Einstein notion of time and the oscillation of the cesium atom

[Salman2]

Your suggestion seems to deny that clocks keep track of time. If that's the case, then I'm wondering what does keep track of time.

OK, now I understand. Yes, I agree that all clocks (with or without arms) can keep track of time by recording a number related to the motion of some entity. The number of time makes motion continuous. Time is not fast or slow just as the motion of the second hand on a clock (tick-tick-tick...) is not fast or slow, there are either few or many such ticks between two moments and if few the time is short and if many the time is long.

I do not understand why Einstein would not agree with this explanation, given that in his 1905 paper he said "hence we conclude that a balance-clock at the equator must go more slowly" ?...e.g., he said the clock goes more slowly (it had fewer ticks), he did not say time goes more slowly. Imo, he implies with this statement that because the clock goes more slowly (has fewer ticks) then time is relatively shorter because the motion at the equator is faster.

 

[Dale]

Yes, I agree that all clocks (with or without arms) can keep track of time by recording a number related to the motion of some entity. ... Time is not fast or slow just as the motion of the second hand on a clock (tick-tick-tick...) is not fast or slow, there are either few or many such ticks between two moments and if few the time is short and if many the time is long.

I think you are getting hung up on the english. You seem to be stuck on "long" and "short" rather than "fast" and "slow". The important part is that dτ/dt<1 for a moving clock, do you understand that?

If so, then the rest is semantics. Fast and slow are equally valid English words as long or short, as long as you are clear that you mean the math above.

 

[ghwellsjr]

Your suggestion seems to deny that clocks keep track of time. If that's the case, then I'm wondering what does keep track of time.

OK, now I understand. Yes, I agree that all clocks (with or without arms) can keep track of time by recording a number related to the motion of some entity. The number of time makes motion continuous. Time is not fast or slow just as the motion of the second hand on a clock (tick-tick-tick...) is not fast or slow, there are either few or many such ticks between two moments and if few the time is short and if many the time is long.

I do not understand why Einstein would not agree with this explanation, given that in his 1905 paper he said "hence we conclude that a balance-clock at the equator must go more slowly" ?...e.g., he said the clock goes more slowly (it had fewer ticks), he did not say time goes more slowly. Imo, he implies with this statement that because the clock goes more slowly (has fewer ticks) then time is relatively shorter because the motion at the equator is faster.

It sounds like you're still denying that clocks keep track of time. It sounds like you are saying that clocks can measure the interval between two events and measure shorter or longer time intervals, but you are not willing to say that if two clocks, present at two events but taking different paths between those two events, measure different intervals, then time is different along those two paths.

So let me ask you about the famous Twin Paradox: if two clocks are present at the same place and at the same time and we set the two clocks to display the same time and then we let them move differently following any arbitrary paths and then eventually reunite them (not necessarily at the same starting location) and we see that they now have different readings on them, would you say that the both legitimately tracked time differently or would you say that one or both of the clocks was influenced by their motions (and/or accelerations) and so did not both keep track of time correctly? Ignore any influences due to gravity or consider the scenario to be carried out far removed from any significant source of gravity.

 

[Nugatory]

I do not understand why Einstein would not agree with this explanation, given that in his 1905 paper he said "hence we conclude that a balance-clock at the equator must go more slowly"...

"Go more slowly" would be a natural way for a turn-of-the-last-century physicist to describe the phenomenon, but (as with the notion of relativistic mass, for example) we've learned that it's not always the best and clearest way of describing it. It's unlikely that Einstein himself would have chosen that description twenty years later and after having developed GR.

It's important to remember that Einstein didn't deliver the modern theory of relativity in a single blinding flash of insight in 1905. The 1905 paper marks the point when the key insights of SR were widely published to the scientific community; but the presentation, mathematical framework, and manner of speaking used by Einstein and others to describe these insights evolved through the following decades.

Thus, we have to be careful about reading too much into the precise wording of a single Einstein quote; we should be approaching his writings the way a historian approaches a historical document, not the way a religious fundamentalist approaches scripture. The fact that Einstein (or anyone else) said something in 1905 means only that that was the clearest way he could find of expressing what he was thinking at the time. (And it doesn't help any that we are often reading English translations of Einstein's German, so we are getting what the translator thought he was saying, not what he actually said).

