clock is a synchroniser

clocks became widespread because they synchronised the activities of the masses of factory workers in the industrial era with the work schedule

5 hours ago, StringJunky said:

Distance is that which is measured with a ruler. Time is that which is measured with a clock. We don't analyse the nature of distance, do we? Time doesn't require an ontological analysis. i.e. What is time? That is philosophy; physics, seeks to only describe the behaviour of natural phenomena.

And a hallmark of phenomena is change. So the only ontic basis we need is that we measure change with other change. (no doubt Swanson or someone else will point out the innate circularity that manifests when we then define "change") A clock is something thet changes in a regular pattern that may be compared with some other change. So a physical description, without ontology, will be a comparison.

A rotting head of cabbage could be a perfectly good clock if cabbage rotted at a consistent rate. If this was so (in this gedanken universe), then we could measure the Earth's positional change with cabbage decomposition. Change measuring change - the Earth orbits in 18.32 cabbage rots. Time remains on the bench, an abstraction. (until we are called upon to define "change" and I would pay good money to watch someone do that without using time-y words!)(but perhaps a row of pictures of deteriorating cabbage would serve? B-b-but wait.... weren't the photos chronologically organized? Argh...)

Edited April 22Apr 22 by TheVat
it was time for editing

2 hours ago, Killtech said:

there is no evidence that they have any mass either.

Being ignorant of this is not the same as it being true.

2 hours ago, Killtech said:

the only reason why it is speculated it to have a mass is due to the discovery of their oscillation. but so far all experiments trying to determine it came empty handed.

Not knowing the specific values is not the same thing as saying we don’t have evidence of it being nonzero.

2 hours ago, Killtech said:

Also no experiment found any evidence of them moving any slower then photons, in fact in observations of cosmic events they do arrive before photons do but that is due to non exotic reasons. So we are coming to a point where the matter is getting more complex and alternative explanations are looked into for a reason.

Doesn’t matter.

16 hours ago, TheVat said:

And a hallmark of phenomena is change. So the only ontic basis we need is that we measure change with other change. (no doubt Swanson or someone else will point out the innate circularity that manifests when we then define "change") A clock is something thet changes in a regular pattern that may be compared with some other change. So a physical description, without ontology, will be a comparison.

yes, that's a good summary. the question is however, what if a regular and reproducible pattern does not uniquely specify a clock?

For example, if someone build a device that was able to calculate the Barycentric Coordinate Time (TCB) at any instance, it would provide a perfectly consistent method of measuring time. But its rate of change differs relative to an atomic clock depending on the frame and location. in particular, TCB ticks faster then a atomic clock on earth (which is TT), but far out of planetary influence, the tick rates are much closer and far enough from the sun they will almost agree.

The consideration of alternative devices that behave differently from regular clocks (those that conform to SI standards), yet still provide a consistent mechanism to measure time is the reason for this thread.

16 hours ago, TheVat said:

A rotting head of cabbage could be a perfectly good clock if cabbage rotted at a consistent rate. If this was so (in this gedanken universe), then we could measure the Earth's positional change with cabbage decomposition. Change measuring change - the Earth orbits in 18.32 cabbage rots. Time remains on the bench, an abstraction. (until we are called upon to define "change" and I would pay good money to watch someone do that without using time-y words!)(but perhaps a row of pictures of deteriorating cabbage would serve? B-b-but wait.... weren't the photos chronologically organized? Argh...)

wasn't the time in office of a Britisch prime minister not so long ago counted in cabbage rots?

Edited April 22Apr 22 by Killtech

14 hours ago, TheVat said:

A rotting head of cabbage could be a perfectly good clock if cabbage rotted at a consistent rate.

consistent rate ?

Surely all it need to be is predictable ie a known function or a function with a known derivative.

This is how radioactive clocks (dating) work.

Nor am I convinced that oscillation require mass.

2 hours ago, Killtech said:

yes, that's a good summary. the question is however, what if a regular and reproducible pattern does not uniquely specify a clock?

