1 Tom Roberts doesn't know how to compare inertial moving clocks

tjrob137 11 April

On 4/10/20 2:32 PM, Ed Lake wrote:

>	The faster you move, the slower time passes for you. AND, the closer you get to a large gravitational mass, the slower time passes for you.

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Tom Roberts: You keep repeating falsehoods. You CLEARLY do not understand this.

No matter how you move, and no matter where you might be located, time ALWAYS passes at its usual rate for you. This is directly related to Einstein's first postulate of SR, and the fact that in GR all local physics is as in SR.

The correct statements corresponding to yours are: the faster you move RELATIVE TO SOME LOCALLY INERTIAL FRAME, the slower your clock ticks RELATIVE TO THAT FRAME. The closer you get to a large gravitational mass, the slower your clock ticks RELATIVE TO A CLOCK FAR AWAY FROM ALL MASSES.

Of course those relative clock comparisons are performed using SIGNALS, and both effects are due to HOW THE SIGNALS ARE MEASURED, and not any effect on the clocks.

You found POPULAR articles that do not describe the physics accurately. In an attempt to simplify the situation they discuss "time running more slowly", when that is not actually the case; the actual situation is more subtle and more complicated to describe.

Tom Roberts

tjrob137 Apr 12

On 4/11/20 10:12 AM, Ed Lake wrote:

>	On Friday, April 10, 2020 at 9:57:10 PM UTC-5, tjrob137 wrote:

>>	On 4/10/20 2:32 PM, Ed Lake wrote:

>>>	The faster you move, the slower time passes for you. AND, the closer you get to a large gravitational mass, the slower time passes for you.

>>	You keep repeating falsehoods. You CLEARLY do not understand this.

>	So, Tom, you believe that when I show you a SCIENCE article I am "repeating falsehoods"?? And you think *I* am the one who does not understand? YOU understand that the science reports are FALSEHOODS??

The POPULAR articles you reference are not telling the story correctly. They have "simplified" it for their audience, and in doing so they get it wrong.

>	Einstein's THEORY says that TIME slows down when you move.

THAT IS THE FALSEHOOD YOU KEEP REPEATING. Well, one of them.

Your claim is directly in conflict with Einstein's first postulate, the Principle of Relativity. You REALLY do not understand SR at all, but are too stupid and ignorant to recognize your own inadequacies.

>>	The correct statements corresponding to yours are: the faster you move RELATIVE TO SOME LOCALLY INERTIAL FRAME, the slower your clock ticks RELATIVE TO THAT FRAME. The closer you get to a large gravitational mass, the slower your clock ticks RELATIVE TO A CLOCK FAR AWAY FROM ALL MASSES.

>

Correct.

And yet you cannot see the difference between what I said and what you said. You REALLY need to learn how to read.

AFAICT your own opinions sound so loudly in your ear that you cannot hear what anybody else is actually saying.

>>	Of course those relative clock comparisons are performed using SIGNALS, and both effects are due to HOW THE SIGNALS ARE MEASURED, and not any effect on the clocks.

>	Ah! MAGICAL SIGNALS that you have dreamed up,

Tom Roberts; They are not "magical", and _I_ did not "dream them up", they are PRESENT IN THE DESCRIPTION OF THE EXPERIMENT (yes, every one). They are ESSENTIAL -- unless clocks are co-moving and co-located, it requires SIGNALS to compare their tick rates. (And even then the most accurate methods of comparing them use electrical signals.)

Nobody has ever DIRECTLY compared the tick rate of a moving clock to the tick rate of a stationary clock -- it is PHYSICALLY IMPOSSIBLE to do so, unless one uses signals. So one is actually comparing the tick rate of one clock to the SIGNAL RATE from the other clock (or frequently, comparing signal rates from both clocks).

Nobody has ever DIRECTLY compared the tick rates of two clocks that are physically separated -- it is PHYSICALLY IMPOSSIBLE to do so, unless one uses signals. So one is actually comparing the tick rate of one clock to the SIGNAL RATE from the other clock (or frequently, comparing signal rates from both clocks).

As soon as signals are involved, one must ask: what are the effects of the physical situation on the signals? -- one finds that the entire difference is due to effects on the signals; the clocks are completely unaffected by both relative motion and difference in gravitational potential.