 

[Salman2]

So let me ask you about the famous Twin Paradox: if two clocks are present at the same place and at the same time and we set the two clocks to display the same time and then we let them move differently following any arbitrary paths and then eventually reunite them (not necessarily at the same starting location) and we see that they now have different readings on them, would you say that the both legitimately tracked time differently or would you say that one or both of the clocks was influenced by their motions (and/or accelerations) and so did not both keep track of time correctly? Ignore any influences due to gravity or consider the scenario to be carried out far removed from any significant source of gravity.

Thank you for the question. In this version of the Twin Paradox there are two simultaneous events for each clock, the first event is when they depart and simultaneously a time is recorded for each, the second event is when they rejoin and simultaneously a second time is recorded for each clock. Thus there are two different frames of reference to keep track of time (1) when and where the clocks depart from each other, and (2) when and where the two clocks unite after each is in motion for some unknown distance and speed.

Let C1 = first clock and C2 = second clock. They depart simultaneously at an event moment M1 and begin an arbitrary motion path and return to a second place simultaneously at a second event moment M2. We observe they record different times during their motions, perhaps C1 records that 100 time ticks during, C2 records 99 ticks.

I would say: (1) because each clock took a unique path of motion between two event moments (M1 = start of motion, M2 = end of motion) they both legitimately tracked time differently because they were synchronized at the start, and because they recorded time simultaneously at two event moments (time measure at event M1 was t=0 for both clocks; time measure at M2 was t=100 for C1 and t=99 for C2).

I also would say (2) the reason the time recorded for C2 was shorter (fewer) than C1 is because C2 moved faster the C1 over identical distances traveled between the two simultaneous events M1 and M2, a result predicted by Einstein relativity theory.

 

[write4u]

What part of the measurement of time is called 'world line' or 'world braid'? And how is it measured?

 

[azoulay]

... If you took two cesium atoms, one on a flying jet and the other on the ground, by the time the atom on the ground produced 9,192,631,770 periods of radiation the one on the jet will have produced say 9,192,631,769 periods of radiation. This is because the atom on the jet experienced less time compared to the atom on the ground.

QuantumPion, what's your definition of time ?

thanks,
jonathan

 

[azoulay]

...Do we not say the second horse was slower than the first because it took a longer time to reach the finish line ? I do not see why Einstein would grant 'time' as a concept the same physical status as 'horse' and say that both move slow or fast ? ...

Salman2, I'm not sure to understand your quote.

Did you mean: " I do not see why Einstein WOULDN'T grant 'time' as a concept the same physical status as 'horse' and say that both move slow or fast ?

 

[azoulay]

Clocks do not keep track of time but keeps track of movements

There is indeed a difference between time as something that locates an event in space-time ("coordinate time") and time as something measured by clocks ("proper time").

LastOneStanding, you say that clocks are measuring "something", what is that "something"?

As far as I'm concerned, ALL clocks ever made in the history of mankind do the same thing: they react to a MECHANICAL MOVEMENT. For example:

-a pendulum clock have physical gears that counts how many swinging back and forth (how many MECHANICAL MOVEMENTS) the pendulum have made.

-a digital clock uses either the oscillations on the power line (60 cycles per second in Canada) or the oscillations of a quartz crystal. The former is a MECHANICAL MOVEMENT of electrons on a copper wire and the latter is MECHANICAL resonance/MOVEMENTof a vibrating crystal.

-an atomic clock responds to Oscillations of the Cesium atom (Oscillations are natural resonance but still MECHANICAL MOVEMENTS of atoms)


So clocks really keep tracks of MECHANICAL MOVEMENTS, not time:

-a pendulum clock displays "one minute" when the pendulum has swing back and forth 60 times. So a pendulum clock keeps track of how many MECHANICAL MOVEMENTS the pendulum have made.

-a digital clock using the power line keeps track of the electrons MECHANICAL MOVEMENT (electrical oscillations) on a copper wire. For clocks that uses quartz crystal, they keep track of the quartz atoms resonance/MECHANICAL MOVEMENT.

-an atomic clock keep track of Oscillation/MECHANICAL MOVEMENT of Cesium atom. When 9,192,631,770 periods have occurred, it adds "one second" the the LCD screen.