For example, if someone build a device that was able to calculate the Barycentric Coordinate Time (TCB) at any instance, it would provide a perfectly consistent method of measuring time. But its rate of change differs relative to an atomic clock depending on the frame and location. in particular, TCB ticks faster then a atomic clock on earth (which is TT), but far out of planetary influence, the tick rates are much closer and far enough from the sun they will almost agree.

There are a number of different timescales out there. UTC, TAI, UT1, and more https://stjarnhimlen.se/comp/time.html

GPS time is a different one as well, since it doesn’t include leap seconds, so it’s offset from UTC

Clocks on earth tick at different rates, depending on their elevation (or possibly altitude)

It simply isn’t a problem, since you can convert one into the other.

Pendulums aren’t, and don’t have to be, a uniform length for a pendulum clock. You can use a variety of atoms in atomic clocks. Calibration/translation is mainly a matter of math.

A regular and reproducible pattern can be made into a clock; but it’s not guaranteed to be straightforward engineering, and the quality of the clock (accuracy and stability) is not a guarantee.

2 hours ago, Killtech said:

The consideration of alternative devices that behave differently from regular clocks (those that conform to SI standards), yet still provide a consistent mechanism to measure time is the reason for this thread.

Most clocks don’t conform to SI standards, or don’t have to. Cs clocks are a small minority of clocks in this world, and an even smaller minority of all clocks when considered over history (probably most of which predate SI units)

On 4/23/2025 at 12:01 AM, swansont said:

Clocks on earth tick at different rates, depending on their elevation (or possibly altitude)

It simply isn’t a problem, since you can convert one into the other.

TCB, implemented as a device, behaves close to a radio clock (with a specifically arranged source signal). These differ from other clocks in how they respond to conditions where time dilation becomes relevant. This is what makes it interesting for consideration.

most constants, as expressed in units of TCB have slightly different values. Moreover, c specifically varies in value depending on the region because the time dilation correction in the time standard moves into c. This isn't anything novel though, as normally it is treated as a coordinate speed for which this is absolutely fine.

However, if we declare such time measurements to count as clocks, we elevate what is normally a coordinate time to count as proper time - therefore we change the interpretation of what is proper. This subtlety is why it is relevant how a clock is defined exactly in terms of the theory. In this instances this would come with the consequence that the covariant form of physical laws have to take the form of how they look specifically in these special coordinates, that is how the coordinate time, coordinate speeds, coordinate forces and so on behave there.

It's not a problem either way, if we know what we are doing. It does however impact the calculus without changing the predictions it makes.

Edited April 26Apr 26 by Killtech

1 hour ago, Killtech said:

TCB, implemented as a device, behaves close to a radio clock (with a specifically arranged source signal). These differ from other clocks in how they respond to conditions where time dilation becomes relevant. This is what makes it interesting for consideration.

most constants, as expressed in units of TCB have slightly different values.

Yup. If you chose imperial units you’d have the same situation. Numerically different constants.

1 hour ago, Killtech said:

Moreover, c specifically varies in value depending on the region because the time dilation correction in the time standard moves into c. This isn't anything novel though, as normally it is treated as a coordinate speed for which this is absolutely fine.

No, that’s not the case. You’d have a different value, but the invariance of c has not changed. The time just ticks faster by about 1.5 x 10^-8

Here’s how you convert between the time conventions

https://cxc.harvard.edu/contrib/arots/time/time_tutorial.html

1 hour ago, Killtech said:

However, if we declare such time measurements to count as clocks, we elevate what is normally a coordinate time to count as proper time - therefore we change the interpretation of what is proper. This subtlety is why it is relevant how a clock is defined exactly in terms of the theory. In this instances this would come with the consequence that the covariant form of physical laws have to take the form of how they look specifically in these special coordinates, that is how the coordinate time, coordinate speeds, coordinate forces and so on behave there.

It's not a problem either way, if we know what we are doing. It does however impact the calculus without changing the predictions it makes.

Moving clocks are still clocks. Clocks in different gravitational potentials or different accelerations are still clocks. I don’t know why you think they aren’t.