Tom Roberts
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dear Tom Roberts,

How wrong you are, when you say that nobody can compare the tick rate of two differently moving clocks:

case a) inertial moving clocks, three identical clocks A, B, C all the 3 clocks are inertially moving. clock A is moving inertially on its own; clock B is moving inertially, it is approaching clock A from one side; clock C is very far from clock A and is moving inertially approaching clock A from the other side; as clock B passes by clock A the two clocks A and B are zeroed and both A and B start running, clock B keep going versus clock C; as soon as clock B passes by clock C the clock C takes the elapsed time of clock B and keep its travel towards clock A; as clock C passes by clock A they compare their elapsed time.

You know very well the result: clock C show less elapsed time of clock A: the three clocks, while traveling at a different absolute inertial speed, had REAL absolute real different time rates.

case b) two identical clocks positioned at different gravity potential; this is easier:

clock A is at ground level; clock B is suspended at the top of the Eiffel Tower; a radio signal from A is sent to set starting both clocks; after 1000 years a radio signal is sent to stop both clocks; then the two clocks are brought together and compared their elapsed time; the clock on the top of the tower show less elapsed time: for 1000 years it has run at a slower time rate: Don't you agree that the tow clocks have been running at absolute different time rates ??

Grateful for your attention regards beda

2 Tom Roberts doesn't know how to compare inertial moving clocks

I didn't say that. What I ACTUALLY said was:

>

Nobody has ever DIRECTLY compared the tick rate of a moving clock to the tick rate of a stationary clock -- it is PHYSICALLY IMPOSSIBLE to do so, unless one uses signals. So one is actually comparing the tick rate of one clock to the SIGNAL RATE from the other clock (or frequently, comparing signal rates from both clocks). As soon as signals are involved, one must ask: what are the effects of the physical situation on the signals? -- one finds that the entire difference is due to effects on the signals; the clocks are completely unaffected by both relative motion and difference in gravitational potential.

You are UTTERLY INCOMPETENT to attempt to paraphrase what I say, because YOU DO NOT UNDERSTAND BASIC PHYSICS. That affects everything you say including your INCORRECT claims of what I said.

>	case a) [...]

This is NOT comparing clock tick rates, it is comparing elapsed proper times. That is a DIFFERENT physical situation, with a DIFFERENT explanation.

>	case b) [...]

This is NOT comparing clock tick rates, it is comparing elapsed proper times. That is a DIFFERENT physical situation, with a DIFFERENT explanation.

Bottom line: when you compare the elapsed proper times of two clocks and find they are different, you CANNOT conclude "they tick at different rates". You can only conclude their elapsed proper times are different (DUH!). For such a difference to arise, in relativity it is required that the clocks follow different paths through spacetime (both your examples do), and those paths must have different path lengths (both your examples do).

Tom Roberts

3 Tom Roberts doesn't know how to compare inertial moving clocks

Because they do.

The "tick rate of a clock" involves ONLY the clock. It cannot possibly be measured unless the measuring instrument is co-moving and co-located with the clock.

>

you don't need any signal to compare those clocks if you wait long enough there will be no effects to change the fact that a clock at the top runs faster; after all, the time elapsed displays of the clocks can be large enough to be seen by each other directly, what are you bringing about, everyone knows that phenomenon.

You keep making the same mistake: THIS IS A DIFFERENT PHYSICAL SITUATION. This is comparing the clocks' ELAPSED PROPER TIMES, not their tick rates. The two clocks do indeed tick at the same rate, but one has a larger elapsed proper time than the other because THEY TRAVELED ALONG DIFFERENT PATHS THROUGH SPACETIME.

The clock at top DOES NOT "run faster". But its path through spacetime has a shorter path length than that of the lower clock.

>

[...]

Since you refuse to STUDY and LEARN about the subject, you just keep making the same mistake over, and over, and over, and over....

Tom Roberts

4 Tom Roberts doesn't know how to compare inertial moving clocks

Nope. I am discussing how tens of thousands of physicists around the world understand SR, and how it is described in hundreds of textbooks.

YOU stand alone in your MISINTERPRETATION of that paper.

(Well, some other idiots around here share your mistakes.)

>	Einstein's paper EXPLAINS why the Second Postulate is "only apparently irreconcilable with" the First Postulate.

Yes, he did. But YOU never read the paper in its entirety, and YOU never understood his explanation.

Challenge to Ed Lake: explain the significance of the equations in section I.5 of his paper. Hint: there is a reason I single out this section.