Another example: The calendar adds "one month" when the moon has finished its cycle around Earth (so the calendar keeps track of a movement). Also, the calendar adds "one year" when the Earth has finished its cycle around the Sun. (The calendar does NOT keep time, it keeps track of a MECHANICAL MOVEMENT)

Conclusion 1: ALL clocks ever built never kept time. ALL clocks ever built keeps track of how many MECHANICAL MOVEMENTS have occurred in a system. If someone wants to argue that point please give me only one example where that should be different.

Conclusion 2: I think, it would be possible in science to never use the word "time" and only use the word "movement". What I was taught in school is exact: "Time is an abstract representation of movement", nothing more.

What I think is so confusing in Einstein theory is that no one seems to know what to relate the notion of time to or it's debated.

So I'm not saying Einstein was wrong, what I'm saying is that Einstein probably could of written all his theory talking only about movements and to never having to use the word "time".

If some genius one day wants to rewrite Einstein theory and set aside the word "time" and use only the word "movement" it would be, I think, a lot more comprehensible and intuitive for everyone.

So yes, "time" is relative (Einstein was right) but only if the definition of time has to do with MECHANICAL MOVEMENTS. Bottom line, to put it simply: it is MECHANICAL MOVEMENTS that is relative.

If anyone wants to reply to the above, PLEASE start your reply with a clear and unambiguous definition of "time".

This post is already very long so I'm sorry about that.

Time dilation isn't something that just happened to the atomic clocks; it happened to every dynamical process.

Could you please give me examples of some dynamical process where time dilation happens ?

thanks, jonathan

 

[Fredrik]

What part of the measurement of time is called 'world line' or 'world braid'? And how is it measured?

A "world line" is the curve in spacetime that describes the motion of a point-like object. The term "world braid" is non-standard, I think. I googled it, and didn't get any physics-related hits on the first two pages. Wikipedia uses the following terminology:

World lines aren't measured. What you measure is the position of the object. If you make multiple measurements, you can draw the object's world line.

 

[Fredrik]

QuantumPion, what's your definition of time ?

SR defines two kinds of time, "coordinate time" and "proper time". A coordinate system is a function x that associates a 4-tuple $(x^0(p),x^1(p),x^2(p),x^3(p))$ with each p in M. The number $x^0(p)$ is the coordinate time (or time coordinate) of p.

Coordinate time is assigned to events, i.e. points in spacetime, but proper time is assigned to curves in spacetime that can describe the motion of a massive particle. If C is such a curve, then the proper time can be defined using some inertial coordinate system. If the time coordinates of the endpoints are $a$ and $b$, then the proper time of the curve is
$$\int_{a}^{b}\frac{1}{\gamma}dt$$ where t is the time coordinate.

LastOneStanding, you say that clocks are measuring "something", what is that "something"?

They "measure" the proper time of the curves in spacetime that describe their motion, in the sense that if a clock displays t at one event and t' at another, then the proper time of the part of the clock's world line from the former event to the latter event is t'-t.

 

[Nugatory]

So I'm not saying Einstein was wrong, what I'm saying is that Einstein probably could of written all his theory talking only about movements and to never having to use the word "time".

Further up in this thread, someone referred to the first section of Einstein's 1905 paper - I hope you've followed up on that. You might also try googling for the phrase "time is what a clock measures" - that will take you to some pretty good explanations of how Einstein defined time and what is meant by "time" in relativity theory and how it relates to movement.

As you're thinking about clocks, time, and movement, you also might want to consider a "radioactivity clock". I have a sample of radioactive material; its strength decreases over time as it decays. We can use it as a clock by defining one tick of the clock be the time it takes for the material to lose 50% of its strength, and there's no movement involved. But it's clear that this device is measuring something, and we choose to call that something "time".

 

[Nugatory]

Could you please give me examples of some dynamical process where time dilation happens ?

The muon decay measurements have always been one of my favorites. High energy cosmic rays hit the atmosphere about 100 km up, giving rise to very short-lived particles called muons. These muons decay so quickly that they shouldn't be able to hit the surface of the Earth - even though they're moving at nearly the speed of light, it still takes a few hundred microseconds for them to travel 100 km, and they don't live that long.

But they do reach the surface of the earth. That's time dilation at work.