27 minutes ago, swansont said:

No, that’s not the case. You’d have a different value, but the invariance of c has not changed. The time just ticks faster by about 1.5 x 10^-8

Here’s how you convert between the time conventions

https://cxc.harvard.edu/contrib/arots/time/time_tutorial.html

these are conversion between various coordinate times, not between TCB and clocks.

the difference you wrote is between TT and TCB, that is it is the conversion valid only for the situation of a clock on earth. it will yield wrong results in space where TT does not align with the reading of clocks. far off from the sun the tick rate discrepancy between TCB and a clock vanishes as they tick at the same rate. the difference depends on the location and frame.

Here for a few more details with proper formulas https://iers-conventions.obspm.fr/content/chapter10/tn36_c10.pdf (though these are lower order approximation; actual formulas are significantly more complicated).

Edited April 26Apr 26 by Killtech

1 hour ago, Killtech said:

these are conversion between various coordinate times, not between TCB and clocks.

A clock located at the appropriate location will give you that time, or something that could be converted to it. (e.g. adjust for the gravitational time dilation, which we do for UTC)

1 hour ago, Killtech said:

the difference you wrote is between TT and TCB, that is it is the conversion valid only for the situation of a clock on earth. it will yield wrong results in space where TT does not align with the reading of clocks. far off from the sun the tick rate discrepancy between TCB and a clock vanishes as they tick at the same rate. the difference depends on the location and frame.

You can do a similar conversion for any other location and frame.

16 minutes ago, swansont said:

A clock located at the appropriate location will give you that time, or something that could be converted to it. (e.g. adjust for the gravitational time dilation, which we do for UTC)

but we are discussing the general case of a clock which can be in any frame or location, hence this specific scenario is not helping.

2 minutes ago, swansont said:

You can do a similar conversion for any other location and frame.

yes, and it is different for every location and frame, so the general conversion is a complicated formula that depends on the trajectory taken over which you need to integrate, hence the result will differ depending on the circumstance.

Along some trajectories TCB will measure the identical time passed as a clock would, along others the TCB time interval will be shorter then what the clock reads and along others again it will be longer. In every case a complicated conversion exists, which

On 4/1/2025 at 6:16 AM, Markus Hanke said:

you need to account not just for location and time, but also for the history of the physical system in question.

if you want to make it entirely correct, not just approximately like in 10.2 section of the article i posted before.

3 hours ago, swansont said:

Moving clocks are still clocks. Clocks in different gravitational potentials or different accelerations are still clocks. I don’t know why you think they aren’t.

where did you get the idea from that i don't think they are clocks? a device reading TCB will not count as a clock though since the time it reads is very different from clocks.

1 hour ago, Killtech said:

but we are discussing the general case of a clock which can be in any frame or location, hence this specific scenario is not helping.

Clocks that contribute to UTC are in different gravitational potentials. How is that different?

There are efforts to come up with a timescale to use on the moon, and for time in arbitrary locations in space (DSAC)

1 hour ago, Killtech said:

yes, and it is different for every location and frame, so the general conversion is a complicated formula that depends on the trajectory taken over which you need to integrate, hence the result will differ depending on the circumstance.

Kinda like the Hafele-Keating experiment, only more complicated.

1 hour ago, Killtech said:

Along some trajectories TCB will measure the identical time passed as a clock would, along others the TCB time interval will be shorter then what the clock reads and along others again it will be longer. In every case a complicated conversion exists, which

Like how clocks in UTC must make elevation corrections.

1 hour ago, Killtech said:

if you want to make it entirely correct, not just approximately like in 10.2 section of the article i posted before.

where did you get the idea from that i don't think they are clocks?

Because you keep arguing points that imply or say so, such as:

1 hour ago, Killtech said:

a device reading TCB will not count as a clock though since the time it reads is very different from clocks.

If it measures time, it’s a clock.

3 hours ago, swansont said:

If it measures time, it’s a clock.

