Relativity and shared realities (split from clocks, rulers...)

[michel123456]

 

 

Don't focus on the acceleration, focus on the speed. The speed dictates what the clock does.

And with this comment we are back to the beginning (the rulers discussion)

The clock "does" nothing, because velocity is relative. IOW all different observers from different frames will observe the clock ticking at different rates.

Like the ruler that remains the same length for the traveler who has the ruler at hand, the clock doesn't change rate for the traveler that has the clock at hand. So, the clock "does" nothing, it continues ticking as usual.

Anyway, the clock cannot tick at multiple rates just because there are multiple observers.

Edited September 1, 2016 by michel123456

[swansont]

And with this comment we are back to the beginning (the rulers discussion)

The clock "does" nothing, because velocity is relative. IOW all different observers from different frames will observe the clock ticking at different rates.

Like the ruler that remains the same length for the traveler who has the ruler at hand, the clock doesn't change rate for the traveler that has the clock at hand. So, the clock "does" nothing, it continues ticking as usual.

Anyway, the clock cannot tick at multiple rates just because there are multiple observers.

 

 

No, this is a distraction from the issue at hand; you're thinking of a different thread. This was never about "realities", it was about frames.

 

But when the moving clock returns to earth and is compared side-by-side, it has accrued less time. It really did run slow, because we know it had accelerated, which means it was moving. The observer with that clock can't claim to have been at rest.

[VandD]

Anyway, the clock cannot tick at multiple rates just because there are multiple observers.

The rate of clock ticking only makes sense if you introduce a reference frame.

A clock ticks at maximum rate if the clock is at rest relative to the reference frame.

But that same clock ticks at a slower rate per a frame if there's relative movement between the clock and the ref frame.

The ticking rate of a clock at rest relative to a frame has no preferred status. It's not more "real" than any other ticking rate.

Hence a clock does "tick at multiple rates".

All inertial reference frames are equally valid: they are 3D sections through 4D spacetime and no frame has a preferred status.

Edited September 1, 2016 by VandD

[michel123456]

The rate of clock ticking only makes sense if you introduce a reference frame.

A clock ticks at maximum rate if the clock is at rest relative to the reference frame.

But that same clock ticks at a slower rate per a frame if there's relative movement between the clock and the ref frame.

The ticking rate of a clock at rest relative to a frame has no preferred status. It's not more "real" than any other ticking rate.

Hence a clock does "tick at multiple rates".

All inertial reference frames are equally valid: they are 3D sections through 4D spacetime and no frame has a preferred status.

This is what I am fighting against.

IMHO it is a wrong interpretation of "All inertial reference frames are equally valid". This last statement says that you can calculate what another observer measures in any other FOR. It does not says that there is no FOR "αφετηριας" (Starting point, I don't know how to translate). You yourself admits that "A clock ticks at maximum rate if the clock is at rest relative to the reference frame." That is a starting point. In this same FOR the length of the measured object is the longest. That is also a starting point. These are 2 very good reasons to consider this FOR different from all the others.

And finally, a clock does not tick at multiple rates. There is only one reality that is observed differently by different observers. That is all. The concept of a clock ticking at multiple rates is a concept of overlapping realities and it is wrong.

[imatfaal]

This is what I am fighting against.

IMHO it is a wrong interpretation of "All inertial reference frames are equally valid". This last statement says that you can calculate what another observer measures in any other FOR. It does not says that there is no FOR "αφετηριας" (Starting point, I don't know how to translate). You yourself admits that "A clock ticks at maximum rate if the clock is at rest relative to the reference frame." That is a starting point. In this same FOR the length of the measured object is the longest. That is also a starting point. These are 2 very good reasons to consider this FOR different from all the others.

And finally, a clock does not tick at multiple rates. There is only one reality that is observed differently by different observers. That is all. The concept of a clock ticking at multiple rates is a concept of overlapping realities and it is wrong.

 

Your argument is persuasive and comforting - unfortunately it is also wrong; it fails to explain observed experimental data. muons hit the earth's surface, ions in a collider are flattened in the CoM frame, gps works...

[swansont]

This is what I am fighting against.

IMHO it is a wrong interpretation of "All inertial reference frames are equally valid". This last statement says that you can calculate what another observer measures in any other FOR.

 

It also states that neither observer can claim that the other's measurement is wrong, based on any physics argument. If I say a 1 kg object moving at 4 m/s has 8J of kinetic energy, and you, in another frame, say that it's moving at 6 m/s and has 18 J of kinetic energy, is one of us wrong?

 

And finally, a clock does not tick at multiple rates. There is only one reality that is observed differently by different observers. That is all. The concept of a clock ticking at multiple rates is a concept of overlapping realities and it is wrong.

