What is a Clock? Syncing Technologies Explained

[jbriggs444]

If clocks are not derived from the same source, they are not said to be synchronous with each other.

The clocks used to maintain TAI do not derive from the same source. They derive from themselves and each other and stay synchronized that way.

 

[Grinkle]

@jbriggs444

Maybe they are, I don't know enough to say if they are synchronized in the stricter sense that I described. From here,

https://en.wikipedia.org/wiki/International_Atomic_Time

I see this -

TAI as a time scale is a weighted average of the time kept by over 400 atomic clocks[4] in over 50 national laboratories worldwide

That tells me they are probably not considered synchronized by the engineers responsible for maintaining TAI.

On the other hand, for all I know the values of the constants of nature do truly synchronize these atomic clocks and they should not / cannot in theory exhibit any drift one to the other.

 

[Torog]

I think the questioner does not understand what they are asking.

I just probably didn't word the question very well.

What I am really interested in is how clocks work. What is the process in one type of clock that makes it synchronize well with another type of clock? Is there a common factor in good clocks that allows the different technologies to offer a reasonable synchronization? ---( just don't tell me it is time! )---

1) My pendulum clock needs the inertial weight and the gravitational weight to be a stable ratio.
2) The world in it's orbit needs the same thing. Cited as a clock in post N. 25
3) An atomic clock. This seems to need the quantized angular momentum of the nucleus as part of the system to generate the necessary hyperfine frequency.
4) What about an electrical oscillator? Does the weight of the electrons affect the frequency?

 

[Grinkle]

Is there a common factor in good clocks that allows the different technologies to offer a reasonable synchronization?

Synchronizing clocks is an exercise of converting tick count on one clock to expected tick count on a different clock.

If two clocks are derived from the same source, for instance one set of gears runs two different clock faces on a clock tower, then one tick on the first clock must equal one tick on the second clock (or some known ratio between the two clocks exists by construction) and these clocks are synchronized to each other as well as any two clocks can be, regardless of how regular the tick on the two clocks is. If one can couple clocks in this manner, one is not as concerned with the quality of the clocks - they stay in synch by construction. If one clock is off by an hour, then both clocks are. They are in synch with each other.

If two clocks have a known period and there is zero error in either period then they needn't be derived from the same source to be synchronized, one just needs to know the periods of the clocks and calculate the ratio to convert from one clock to another. I don't know if atomic clocks fit this description or not, maybe they do. Barring that, I would say that this is just an ideal and no clock will have zero cycle-to-cycle variation in tick duration.

So, good clocks in the sense that you are asking have very low cycle-to-cycle variation in tick duration. The lower this variation, the less two not-coupled clocks will drift away from each other over time.

 

[Robert Albertson]

The way I see it is like this. Time is a measure of change. Hence what we call time is our way of quantifying the change of the universe. One may also use the entropy of the universe. In fact, this may be a better drfinition, i.e. time is a measure of increasing entropy of the universe. Hence, a clock is a numerical device that allows us to keep track of the changing state of the universe (increasing entropy).

 

[Mister T]

1) My pendulum clock needs the inertial weight and the gravitational weight to be a stable ratio.

How could you know that? You'd need another clock to compare it to, and some way to know that it's the pendulum clock's behavior that makes the ratio unstable, and not the behavior of that other clock.

2) The world in it's orbit needs the same thing. Cited as a clock in post N. 25

Same comment applies.

3) An atomic clock. This seems to need the quantized angular momentum of the nucleus as part of the system to generate the necessary hyperfine frequency.

Again, how would you know its oscillations occur with a constant frequency? You'd need another clock for comparison and some way of attributing any discrepancies to the other clock instead of to the atomic clock.

 

[Torog]

How could you know that? You'd need another clock to compare it to, and some way to know that it's the pendulum clock's behavior that makes the ratio unstable, and not the behavior of that other clock.
Same comment applies.
Again, how would you know its oscillations occur with a constant frequency? You'd need another clock for comparison and some way of attributing any discrepancies to the other clock instead of to the atomic clock.

These quoted are all "good" clocks. It is fairly easy to see them synchronized. I didn't say that we didn't need another clock. It is obvious that a clock cannot exist by itself. The existence of one clock implies a second clock.

