The Relativity of Simultaneity: A Fundamental Concept in Special Relativity

[harrylin]

[..] My understanding is that neo-Lorentzian relativity includes, or is compatible with, presentism, but that presentism isn't compatible with RoS, which would lead to the conclusion that neo-Lorentzian relativity doesn't include RoS and so the Lorentz transform doesn't necessarily include RoS.

I don't know what you call "neo-Lorentzian relativity". Do you have a quality reference for that? And is it useful?

But, if RoS is included by necessity in the LT, then there must be two different interpretations of RoS - unless there is an issue with the reasoning above.

Yes, and several of us have mentioned and explained this several times to you...

Are there other interpretations of RoS?

Sure - as you know. Lorentz's "Local time" is RoS with an interpretation that differs from Minkowski's interpretation.

Apologies, I don't fully understand the comparison.

It's useful to first understand the basis of such discussions - thus, can you explain how there can be both absolute and relative velocity in Newton's mechanics? Or, in other words, is velocity absolute or relative in his theory?

I would say that when it is 2pm in England, it is 3pm in Germany, but both exist, simultaneously, in the present moment.

In SR (that is, the Lorentz transformation), when a certain clock of S indicates for example 2PM, another clock of S' that passes that clock at that time (thus at the same place and moment) will indicate for example 3PM. For some reason (a reason that escapes me), you think that this has big philosophical implications, while a similar case with time zones on Earth has none...

 

[mangaroosh]

"Speed" is a measurement. If the length of his ruler and times on his clock comply with the physical definition of the metre and second, then the actual speed he has measured is c.

Yes, but if the instruments used by one observer are contracted compared to anothers, then the same measurement of 300,000 km/s would represent different actual speeds.

Lorentz's aether assumed Galilean Relativity and proposed ad hoc physical changes in objects due to an unknown mechanical interation between matter and the substance of the aether to explain the invariance of the speed of light so it is compatible with both presentism and eternalism. However the Relativity of Simultaneity refers to events having different separation of their time coordinates in mutually moving frames so it still occurs in LET. LET offers an alternative philosophical explanation for the RoS but since it is an observed effect, it could not discard it without being falsified.

Apologies, I thought I had posted this already in this thread, but it must have been a different one:

the last vestiges of a substantial ether had been eliminated from Lorentz's "ether" theory, and it became both empirically and deductively equivalent to special relativity. The only difference was the metaphysical[C 7] postulate of a unique absolute rest frame, which was empirically undetectable and played no role in the physical predictions of the theory. As a result, the term "Lorentz ether theory" is sometimes used today to refer to a neo-Lorentzian interpretation of special relativity

This suggests, and has been echoed by others on here, that the concept of the aether has been removed from Lorentzian relativity, leaving just the concept of an "absolute reference frame".

The RoS in Lorentzian relativity is materially different to Einsteinian; indeed, absolute simultaneity is incorporated in Lorentzian relativity - as it must if presentism is to prevail - so I think referring to it as RoS is somewhat of a misnomer - but that might just be my interpretation of the concepts of absolute simultaneity and RoS.

Would you say that absolute simultaneity is compatible with RoS?

c can be derived from the permitivity and permeability in Maxwell's Equations. Both are scalar hence the speed must be scalar and therefore it must be isotropic.

apologies, I don't fully understand the point pertaining to the P & P in Maxwell's equations.

I'm not sure if it would help to give some context for the discussion, but this thread stems from a different discussion, where the contention was that the speed of c from Maxwell's equations tacitly assumes the Earth as the rest frame for measurements, so the conclusion would be that Maxwell's equations include the tacit assumption that the constancy of c is relative to the earth.

To avoid dragging this thread off on a tangent, here is a link to the constancy of c thread.

No, SR says that spacetime has fixed Reimann geometry. Draw two dots on a plain white sheet of paper. Place a grid drawn on a transparent sheet over the top and measure the X and Y coordinates of the dots. Now rotate the transparency a little. You get different coordinate separations but the white sheet of paper has neither shrunk nor stretched and the dots haven't moved. SR says changing your coordinate scheme will change the numbers that label an event but that's all. Spacetime intervals are invariant for the same reason that Pythagoras will give the same result for the separation of the dots regardless of how you orient the transparency with the gridlines.

Is spacetime a physical property/substance?

 

[mangaroosh]

Scientifically there is no issue since, as I have mentioned several times, any unmeasurable aspects are scientifically irrelevant. This site is for discussing science, not philosophy.

Is this site not also for discussing the philosophy of science, no? The conclusions drawn from experiments are largely a matter of philosophy, as this discussion on RoS is demonstrating.

We cannot determine that the actual speed of light remains constant, but some of the conclusions drawn assume it to be so; insofar as those conclusions are scientifically relevant, then so to are the unmeasurable aspects.

Correct, as we have discussed previously TD and RoS are two entirely different concepts.

No. In LET local time exhibits RoS.

OK, this is where we are at cross purposes I think.

It has been mentioned in a thread on Lorentzian relativity that it incorporates absolute simultaneity, in the form of presentism; to my mind - and this could be where the issue lies - RoS is not compatible with absolute simultaneity.

Again, to my understanding, form discussions on here and elsewhere, local time in LR isn't "real" time; the difference in time co-ordinates is due to the mechanics of the clock being affected by motion, as opposed to "time itself" being affected.

Again, how I understand it is, under an LR interpretation, absolute simultaneity, and a shared present moment, prevails, while under ER, the present moment is entirely relative and one observers past can be another's present, while one observers future can be another observers present; and other such combinations.


That is the distinction I would draw between RoS and absolute simultaneity; which I think is necessary because it refers to the simultaneity of physical events, as opposed to the ascription of mathematical time co-ordinates.

We cannot. That is why the distinction is scientifically meaningless.

I don't think it is scientifically meaningless when distinction materially affects the scientific models; where claims to the physicality of time are made, surely it is an important distinction.

 

[GeorgeDishman]

"Speed" is a measurement. If the length of his ruler and times on his clock comply with the physical definition of the metre and second, then the actual speed he has measured is c.

Yes, but if the instruments used by one observer are contracted compared to anothers, then the same measurement of 300,000 km/s would represent different actual speeds.

If the length of his ruler complies with the physical definition of the metre, his ruler is not contracted, though he might question that of the other observer. As I said "actual speed he has measured is c" unless you have some other meaning of "actual".

Apologies, I thought I had posted this already in this thread, but it must have been a different one:

No apology needed, you had it at the bottom of your previous message but I had already commented on it in the one before so I skipped repeating it:

the last vestiges of a substantial ether had been eliminated from Lorentz's "ether" theory, and it became both empirically and deductively equivalent to special relativity. The only difference was the metaphysical[C 7] postulate of a unique absolute rest frame, which was empirically undetectable and played no role in the physical predictions of the theory. As a result, the term "Lorentz ether theory" is sometimes used today to refer to a neo-Lorentzian interpretation of special relativity

You will see that suggestion made by people who don't understand LET (or basic physics for that matter) but it has never been a theory. In LET, the mechanism that causes the various effects is an interaction with the aether hence the velocity that goes into the transforms is that of the object relative to the aether. Without some physical substance against which to measure velocity, there is no way to define the quantity.

This suggests, and has been echoed by others on here, that the concept of the aether has been removed from Lorentzian relativity, leaving just the concept of an "absolute reference frame".

To be blunt, the idea that you can have an aether theory without an aether is brain-dead nonsense posted by idiots. You will see it said in many places but popularity is not a usable indicator.

The RoS in Lorentzian relativity is materially different to Einsteinian; indeed, absolute simultaneity is incorporated in Lorentzian relativity - as it must if presentism is to prevail

Aether theory was not based on presentism, it comes from assuming Galilean relativity and the "absolute time" defined by Newton in the Principia. See the third paragraph here:

http://plato.stanford.edu/entries/Newton-stm/scholium.html

Would you say that absolute simultaneity is compatible with RoS?