>	The Second Postulate says "that light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body." In other words, no matter how fast an emitter is moving, the emitter still emits light at c.

Yes, WHEN MEASURED IN THE "STATIONARY" SYSTEM. You keep omitting in which frame a measurement is made, thus adding to your own confusion.

>	That APPEARS to violate the First Postulate because the First Postulate says, "the same laws of electrodynamics and optics will be valid for all frames of reference for which the equations of mechanics hold good."

In 1905, when only Newtonian mechanics was known, yes there was that appearance. Today, when SR is well known AMONG PHYSICISTS, such "appearance" has disappeared, because we UNDERSTAND how his two postulates are related, to each other and to local Lorentz invariance.

>	In other words, if light travels at c in a "stationary laboratory" AND in a moving laboratory, it should be a MEASURABLE DIFFERENCE WITHIN those two laboratories.

No. This is the basis of your misunderstanding.

Go back and ACTUALLY READ section I of his paper, with recognition of its context and conventions. Note that the very first sentence of that section is selecting an ARBITRARY inertial frame and labeling it "the stationary system". The entire paper is describing how it is that light moves (in vacuum) with speed c in an ARBITRARY frame, which clearly includes both the stationary laboratory AND ALSO THE MOVING LABORATORY.

This is a crucial point: he is discussing an ARBITRARY frame, not a specific frame in which an aether is at rest.

>	Each should measure a DIFFERENT SPEED OF LIGHT.

Nope. That is YOUR MISUNDERSTANDING. The actual paper, if you ever bothered to read it, shows in several different ways that light moves with speed c (in vacuum) relative to EVERY inertial frame, not just the one with the label "stationary system".

This is, of course, a direct consequence of his first postulate and the presumption that the speed of light is determined by physical laws.

This is the RADICAL NEW CONCEPT that revolutionized physics, and YOU COMPLETELY MISSED IT: the vacuum speed of light is c in EVERY inertial frame. So the Galilean addition of velocities DOES NOT APPLY to light.

In 1905 this was not well understood; today it is, and the collection of phenomena are collected in the phrase: the local laws of physics are Lorentz invariant.

>	Because TIME ticks at a different rate in those two labs.

Nope. This is something YOU JUST MADE UP. It is IRRECONCILABLE with Einstein's first postulate (and the rest of the paper).

Challenge to Ed Lake: show where in the paper it is stated that "time ticks at a different rate" anywhere. Don't give your personal "interpretation", quote directly from the paper. Hint: If you cannot do that, why do you think he left out such an important point?

>	[... further elaboration of this fundamental MISUNDERSTANDINGS]

Tom Roberts

5 Tom Roberts doesn't know how to compare inertial moving clocks

>	On 4/10/20 2:32 PM, Ed Lake wrote:

>	Tom Roberts wrote: No matter how you move, and no matter where you might be located, time ALWAYS passes at its usual rate for you.

What do you mean with its usual rate? IMO if you consider the universe in total the time passes everywhere at the same rate. The universe evolves everywhere. That does not mean that certain processes are not dependent when movement is involved. Shaking a bottle will speed up the mixing process.

>	This is directly related to Einstein's first postulate of SR, and the fact that in GR all local physics is as in SR.

I don't understand what the fact that: "The laws of physics take the same form in all inertial frames" has to do with this. It should be mentioned that in general in experiments involving moving clocks also acceleration is involved. The experiment discussed in Comment 1 (see bottom) IMO is an artefact.

>	The correct statements corresponding to yours are: the faster you move RELATIVE TO SOME LOCALLY INERTIAL FRAME, the slower your clock ticks RELATIVE TO THAT FRAME.

written different: The correct statements corresponding to yours are: the faster your clock B moves RELATIVE TO clock A, the slower your clock B ticks RELATIVE TO Clock A

This is the same (?) as the experiment discussed at the bottom of this document. See Comment 1 In that experiment at the end Clock B meets Clock A

>	Of course those relative clock comparisons are performed using SIGNALS, and both effects are due to HOW THE SIGNALS ARE MEASURED, and not any effect on the clocks.

Comment 2: Why do you use signals? Of course, you need signals if the distance between the two clocks starts increasing. However, using signals makes the whole exercise overly complex.

