What is a Clock? Syncing Technologies Explained

[Torog]

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

 

[Ibix]

Something that repeats regularly is a clock. You may wish to add a counter. They stay synched (leaving aside relativistic effects and noise) because that's what "repeats regularly" means.

 

[russ_watters]

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

I add the fact that "time" works similarly to other dimensions, so it is treated as a dimension...and describe that: Time is a non-spatial dimension that forms a continuum, separating events.
https://www.merriam-webster.com/dictionary/time

Regarding how we synchronize clocks of different technologies: At this point, the scale of time is defined to fit the caesium clock. The actual value of how many shakes equals 1 second is of course arbitrary.

 

[DrStupid]

How do we decide what is a clock

If the output of two or more devices comply with Einstein's clock synchronisation, the devices are a clocks and their output is a measure of time.

 

[PeterDonis]

If the output of two or more devices comply with Einstein's clock synchronisation, the devices are a clocks and their output is a measure of time.

This is certainly a sufficient condition, but it's much too strong to be a necessary condition. Two clocks in relative motion in flat spacetime don't meet the condition, but that does not mean they can't be considered clocks.

 

[hilbert2]

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

If you have two processes that are based on completely different mechanisms, and seem to be periodic with $n$ periods of process 1 taking the same time as $m$ periods of process 2, then it's an even stronger proof that both processes are actually periodic than two similar mechanisms behaving in that way. It's unlikely that the period of two different kinds of processes would happen to be changing at the same rate.

 

[Paul Colby]

A clock is just like a meter stick but for time intervals instead of distances.

 

[DrStupid]

Two clocks in relative motion in flat spacetime don't meet the condition, but that does not mean they can't be considered clocks.

Yes, they can be clocks. But how do you check that?

 

[Nugatory]

Yes, they can be clocks. But how do you check that?

First you use each clock to establish a length standard usable when that clock is at rest (for example, the meter is the distance traveled by light in 1/299792458 second, using the cesium clock definition of the second). Then you calculate the proper time between two consecutive readings of one clock using that clock and the other clock. If these calculations agree to the limits of your measurement accuracy then they are good clocks.

 

[MarekKuzmicki]

Something that counts any events is clock. Of course you want clock to be precise. You want to control what you count. For example: You need to construct "tick" - which is event to count. Then end of your event is starting new event in loop. Or, another example - you know atomic decay law. "Tick" is not too reliable here, but statistick over atomic decay is reliable, and you can compute timeframe from that.

 

[Torog]

I have a lovely pendulum clock on my wall. It is accurate to within a minute a week. The speed of the clock is regulated by the equivalence of inertial mass and gravitational mass. What about the other clocks? What do they depend on to be stable (lets assume we are not traveling at enormous speeds and we are all in the same gravitational field).

 

[russ_watters]

I have a lovely pendulum clock on my wall. It is accurate to within a minute a week. The speed of the clock is regulated by the equivalence of inertial mass and gravitational mass. What about the other clocks? What do they depend on to be stable (lets assume we are not traveling at enormous speeds and we are all in the same gravitational field).

https://en.m.wikipedia.org/wiki/Caesium_standard

Why do I feel like I'm providing research for a paper?

 

[Nugatory]

What do they depend on to be stable (lets assume we are not traveling at enormous speeds and we are all in the same gravitational field).

The "travelling at enormous speeds" part of this question is a red herring that you would do well to let go of. Everything is traveling at enormous speeds relative to something somewhere. For example, your pendulum clock works just fine (in the sense that I described in #9 above and to the limits of its accuracy) whether you or someone on Mars watching through a telescope and moving at a few kilometers per second relative to it is depending on it to measure time.

Where the stability comes from depends on the construction of the clock. Use an electronic LC circuit oscillator and you're depending on the laws of electricity and magnetism which govern the behavior of electronic circuits... Use the slowly increasing length of your hair and fingernails, and you're depending on the biological processes that control their growth... Use an ordinary bedside alarm clock plugged into a wall outlet and you're depending on your electrical utility's ability to provide 50 or 60 (depending on where you live) cycles per second, which in turn depends on classical physics applies to elextrical power generators... And long ago we used sandglasses based on some faiurly complex Newtonian mechanics, sundials based on the Earth's motion through space, candles that burned at a more or less constant rate because the laws of chemistry are stable.

 

[Torog]

https://en.m.wikipedia.org/wiki/Caesium_standard

Why do I feel like I'm providing research for a paper?

No not a research paper. Trying to get my own thoughts in some sort of a shape.

So in my clock one of the stabilizers is the inertial weight of the pendulum.

Does the inertial weight of the bits of the cesium atom provide stability to the atomic clock?

 

[russ_watters]

Does the inertial weight of the bits of the cesium atom provide stability to the atomic clock?

No, weight/mass have nothing to do with the operation of an atomic clock.

 

[Torog]

Thanks Russ,

I like this:

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

 

[Torog]

No, weight/mass have nothing to do with the operation of an atomic clock.

From: http://hyperphysics.phy-astr.gsu.edu/hbase/Nuclear/nspin.html#c1
"Nuclear Spin
It is common practice to represent the total angular momentum of a nucleus by the symbol I and to call it "nuclear spin". For electrons in atoms we make a clear distinction between electron spin and electron orbital angular momentum, and then combine them to give the total angular momentum. But 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. "

Surely the Spin or angular momentum - inertia - is an integral part of the mechanism to the hyperfine structure of the nucleus.