I think I said before though perhaps not clearly, RoS refers to the time coordinates given to events so it is occurs in LET as much as SR. LET only provides an alternative interpretation of why it is unavoidable so I would state it differently, I would say that presentism is not compatible with the non-existence of an aether. I also suspect that an aether-based model s not compatible with the observation of polarisation of light. Philosophically, that leads me to a perdurantist view, but that should really be left to the philosophy forum.

apologies, I don't fully understand the point pertaining to the P & P in Maxwell's equations.

1/√(ε*μ)

If ε and μ are just scalar numbers then they cannot have different values in different directions. That means the speed of light cannot have different values in different directions, but that is what is required in aether theory for any observer moving relative to the aether.

I'm not sure if it would help to give some context for the discussion, but this thread stems from a different discussion, where the contention was that the speed of c from Maxwell's equations tacitly assumes the Earth as the rest frame for measurements ...

That's another common error made by clueless cranks, if that were the case, the velocity of the observer relative to the Earth would appear in Maxwell's Equations. In fact they are independent of the choice of frame.

Is spacetime a physical property/substance?

That's a whole different question ;-)

http://plato.stanford.edu/entries/spacetime-holearg/

For SR, the question needn't arise as long as you can assume that a hypothetical right-triangle in empty space still obeys Pythagoras Theorem. SR says the vacuum is 4-dimensional and extends Pythagoras as:

s^2 = x^2 + y^2 + z^2 - (ct)^2

All we need say is that the vacuum of SR has the property that it exhibits Euclidean geometry in any spatial 3D slice and Riemann geometry with signature {+++-} in 4D.

 

[mangaroosh]

I don't know what you call "neo-Lorentzian relativity". Do you have a quality reference for that? And is it useful?

I've come across it in a few places.

the last vestiges of a substantial ether had been eliminated from Lorentz's "ether" theory, and it became both empirically and deductively equivalent to special relativity. The only difference was the metaphysical[C 7] postulate of a unique absolute rest frame, which was empirically undetectable and played no role in the physical predictions of the theory. As a result, the term "Lorentz ether theory" is sometimes used today to refer to a neo-Lorentzian interpretation of special relativity. The prefix "neo" is used in recognition of the fact that the interpretation must now be applied to physical entities and processes (such as the standard model of quantum field theory) that were unknown in Lorentz's day.

wiki


neo-Lorentzian relativity

I've come across it in a few other papers too, by Brown & Pooley, Gürel & Gürel, among others.

Yes, and several of us have mentioned and explained this several times to you...

Sure - as you know. Lorentz's "Local time" is RoS with an interpretation that differs from Minkowski's interpretation.

OK, I think I understand the distinction now. As I mentioned in the post to DS, to my understanding LR includes absolute simultaneity, in the form of presentism; for that reason I think it is a misnomer to refere to RoS with respect to LR, because it implies two different notions of simultaneity of events.

It's useful to first understand the basis of such discussions - thus, can you explain how there can be both absolute and relative velocity in Newton's mechanics? Or, in other words, is velocity absolute or relative in his theory?

Are both concepts not included? I'm not entirely sure how they might be, but I thought I had read that both were; just as both are in Galilean relativity (aren't they?)

In SR (that is, the Lorentz transformation), when a certain clock of S indicates for example 2PM, another clock of S' that passes that clock at that time (thus at the same place and moment) will indicate for example 3PM. For some reason (a reason that escapes me), you think that this has big philosophical implications, while a similar case with time zones on Earth has none...

I don't think the fact that the clocks in S and S' tick at different rates should have big philosophical implications at all; the philosophical implications arise with the interpretation that it is time that is ticking slower or faster, as opposed to the mechanics of the clock being affected.

We can - and do - arbitrarily wind the clocks in each time zone to afford us more daylight hours; some time zones do this, while others don't; but we don't conclude that time moves forward or backward when we do so.

 

[harrylin]

I've come across it in a few places.

wiki [..]

"[citation needed]" .. Perhaps the anonymous editor meant that one should not think of an ether made of matter... But it's not useful to guess what an anonymous editor may have meant.
However, if one means interpretations such as by Bell and Ives, who are also mentioned: these explicitly spoke of "ether" interpretations.

[rearrange:]

Are both concepts not included? I'm not entirely sure how they might be, but I thought I had read that both were; just as both are in Galilean relativity (aren't they?)

I never read anything about absolute velocities in my textbooks on classical mechanics. Looking at your other remark, which I now placed here below, do you think that it is a misnomer to talk of relative velocities in Newtonian mechanics, because it implies two different notions of velocities?

OK, I think I understand the distinction now. As I mentioned in the post to DS, to my understanding LR includes absolute simultaneity, in the form of presentism; for that reason I think it is a misnomer to refere to RoS with respect to LR, because it implies two different notions of simultaneity of events.

Following along the same lines, do you think that it is a misnomer to talk of local time zones on earth, because we have Universal Time?

I don't think the fact that the clocks in S and S' tick at different rates should have big philosophical implications at all;

I did not mention rates at all; instead I mentioned the disagreeing clock readings of RoS...

the philosophical implications arise with the interpretation that it is time that is ticking slower or faster, as opposed to the mechanics of the clock being affected.

In physics, mechanical clocks provide a measure of what we call "time", just as mercury thermometers provide a measure of what we call "temperature"; both are "affected" by what they measure.

We can - and do - arbitrarily wind the clocks in each time zone to afford us more daylight hours; some time zones do this, while others don't; but we don't conclude that time moves forward or backward when we do so.

Exactly - then why would we conclude strange things from different clock synchronizations in SR?

 

[Dale]

Is this site not also for discussing the philosophy of science, no?

No. The forum for philosophy is:
https://www.physicsforums.com/forumdisplay.php?f=112

We cannot determine that the actual speed of light remains constant, but some of the conclusions drawn assume it to be so; insofar as those conclusions are scientifically relevant, then so to are the unmeasurable aspects.

No, the unmeasurable aspects are NOT scientifically relevant, your personal fascination notwithstanding. The scientific method is a method for systematically checking the predictions of theories against the results of experiments, and experiments are measurements. If an aspect of a theory is unmeasurable then it is not experimentally testable and therefore it is scientifically irrelevant.

If you can't measure it then you can't experiment with it and if you can't experiment with it then it is not amenable to the scientific method.

Again, to my understanding, form discussions on here and elsewhere, local time in LR isn't "real" time; the difference in time co-ordinates is due to the mechanics of the clock being affected by motion, as opposed to "time itself" being affected.

The local time is the only time available for experimental testing in LET. So since LET uses local time for all experimental testing and since local time exhibits RoS therefore RoS is a testable aspect of LET, as I have claimed from the beginning.

All of my comments in this thread apply for measurements; I make no claims nor do I have any interest in any unmeasurable aspects of reality. Under that stipulation it is 100% clear that $(\text{C} \cap \text{PoR}) \rightarrow (\text{LC} \cap \text{TD} \cap \text{RoS})$ and that it is not circular. If you wish to discuss that further then I will contribute, if you wish to discuss non-scientific topics about the unmeasurable ghosts that haunt your thoughts then I am done responding. I will let you have the last word on the non-scientific unmeasurable-reality topic if that is your desire.

 

[mangaroosh]

"[citation needed]" .. Perhaps the anonymous editor meant that one should not think of an ether made of matter... But it's not useful to guess what an anonymous editor may have meant.
However, if one means interpretations such as by Bell and Ives, who are also mentioned: these explicitly spoke of "ether" interpretations.

