High School What is a Clock? Syncing Technologies Explained

[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.

 

[Herman Trivilino]

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.

 

[Herman Trivilino]

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.

 

[Herman Trivilino]

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

 

[Umaxo]

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.

The theorem is actually statement about symmetry, not just some predefined time. So doesn't requirement, that definition of time must respect the symmetry of physical world creates some restriction on the possible definition of time?

 

[Ross Arden]

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

a clock is any mechanism that is capable of measuring time ? for instance we could count the number of pulses from a pulsar . If we know the period of the pulsar then we can accurately measure time, without a feed back mechanism.

The period of the pulsar is prolly a function of its mass or some other, non time dependent, parameter that can be accurately measured.

 

[Ross Arden]

a clock is any mechanism that is capable of measuring time ? for instance we could count the number of pulses from a pulsar . If we know the period of the pulsar then we can accurately measure time, without a feed back mechanism.

The period of the pulsar is prolly a function of its mass or some other, non time dependent, parameter that can be accurately measured.

I suppose all clocks only measure a subset of infinite time. What I mean by that is an egg timer only measures three minutes (say). But of course time goes more than three minutes. But unless it is possible to build a clock that goes for all time, all clocks only measure a subset of the entire time of the universe. In other words all clocks are egg timers, that just run longer than three minutes. I suppose going in the other direction you could have a clock that consisted of a single tick? which would be just a very short egg timer

the big bang is a clock that ticks every 15 billion yrs ?

 

[Paul Colby]

A clock, much like a meter stick for distance, measures time intervals, the time passed between events.

 

[PeterDonis]

the big bang is a clock that ticks every 15 billion yrs ?

No; the Big Bang is not a periodic phenomenon. Unless you are expecting to see another one real soon now...

 

[Ross Arden]

No; the Big Bang is not a periodic phenomenon. Unless you are expecting to see another one real soon now...

assuming there was a big bang. That means there was enough mass in the universe , or some unknown phenomena, to cause the universe to collapse in on itself, to a singularity, and then expand again from that point. Unless there has been significant mass loss, or the phenomena no longer exists, then it is reasonable to assume at some time in the future there will be a second big bang ?

It may be a repeating phenomena with a say 200 billion year period

Another possibility is there are several universes and the material from one big bang is ejected towards another universe causing it to collapse so you have several neighboring universes in varying degrees of expansion and collapse.

 

[weirdoguy]

That means there was enough mass in the universe , or some unknown phenomena, to cause the universe to collapse in on itself, to a singularity, and then expand again from that point.

No, Big Bang definitely does not mean that... Big Bang theory states that universe was in a hot dense state a long long time ago, was expanding, etc.. No collapsing on itself, no singularity treated as a physical thing, no expanding from a point. Use "search" option, there has been many threads about BB clearing that kind of misconceptions.

 

[Herman Trivilino]

assuming there was a big bang. That means there was enough mass in the universe , or some unknown phenomena, to cause the universe to collapse in on itself, to a singularity, and then expand again from that point.

I think you have somehow misunderstood that line of reasoning. The latter is not a consequence of the former. That is, having a big bang does not imply that it was preceded by a big crunch. Cosmologists used to speculate that such a thing was possible and that a big crunch might be in our future; but ever since it was discovered, about 20 years ago, that the expansion is accelerating, they stopped. AFAIK.

 

[russ_watters]

the big bang is a clock that ticks every 15 billion yrs ?

Clocks do not require periodic phenomena, just a measurable physical process with a predictable time rate. See: hourglass, radioactive decay...

...and in Jurassic Park, cases of beer.

 

[Ross Arden]

we seem to have drifted off the point ...can someone tell me where I went wrong with my analysis

 

[jbriggs444]

we seem to have drifted off the point ...can someone tell me where I went wrong with my analysis

What analysis and what point?

 

[Torog]

It's not an inertial factor. The nucleus doesn't rotate in the way that a bar magnet rotates.

OK as I said I’m not the expert.
But then you say:

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.

Here it sounds as if you are not sure how it works and I never suggested it might be a sphere.
You say:

Inertia is not the well-formed concept in relativistic physics that it is in the Newtonian approximation.

Well it should be or if it is not then something is wrong – IMHO- tell somebody who has just had his car smashed by inertial forces “well sorry your car is all bent up but we have no way to understand the forces that caused all that destruction” Blame Newton not Einstien.

To get back to “it is not an inertial factor”
Lets see what I understand about Cs133. It has mass so the bits that make up the nucleus, the protons and neutrons have mass and even the electrons have a small amount of mass. The nucleus is emitting a radio wave at a frequency of 9,192,631,770 Hz.
( Getting my information in a cursory manner from : http://hyperphysics.phy-astr.gsu.edu/hbase/acloc.html)
According to the information source above the hyperfine emission comes from an interaction between a lone distant electron and the nucleus (& the dimensions are given for the nucleus and it doesn’t matter if it's round or shaped like a unicorn). It is a dynamic system. It moves – it’s some sort of an engine that produces these electromagnetic waves. You say the mass of the parts have no effect on the emission? It seems to me that if there is any movement involved in the hyperfine emission then the mass/weight of the parts must come into the equation.