 

[write4u]

Still looking for the science article with the term world braids, but perhaps this may clarify,
http://en.wikipedia.org/wiki/Braid_group

If anyone wants to reply to the above, PLEASE start your reply with a clear and unambiguous definition of "time".

IMHO, time is a potential measurement of duration of motion and becomes explicate and measurable only during that motion or change.

I see Time as a fundamental potential, a "latency" which becomes an expressed non-physical property of an event or movement, which by needs 'requires' and 'uses' time. These individual chronological histories (in time) I believe are called world lines.
(see illustration)

World lines aren't measured. What you measure is the position of the object. If you make multiple measurements, you can draw the object's world line.

IOW, 'multiple measurements' can only be made after the new coordinates have been established (after the event). Before then the destination coordinates were not yet known and duration of time was only a latent 'probability' for that event.

 

[Fredrik]

You should use the quote button when you quote people. This way the tags will automatically contain the name of the person who said it, and the quote box will also contain a link to the post where it was said.

Still looking for the science article with the term world braids, but perhaps this may clarify,
http://en.wikipedia.org/wiki/Braid_group

That doesn't have anything to do with world lines.

IMHO, time is a potential measurement of duration of motion and becomes explicate and measurable only during that motion or change.

I see Time as a fundamental potential, a "latency" which becomes an expressed non-physical property of an event or movement, which by needs 'requires' and 'uses' time.

This is at best philosophy. It certainly isn't physics.

 

[Dale]

So the definition of time for me has always been that it's an abstract representation of some movement and nothing else.

So clocks really keep tracks of MECHANICAL MOVEMENTS, not time:

You are contradicting yourself yet again. First you say that time represents some movement, then you say that clocks measure some movement. Therefore your obvious conclusion should be that clocks measure time. For you to conclude what clocks measure is "not time" is a self-contradiction.

So yes, "time" is relative (Einstein was right) but only if the definition of time has to do with MECHANICAL MOVEMENTS. Bottom line, to put it simply: it is MECHANICAL MOVEMENTS that is relative.

Exactly.

If anyone wants to reply to the above, PLEASE start your reply with a clear and unambiguous definition of "time".

I like Einstein's definition (simplified): "time is what a clock measures (proper time) together with a simultaneity convention (coordinate time)". That is the essence of Einstein's section 1, and is a clear and unambiguous experimental definition of time.

Could you please give me examples of some dynamical process where time dilation happens ?

Time dilation occurs with EM processes (e.g. atomic clocks), weak force processes (e.g. muon decay), strong force processes (e.g. pion decay), and gravity (e.g. gravitational potential). All dynamical processes are based on one or more of those fundamental forces so all dynamical processes exhibit time dilation.

I think that the problem you are having is simply an emotional reaction to the idea of time dilating. The logic is clear, even based on your own definitions, but you are emotionally unwilling to follow the logic and instead let your emotional reaction lead you to make self-contradictory statements.

 

[ghwellsjr]

...
Conclusion 2: I think, it would be possible in science to never use the word "time" and only use the word "movement".
...
Einstein probably could of written all his theory talking only about movements and to never having to use the word "time".

If some genius one day wants to rewrite Einstein theory and set aside the word "time" and use only the word "movement" it would be, I think, a lot more comprehensible and intuitive for everyone.
...
If anyone wants to reply to the above, PLEASE start your reply with a clear and unambiguous definition of "time".

It will take a real genius to fulfill your request.

However, I have a question:

Do you consider a light clock to be another example of MECHANICAL MOVEMENT? I'm asking about a pair of mirrors rigidly separated by a fixed distance and with flash of light bouncing between the two mirrors and a counter that increments each time the reflection bounces off one of the mirrors? (Notice I didn't use the forbidden word.)

 

[Bhumble]

Events don't have speeds. And an observer's view of events does not change depending on anything.

I don't understand how an event does not have a speed (or more specifically a time dependence). I'm not sure how else would you describe an event other than some setting changing as a function of time?
Assuming that you agree that an event does have a time dependence. Then doesn't it follow that the perception of time passing depends on the reference frame of the observer. Say you describe an event as a ball dropping into a hole. Is the time that this event occurred invariant to the speed that the ball drops and the reference frame of the observer?