I've PM'd George to see where he came across it; he mentions it here

[rearrange:]

I never read anything about absolute velocities in my textbooks on classical mechanics. Looking at your other remark, which I now placed here below, do you think that it is a misnomer to talk of relative velocities in Newtonian mechanics, because it implies two different notions of velocities?

I wouldn't be that familiar with classical mechanics, as is probably clear; I'm familiar with the concept of absolute rest and absolute motion, which I believed to be concepts in classical mechanics; I've come across the notion of absolute velocity before when it's been said that if absolute space could be detected, then absolute velocity could be defined.

From my understanding of the concepts of relative and absolute velocities, I wouldn't say that it is a misnomer as such, as the two concepts are not mutually exclusive, as I think RoS and absolute simultaneity are.

Following along the same lines, do you think that it is a misnomer to talk of local time zones on earth, because we have Universal Time?

It depends on the ontological status ascribed to both, but I would say no again, becaue they are not necessarily mutually exclusive.

The reason I see the term RoS as a misnomer with regard to the Lorentz transform is that the transform appears to lead to relativity of time co-ordinates; it is the ontological assumption about what those time co-ordinates represent which determines whether or not RoS or absolute simultaneity is deduced.

It might be the fact that Einsteinian interpretation has been the primary one for over a hundred years (or thereabouts) that this relativity of time co-ordinates is taken to mean RoS, but insofar as we are talking about the simultaneity of events in the physical world, the relativity of time co-orindates doesn't necessarily imply RoS of physical events; as the Lorentzian interpretation demonstrates.

In short, I see absolute simultaneity as being incompatible with RoS, because RoS implies that evetns are not absolutely simultaneous; if Lorentzian relativity (neo- or LET) incorporates absolute simultaneity, then I think it is a misnomer to refer to the relativity of time co-ordinates as RoS.

I did not mention rates at all; instead I mentioned the disagreeing clock readings of RoS...

Why would relatively moving clocks have different time readings?

In physics, mechanical clocks provide a measure of what we call "time", just as mercury thermometers provide a measure of what we call "temperature"; both are "affected" by what they measure.

This is a fairly contentious issue, and, unfortunately, one I don't think I can get into without fear of reprisal; but here is a link to a locked thread on the question of How does a clock measure time?.

I have appealed the decision to close the thread, so it may perhaps be re-opened; if you would be interested in continuing the discussion it might be worth PMing a relevant mentor.

Exactly - then why would we conclude strange things from different clock synchronizations in SR?

I don't think I'm the person to be asking; I wouldn't conclude such things, but it appears that it is a fairly common conclusion; I'm sure you're familiar with the concept of the block universe.

 

[mangaroosh]

If the length of his ruler complies with the physical definition of the metre, his ruler is not contracted, though he might question that of the other observer. As I said "actual speed he has measured is c" unless you have some other meaning of "actual".

If the length of his ruler complies with the physical definition of the metre, but his counterparts ruler is contracted, such that it is shorter, and his clock is ticking slower, then the actual speeds, represented by the measurements of 300,000km/s, must be different.

If both of their instruments conform to the definitions, but if any of them are contracted compared to the other, then it means that the definitions are variable and the actual speeds represented by both measurements are still different. Alternatively it means that neither is contracted.

No apology needed, you had it at the bottom of your previous message but I had already commented on it in the one before so I skipped repeating it:

To be blunt, the idea that you can have an aether theory without an aether is brain-dead nonsense posted by idiots. You will see it said in many places but popularity is not a usable indicator.

I think the whole point is that it is no longer an aether theory.

It was mentioned in this thread. I've PM'd the author to see if there are articles to support the contention.

Aether theory was not based on presentism, it comes from assuming Galilean relativity and the "absolute time" defined by Newton in the Principia. See the third paragraph here:

http://plato.stanford.edu/entries/Newton-stm/scholium.html

It's not necessarily based on presentism, but I think it is fair to say that presnetism is incorporated for the very reason you've mentioned. It is, at the very least, compatible with presentism, while RoS doesn't appear to be.

I think I said before though perhaps not clearly, RoS refers to the time coordinates given to events so it is occurs in LET as much as SR. LET only provides an alternative interpretation of why it is unavoidable so I would state it differently, I would say that presentism is not compatible with the non-existence of an aether. I also suspect that an aether-based model s not compatible with the observation of polarisation of light. Philosophically, that leads me to a perdurantist view, but that should really be left to the philosophy forum.

As I mentioned in response to Harry, the Lorentz transform appears to result in relativity of time co-ordinates, but not necessarily the RoS of physical events; the relativity of time co-ordinates requires a particular interpretation to conclude RoS of physical events. It could be the fact that this relativity of time co-ordinates has been given the Einsteinian interpretation for so long, that it is asssumed that the relativity of time co-ordinates, that the Lorentz transform produces, is actually RoS.

As I see it, absolute simultaneity is the case where two events are simultaneous for everybody in the universe; while this is not necessarily the case under RoS.

Lorentzian relativity incorporates absolute simultaneity and the Lorentz transform, so my reasoning would be that the Lorentz transform cannot necessarily result in RoS; it can result in relativity of time co-ordinates, however.

1/√(ε*μ)

If ε and μ are just scalar numbers then they cannot have different values in different directions. That means the speed of light cannot have different values in different directions, but that is what is required in aether theory for any observer moving relative to the aether.

Again, apologies, I'm not well up enough on that sort of thing to fully comprehend the point.

Why could the speed of light not have different values because those numbers are scalar?

That's another common error made by clueless cranks, if that were the case, the velocity of the observer relative to the Earth would appear in Maxwell's Equations. In fact they are independent of the choice of frame.

But if Maxwell's equations were derived from measurements made, using instruments, at rest relative to the earth, then that would be tacit assumption of the equation, not necessarily something expressed.

That's a whole different question ;-)

http://plato.stanford.edu/entries/spacetime-holearg/

For SR, the question needn't arise as long as you can assume that a hypothetical right-triangle in empty space still obeys Pythagoras Theorem. SR says the vacuum is 4-dimensional and extends Pythagoras as:

s^2 = x^2 + y^2 + z^2 - (ct)^2

All we need say is that the vacuum of SR has the property that it exhibits Euclidean geometry in any spatial 3D slice and Riemann geometry with signature {+++-} in 4D.

But are space and time i.e. spacetime, physical?

 

[mangaroosh]

No. The forum for philosophy is:
https://www.physicsforums.com/forumdisplay.php?f=112

But this forum is for peope who wish to discuss Einsteinian relativity though, and to develop their understanding of it.

No, the unmeasurable aspects are NOT scientifically relevant, your personal fascination notwithstanding. The scientific method is a method for systematically checking the predictions of theories against the results of experiments, and experiments are measurements. If an aspect of a theory is unmeasurable then it is not experimentally testable and therefore it is scientifically irrelevant.

If you can't measure it then you can't experiment with it and if you can't experiment with it then it is not amenable to the scientific method.

The local time is the only time available for experimental testing in LET. So since LET uses local time for all experimental testing and since local time exhibits RoS therefore RoS is a testable aspect of LET, as I have claimed from the beginning.

I think the confusion might be down to a matter of interpretation.

My understanding is that the Lorentz transform results in relativity of time co-ordinates, not necessarily RoS.

RoS as I see it is contrasted with absolute simultaneity, where absolute simultaneity means that two events that are simultaneous in one reference frame are simultaneous in every reference frame i.e. for all observers in the universe. RoS on the other hand means that events which are simultaneous in one referene frame may not necessarily be simultaneous in another. This means that the two are essentially mutually exlusive.

The relativity of time co-ordinates are a consequence of the Lorentz transform; but the Lorentzian interpretation incorporates absolute simultaneity, while the Einsteinian interpretation incorporates RoS.

This would mean that RoS is not necessarily a consequence of the Lorentz transform, rather that a specific interpretation, or assumption, is required to interpret the relativity time co-ordinates as meaning RoS.