>	On 4/11/20 10:12 AM, Ed Lake wrote:

> >	On Friday, April 10, 2020 at 9:57:10 PM UTC-5, tjrob137 wrote:

>	Your claim is directly in conflict with Einstein's first postulate, the Principle of Relativity. You REALLY do not understand SR at all, but are too stupid and ignorant to recognize your own inadequacies.

What is wrong by first studying the experiment as discussed in Comment 1. The purpose of each experiment is to unravel the details of the behaviour of what you want to understand. (i.e. of a clock)

>

Tom Roberts wrote; They are not "magical", and _I_ did not "dream them up", they are PRESENT IN THE DESCRIPTION OF THE EXPERIMENT (yes, every one). They are ESSENTIAL -- unless clocks are co-moving and co-located, it requires SIGNALS to compare their tick rates. (And even then the most accurate methods of comparing them use electrical signals.)

I have never seen any experiment related to the clock paradox or twin paradox where it is essential to use electrical i.e light signals during the trip. It is essential that each clock operates based on a light signal, but that signal is not required for communication between the two clocks. Maybe what you mean is discussed at pages 148 (Figure 5-7) and 149 (Figure 5-8) in the book: Space-Time Physics II. At page 148 the "Path in Space" and at page 149 the "Worldline in Spacetime" are compared. A much simpler experiment is to place clocks at equal distances in the frame (considered at rest) identified in Figure 5.7. All these clocks have to be synchronized. During your trip when your moving clock meets a clock at rest, comparing both, immediately shows that the moving clock ticks slower.

>	As soon as signals are involved, one must ask: what are the effects of the physical situation on the signals? -- one finds that the entire difference is due to effects on the signals; the clocks are completely unaffected by both relative motion and difference in gravitational potential.

6 Tom Roberts doesn't know how to compare inertial moving clocks

I mean that a cock constructed to tick at 1 Hz will always tick at 1 Hz. Because 1 Hz is its usual rate. I describe this in terms of clocks, because

"Time is what clocks measure." -- Einstein and others.

>>	This is directly related to Einstein's first postulate of SR, and the fact that in GR all local physics is as in SR.

>	I don't understand what the fact that: "The laws of physics take the same form in all inertial frames" has to do with this.

Essentially all laws of physics involve time derivatives, usually relating them to spatial derivatives or other quantities. If time "flowed" at a different rate, such laws could not be valid because the time derivatives would be affected but the other terms would not.

>>	Of course those relative clock comparisons are performed using SIGNALS, and both effects are due to HOW THE SIGNALS ARE MEASURED, and not any effect on the clocks.

>	Comment 2: Why do you use signals?

Because if two clocks are not co-located and co-moving, it is impossible to compare their tick rates without signals. This OUGHT to be obvious.

Do not confuse this with comparing their elapsed proper times.

No. The signals are ESSENTIAL, because you cannot compare tick rates without them. And once you use signals, to compare the clocks' tick rates you MUST account for any effects on the signals.

Indeed, in essentially every physical situation that compares two clocks, signals are used -- even when they are co-located and co-moving. For instance, comparing your wristwatch to a clock on the wall involves light signals.

Because such experiments are NOT comparing tick rates, they are comparing elapsed proper times. That is a DIFFERENT physical situation with a DIFFERENT description and explanation.

[... overly complex references to books I do not have]

Tom Roberts

7 Tom Roberts doesn't know how to compare inertial moving clocks

Tom, poor idiot, have you ever heard of broken clocks?

>	"Time is what clocks measure." -- Einstein and others. This is manifestly true, because in every experiment involving "time" in any way, clocks are used to measure it.

And clocks of GPS indicate t'=t, just like serious clocks always did. Good bye, The Shit.

8 Tom Roberts doesn't know how to compare inertial moving clocks

> > >>

Tom Roberts wrote: No matter how you move, and no matter where you might be located, time ALWAYS passes at its usual rate for you.

> > >

What do you mean with its usual rate?

> >	I mean that a cock constructed to tick at 1 Hz will always tick at 1 Hz. Because 1 Hz is its usual rate.

>	Tom, poor idiot, have you ever heard of broken clocks?

Maluw, my response to Tom is as follows:

What you have done is replaced the words 'usual rate' with 'always ticks'. You have added the word 1 Hz which means 1 tick per second. That is a 'tricky' a concept, related to the behaviour of clocks which are used to measure time.