 

[Paul Colby]

I love the sorry of John Harrison and the Longitude problem. Around the time of Newton people needed a means of navigation at sea, not a small issue. Harrison, basically considered a layperson at the time, approached the problem from the point of view of clocks that could function for months at a time and at sea. He's credited with several major technological innovations such as jeweled bearings. Those fancy looking pendulum clocks from that period are actually temperature compensated so they don't change length to first order as the room temperature changes. After years of work and many attempts he solved the problem. His final clock looks very much like a pocket watch with jeweled bearings. Sadly, the intellectual elite at the time (including Newton who was kind of a dick about it) tried to stiff Harrison out of the millions in prize money and the recognition. Newton failed to do so in the fullness of time.

 

[Mister T]

These quoted are all "good" clocks. It is fairly easy to see them synchronized.

Then it seems you've answered your original question:

How do we decide what is a clock and how do clocks that rely on different technologies stay synchronized?

Unless I'm missing something.

 

[Torog]

Then it seems you've answered your original question:
Unless I'm missing something.

Not in the least. Most people who contributed to this little discussion talked about synchronizing clocks. I'm not interested in that at all.

I love the sorry of John Harrison and the Longitude problem. Around the time of Newton people needed a means of navigation at sea, not a small issue. Harrison, basically considered a layperson at the time, approached the problem from the point of view of clocks that could function for months at a time and at sea. He's credited with several major technological innovations such as jeweled bearings. Those fancy looking pendulum clocks from that period are actually temperature compensated so they don't change length to first order as the room temperature changes. After years of work and many attempts he solved the problem. His final clock looks very much like a pocket watch with jeweled bearings. Sadly, the intellectual elite at the time (including Newton who was kind of a dick about it) tried to stiff Harrison out of the millions in prize money and the recognition. Newton failed to do so in the fullness of time.

This above is interesting to me - how clocks work - for example the balance wheel clock as perfected by Harrison shifts energy between the inertia of the balance wheel and the hair spring and this provides the stable rate and allows synchronization with the Earth clock. How do all the other clocks work?

 

[Mister T]

Most people who contributed to this little discussion talked about synchronizing clocks. I'm not interested in that at all.

It was part of your original question.

How do we decide what is a clock and how do clocks that rely on different technologies stay synchronized?

 

[russ_watters]

How could you know that? You'd need another clock to compare it to, and some way to know that it's the pendulum clock's behavior that makes the ratio unstable, and not the behavior of that other clock.

Same comment applies.

Again, how would you know its oscillations occur with a constant frequency? You'd need another clock for comparison and some way of attributing any discrepancies to the other clock instead of to the atomic clock.

I'm not sure if I'm accidentally arguing for The Empire here, but the difference between today and 500 years ago is that we know and use the physics by which clocks operate to accurately predict their accuracy. Before Newton (or perhaps Galieo) people didn't know how pendulums work, so they couldn't pre-calculate the oscillation rate. Hourglasses would have been even worse. And I doubt even Harrison in the 1700s used the underlying physics to calculate the performance of his chonometer. So all of these had to be calibrated against a master clock (the sun) to work at all. That just isn't the case today.

So we can take a clock up a mountain or fly it around the world in a plane (or GPS satellite) and have a pretty good idea of how it will behave.

 

[Mister T]

So all of these had to be calibrated against a master clock (the sun) to work at all.

But the only reason people knew that was that they saw that those primitive clocks couldn't stay in sync with each other or with the "master". It was only when the technology developed enough that people saw that they could do a better job of keeping them in sync with each other that they noticed that the master did a good job of joining them.

But even that didn't last as the technology advanced.

 

[russ_watters]

But the only reason people knew that was that they saw that those primitive clocks couldn't stay in sync with each other or with the "master".

I suspect that when designing those primitive clocks, the designers knew they were guessing and what it meant.

 

[Paul Colby]

This above is interesting to me - how clocks work - for example the balance wheel clock as perfected by Harrison shifts energy between the inertia of the balance wheel and the hair spring and this provides the stable rate and allows synchronization with the Earth clock. How do all the other clocks work?

