressing? Relativity of simultaneity implies the universe is basically a giant crystal, future and past both actually exist. They almost have to for relativity of simultaneity to be the way it is. That means everything happening is happening forever, all at once. I guess if you live a shitty existence, then its infinitely shittier, but if not, its infinitely meh. Guess it depends on how you look at it.