Again, it might be the fact that the Einsteinian iterpretation has been so prevalent for so long, that the relativity of time co-ordinates has been conflated with RoS, but I think they are demonstrably different.

All of my comments in this thread apply for measurements; I make no claims nor do I have any interest in any unmeasurable aspects of reality. Under that stipulation it is 100% clear that $(\text{C} \cap \text{PoR}) \rightarrow (\text{LC} \cap \text{TD} \cap \text{RoS})$ and that it is not circular. If you wish to discuss that further then I will contribute, if you wish to discuss non-scientific topics about the unmeasurable ghosts that haunt your thoughts then I am done responding. I will let you have the last word on the non-scientific unmeasurable-reality topic if that is your desire.

It has been mentioned in another thread, and I think we can reason that it is true, that RoS is not actually measurable. What we have is relative time co-ordinates which require a specific interpretation, and assumption, to conclude that RoS results. The same can be said for absolute simultaneity, as it requires a specific interpretation of the relativity of time co-ordinates; however, it arguably requires fewer assumptions.

 

[lmoh]

Again, apologies, I'm not well up enough on that sort of thing to fully comprehend the point.

Why could the speed of light not have different values because those numbers are scalar?

I think that another way to put it is to say that those numbers are constant. As such, the value of the speed of light, being based upon two constants, is also constant.

 

[Dale]

My understanding is that the Lorentz transform results in relativity of time co-ordinates, not necessarily RoS.

Simultaneity means that two events have the same time coordinate. I.e. two events A and B with spacetime coordinates $(t_A,x_A,y_A,z_A)$ and $(t_B,x_B,y_B,z_B)$ respectively are called simultaneous if and only if $t_A=t_B$. Relativity of time coordinates is therefore necessarily the same as RoS by the definition of simultaneity.

It has been mentioned in another thread, and I think we can reason that it is true, that RoS is not actually measurable.

Yes it is. I even described an experiment for doing so.

The rest of your post seems to be focused on non-scientific unmeasurable interpretations.

 

[GeorgeDishman]

If the length of his ruler complies with the physical definition of the metre, but his counterparts ruler is contracted, such that it is shorter, and his clock is ticking slower, then the actual speeds, represented by the measurements of 300,000km/s, must be different.

OK, we are talking LET here. If he measures over a shorter distance than he thinks, the time taken should appear reduced. If his clocks run slow, again the time should be reduced. What you have forgotten is the RoS which results in his clocks being mis-synchronised by an amount that exactly compensates for the other errors hence he gets the same speed.

I think the whole point is that it is no longer an aether theory.

There are two points here. First is that there is only one theory which is the Lorentz Transforms. Remember that a scientific theory is an equation together with a definition of its variables as measurable quantities. The difference between SR and LET is only the philosophy.

The second point is that any mechanistic explanation for the cause of those equations (such as Lorentz's attempts) needs a physical substance with which matter can interact to produce the various ad-hoc phenomena. Anyone who tells you they have a theory that can model those interactions without an aether is lying to you.

I've PM'd the author to see if there are articles to support the contention.

OK, I'm not going to waste my time discussing something that doesn't exist, if he can cite an actual model, that's a different thing.

It is, at the very least, compatible with presentism, while RoS doesn't appear to be.

Yes and no, remember you need RoS to get the right results in LET as mentioned above.

As I mentioned in response to Harry, the Lorentz transform appears to result in relativity of time co-ordinates, but not necessarily the RoS of physical events;

It applies to the coordinates we apply to events. Nature doesn't provide us with coordinates as properties we can measure like quantum numbers.

As I see it, absolute simultaneity is the case where two events are simultaneous for everybody in the universe; while this is not necessarily the case under RoS.

Right, absolute simultaneity would mean that all observers would label events with the same time coordinates given agreement on a reference event for the origin of the scale.

Lorentzian relativity incorporates absolute simultaneity and the Lorentz transform, so my reasoning would be that the Lorentz transform cannot necessarily result in RoS; it can result in relativity of time co-ordinates, however.

What you need to realize is that the term "RoS" refers to coordinates, nothing else. You seem to be getting there though.

Again, apologies, I'm not well up enough on that sort of thing to fully comprehend the point.

Why could the speed of light not have different values because those numbers are scalar?

OK, you seem to have a problem with this. Take another example of a scalar value, say temperature. If I say the temperature at a particular point in my room is 22C, that should seem reasonable. If I said the temperature at that point was 23C east but 21C west, you should think I am confused. Temperature cannot have two values at the same location. The same is true of permeability and permitivity and their product must similarly be single-valued at any particular location, and hence so must the speed. If you don't get that, I think you need to lay relativity aside and sort out some basics first.

But if Maxwell's equations were derived from measurements made, using instruments, at rest relative to the earth, then that would be tacit assumption of the equation, not necessarily something expressed.

Maxwell's equations are just that, equations. You put numbers in and you get numbers out and the output numbers are valid in the same frame as the input numbers, end of story.

But are space and time i.e. spacetime, physical?

That's a complex philosophical question and the pertinent evidence is far beyond SR, no offence but you need to learn these basics before you try the more advanced stuff. It would also be inappropriate for this group, if you read the article on the Hole Argument and don't follow it, you might like to discuss it in the philosophy forum but first look back for previous discussions on it first.

 

[GeorgeDishman]

I think that another way to put it is to say that those numbers are constant. As such, the value of the speed of light, being based upon two constants, is also constant.

I try to avoid that term. In another post I give the example of temperature and we can use that as an analogy noting that the speed of sound depends on air temperature. Temperature can vary from place to place and as a function of time at anyone location so to call it a "constant" would be inappropriate. However, in still air at any temperature, the speed of sound is isotropic. Contrast that with wind speed. Since that is a vector and has associated direction, any non-zero value will produce anisotropy in the speed of sound. I think a better term might be "single-valued".

I dislike the term "Hubble Constant" for the same reason, it varies inversely with time in a matter or radiation-dominated universe and will only become asymptotically constant in the limit of the de Sitter solution. It would be clearer to call it the "Hubble Coefficient" IMHO.

 

[lmoh]

Sorry, but that is just how my Natural Science Prof. (also a physicist BTW) described the equation as a background to relativity and I thought the terminology would be easier for mangaroosh to understand. If I wasn't familiar with Maxwell before, I probably wouldn't be able to easily get your description either IMO (no offense), so I thought I should provide my own interpretation, but I hope the description isn't too inaccurate.

 

[GeorgeDishman]

Sorry, but that is just how my Natural Science Prof. (also a physicist BTW) described the equation as a background to relativity and I thought the terminology would be easier for mangaroosh to understand. If I wasn't familiar with Maxwell before, I probably wouldn't be able to easily get your description either IMO (no offense), so I thought I should provide my own interpretation, but I hope the description isn't too inaccurate.

Not at all, I'm essentially a layman myself. I got my degree in the 1970's but then got a job in communications and currently specialise in FPGA design. I've been studying relativity and cosmology just to keep my hand in for about 20 years. By all means show the posts to your prof. if you like, it's a bad idea to take anything on anyone's authority. That's why I gave the Hubble Constant as an example, I have seen many people surprised to find out it varies with time even though it is universally called a "constant".

 

[mangaroosh]

Simultaneity means that two events have the same time coordinate. I.e. two events A and B with spacetime coordinates $(t_A,x_A,y_A,z_A)$ and $(t_B,x_B,y_B,z_B)$ respectively are called simultaneous if and only if $t_A=t_B$. Relativity of time coordinates is therefore necessarily the same as RoS by the definition of simultaneity.