I think your usage of the word "synchronized" is a bit off. A better term is clock rate for what you are discussing. For example, Harrison made pendulum (grandfather) clocks before he became interested in the Longitude issue. If all you have is a pendulum clock, how do you know it's quality? What Harrison did was build multiple clocks and compare them against one another. For example, he would run one clock with his front door open in winter while building a large fire in his living room. He would compare the clock by the front door with the one by the fire. Then he would switch the location of the clocks. This way he could make precision measurements of the thermal stability of his designs.

 

[Torog]

It was part of your original question.

I said: How do we decide what is a clock and how do clocks that rely on different technologies stay synchronized?

The how was the interesting part for me.

the difference between today and 500 years ago is that we know and use the physics by which clocks operate to accurately predict their accuracy.

That was the discussion that I hoped for - the physics of clocks - how do clocks that rely of different principles stay synchronized? (or almost synchronized)

Most people who have chipped in here apply what you said in the beginning:

Physicists seem to use the circular definitions:
-Clocks are devices that tell time.
-Time is what a clock measures.

 

[nitsuj]

I said: How do we decide what is a clock and how do clocks that rely on different technologies stay synchronized?

The how was the interesting part for me.
That was the discussion that I hoped for - the physics of clocks - how do clocks that rely of different principles stay synchronized? (or almost synchronized)

Most people who have chipped in here apply what you said in the beginning:

I am sure a google search would mention which clock is referenced most often and how. Your point with "Decide on" is interesting if asking what time did they decided to set and why?

Gravity was one of the first ways I think and used for the longest.

 

[Wes Tausend]

How do we decide what is a clock and how do clocks that rely on different technologies stay synchronized?

I think we decide that something may be used as a clock if it seems to possesses rhythm or flow. Any crude clock rhythm can be checked to the second (during daylight) against a sufficiently large sundial where the shadow pointer moves in great enough increments to see to mark the correct division of seconds off in a 24 hour day. Note that Earth is an object that possesses more than one angular momentum and was thereby our first accurate timepiece.

All our clocks have this common denominator. They all rely on angular momentum, or a portion thereof , one way or another, to stay synchronized and count off rotations or portions thereof (pendulum). Two very different clocks, such as a pendulum and flywheel/hairspring, can be perfectly synchronized by having proportional mechanical ratios designed to some rhythmic multiple of a harmonic tick to the other, or at least achieving a repeating periodic momentary synchrony after a certain number of ticks (For the nearly smooth rotation of a planet, the ticks may have to reduce to Planck motions in a ridiculous micro-sense).

Since all clocks rely on angular momentum, all are likely sensitive to rotation; for instance any common flywheel/hairspring clock can be stopped by "rocking it" in a gradually decreasing opposing rhythm to the reciprocating flywheel direction. All other clocks are also likely sensitive to a rotational motion in a similar way, as it disturbs angular momentum. I have wondered, but not yet tested, if an old tick-tock pocket watch will keep the same time when placed face-up on a continuously rotating turntable.

A pendulum clock is sensitive to being level, to gravity and the length of it's pendulum. Whereas a flywheel/hairspring clock should run "relatively" slower on the surface of Earth than the moon (greater gravity on earth), a pendulum clock will run slower on the moon because the pendulum will "fall" slower in lower gravity (swing slower). A pendulum clock moved from sea level to 4,000 feet (1,200 m) will lose 16 seconds per day.

It is the hairspring adjustment on the reciprocating flywheel clock that determines it's fine time-rate adjustment. If left unadjusted from Earth setting, it should run faster on the moon, wear out and not live as long as it's identical twin on earth. If such a flywheel clock were large enough, we might be able to read it with a powerful telescope on earth. Barring other interference, it would at first automatically read behind 1.3 seconds just because we would see it in history, the time the picture of light takes to reach us. But then the wind-up moon-clock would very gradually catch up because it ran faster in 1/6th the gravity of Earth (We'd have to somehow wind it with Earth tide). And if time runs faster on the moon, has it affected the apparent rotation position of it's accumulated orbits around Earth over the millions of years.

Wes
EDIT: Earth tide wouldn't work. We'd have to use solar tide to wind the moon-watch mainspring.

 

[Dale]

I said: How do we decide what is a clock and how do clocks that rely on different technologies stay synchronized?

The how was the interesting part for me.

That was the discussion that I hoped for - the physics of clocks - how do clocks that rely of different principles stay synchronized? (or almost synchronized)

I think the “how” is simply calibration. E.g. we find that a pendulum of a given length cycles once for every 60,000 cycles of a given quartz oscillator. So we divide the quartz oscillator by a calibration factor of 1/60000, and then they “stay synchronized” as I think you intended it.