 

The question is how can a moving object have more than one kinetic energy, as in the above scenario? Who is right, and what physics can you point to to prove that?

[michel123456]

 

It also states that neither observer can claim that the other's measurement is wrong, based on any physics argument. If I say a 1 kg object moving at 4 m/s has 8J of kinetic energy, and you, in another frame, say that it's moving at 6 m/s and has 18 J of kinetic energy, is one of us wrong?

 

 

The question is how can a moving object have more than one kinetic energy, as in the above scenario? Who is right, and what physics can you point to to prove that?

It means that kinetic energy is relative.

IOW an object does not "have" a kinetic energy. The same as an object does not "have" a speed.

I don't see any problem.

[swansont]

It means that kinetic energy is relative.

IOW an object does not "have" a kinetic energy. The same as an object does not "have" a speed.

I don't see any problem.

 

 

An object doesn't have a speed? Then how can it have a tick rate?

[michel123456]

 

 

An object doesn't have a speed? Then how can it have a tick rate?

I don't understand the question.

[VandD]

It means that kinetic energy is relative.

IOW an object does not "have" a kinetic energy. The same as an object does not "have" a speed.

I don't see any problem.

A clock does not "have" a ticking rate either. Only a reference frame 'adds' a ticking rate: the rate depends on the relative speed between clock and frame. If speed is zero, then the clock has the fastest ticking rate of all frames. But it's not a 'special frame'.

[swansont]

I don't understand the question.

 

 

You have sidestepped the issue of speed being relative by saying an object doesn't have a speed, but insist that a frequency can't be relative. Why can't you apply the same thinking to the tick rate (oscillatory behavior) as to linear motion?

[VandD]

This is what I am fighting against.

IMHO it is a wrong interpretation of "All inertial reference frames are equally valid". This last statement says that you can calculate what another observer measures in any other FOR. It does not says that there is no FOR "αφετηριας" (Starting point, I don't know how to translate). You yourself admits that "A clock ticks at maximum rate if the clock is at rest relative to the reference frame." That is a starting point. In this same FOR the length of the measured object is the longest. That is also a starting point. These are 2 very good reasons to consider this FOR different from all the others.

 

Why do you need a train at rest as a starting point?

You measure a train passing by. You measure with your measuring stick simultaneous events -in your frame- of the front and rear of the train. That's it. You don't need to 'start' with the length of the train at rest. You don't even have to know the length of the train at rest.

 

And finally, a clock does not tick at multiple rates. There is only one reality that is observed differently by different observers. That is all. The concept of a clock ticking at multiple rates is a concept of overlapping realities and it is wrong.

 

The 'reality' we all observer/measure is 4D spacetime, not one 3D world of simultaneous events. Since Einstein we know we all live and move in 4D spacetime. There is only one 'reality' and that's all the events of 4D spacetime. A 3D reality is only one of the many sections through 4D spacetime.

 

A few Einstein quotes:

 

<< From a "happening" in three-dimensional space, physics becomes, as it were, an "existence" in the four-dimensional "world". >> (Albert Einstein. "Relativity: The Special and the General Theory." 1916. Appendix II Minkowski's Four-Dimensional Space ("World") (supplementary to section 17 - last section of part 1 - Minkowski's Four-Dimensional Space).

 

<< Since there exists in this four dimensional structure [space-time] no longer any sections which represent "now" objectively, the concepts of happening and becoming are indeed not completely suspended, but yet complicated. It appears therefore more natural to think of physical reality as a four dimensional existence, instead of, as hitherto, the evolution of a three dimensional existence. >> (Albert Einstein, "Relativity", 1952).

 

<<...for us convinced physicists the distinction between past, present, and future is only an illusion, although a persistent one." >> ( Letter to Michele Besso family, March 21, 1955. Einstein Archives 7-245).

 

Karl Popper about his encounter with Einstein:

<< The main topic of our conversation was indeterminism. I tried to persuade him to give up his determinism, which amounted to the view that the world was a four-dimensional Parmenidean block universe in which change was a human illusion, or very nearly so. He agreed that this had been his view, and while discussing it I called him "Parmenides".... >> (Karl Popper, Unended Quest: An Intellectual Autobiography.Routledge Classics. Routledge. pp.148–150).

 

[michel123456]

And what about rest mass then? It is a 3rd reason to consider the frame at rest different from all the others.

Rest mass is the mass in the frame ...at rest.
Why don't we speak about rest time, and rest length then?