Clinging to the idea of an absolute reference frame does not change any observations. It also does not change any predictions (as long as you have a correctly working theory based on an absolute reference frame). That sounds like a modern incarnation of Lorentz's Ether Theory. You should be clearer when making statements like this, as is, they sound confusing.

Fair enough. I agree that even if there is some absolute reference frame it doesn't change the way that we will ever be able to perceive things and maybe it is my own ability to accept the speed of light as a universal limitation on all forms of matter that leads me stipulate the MAYBE about the absolute frame of reference.

I agree completely for matter that has an electromagnetic interaction but I suppose I still have reservations considering the majority of the matter in the universe seemingly does not interact with light and COULD very well have different limitations. But this is irrelevant to the conversation and I could have omitted that unfounded opinion.

If you want to take Einstein's special theory of relativity, then you must reconcile with time dilation. It's not an option. And it is more than simply our ability to observe, given our medium. Are you talking about Ether?

I was referring to photons in a vacuum. Or the limitation of information transfer by the speed of light constant. I'm completely in agreement with time dilation (not that it would change anything if I wasn't) and convoluted what I was saying based on my previous opinion. What I meant is that it is more difficult for some people to accept than others because it is non-intuitive based on day to day observations. I'm not saying that it is an option, just that it is easier for some people to completely disregard their intuition and accept it as fact than others. It isn't like student's are exposed to lots of relativistic experiments (especially compared to daily living) before learning about special relativity.

You sound like you're on shaky ground.

Shaky ground for being skeptical? I think skepticism within reason is a great approach to life and learning.

 

[Dale]

I don't understand how an event does not have a speed (or more specifically a time dependence). I'm not sure how else would you describe an event other than some setting changing as a function of time?

An event is a point in the spacetime manifold. It has no spatial nor temporal extent, and as a result it does not have a speed. It most definitely does not change as a function of time.

This is standard terminology, so it is important to use it correctly otherwise you will have lots of communication problems.

 

[VantagePoint72]

I agree completely for matter that has an electromagnetic interaction but I suppose I still have reservations considering the majority of the matter in the universe seemingly does not interact with light and COULD very well have different limitations.

The fact that $c$ is a universal speed limit has nothing to do with the fact that light propagates at it. All four fundamental forces are Lorentz covariant. It would be more accurate to say that "the speed of light is $c$" than to say "$c$ is the speed of light". Whether or not something interacts with light has nothing to do with whether it obeys the dynamics of special relativity.

 

[Salman2]

An event is a point in the spacetime manifold. It has no spatial nor temporal extent, and as a result it does not have a speed. It most definitely does not change as a function of time.

Is there any suggestion in quantum theory that an event, as a point in spacetime manifold, has the spatial and temporal extent of Planck-space and Planck-time ? Thus, given that both Planck-space and Planck-time are outside possibility of human measurement, could this help explain why all events in spacetime manifold do not change as a function of time ? The suggestion being that events as points in spacetime would be outside the limit of human ability to measure change because they occur within Planck-space and Planck-time, which by definition also are outside the spacetime manifold ?

 

[VantagePoint72]

Is there any suggestion in quantum theory that an event, as a point in spacetime manifold, has the spatial and temporal extent of Planck-space and Planck-time ? Thus, given that both Planck-space and Planck-time are outside possibility of human measurement, could this help explain why all events in spacetime manifold do not change as a function of time ?

Events don't have spatial or temporal extent because they are defined to be points in space-time. Quantum theory has nothing to do with it.

 

[Salman2]

I think you are getting hung up on the english. You seem to be stuck on "long" and "short" rather than "fast" and "slow". The important part is that dτ/dt<1 for a moving clock, do you understand that?

OK. Suppose we have two synchronized clocks and they start motion at the same place in spacetime, and we find that they return to that place simultaneously as an event, and the dτ/dt = 0.99 for one clock, and dτ/dt = 0.90 for the second. I do not see why it is semantics to say that one clock moved faster or slower relative to the other because time as measured by dτ/dt was shorter or longer ? Sorry, but I just do not understand how the math dτ/dt demands that time cannot be understand as long (or many) or short (or few) when the motion of what the time measures is labeled as fast or slow.

 

[Salman2]

Events don't have spatial or temporal extent because they are defined to be points in space-time. Quantum theory has nothing to do with it.

OK, then how are these 'points in space-time' defined ? If they are defined using Planck scale does this not open a door for a way to unite relativity theory and quantum theory ?