Time co-ordinates are given by clocks in experiments; Lorentzian relativity, apparently, says that two events can have different time co-ordinates but still be absolutely simultaneous, because the different time co-ordinates given by the clocks are a result of the mechanics of the clock. In order to deduce RoS a specific interpretation is required, based on certain assumptions about time and clocks.

Therefore, relativity of time co-ordinates is not necessarily the same as RoS; they are the same thing in Einsteinian relativity, but not in Lorentzian; if this is the case then RoS cannot be a consequence of the Lorentz transform.

It might be easier to answer the question; if two events are simultaneous in one reference frame, but not in another (RoS) can they be said to be simultaneous in all reference frames (AS)?

The answer is quite clearly no. If that is the case, then RoS cannot be a consequence of the Lorentz transform.

The issue appears to be in conflating relativity of time co-ordinates with RoS; undoubtedly bcos the Einsteinian interpretation has been the dominant interpretation for so long, that the association has never been questioned.

Yes it is. I even described an experiment for doing so.

I can't really remember the experiment, but presumably the Lorentzian interpretation would incorporate absolute simultaneity, such that RoS could only be demonstrated on the basis of certain assumptions.

The rest of your post seems to be focused on non-scientific unmeasurable interpretations.

It probably just boils down to the question of the relativity of time co-ordinates and RoS anyway.

Even if we allow that RoS is a consequence of the Lorentz transform, we are still discussing two different interpretations of it, such that the interpretation that doesn't involve absolute simultnaeity of events, would still be circular reasoning; because only by assuming the interpretation of RoS where the actual speed of light remains invariant, results in RoS of events.

 

[mangaroosh]

OK, we are talking LET here. If he measures over a shorter distance than he thinks, the time taken should appear reduced. If his clocks run slow, again the time should be reduced. What you have forgotten is the RoS which results in his clocks being mis-synchronised by an amount that exactly compensates for the other errors hence he gets the same speed.

But if we talk Einsteinian relativity; do contractions of the instruments actually occur or are they just optical illusions? If they do occur then the point holds.

The point about RoS is the subject of the discussion with DaleSpam; RoS is a consequence of the actual speed of light remainging invariable, while an invariable measurement of c doesn't result in RoS - as mentioned, because the actual speeds represented by the measurments are different. Saying that RoS has been neglected is circular reasoning.

This has lead to the point about RoS and relativity of time co-ordinates.

There are two points here. First is that there is only one theory which is the Lorentz Transforms. Remember that a scientific theory is an equation together with a definition of its variables as measurable quantities. The difference between SR and LET is only the philosophy.

Cheers; I've been learning about that on here alright.

The second point is that any mechanistic explanation for the cause of those equations (such as Lorentz's attempts) needs a physical substance with which matter can interact to produce the various ad-hoc phenomena. Anyone who tells you they have a theory that can model those interactions without an aether is lying to you.

What causes the contractions in Einsteinian relativity? I've been told that it isn't a matter of cause and effect, which seems a bit nonsensical, that physical effects don't have a cause. I've heard people mention that it is just geometry, but again, that suggests that physical phenomena are caused by mathematics, as opposed to the mathematics representing the physical phenomena. Does Einsteinian relativity require the same kind of physical substance?

Given that gravity is equivalent to acceleration, could acceleration and/or gravity cause the effects?

OK, I'm not going to waste my time discussing something that doesn't exist, if he can cite an actual model, that's a different thing.

cool. I'll wait to see if he mentions any articles.

Yes and no, remember you need RoS to get the right results in LET as mentioned above.
...
It applies to the coordinates we apply to events. Nature doesn't provide us with coordinates as properties we can measure like quantum numbers.

This is the point about the relativity of time co-ordinates (RoTC). I would agree that RoTC is included in LET, but not RoS.

I think RoS refers to the simultaneity of events - as per the name - such that two events that are simultaneous in one reference frame might not be simultaneous in another.

LET doesn't incorporate this concept at all; it is based on the idea that two events that are simultaneous in one reference frame are simultaneous in all reference frames.

What LET does incorporate, however, is RoTC. I think that RoTC has become conflated with RoS because the Einsteinian interpretation has dominated for so long, and under that interpretation RoTC does mean RoS.

Right, absolute simultaneity would mean that all observers would label events with the same time coordinates given agreement on a reference event for the origin of the scale.

Indeed, but in effect observers can disagree on time co-ordinates, because they don't have the reference event for the origin of the scale, but absolute simultaneity would still prevail.

What you need to realize is that the term "RoS" refers to coordinates, nothing else. You seem to be getting there though.

That's the point of contention. I think that RoS refers to the simultaneity of events not necessarily the co-ordinates; I think the co-ordinates require a certain interpretation, and certain assumptions about what the co-ordinates represent, in order to make conclusions about the simultaneity of events i.e. RoS or AS.

OK, you seem to have a problem with this. Take another example of a scalar value, say temperature. If I say the temperature at a particular point in my room is 22C, that should seem reasonable. If I said the temperature at that point was 23C east but 21C west, you should think I am confused. Temperature cannot have two values at the same location. The same is true of permeability and permitivity and their product must similarly be single-valued at any particular location, and hence so must the speed. If you don't get that, I think you need to lay relativity aside and sort out some basics first.

Ah yes, apologies, I'd come across scalar values before but had forgotten precisely what they meant; what do you call the ones with directions again?

EDIT: Vectors, that's it! I just read it in one of your replies.

Forgive the naiivey of this question but what are permeability and permitivity, and why do they dictate that an observer moving relative to the source of light cannot measure the speed to be lower than c.

Maxwell's equations are just that, equations. You put numbers in and you get numbers out and the output numbers are valid in the same frame as the input numbers, end of story.

Indeed, but if the measurements that go into the equation tacitly assume the Earth as the rest frame for experiments, then is it not possible that the laws deduced from them - such as the constancy of c regardless of the state of motion relative to the source - equally tacitly assume the Earth as the rest frame?

That's a complex philosophical question and the pertinent evidence is far beyond SR, no offence but you need to learn these basics before you try the more advanced stuff. It would also be inappropriate for this group, if you read the article on the Hole Argument and don't follow it, you might like to discuss it in the philosophy forum but first look back for previous discussions on it first.

I'm not familiar with the Hole Argument, but I'll check it out at some stage.

Cheers!

 

[harrylin]

[..] I wouldn't be that familiar with classical mechanics, as is probably clear; I'm familiar with the concept of absolute rest and absolute motion, which I believed to be concepts in classical mechanics; I've come across the notion of absolute velocity before when it's been said that if absolute space could be detected, then absolute velocity could be defined.

From my understanding of the concepts of relative and absolute velocities, I wouldn't say that it is a misnomer as such, as the two concepts are not mutually exclusive, as I think RoS and absolute simultaneity are.

I made the comparisons because absolute and relative simultaneity are not mutually exclusive, just as time zones and universal time aren't, and just as relative and absolute velocities aren't.

[..] The reason I see the term RoS as a misnomer with regard to the Lorentz transform is that the transform appears to lead to relativity of time co-ordinates; it is the ontological assumption about what those time co-ordinates represent which determines whether or not RoS or absolute simultaneity is deduced.

It might be the fact that Einsteinian interpretation has been the primary one for over a hundred years (or thereabouts) that this relativity of time co-ordinates is taken to mean RoS, but insofar as we are talking about the simultaneity of events in the physical world, the relativity of time co-orindates doesn't necessarily imply RoS of physical events; as the Lorentzian interpretation demonstrates.

Here I can't follow at all what you say... Lorentz called the relativity of time co-ordinates "local time" and later Einstein called it "RoS". And Einstein's descriptions were purely operational, without any implied metaphysics - he tried to eliminate metaphysics from physics.

When you say that based on your time reckoning two distant events both happened about 100 years ago, and someone else who uses a reference system that is moving relative to yours says that the one event happened about 99 years ago, and the other about 101 years ago, that is what is called "relativity of simultaneity". It is what Lorentz and Poincare called "local time", and it is about physical events.