 

[DrGreg]

All our clocks have this common denominator. They all rely on angular momentum,

Not all clocks involve rotation. What about water clocks? Candle clocks? Hourglasses? Quartz clocks? Atomic clocks? Carbon dating?

Even for those clocks that do involve oscillating rotation, it doesn't seem to me that "conservation of angular momentum" is the principle that makes them work.

 

[Torog]

All our clocks have this common denominator. They all rely on angular momentum, or a portion thereof , one way or another, to stay synchronized and count off rotations or portions thereof (pendulum).

You qualify the above with (pendulum). Isn't it possible that if you drill down into the mechanism of all clocks you will find Inertial mass somewhere in the regulating mechanism.

Thanks, this is what interests me, the how or physics of the regulating mechanisms of clocks.

 

[Dale]

Thanks, this is what interests me, the how or physics of the regulating mechanisms of clocks

This has been answered already. If you feel that the answers received have not actually addressed your question then you need to rephrase. You are not communicating your question. People are answering what you are asking, so you need to change what you are asking not just repeat it again.

Did you not understand the previous answers or what else do you want?

 

[Torog]

I do understand English. Most people in this thread talked about how to synchronise clocks - very little on the physics.

Cut me out if you wish.

Tired of being bullied by the powers on this forum.

 

[PeterDonis]

Isn't it possible that if you drill down into the mechanism of all clocks you will find Inertial mass somewhere in the regulating mechanism.

Atomic clocks are at least one counterexample.

 

[PeterDonis]

Most people in this thread talked about how to synchronise clocks

That's because you asked how clocks were kept synchronized in your OP.

very little on the physics

Plenty of posts have talked about possible physical mechanisms for clocks. But the question you asked in your OP wasn't about specific physical mechanisms, it was a general question about how we can tell that any physical mechanism is a "clock". That question has been answered.

the how or physics of the regulating mechanisms of clocks

If you are looking for some single physical principle, like "inertial mass", that appears in all clocks, there isn't one.

 

[Dale]

I do understand English. Most people in this thread talked about how to synchronise clocks - very little on the physics.

Cut me out if you wish.

Tired of being bullied by the powers on this forum.

Wow. I was asking for you to describe what you want better. I have no idea how asking for clarification is bullying.

You are getting answers, but you do not seem satisfied with the answers. So I am asking you to help get you the answers by refining the question.

You keep saying “the how” and I thought I had answered “the how” but you didn’t think it was satisfactory. So we need you to be more communicative about your question. (The opposite of cutting you out)

 

[russ_watters]

@Torog It is also worth noting that you may have been led astray by some incorrect posts(some now deled) from another poster. The only thing even close to aggressive/negative I've seen here were responses to that poster, not to you. You're doing fine, even if that caused some issues; not your fault.

 

[Mister T]

Most people in this thread talked about how to synchronise clocks - very little on the physics.

Synchronizing two co-located clocks is trivial, you originally asked about how they are kept synchronized. The former is an issue of accuracy while the latter is an issue of precision. There really is no physical mechanism at work in the background that keeps clocks synchronized. In fact, no two clocks ever stay perfectly synchronized, there is always some drift, or to put it in technical terms, imprecision.

The science of metrology is all about improving the precision, but there is no way to make it perfect. Like any machinist will tell you, regardless of how precise the machining, there is always some level of tolerance (or imprecision) that's considered acceptable for the purpose at hand.

 

[Torog]

Atomic clocks are at least one counterexample.

I got this from: http://hyperphysics.phy-astr.gsu.edu/hbase/Nuclear/nspin.html

“nuclei often act as if they are a single entity with intrinsic angular momentum I. Associated with each nuclear spin is a nuclear magnetic moment which produces magnetic interactions with its environment.”​

As I understand (& I am winging it here) the frequency developed by the nucleus of the cesium 131 used in the resonators of atomic clocks is based on the following:

From: https://quantummechanics.ucsd.edu/ph130a/130_notes/node357.html

“Hyperfine Structure
The interaction between the magnetic moment, due to the spin of the nucleus, and the larger magnetic moment, due to the electron's spin, results in energy shifts which are much smaller than those of the fine structure. ”​

Now I admit that I don’t know what I am talking about in QM but I notice that magnetic moment and spin of the nucleus come up in the description of the hyperfine structure and that magnetic moment is tied to the angular momentum of the nucleus. This sounds to me like an inertial factor involved in the stability of atomic clocks.