A much better scientific way is to compare the clock counts of two identical clocks using light signals.
Suppose we send clock #2 to a faraway distance and back such that they meet again and the clock counts can be compared. As far as I understand the clocks counts will be different and the clock count of clock #2 will be less than clock #1.
If we agree about that what is the meaning to claim that both clocks always tick at 1 Hz or 1 tick per second?

IMO it is much more interesting to identify the cause of this physical difference.

Let us treat each other the same, in the way we want to be treated.

Nicolaas Vroom

9 Tom Roberts doesn't know how to compare inertial moving clocks

Nicolaas Vroom wrote:

>

A much better scientific way is to compare the clock counts of two identical clocks using light signals. Suppose we send clock #2 to a faraway distance and back such that they meet again and the clock counts can be compared. As far as I understand the clocks counts will be different and the clock count of clock #2 will be less than clock #1. If we agree about that what is the meaning to claim that both clocks always tick at 1 Hz or 1 tick per second?

No you can't. A comparison always involves a minimum of two steps. And an 1 Hz clock always ticks exactly at 1000 mHz.

10 Tom Roberts doesn't know how to compare inertial moving clocks

Man, get conscious. Compare 2 identical pendulum, one here, the second one on Moon. What will you get?
Time dilation?
The scientific way is - assuming axioms and match clocks to them. It was that way when physicists were mostly sane and it is that way after they got mad.

11 Tom Roberts doesn't know how to compare inertial moving clocks

Maybe what I wrote is misleading. At hindsight it should have been:

A much better scientific way is to compare the clock counts of two identical clocks (which internal operation uses light signals). Suppose we send clock #2 to a faraway distance and back such that they meet again and the clock counts can be compared. As far as I understand the clocks counts will be different and the clock count of clock #2 will be less than clock #1. If we agree about that what is the meaning to claim that both clocks always tick at 1 Hz or 1 tick per second?

>	Compare 2 identical pendulum, one here, the second one on Moon. What will you get?

Nonsense

Nicolaas Vroom.

12 Tom Roberts doesn't know how to compare inertial moving clocks

> > > >

What do you mean with its usual rate?

> > >

I mean that a cock constructed to tick at 1 Hz will always tick at 1 Hz. Because 1 Hz is its usual rate.

> >

>	What you have done is replaced the words 'usual rate' with 'always ticks'. You have added the word 1 Hz which means 1 tick per second. That is a 'tricky' a concept, related to the behaviour of clocks which are used to measure time.

It is obvious you do not know what a clock is or does!!

>	A much better scientific way is to compare the clock counts of two identical clocks using light signals.

The situation here is to compare clock "ticks". A clock is built to "tick" at 1 second per second (where 1 second is 1/86400 of a day). When you use the word "count" you are referring to the elapsed time, that is the total number of "ticks" between two events.

>	Suppose we send clock #2 to a faraway distance and back such that they meet again and the clock counts can be compared. As far as I understand the clocks counts will be different and the clock count of clock #2 will be less than clock #1.

You are talking here of the traveling twin situation, where what it is being compared is not the "ticks" of each clock but the elapsed time of each clock!!

13 Tom Roberts doesn't know how to compare inertial moving clocks

>	And a 1 Hz clock always ticks exactly at 1000 mHz.

a 1 Hz clock always ticks the same as a 1000 mHz (milliHz) clock.

My two questions are: 1) Do you agree that the clock counts of both clocks are different? If yes: 2) Do you agree that both clocks always ticked at there usual rate i.e at 1 Hz or at 1 tick per second?

Nicolaas Vroom.

14 Tom Roberts doesn't know how to compare inertial moving clocks

It is obvious that this problem is related to a butcher who has to examine his own meat. The issue is to explain the meaning of the concept: A clock its usual rate (of 1 Hz). That is tricky because to explain that most probably you need another clock.

>

> >	A much better scientific way is to compare the clock counts of two identical clocks using light signals.

>	The situation here is to compare clock "ticks".

No, the real question is to explain why each clock always ticks at the same rate. i.e. for example at 1 Hz

>	When you use the word "count" you are referring to the elapsed time, that is the total number of "ticks" between two events.

No, for me the concept of counts and ticks are synonyms. That 1 count is 1 second or 5 second or 10^-6 seconds is irrelevant.

> >	Suppose we send clock #2 to a faraway distance and back such that they meet again and the clock counts can be compared. As far as I understand the clocks counts will be different and the clock count of clock #2 will be less than clock #1.