In short, I see absolute simultaneity as being incompatible with RoS, because RoS implies that evetns are not absolutely simultaneous [..]

That is wrong, for (again) the same reason as why the following sentence is wrong:
"absolute velocity is incompatible with relative velocity, because relative velocity implies that velocities are not absolute."

Why would relatively moving clocks have different time readings? [..]

That is at the heart of Relativity of Simultaneity...
Here is again a famous illustration of independent reference systems:
http://www.bartleby.com/173/9.html
Now put clocks at the front and back of the train, as well as one in the middle of the train, next to you; and synchronize your clock with a clock that happens to be just next to it at the station at t=0 (so that at x=0 and t=0, also t'=0: the LT assumption). I hope that you understand that the distant clocks on the train cannot indicate the same times as clocks next to them at the station.

[..] I don't think I'm the person to be asking; I wouldn't conclude such things, but it appears that it is a fairly common conclusion; I'm sure you're familiar with the concept of the block universe.

In several recent threads this was discussed and explained that it's just one of several interpretations.

 

[Dale]

Therefore, relativity of time co-ordinates is not necessarily the same as RoS;

Yes, it is. Again, it is part of the definition of simultaneity:
http://en.wikipedia.org/wiki/Simultaneity
"Simultaneity is the property of two events happening at the same time in at least one frame of reference. "

http://www.thefreedictionary.com/simultaneity
"Happening, existing, or done at the same time."

If you wish to assert the contrary, please find a more credible source than Wikipedia and the Dictionary, which defines simultaneity as being something other than occurring at the same time.

I would also point out Einstein's comments on the importance of testability:
http://www.bartleby.com/173/8.html
" We encounter the same difficulty with all physical statements in which the conception “simultaneous” plays a part. The concept does not exist for the physicist until he has the possibility of discovering whether or not it is fulfilled in an actual case. We thus require a definition of simultaneity such that this definition supplies us with the method by means of which, in the present case, he can decide by experiment whether or not both the lightning strokes occurred simultaneously. As long as this requirement is not satisfied, I allow myself to be deceived as a physicist (and of course the same applies if I am not a physicist), when I imagine that I am able to attach a meaning to the statement of simultaneity. (I would ask the reader not to proceed farther until he is fully convinced on this point.)"

The scientific definition of simultaneity is clear. Any other definition is non-testable. RoS is the same as relativity of time coordinates.

 

[GeorgeDishman]

But if we talk Einsteinian relativity; do contractions of the instruments actually occur or are they just optical illusions?

Neither, they are not illusions, they are entirely real but in relativity they arise from geometry as you mention. The length of an object is the difference between the spatial coordinates of its endpoints and that difference will vary if you rotate the axes.

What causes the contractions in Einsteinian relativity? I've been told that it isn't a matter of cause and effect, which seems a bit nonsensical, that physical effects don't have a cause.

There is no physical effect, in its rest frame the object is unchanged so no cause is required. In relativity, "contraction" is the difference between the extent measured using two different coordinate schemes and the cause of that is the angle between the axes.

{p.s. You can say that it was the mistake of assuming 3D Euclidean space and time were separate rather than having a composite Reimann geometry that creates the illusion of effects described by LET.}

I've heard people mention that it is just geometry,

Correct.

but again, that suggests that physical phenomena are caused by mathematics, as opposed to the mathematics representing the physical phenomena.

That's the key point, unlike LET, there are no physical changes involved in the object's rest frame.

Does Einsteinian relativity require the same kind of physical substance?

SR does not. GR is much more complex because gravitational waves which are in part "ripples of time" can transport energy. You need to get a solid grasp of the geometrical nature of SR and a lot more before you will have any chance of following those arguments.

Given that gravity is equivalent to acceleration, could acceleration and/or gravity cause the effects?

There are no physical effects in the rest frame to be caused, just geometry.

I think RoS refers to the simultaneity of events - as per the name - such that two events that are simultaneous in one reference frame might not be simultaneous in another.

A) Two events are simultaneous if they "happen at the same time".
B) Two events are simultaneous if they "have the same value of time coordinate".

The two sentences above are synonomous and would are valid in both LET and SR, and Newton would have agreed with that definition too. I think your problem is that you have a vague notion of some other definition of what events being simultaneous might mean that is different from what everyone else understands by the term.

LET doesn't incorporate this concept at all ...

See above, LET includes precisely the same concept, you cannot get the correct answers without it.

What LET does incorporate, however, is RoTC. I think that RoTC has become conflated with RoS because the Einsteinian interpretation has dominated for so long, and under that interpretation RoTC does mean RoS.

The term was first invented for SR so that is its meaning. It can also be applied the same way to LET. If you want something different, you need to define your new concept and how to measure it.

Forgive the naiivety of this question but what are permeability and permitivity, and why do they dictate that an observer moving relative to the source of light cannot measure the speed to be lower than c.

You can look them up but in simple terms, if you put a charge onto two metal plates separated by a vacuum, the permittivity is the ratio of the amount of charge to the voltage (similar to a battery). Permeability similarly relates the current in a coil to the strength of the resulting magnetic field.

Since both numbers are scalar (single-valued), you can only get a single value of the speed of light from them hence if two flashes of light pass your nose in opposite directions, the speed at the point where they cross must be the same in both directions. SR follows from that.

Indeed, but if the measurements that go into the equation tacitly assume the Earth as the rest frame for experiments, ..

If an engineer used Maxwell's Equations to design an antenna for the Cassini Mission currently orbiting Saturn, the dimensions of the antenna are quite explicitly in the rest frame of the spacecraft , not the Earth! :-)

 

[harrylin]

But this forum is for peope who wish to discuss Einsteinian relativity though, and to develop their understanding of it. [..]

Einsteinian relativity is one option; however he was foremost of the "shut up and calculate" philosophy, which was followed by for example Feynman. As a result his "metaphysical" interpretation flip-flopped and drifted a bit along with popular opinions (from no ether and no block universe, to ether as well as block universe).

Main alternatives are Minkowskian relativity ("block universe") and Lorentzian relativity (which had been lurking in a corner but re-emerged thanks to Bell's Theorem).

Note: what you seem to deny is the fact that what you call "RoTC", is exactly what Einstein called "RoS".

 

[Dale]

Note: what you seem to deny is the fact that what you call "RoTC", is exactly what Einstein called "RoS".

And everyone else. Nobody besides mangaroosh has ever used the term Relativity of Time Coordinates AFAIK, and when everyone uses the term RoS they mean what he is calling Relativity of Time Coordinates. He is just making up things as he goes along.

Mangaroosh, please provide a mainstream scientific reference supporting your use of the term Relativity of Time Coordinates and your alternative definition of Relativity of Simultaneity.

 

[mangaroosh]

This is just a quick point with regard to "the relativity of time co-ordinates", because I'm using the term again in replies.

The term is being coigned for the sole purpose of clarity of discussion; the intention is to avoid equivocation and thus facilitate a more cogent discussion.

 

[Dale]

Find a mainstream reference that documents the term and explains the concept in detail then. Otherwise it brings confusion rather than clarity, and violates the rules.

 

[mangaroosh]

I made the comparisons because absolute and relative simultaneity are not mutually exclusive, just as time zones and universal time aren't, and just as relative and absolute velocities aren't.

We seem to be talking at cross purposes here, probably because of the different interpretations associated with the term, RoS.

It appears as though reference is being made to an RoS in the Lorentz transform, which I am referring to as the relativity of time co-ordinates (RoTC RoS), for the sake of discussion; and for the sake of distinguishing between the LET interpretation and the Einsteinian. There also appears to be an RoS which refers to the simultaneity of physical events, which is distinct from, but related to, the RoS of the Lorentz transform.