Look at it from a GR (or SR?) perspective and with the principle of equivalence gravity and inertia can be interchanged so if the intensity gravitational field effects the clock - proven,of course – then why can’t we postulate that if the inertial mass of the clock changes then its rate will change?

 

[jbriggs444]

Lets see what I understand about Cs133. It has mass so the bits that make up the nucleus, the protons and neutrons have mass and even the electrons have a small amount of mass. The nucleus is emitting a radio wave at a frequency of 9,192,631,770 Hz.
( Getting my information in a cursory manner from : http://hyperphysics.phy-astr.gsu.edu/hbase/acloc.html)
According to the information source above the hyperfine emission comes from an interaction between a lone distant electron and the nucleus (& the dimensions are given for the nucleus and it doesn’t matter if it's round or shaped like a unicorn). It is a dynamic system. It moves – it’s some sort of an engine that produces these electromagnetic waves.

None of this is accurate. A nucleus is not an engine - it does not produce energy. In addition, "dynamic" and "it moves" are not synonyms.

A "state space" within which a dynamic system evolves need not involve three dimensional locations.

 

[Paul Colby]

The hyperfine interaction is between the magnetic moment of the nucleus, which is a constant, and the electrons in the atom. The transition frequency should be a know function of electron mass.

 

[Torog]

None of this is accurate. A nucleus is not an engine - it does not produce energy. In addition, "dynamic" and "it moves" are not synonyms.

A "state space" within which a dynamic system evolves need not involve three dimensional locations.

I realize there it isn't possible to pin down shape of the nucleus or where any bits are at anyone time but is there movement or rotation in the nucleus?

I have heard that "spin" is actually spin with angular momentum and other that say it is "intrinsic" (whatever that means) and doesn't connote any movement.

 

[Nugatory]

I have heard that "spin" is actually spin with angular momentum and other that say it is "intrinsic" (whatever that means) and doesn't connote any movement.

They're both right. The spin of a subatomic particle is indeed angular momentum, and it doesn't connote any movement or physical rotation. "Intrinsic" just means that nothing you do the particle will change its spin.

 

[jbriggs444]

The hyperfine interaction is between the magnetic moment of the nucleus, which is a constant, and the electrons in the atom. The transition frequency should be a know function of electron mass.

Since the frequency of the radiation associated with that transition (as opposed to the "transition frequency") is a defined constant, whatever it is a function of, it is a constant function.

 

[Herman Trivilino]

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.

Here it sounds as if you are not sure how it works and I never suggested it might be a sphere.

Not sure how what "works"? Do you mean that the nucleus has a magnetic moment and an angular momentum? You measure those two quantities and don't get values of zero for either one. Is that what you mean by "how it works"?

And I agree that you never suggested it was a sphere.

Well it should be or if it is not then something is wrong – IMHO- tell somebody who has just had his car smashed by inertial forces “well sorry your car is all bent up but we have no way to understand the forces that caused all that destruction” Blame Newton not Einstien.

As I told you, it's not about the physics, it's about the meaning of a word. Inertia. Inertial forces are not the same thing as inertia, their values don't even have the same units.

When cars collide, by the way, they get smashed by electromagnetic forces.

 

[Dale]

tell somebody who has just had his car smashed by inertial forces

Inertial forces never ever smash a car. They are strain free. They occur in non inertial frames, and can be made arbitrarily large by choosing appropriate coordinates. Cars don’t get smashed or not if you choose a different coordinate system.

It has mass so the bits that make up the nucleus, the protons and neutrons have mass and even the electrons have a small amount of mass.

All clocks have mass, so they all have inertia. So what do you mean by “inertial factor”? Do you merely mean that it has inertia? If so then it is a fairly trivial statement that doesn’t describe much about clocks. Do you mean something more?

Clocks have inertia. Cars have color. Color is not the operating principle of a car. Are you simply stating that clocks have inertia or are you trying to say that inertia is the operating principle for all clocks? Are you merely saying the equivalent of “all cars have a color factor”.

 

[Paul Colby]

Since the frequency of the radiation associated with that transition (as opposed to the "transition frequency") is a defined constant, whatever it is a function of, it is a constant function.

Google yields...

"Transition frequency may refer to: A measure of the high-frequency operating characteristics of a transistor, usually symbolized as f. A characteristic of spectral lines. The frequency at which changes in the hyperfine structure of atoms occur. Turnover frequency in enzymology."

Seems to match my usage? Did I miss a memo?