Why do you need a train at rest as a starting point?
You measure a train passing by. You measure with your measuring stick simultaneous events -in your frame- of the front and rear of the train. That's it. You don't need to 'start' with the length of the train at rest. You don't even have to know the length of the train at rest.


The 'reality' we all observer/measure is 4D spacetime, not one 3D world of simultaneous events. Since Einstein we know we all live and move in 4D spacetime. There is only one 'reality' and that's all the events of 4D spacetime. A 3D reality is only one of the many sections through 4D spacetime.

A few Einstein quotes:

<< From a "happening" in three-dimensional space, physics becomes, as it were, an "existence" in the four-dimensional "world". >> (Albert Einstein. "Relativity: The Special and the General Theory." 1916. Appendix II Minkowski's Four-Dimensional Space ("World") (supplementary to section 17 - last section of part 1 - Minkowski's Four-Dimensional Space).

<< Since there exists in this four dimensional structure [space-time] no longer any sections which represent "now" objectively, the concepts of happening and becoming are indeed not completely suspended, but yet complicated. It appears therefore more natural to think of physical reality as a four dimensional existence, instead of, as hitherto, the evolution of a three dimensional existence. >> (Albert Einstein, "Relativity", 1952).

<<...for us convinced physicists the distinction between past, present, and future is only an illusion, although a persistent one." >> ( Letter to Michele Besso family, March 21, 1955. Einstein Archives 7-245).

Karl Popper about his encounter with Einstein:
<< The main topic of our conversation was indeterminism. I tried to persuade him to give up his determinism, which amounted to the view that the world was a four-dimensional Parmenidean block universe in which change was a human illusion, or very nearly so. He agreed that this had been his view, and while discussing it I called him "Parmenides".... >> (Karl Popper, Unended Quest: An Intellectual Autobiography.Routledge Classics. Routledge. pp.148–150).

No (the bold part). We don't "move" in 4D spacetime, following Einstein we are "frozen" in 4D spacetime. That's the reason behind your last Karl Popper's quote.https://en.wikipedia.org/wiki/Parmenides

 

(edited for Parmenides link)

Edited September 2, 2016 by michel123456

[swansont]

And what about rest mass then? It is a 3rd reason to consider the frame at rest different from all the others.

 

 

Rest mass is invariant.

[michel123456]

 

Rest mass is invariant.

Aha, rest mass is different from all other masses then!

Why don't you accept the concept of an "invariant length"? Even you yourself have admitted that this length does not "really" change.

Edited September 2, 2016 by michel123456

[Strange]

Aha, rest mass is different from all other masses then!

Why don't you accept the concept of an "invariant length"?

 

Because there is no such thing?

 

Well, actually, there is: the distance between events in space-time is invariant. And this is what leads to different observers getting different measurements of length or time.

[swansont]

Aha, rest mass is different from all other masses then!

Why don't you accept the concept of an "invariant length"? Even you yourself have admitted that this length does not "really" change.

 

 

 

Because length is not invariant, as a consequence of the speed of light being invariant.

 

What other masses are you thinking of? Relativistic mass is relative, and also conceptually unnecessary as it's just a proxy for total energy.

 

As far as not changing, that comes with the context of changing being mired in the wrong way of thinking about it. The length is different in different frames.

[michel123456]

 

 

 

Because length is not invariant, as a consequence of the speed of light being invariant.

 

What other masses are you thinking of? Relativistic mass is relative, and also conceptually unnecessary as it's just a proxy for total energy.

 

 

Well, actually, there is: the distance between events in space-time is invariant. And this is what leads to different observers getting different measurements of length or time.

So you accept that there exist a mass "starting point", you call all other measured masses as "relativistics" but you do not agree that the exact same thing applies to length and time?

Please explain me the difference. Why are all lengths equally valid but masses not?

[Strange]

Please explain me the difference. Why are all lengths equally valid but masses not?

 

All observers measure the same mass.

They don't measure the same length.

Because mass is invariant (the same for all observers) but length isn't.

 

But if you start comparing rest mass with total mass-energy (sometimes called, misleadingly, "relativistic mass") then you are not comparing the same thing.

 

As swansont has said, energy is observer dependent (while mass isn't).

[swansont]

So you accept that there exist a mass "starting point", you call all other measured masses as "relativistics" but you do not agree that the exact same thing applies to length and time?

Please explain me the difference. Why are all lengths equally valid but masses not?

 

 

The mass used in physics equations (other than the ad-hoc and unnecessary m = E/c^2) is invariant. The physics that tells you this also tells you that length and time are relative.

 

m^2c^4 = E^2 - p^2c^2

 

The total energy is relative, as is the energy from motion. But as calculated above, you can find the mass energy, and that's invariant. There are other invariant quantities as well. The four-velocity is similarly an invariant. As your speed through space increases, your speed through time decreases. Strange mentioned the invariant spacetime interval.