 

[Mister T]

Now I admit that I don’t know what I am talking about in QM but I notice that magnetic moment and spin of the nucleus come up in the description of the hyperfine structure and that magnetic moment is tied to the angular momentum of the nucleus. This sounds to me like an inertial factor involved in the stability of atomic clocks.

It's not an inertial factor. The nucleus doesn't rotate in the way that a bar magnet rotates. The nucleus, like the spinning bar magnet, has angular momentum. The nucleus, like the bar magnet, has a magnetic moment. So in these respects the nucleus behaves "as if" it were a spinning bar magnet, and that is the reason it's called nuclear spin.

But if you try to account for these behaviors by modeling the nucleus as a sphere, or really an object of any shape, given its known mass and charge distribution, you just can't get it to work out. In other words, the nucleus cannot be modeled as a rotating object. It just doesn't work.

Inertia is not the well-formed concept in relativistic physics that it is in the Newtonian approximation. For example, you will find some physicists saying that the inertia of an object increases with its speed, and others saying it doesn't. It's not a debate about the physics, it's a debate about the meaning of a word.

I think the best you can do with drawing the kind of generality you're looking for is to say that all clocks involve a change in energy state. But I'm not sure even that will work.

 

[Dale]

Several posts claiming that time is non-physical have been removed. Please stick to accepted science

 

[rootone]

A clock is a device which measures time as a quantity.
Some clocks are a lot more accurate, atomic clocks are the best.
You won't need that accurracy to set your wake up alarm clock though

 

[Sorcerer]

Aren't all clocks ultimately tied to the conservation of energy, because the conservation of energy is tied to the translation symmetry of time? So if you wanted to build perfect, eternal clocks, you'd need them to be in isolated systems and based somehow on conservation of energy, right?

And, since all events in the universe presumably must obey the law of conservation of energy, wouldn't that right there be the answer to the OP's question? I.e., the reason why two clocks built from different principles remain synchronized is that both are subject to the same laws about conservation of energy?

*I chose conservation of energy because as a noob physics student I am under the impression that ENERGY is tied to time while MOMENTUM is tied to space. But then again, time and space and energy and momentum are also intertwined, so let me just run away... ~~~ (>o_o)>Of course in real life no clock is in an isolated system, so two clocks won't remain eternally synchronized. But in an isolated system where things like drag, etc are controlled, once synchronized they should remain that way forever regardless of how they are built, shouldn't they?

 

[Dale]

Aren't all clocks ultimately tied to the conservation of energy, because the conservation of energy is tied to the translation symmetry of time?

This is an excellent and appropriate use of Noether’s theorem. It is very appealing.

All clocks are physical systems, so they have physical characteristics like energy, inertia, angular momentum, etc. So it is hard to say if a given property is the operating principle of all clocks.

So, for example, with the rotation of the Earth energy is conserved and angular momentum is conserved (linear momentum is not), but which is the one that we dub as being the operating principle of this specific clock? I would lean towards angular momentum over energy for that specific clock, but it isn’t clear since it has both and without both it would fail.

 

[Mister T]

This is an excellent and appropriate use of Noether’s theorem. It is very appealing.

I think it's circular. You first need to introduce the concept of time before you can state, address, prove, or otherwise have, that Noether's theorem. The theorem is a statement about time, it is not a definition of time or an operational definition of how to measure it.

All clocks are physical systems, so they have physical characteristics like energy, inertia, angular momentum, etc. So it is hard to say if a given property is the operating principle of all clocks.

You need to first have in hand an operational definition of time before you can define any of those quantities. Perhaps size is the one physical quantity that is the exception that all clocks possess.From Relativity and Common Sense: A New Approach to Einstein (1980), 65

A quantity like time, or any other physical measurement, does not exist in a completely abstract way. We find no sense in talking about something unless we specify how we measure it. It is the definition by the method of measuring a quantity that is the one sure way of avoiding talking nonsense about this kind of thing.

— Sir Hermann Bondi