When I say RoS of physical events, I mean that two events which are simultaneous in one rerference frame are not simultaneous in another. This is contrasted with absolute simultaneity where two events which are simultaneous in one reference frame, are simultaneous across all reference frames. This notion of RoS is incompatible with absolute simultaneity, because absolute simultaneity doesn't allow for the conditions which constitute RoS i.e. if events, absolutely, happened simultaneously ("at the same time") for all observers, then it isn't possible that they weren't simultaneous for specific, idividual observers.

From the discussions I have had, on here and elsewhere, together wth pretty much all of the information I have encountered on Einsteinian relativity, it appears as though Einsteinian relativity incorporates the notion of RoS of physical events (as clarified above), while Lorentzian relativity incorporates absolute simultaneity of physical events. Given that both use the Lorentz transform, it suggests that the RoS of physical events is not a consequence of the Lorentz transform, while the (RoTC) RoS is.

The (RoTC) RoS appears to be distinct from the RoS of physical events, because Lorentzian relativity incorporates one but not the other. The RoS of physical events is related to the (RoTC) RoS because the RoS of physical events is based on an interpretation of the (RoTC) RoS.

The point I am making, with reference to the interpretation of RoS, is that it appears as though the Einsteinian interpretation is being applied to the Lorentz transform, when arguably it isn't the case - a point I will try to make more clearly below, in response to the next paragraph.

Alternative interpretaions of RoS
You have, on occasion, alluded to possible alternative interpretations of RoS under Einsteinian relativity; as outlined above, I am not really familiar with any interpretation that could not be distinguished as the RoS of physical events, as outlined above.

Are there such interpretations that could not be distinguished in the manner I have done, in representing my understanding; that is, is there an Einsteinian interpretation of RoS that is entirely disimilar to what I refer to as (RoTC) RoS but which doesn't result in the RoS of physical events, and so would make it compatible with absolute simultaneity - as outlined above?

Here I can't follow at all what you say... Lorentz called the relativity of time co-ordinates "local time" and later Einstein called it "RoS". And Einstein's descriptions were purely operational, without any implied metaphysics - he tried to eliminate metaphysics from physics.

OK, if we re-state the question in the context of this point.

Is RoS a consequence of the Lorentz transform, or is RoS the Einsteinian interpretation of the relativity of time co-ordinates, which are a consequence of the Lorentz transform? Did Lorentz refer to the RoTC as RoS?

The impression I get is that RoS is the Einsteinian interpretation, but because it has been the dominant interpretation for so long, it has become conflated with what I refer to - for the sole purpose of clarity of discussion - as the relativity of time co-ordinates. It appears as though the RoTC are a consequence of the Lorentz transform, but the Einsteinian interpretation isn't necessarily, given that there is an alternative, incompatible Lorentzian interpretation; pending any alternative interpretations.

When you say that based on your time reckoning two distant events both happened about 100 years ago, and someone else who uses a reference system that is moving relative to yours says that the one event happened about 99 years ago, and the other about 101 years ago, that is what is called "relativity of simultaneity". It is what Lorentz and Poincare called "local time", and it is about physical events.

That's precisely how I understand it; the issue lies in the assumptions about time, as represented by the term years.

If we take the year to be measured by a clock: if the difference in the recorded years is due to the mechanics of one clock causing it to tick slower - for example, the photon in the relatively moving atomic clock having to travel a longer path between the point of emission and the point of detection, than my clock - then, while the time co-ordinates of the events may be recorded differently by each of us, it doesn't mean that the events weren't simultaneous for both of us; it just means that our clocks tick at different rates due to the mechanics of the clock.

That is wrong, for (again) the same reason as why the following sentence is wrong:
"absolute velocity is incompatible with relative velocity, because relative velocity implies that velocities are not absolute."

Hopefully the distinction between (RoTC) RoS and RoS of physical evetns demonstrates that they are slighty different issues; such that RoS of physical events is incompatible with absolute simultaneity.

That is at the heart of Relativity of Simultaneity...
Here is again a famous illustration of independent reference systems:
http://www.bartleby.com/173/9.html
Now put clocks at the front and back of the train, as well as one in the middle of the train, next to you; and synchronize your clock with a clock that happens to be just next to it at the station at t=0 (so that at x=0 and t=0, also t'=0: the LT assumption). I hope that you understand that the distant clocks on the train cannot indicate the same times as clocks next to them at the station.

don't worry, I understand the above; the point was why do relatively moving clocks indicate different times? The thought experiments usually highlight the fact that one clock ticks more slowly than the other i.e. they tick at different rates.

In several recent threads this was discussed and explained that it's just one of several interpretations.

You have indeed alluded to it, however, I wouldn't necessarily say that it has been explained.

What are the interpretations of RoS that is compatible with absolute simultaneity (and presentism) that isn't, essentially, the same as the RoTC outlined above?

Would you, by any chance, know where I could read up on them?

 

[mangaroosh]

Yes, it is. Again, it is part of the definition of simultaneity:
http://en.wikipedia.org/wiki/Simultaneity
"Simultaneity is the property of two events happening at the same time in at least one frame of reference. "

http://www.thefreedictionary.com/simultaneity
"Happening, existing, or done at the same time."

If you wish to assert the contrary, please find a more credible source than Wikipedia and the Dictionary, which defines simultaneity as being something other than occurring at the same time.

I am in complete agreement with that; the concept of simultaneity isn't in question.

The question is whether or not relativity of time co-ordinates, which are a consequence of the Lorentz transform, are the same thing as RoS. If indeed they are, then there are two interpretations of the RoS of the Lorentz transform - which I am referring to as RoTC for the sake of clarity.

There is the Einsteinian interpretation of (RoTC) RoS, which is the RoS of physical events i.e. the RoS which is incompatible with absolute simultaneity; and there is the Lorentzian interpretation of (RoTC) RoS which is "local time", and which is compatible with absolute simultaneity.

Is that much agreed?

I would also point out Einstein's comments on the importance of testability:
http://www.bartleby.com/173/8.html
" We encounter the same difficulty with all physical statements in which the conception “simultaneous” plays a part. The concept does not exist for the physicist until he has the possibility of discovering whether or not it is fulfilled in an actual case. We thus require a definition of simultaneity such that this definition supplies us with the method by means of which, in the present case, he can decide by experiment whether or not both the lightning strokes occurred simultaneously. As long as this requirement is not satisfied, I allow myself to be deceived as a physicist (and of course the same applies if I am not a physicist), when I imagine that I am able to attach a meaning to the statement of simultaneity. (I would ask the reader not to proceed farther until he is fully convinced on this point.)"

The scientific definition of simultaneity is clear. Any other definition is non-testable. RoS is the same as relativity of time coordinates.

Under Lorentzian interpretation the lightning strikes would be absolutely simultaneous for all observers i.e. they occur at the same actual (as opposed to "local") time; under the Einsteinian interpretation they could be simultaneous for one observer, but not for another.

As far as I am aware, there is no experiment, to date, which can distinguish the Lorentzian interpretation from the Einsteinian i.e. there is no way to experimentally distinguish whether or not absolute simultaneity or RoS prevails; defining the issue one way or the other doesn't resolve this - at least not logically anyway.

 

[mangaroosh]

Neither, they are not illusions, they are entirely real but in relativity they arise from geometry as you mention. The length of an object is the difference between the spatial coordinates of its endpoints and that difference will vary if you rotate the axes.
...
There is no physical effect, in its rest frame the object is unchanged so no cause is required. In relativity, "contraction" is the difference between the extent measured using two different coordinate schemes and the cause of that is the angle between the axes.
...
There are no physical effects in the rest frame to be caused, just geometry.

This is an issue I have real difficulty with. I can't see how physical effects can be caused by geometry; I can see how geometry might be used to represent the physical effects, but a cause is still required to explain the effects; which geometry doesn't appear to satisfy.