 

It all stems from c being invariant. You don't get to pick and choose what is relative and what isn't.

[Delta1212]

So you accept that there exist a mass "starting point", you call all other measured masses as "relativistics" but you do not agree that the exact same thing applies to length and time?

Please explain me the difference. Why are all lengths equally valid but masses not?

All masses are equally valid. It's just that they all also happen to be the same, whereas all lengths are not the same.

[Tim88]

And what about rest mass then? It is a 3rd reason to consider the frame at rest different from all the others.

 

Rest mass is the mass in the frame ...at rest.

Why don't we speak about rest time, and rest length then?

 

No (the bold part). We don't "move" in 4D spacetime, following Einstein we are "frozen" in 4D spacetime. That's the reason behind your last Karl Popper's quote.https://en.wikipedia.org/wiki/Parmenides

 

(edited for Parmenides link)

 

"the frame at rest" is moving according to other frames. However for consistency I reckon with relativistic mass as well as rest mass. Other words for rest length and rest frequency are proper length and proper frequency.

 

Further I agree with you on several points. We cannot "move" in 4D spacetime (a concept that originates not with Einstein but Minkowski). Moreover, I'm not part of the "we all" of VanD, as the "reality" that I observe is not 4D spacetime; instead, the "reality" that I observe consists of many physical phenomena such as temperature, frequencies, distances and forces.

 

However, such things are measured with a consistent standard measurement system. According to all consistent measurement systems in which the accepted laws of physics are valid, the clock did not continue ticking as usual. Instead, its changes of velocity made it loose ticks compared to clocks with which nothing physical happened.

 

On the other hand, I agree that the clock of course did not simultaneously tick at multiple rates, just as it did not simultaneously have multiple speeds or multiple kinetic energies. The equivalent reference systems are mutually exclusive: when one is chosen, for convenience, as assumed reality, then the others are at the same time assumed to be non-rest systems in which measurements are affected by motion. That already was the standard way of dealing with reference systems in Newtonian physics: you pretend that one reference frame is in rest, and calculate consistently from that perspective. A different opinion leads to a different calculation and corresponds to a different assumed reality. Calculations mess up if we assume that everyone is all the time in rest so that nothing happens (Parimedes again)!

 

Edit: slight improvement in phrasing

Edited September 2, 2016 by Tim88

[Strange]

And what about rest mass then? It is a 3rd reason to consider the frame at rest different from all the others.

 

Rest mass is the mass in the frame ...at rest.

 

Rest mass is the same even from other frames. Unlike, say, energy or length.

[michel123456]

 

"the frame at rest" is moving according to other frames. However for consistency I reckon with relativistic mass as well as rest mass. Other words for rest length and rest frequency are proper length and proper frequency.

 

Further I agree with you on several points. We cannot "move" in 4D spacetime (a concept that originates not with Einstein but Minkowski). Moreover, I'm not part of the "we all" of VanD, as the "reality" that I observe is not 4D spacetime; instead, the "reality" that I observe consists of many physical phenomena such as temperature, frequencies, distances and forces.

 

However, such things are measured with a consistent standard measurement system. According to all consistent measurement systems in which the accepted laws of physics are valid, the clock did not continue ticking as usual. Instead, its changes of velocity made it loose ticks compared to clocks with which nothing physical happened.

 

On the other hand, I agree that the clock of course did not simultaneously tick at multiple rates, just as it did not simultaneously have multiple speeds or multiple kinetic energies. The equivalent reference systems are mutually exclusive: when one is chosen, for convenience, as assumed reality, then the others are at the same time assumed to be non-rest systems in which measurements are affected by motion. That already was the standard way of dealing with reference systems in Newtonian physics: you pretend that one reference frame is in rest, and calculate consistently from that perspective. A different opinion leads to a different calculation and corresponds to a different assumed reality. Calculations mess up if we assume that everyone is all the time in rest so that nothing happens (Parimedes again)!

 

Edit: slight improvement in phrasing

This is the most sensible post I have read for a while. +1

But:

The weird thing is about your statement in bold, because you could say that the same happens to length: the object is observed as being contracted.

However it seems to me (from another thread) that nothing "physically happened " to the ruler, it remains the same length all the time. Simply it is been observed as contracting.

[Delta1212]

All frames exist simultaneously. Different observers observe the clock as ticking at different rates and the stick as being at different lengths over the same period as each other.

 

Every possible length and tick rate already "exists" at all times. When something changes frames, it is not physically changing, it is simply changing which length and tick rate is measured by which frame.