>	You are talking here of the travelling twin situation, where what it is being compared is not the "ticks" of each clock but the elapsed time of each clock!!

Yes, you are correct but: It makes much more sense to compare ticks or clock counts. That is much closer what each clock physical does.

> >	If we agree about that, what is the meaning to claim that both clocks always tick at 1 Hz or 1 tick per second?

>	Because, again, the ticking of a clock (1 tick/second) has nothing to do with the elapsed time of that clock (number of ticks in X hours).

Do you agree when the two clocks meet, that their clock counts are different?

Nicolaas Vroom

15 Tom Roberts doesn't know how to compare inertial moving clocks

> >	It is obvious you do not know what a clock is or does!!

>	It is obvious that this problem is related to a butcher who has to examine his own meat. The issue is to explain the meaning of the concept: A clock its usual rate (of 1 Hz). That is tricky because to explain that most probably you need another clock.

The "tick" of a clock is determined by the physical laws governing its mechanisms. A cesium atomic clock "tick" is defined by the hyperfine transition frequency in the microwave, or electron transition frequency in the optical or ultraviolet region of the electromagnetic spectrum of atoms.

> >	The situation here is to compare clock "ticks".

>	No, the real question is to explain why each clock always ticks at the same rate. i.e. for example at 1 Hz

The real question is: do clocks in certain physical situations "run slow" than clocks in different physical situatios?

The answer is that in SR, clocks do not "run slow" but are "measured to run slow"

The word "measured" is the word many authors of papers and journals forget to put, because among physicists, this concept of "measuring here what is happening there" is well known!!!

> >	When you use the word "count" you are referring to the elapsed time, that is the total number of "ticks" between two events.

>	No, for me the concept of counts and ticks are synonyms. That 1 count is 1 second or 5 second or 10^-6 seconds is irrelevant.

Well if you want to discuss physics you have to use the proper language!!

One clock ticks at 1 second/second. One clock elapsed time is the number of ticks in a given interval of time-

> >	You are talking here of the travelling twin situation, where what it is being compared is not the "ticks" of each clock but the elapsed time of each clock!!

>	Yes, you are correct but: It makes much more sense to compare ticks or clock counts. That is much closer what each clock physical does.

Nonsense

> > >

If we agree about that, what is the meaning to claim that both clocks always tick at 1 Hz or 1 tick per second?

> >	Because, again, the ticking of a clock (1 tick/second) has nothing to do with the elapsed time of that clock (number of ticks in X hours).

>	Do you agree when the two clocks meet, that their clock counts are different? Nicolaas Vroom

In the traveling twin problem, the traveling twin "elapsed time" is shorter than the at rest twin "elapsed time"

16 Tom Roberts doesn't know how to compare inertial moving clocks

>	On Saturday, 2 May 2020 12:26:48 UTC+2, Kip Miner wrote:

>	My two questions are:

>	1) Do you agree that the clock counts of both clocks are different? If yes: 2) Do you agree that both clocks always ticked at there usual rate i.e at 1 Hz or at 1 tick per second?

According to the SR model, and the deductions from other experiments that imply the answers, the answers to both questions is yes.

The only explanation for the facts, is that the traveling clock covered more time, just as the odometers would do for space in the equivalent situation.

The only explanation for this, for the SR model, is the TARDIS & Dr. Who time travel scenery.

17 Tom Roberts doesn't know how to compare inertial moving clocks

>	El s�bado, 2 de mayo de 2020, 12:03:42 (UTC-4), Nicolaas Vroom escribi�: The "tick" of a clock is determined by the physical laws governing its mechanisms.

One tick or count of a clock is defined as the passage of one photon (starting) from one mirror towards the mirror on the opposite side and back. This has nothing to do with any physical law except see (*)

>	A cesium atomic clock "tick" is defined by the hyperfine transition frequency in the microwave, or electron transition frequency in the optical or ultraviolet region of the electromagnetic spectrum of atoms.

I agree with this definition based on physical issues. Why did not you write as above: The "tick" of a cesium atomic clock is determined by the physical laws governing its mechanisms? It is very wise, you did not do that.

> >	No, the real question is to explain why each clock always ticks at the same rate. i.e. for example at 1 Hz

>	The real question is: do clocks in certain physical situations "run slow" than clocks in different physical situations?

The real question is: do clocks in certain physical situations "tick different" than clocks in different physical situations?