 

[russ_watters]

Surely the Spin or angular momentum - inertia - is an integral part of the mechanism to the hyperfine structure of the nucleus.

I don't know. I'm pretty thin on QM. What does this have to do with the topic?

 

[Paul Colby]

Surely the Spin or angular momentum - inertia - is an integral part of the mechanism to the hyperfine structure of the nucleus.

I think what @russ_watters was getting at is the ratio of weight to mass (weight/mass) has nothing to do with atomic clocks, which is correct. Certainly the mass of the particles involved will effect the transition frequencies in an atomic clock. Current theory is these masses are fixed.

 

[Torog]

I don't know. I'm pretty thin on QM. What does this have to do with the topic?

The question is: What is it that stabilizes the clock rate? And does the inertial weight/mass of the bits form part of the stabilizing mechanism?

 

[Grinkle]

The question is: What is it that stabilizes the clock rate? And does the inertial weight/mass of the bits form part of the stabilizing mechanism?

Its not fundamentally a clock rate, it takes a human to interpret it as a clock. Its a stable periodic thing that can be counted, and that is why it us useful as a clock. Why it is stable, and whether the mechanism for its stability has anything to do with why your pendulum clock is stable is not part of what makes it a handy clock. Some people may say "that is not a good clock" and have their own subjective value judgements on what makes a good clock. They may value ease of observing over accuracy, for instance.

I think that is what @russ_watters means by saying you are now asking a different question.

 

[jbriggs444]

The question is: What is it that stabilizes the clock rate? And does the inertial weight/mass of the bits form part of the stabilizing mechanism?

As I understand the mechanism, the energy requirement to make the hyperfine transition is quite precise. One tunes a microwave beam accurately to maximize the rate at which the hyperfine transition is made and uses the associated frequency as the basis for a clock.

The stabilising "mechanism" to the extent that there is one is the fact the the hyperfine transition has a well defined energy level.

Empirically, the fact that atomic clocks agree with one another is a demonstration that the stability exists regardless of why it does.

 

[Ibix]

The question is: What is it that stabilizes the clock rate?

What would you consider to be an acceptable answer? You say earlier that the equivalence of gravitational and inertial mass stabilises your pendulum clock, but you don't justify that statementand I'm not at all sure it's correct. For example, I would think that I could take the clock into zero g, give the pendulum bob an electric charge, place it in a uniform electric field and expect it to work (or at least, I could design a pendulum clock for which that was true - too much metal in an off-the-shelf model). I don't immediately see a reason why it would be any more or less stable operating in an electric or gravitational field.

 

[John M]

A layman's answer to the second part of the very first question - 'how do clocks that rely on different technologies stay synchronized?' It depends on the technology utilised to make the clock i.e. a mechanical clock, an electrical clock or an atomic clock. Each device has a built in regulator i.e. centrifugal weights, pendulums for mechanical clocks, pulses or crystals for electrical clocks and the movement of atoms for atomic clocks. Each can be adjusted until synchronised to a similar device. Devices of a dissimilar technology will not synchronise.

 

[Ibix]

Devices of a dissimilar technology will not synchronise.

The Earth is a sort of clock - it rotates at a steady rate. A quartz watch is a sort of clock which vibrates a crystal at a steady rate. These are dissimilar technologies. Are you telling me you can't tell the time of day with a quartz watch?

 

[russ_watters]

The Earth is a sort of clock - it rotates at a steady rate. A quartz watch is a sort of clock which vibrates a crystal at a steady rate. These are dissimilar technologies. Are you telling me you can't tell the time of day with a quartz watch?

Right: I would say it is a by-definition requirement that a "clock" be capable of synchronizing with other clocks, to within its capable accuracy.

 

[hilbert2]

Right: I would say it is a by-definition requirement that a "clock" be capable of synchronizing with other clocks, to within its capable accuracy.

Exactly. Similarly, if someone would have built the first "thermometer" hundreds of years ago by saying "the length of this metal rod multiplied by a unit conversion factor defines the temperature", there would have been no reason for anyone else to acknowledge the significance of this invention. Only when independently working people are able to make thermometers based on different physics (thermal expansion, pressure of a low density gas in closed system, thermal radiation intensity), and these devices consistently give mutually agreeing results when applied on the same sample system, it makes sense to say that the thing (temperature) that they're measuring is actually something objective and worthwhile to measure.

 

[r8chard]

I think the questioner does not understand what they are asking.
A clock or any similar function is what we arbitrarily use as an artificial measure of the span of time as we perceive that interlude.

What we use is a completely artificial and imaginary guesstimate of mechanical and biological functions. Check out the history of daylight savings time. And the struggles with determining longitude.

Our ancestors, a thousand years ago who were serfs determined seasons as plowing, growing and harvesting and starving. A priest would listen for the bells announcing primes. A merchant might use a burning candle to estimate time or if rich a waterclock. A noble would measure time by when the roads were to muddy to travel on and after the harvest, it an army could move to steal their neighbors harvest.

Their ancestors, a thousand years before them would go by wet or dry, cold or hot seasons. When the fish came upstream or the fur pelts were of quality to take. When to girdle a tree or set fire to thee scrub that grasses can grow for thee cattle.

And, to confuse the issue for historians. Every locality, village, tribe, cult festival would use a wild mishmash of calendars. Based on the whims of the pharaoh or king or primate or even the scribe making crap up instead of just admitting he didn't know!

 

[Paul Colby]

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.

 

[russ_watters]

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.

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

 

[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.

 

[Mister T]

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.