Argh, but it does not. A coordinate time is not the same as time, i hope you understand that distinction. a pendulums position can be measured in spherical coordinates, but you wouldn't mistake \(\phi\) for a measure of length? coordinate times may be similar or even numerically equal to a clocks reading in some instances, specifically when defined via theoretical clock in a special location. But they are conceptionally something else and interpreted differently.

However, TCB is very close to Newtons idea of absolute time since as coordinates are not dependent on the frame. In that sense it can be considered as an alternative to clocks. in theory it is just as consistent and reproducible means record events as a clocks reading. in practice, it is usually far simpler to measure proper time then a coordinate time. but when it comes to calculating collisions of celestial bodies in the solar system, we do prefer to do them in TCB coordinate time rather then any proper time involved.

Edited April 27Apr 27 by Killtech

I think it needs to be clarified precisely what a clock measures. A clock (specifically the part that physically responds to time) measures proper time along the spacetime trajectory (aka world line) of the clock. Ideally, a clock is not affected by any form of motion or gravity. This is a consequence of the principle of relativity, the principle that the laws of physics (and therefore the behaviour of clocks) are the same in all frames of reference. It should also be noted that, according to the equivalence principle, a local gravitational field behaves like an accelerated frame of reference. This means that gravitational time dilation is the same as time dilation in an accelerated frame of reference. It also means that freefall in a gravitational field is locally the same as an inertial frame of reference (btw, this means that special relativity is an important part of general relativity, not merely a precursor of it).

A device that receives signals from a remote clock is not itself a clock. It is merely relaying to the observer of the device the measurement of proper time along the spacetime trajectory of the remote clock. Suppose the remote clock is ticking exactly once per second. It will tick exactly once per second irrespective of where it is or how fast it is moving. The intervals in spacetime marked by the ticks will be genuine one second intervals (I feel I can't stress this enough). Observing the remote clock involves null geodesics in spacetime from each tick of the remote clock to the observer, the time interval between the observed ticks being measured by a local clock. The interval between the ticks at the location of remote clock is exactly one second, the interval between the observed ticks measured by a local clock need not be one second. Both intervals are proper times at their own locations, but in no way is the interval between the observed ticks a measure of time at the remote clock. Nor is the interval between the observed ticks of the remote clock a measure of local time.

What is coordinate time? Coordinate time is the value of a particular coordinate of a particular type of coordinate system. If spacetime is sliced into spacelike three-dimensional slices, coordinate time identifies each spacelike slice. The spacelike three-dimensional slices are usually considered to be defined by hypothetical observers whose spacetime trajectories are normal to the spacelike three-dimensional slices. The coordinate time may be the proper time for one particular spacetime trajectory. If the spacetime is stationary, then this coordinate system is naturally defined by the isometry between the spacelike three-dimensional slices. In the case of a black hole solution, the t coordinate corresponds to proper time at spatial infinity. If the spacetime has a Friedmann-Lemaître-Robertson-Walker metric (FLRW), then the t coordinate is the proper time everywhere (the age of the universe), but only for trajectories that are at rest relative to the comoving frame of reference.

10 hours ago, Killtech said:

Argh, but it does not. A coordinate time is not the same as time, i hope you understand that distinction. a pendulums position can be measured in spherical coordinates, but you wouldn't mistake ϕ for a measure of length? coordinate times may be similar or even numerically equal to a clocks reading in some instances, specifically when defined via theoretical clock in a special location. But they are conceptionally something else and interpreted differently.

Clocks don’t measure coordinate time, they measure proper time.

10 hours ago, Killtech said:

However, TCB is very close to Newtons idea of absolute time since as coordinates are not dependent on the frame. In that sense it can be considered as an alternative to clocks. in theory it is just as consistent and reproducible means record events as a clocks reading. in practice, it is usually far simpler to measure proper time then a coordinate time. but when it comes to calculating collisions of celestial bodies in the solar system, we do prefer to do them in TCB coordinate time rather then any proper time involved.

TCB corresponds a particular frame - the barycenter of the solar system, with an offset for gravitational time dilation. Similar to how we offset clocks when calculating UTC.

edit: xpost with KJW