>	The answer is that in SR, clocks do not "run slow" but are "measured to run slow"

In order to understand this sentence, you must first define what SR is.

My simple answer is because the length travelled by a photon is different when the length travelled by the clock is different (compared with another clock) As a result, the clock counts will be different.

>	The word "measured" is the word many authors of papers and journals forget to put, because among physicists, this concept of "measuring here what is happening there" is well known!!!

The concept "measuring here what is happening there" is extremely complex, because it involves light travel time.

> > >

When you use the word "count" you are referring to the elapsed time, that is the total number of "ticks" between two events.

> >	No, for me the concept of counts and ticks are synonyms. That 1 count is 1 second or 5 second or 10^-6 seconds is irrelevant.

>	Well if you want to discuss physics you have to use the proper language!!

Sorry, I always try to write as clear as possible.

>	In the travelling twin problem, the travelling twin "elapsed time" is shorter than the at rest twin "elapsed time"

In the travelling twin problem, the travelling twin "# of counts of his clock" is less than the "# of counts of the clock" of the twin at rest. (# of counts of a clock implies synchronization between the two clocks) IMO that is a physical fact which has nothing to do with the laws of physics and which can be demonstrated by experiments. (*) The only assumption is that locally the speed of light in all directions is the same.

There is nothing wrong to use "time" instead of "clock counts" in normal life (when we use a wristwatch to see what the time is)

Nicolaas Vroom.

18 Tom Roberts doesn't know how to compare inertial moving clocks

19 Tom Roberts doesn't know how to compare inertial moving clocks

Speaking rather loosely, yes.

>	The only explanation for this, for the SR model, is the TARDIS & Dr. Who time travel scenery.

NONSENSE! The actual explanation is that different timelike paths through spaceTIME can have different elapsed proper times, even though they begin and end at the same points in spaceTIME. This is fully justified by actual calculations.

Attempting to use fictional characters as an "explanation" for observed physical facts is downright stupid.

20 Tom Roberts doesn't know how to compare inertial moving clocks

Sure. That is how I chose to answer your question "What do you mean by that?" -- nothing unusual here.

>	That is a 'tricky' a concept, related to the behaviour of clocks which are used to measure time.

It's not "tricky" at all, it is what is meant by those words.

>	A much better scientific way is to compare the clock counts of two identical clocks using light signals.

Your words are ambiguous. I assume that you mean to compare the TOTAL clock counts of two clocks, each of which is implemented by using light signals. Those light signals do not propagate between the clocks, only internally within each clock.

Note that SR and GR make predictions about the behavior of clocks that do not depend on how the clocks are implemented. All that is required is that the clock be good clocks that are not damaged.

Yes, assuming the clocks are sufficiently accurate and the speed and distance of clock #2's travel are sufficiently large.

>	If we agree about that what is the meaning to claim that both clocks always tick at 1 Hz or 1 tick per second?

I keep repeating this and you keep ignoring it:

The phrase "that clock ticks at 1 Hz" means that its PROPER tick rate is 1 Hz -- a co-located and co-moving frequency standard will measure 1 Hz. That phrase mentions nothing except the clock, so nothing else can be involved -- including observing the clock from far away or by an observer moving differently. ONLY THE CLOCK ITSELF IS INVOLVED.

The tick rate of a clock is an instantaneous measurement necessarily performed locally, in the rest frame of the clock. Elapsed proper time is an INTEGRAL of the clock's tick rate over the path followed by the clock. The latter MANIFESTLY depends on the path, while the former MANIFESTLY does not.

What is the "cause" of two sides of a triangle summing to a longer path length than the third side?

Geometry has consequences that cannot be identified as "physical causes", yet are ineluctably part of physics. For your example, which is the twin paradox, the difference is GEOMETRICAL -- the paths followed by the two clocks are different, and it is that difference in paths that induces a difference in their elapsed proper times, EVEN THOUGH EACH CLOCK TICKED AT ITS USUAL RATE (here 1 Hz).

It seems to me that you are implicitly using an "absolute" meaning of "tick rate", where YOU are special and unique, and all tick rates are referenced to YOURSELF. That's invalid, and the words involved do not include that. "The tick rate of this clock" includes ONLY the clock, and NOTHING else can be involved, including your personal and unique perspective. The ONLY way to measure "the tick rate of this clock" is by using a co-moving and co-located instrument -- ANYTHING else involves something other that the clock itself.

Tom Roberts