 

[ghwellsjr]

Events don't have speeds. And an observer's view of events does not change depending on anything.

I don't understand how an event does not have a speed (or more specifically a time dependence). I'm not sure how else would you describe an event other than some setting changing as a function of time?

In SR, we describe events with their coordinates according to a specified Inertial Reference Frame (IRF). There are four coordinates--three spatial and one time. We can then transform the coordinates of all the events according to a new IRF moving with respect to the original IRF and we will get a new set of coordinate values but we should never conflate the coordinates of one IRF with the coordinates of another IRF so we don't ever want to let the fact that their is motion between the IRF's lead us into the false notion that their is any motion to events. Each event is described as occurring at an instant in time at a specific location in space according to the coordinates of a specific IRF.

Assuming that you agree that an event does have a time dependence. Then doesn't it follow that the perception of time passing depends on the reference frame of the observer. Say you describe an event as a ball dropping into a hole. Is the time that this event occurred invariant to the speed that the ball drops and the reference frame of the observer?

If you are talking about a scenario where you don't specify when the ball dropped into the hole but rather when the ball was launched at some speed and angle from a cannon for example and we have to figure out its trajectory, then the IRF matters because distances as well as times are relative to the IRF and we can get different answers to the question of when the ball dropped into the hole as well as different answers to the question of how fast was the ball moving. Is that what you are concerned about?

Observers are also described according to events in a specified IRF. It has become common parlance in discussions of relativity to refer to the "reference frame of the observer" which usually means the observer starts at the event defined as the origin of the IRF (the event where all four coordinates equal zero) and then remains at the same spatial location but his Proper Time is considered to be equal to the Coordinate Time of the IRF. However, the observer's perception of time passing does not depend in any way on any reference frame. His perception of time is his Proper Time and all his observations of all events will be the same no matter what IRF we transform the coordinates of the events to. If he wants to, he can use radar methods to determine when and where events occurred relative to "his reference frame" but he can't do this as it is happening in the Coordinate Time of "his reference frame", he can only do it after the fact because he assumes that the speed of light is the same for both the outgoing and the incoming paths of his radar signal and after he has done some calculations to create "his reference frame".

 

[VantagePoint72]

OK, then how are these 'points in space-time' defined ? If they are defined using Planck scale does this not open a door for a way to unite relativity theory and quantum theory ?

They are defined by basic topology. I think you need to learn what a manifold is. The Planck scale does not enter into it anywhere.

 

[Dale]

Is there any suggestion in quantum theory that an event, as a point in spacetime manifold, has the spatial and temporal extent of Planck-space and Planck-time ?

The spacetime manifold is part of relativity, which is a classical theory, not a quantum theory. I think your question will be answered once we get a working quantum theory of gravity

 

[Salman2]

They are defined by basic topology. I think you need to learn what a manifold is. The Planck scale does not enter into it anywhere.

I appreciate your comments. Here is an unpublished report from a physicist associated with CERN where a suggestion is made how the Planck scale could enter into a spacetime manifold, so it does appear that my question is not completely off base:

http://cds.cern.ch/record/368952/files/9810174.pdf

 

[VantagePoint72]

I appreciate your comments. Here is an unpublished report from a physicist associated with CERN where a suggestion is made how the Planck scale could enter into a spacetime manifold, so it does appear that my question is not completely off base:

http://cds.cern.ch/record/368952/files/9810174.pdf

That, as DaleSpam said, is with regards to a quantum theory of gravity. The point is that you do not need such a theory to understand special relativity alone. It is completely consistent in what it says about space and time. From the very beginning, this thread has not been about, "What can we say about time according to the most hypothetical and modern theories of physics?" It is about Einstein's notion of time and how that relates to SR.

 

[Dale]

Sorry, but I just do not understand how the math dτ/dt demands that time cannot be understand as long (or many) or short (or few) when the motion of what the time measures is labeled as fast or slow.

I didn't say that you couldn't understand it in terms of English words, just that whatever words you choose use to express the ideas need to correspond to that mathematical expression. Einstein used the word "slow" to refer to dτ/dt<1. You prefer "long" or "short". As long as you are using those words to refer to dτ/dt<1 then you are correct, if you are not then you are wrong.