High School What is a Clock? Syncing Technologies Explained

[Paul Colby]

Nor do I...but the way you say it implies you think there should be a difference...?

Just hedging my bets. Time intervals and Space intervals are definitely different for some value of different. Their measurements have many issues in common though.

 

[jbriggs444]

I guess I don't see a huge difference between clocks used to measure time being synchronized and rulers used to measure distances maintaining a stable length.

Depends on what you mean by synchronized. If you mean that the elapsed time between one tick and the next on this clock over here should match the elapsed time between one tick and the next on that clock over there then I would count that as "syntonized". That would correspond to the centimeter markings on my ruler over here being separated by one centimeter, just like the centimeter markings on your ruler over there.

By contrast, two clocks are "synchronized" when they both tick off time zero at the "same time" (whatever that is chosen to mean). That would correspond to my ruler over here being placed on the same start line as your ruler over there. Just like "at the same time", "on the same start line" is a convention, not a fact of physics.

 

[Paul Colby]

Depends on what you mean by synchronized.

Independent of what I said, I had intervals of time and space in mind. An inch measured by ruler A and ruler B agree when I use them at my desk to measure things. Same with time, a second of lapsed time measured with clock A agrees with clock B when in the same room moving at sufficiently slow relative and so on, and so on.

 

[Herman Trivilino]

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

Metrologists decide, and they base their decision on precision, or as you've put it, synchronization.

You need two devices that repeat some kind of a pattern of behavior, you count the number of repetitions, and compare. For example, the hour hand on my watch makes 24 revolutions while the sun makes one. I do this kind of comparison over and over to see if that comparison stays the same every time I make it. If it does, the two are candidates for clocks. I can then repeat this process with other kinds of devices, and see if they stay synchronized, too. The ones that do are good candidates, the ones that don't get rejected.

By the way, don't confuse this type of synchronization between clocks that share the same location with the type that's done with separated clocks. When the clocks are separated synchronization becomes more complicated and the results counter-intuitive.

 

[Grinkle]

An engineer says clocks are synchronized if they are derived from the same source and hence by construction cannot drift away from each other. The only discrepancy is the accuracy of a single derived tick, one clock to the other. The per-tick error does not accumulate tick-by-tick because the construction of the clocks causes them to start each tick from the same source.

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

 

[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).

 

[Herman Trivilino]

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.

 

[Herman Trivilino]

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?

 

[Herman Trivilino]

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.

 

[Herman Trivilino]

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.