Take the Hafele-Keating experiment for example; there we have three physical clocks which, physically, record different numbers of oscillations for the caesium atom. Geometry cannot be the cause of this; a physical explanation is required, as far as I can see.

We can represent the experiment, the evetns, etc. using geometry, but the geometry doesn't explain why the clocks display different values.

{p.s. You can say that it was the mistake of assuming 3D Euclidean space and time were separate rather than having a composite Reimann geometry that creates the illusion of effects described by LET.}

This is also an interesting point. How do we determine that a composite Reimann geometry creates the illusion of effects described by LET? Is it not from measuring physical objects? LET suggests that the microstructure of matter is affected; does the composite Riemann gemoetry affect the microstructure of physica objects, or do contractions occur without any affect on the physical objects and their microstructure?

Presumably the same could be said in reverse though, that effects described by LET give the illision of a composite Reimann geometry?

That's the key point, unlike LET, there are no physical changes involved in the object's rest frame.

This is another thing I stuggle with, but it relates to the question on the meaning of "at rest" which is the subject of a different thread - I might quote this in there, if that's alright?

SR does not. GR is much more complex because gravitational waves which are in part "ripples of time" can transport energy. You need to get a solid grasp of the geometrical nature of SR and a lot more before you will have any chance of following those arguments.

I can immediately tell I will struggle with the notion of "ripples of time".

A) Two events are simultaneous if they "happen at the same time".
B) Two events are simultaneous if they "have the same value of time coordinate".

The two sentences above are synonomous and would are valid in both LET and SR, and Newton would have agreed with that definition too. I think your problem is that you have a vague notion of some other definition of what events being simultaneous might mean that is different from what everyone else understands by the term.
...
See above, LET includes precisely the same concept, you cannot get the correct answers without it.

It's not so much the definition of simultaneous that is causing the problem, as it is the definition of time.

I think it is accurate enough to say that, in LET, time co-ordinates are provided by "local" clocks which give "local time"; however, these time co-ordinates can differ but the events would still be absolutely simultaneous; which suggests that A and B above are not necessarily synonymous under LET.

Would that be fair enough?

The term was first invented for SR so that is its meaning. It can also be applied the same way to LET. If you want something different, you need to define your new concept and how to measure it.

This is essentially the point that is being made; the impression I get is that the term was invented for SR because it implies a specific interpretation of simultaneity that isn't compatible with absolute simultaneity; it also appears to be based on a particular interpretation of what the relativity of time co-ordinates imply.

That is, absolute simultaneity means that events that are simultaneous in one reference frame, absolutely, are simultaneous in all reference frames. The common interpretation of RoS, that I have come across - the only one to be precise - is that events which are simultaneous in one reference frame are not necessarily, and absolutely, simultaneous across all reference frames. Meaning that the two concepts of simultaneity are incompatible.

Lorentzian relativity incorporates absolute simultaneity, while Einsteinian appears to incorporate the RoS described above. If this is true, and there is no interpretation of RoS that is compatible with absolute simultaneity - that is not essentially what I have been referring to as RoTC - then it means that RoS cannot equally be applied to LET.

If are to apply it, then we need to come up with a term to distinguish the RoS of physical evetns from the RoS of time co-ordinates.

You can look them up but in simple terms, if you put a charge onto two metal plates separated by a vacuum, the permittivity is the ratio of the amount of charge to the voltage (similar to a battery). Permeability similarly relates the current in a coil to the strength of the resulting magnetic field.

Since both numbers are scalar (single-valued), you can only get a single value of the speed of light from them hence if two flashes of light pass your nose in opposite directions, the speed at the point where they cross must be the same in both directions. SR follows from that.

Cheers, I'll look them up alright; I find it helpful to read it in laymans terms though, and a lot of the articles I come across, in relation to such things, tend to be a little on the technical side - for that reason it helps to have a basis before approaching them.

I suppose, initially I would be wondering if the scalal numbers in the equations tacitly assume the Earth as the rest frame, relative to which the light is traveling, because the measurements of the speed of light, that go to form the basis of Maxwell's equations, tacitly assume the Earth as the rest frame i.e. the Earth was initially, tacitly, assumed to be the rest frame for the measurements.

If an engineer used Maxwell's Equations to design an antenna for the Cassini Mission currently orbiting Saturn, the dimensions of the antenna are quite explicitly in the rest frame of the spacecraft , not the Earth! :-)

When building the spacecraft is it at rest relative to the earth?

 

[mangaroosh]

Einsteinian relativity is one option; however he was foremost of the "shut up and calculate" philosophy, which was followed by for example Feynman. As a result his "metaphysical" interpretation flip-flopped and drifted a bit along with popular opinions (from no ether and no block universe, to ether as well as block universe).

Main alternatives are Minkowskian relativity ("block universe") and Lorentzian relativity (which had been lurking in a corner but re-emerged thanks to Bell's Theorem).

Note: what you seem to deny is the fact that what you call "RoTC", is exactly what Einstein called "RoS".

OK, this helps to clarify the issue I think.

It is probably worth noting, that I am not, necessarily, denying that what I refer to as RoTC, is what Einsteinian relativity terms RoS.

What I am saying is that RoS is a particular interpretation of, what I refer to as, RoTC.

I am saying that RoTC is a consequence of the Lorentz transform; but that RoTC can be interpreted in two (or maybe more) ways; it can be interpreted in such a way that incorporates absolute simultaneity, or it can be interpreted in such a way that RoS is incorporated.

Where RoS means that two events need not, absolutely, be simultaneous, across all reference frames, but absolute simultaneity means that they are. It is effectively the two main alternatives mentioned above; the block universe and the Lorentzian interpretation.

Both appear to be incompatible.


This would mean that RoTC, not RoS is a consequence of the Lorentz transform; because RoS is a particular interpretation of RoTC, but not the only possible one.

 

[mangaroosh]

And everyone else. Nobody besides mangaroosh has ever used the term Relativity of Time Coordinates AFAIK, and when everyone uses the term RoS they mean what he is calling Relativity of Time Coordinates. He is just making up things as he goes along.

Mangaroosh, please provide a mainstream scientific reference supporting your use of the term Relativity of Time Coordinates and your alternative definition of Relativity of Simultaneity.

as mentioned, I'm using the term for the purpose of clarity in this discussion, and to help avoid any equivocation.

EDIT:
Just saw this;

Find a mainstream reference that documents the term and explains the concept in detail then. Otherwise it brings confusion rather than clarity, and violates the rules.

Harry appears to be following the discussion, as do you; the confusion was earlier in the discussion when we were talking at cross purposes due to the different interpretations, or meaning of the term RoS; I introduced the term RoS for the purpose of greater clarity, which it seems to have brought because we have been able to distinguish what is meant.

I'm not claiming it as a scientific term, I'm using it as means of clarity in a discussion using the english language; it is more a literary technique than an attempt to define a scientific term. As far as I am aware, citations aren't required for every single english word used in the discussions here, nor for turns of phrase, so I can only presume that a citation isn't required for what is nothing more than an attempt to employ greater clarity of the english language, to faciliate the process of developing a greater understanding of Einsteinian relativity and reconciling issues that affect that understanding.

 

[GeorgeDishman]

I'll give separate replies to different points as the posts are getting too long.

If an engineer used Maxwell's Equations to design an antenna for the Cassini Mission currently orbiting Saturn, the dimensions of the antenna are quite explicitly in the rest frame of the spacecraft , not the Earth! :-)

When building the spacecraft is it at rest relative to the earth?

When the signal is transmitted, it is in orbit around Saturn. Maxwells' Equations allow you to calculate the speed of the emitted signal and give the value 'c'. You haven't tried to actually use the equations so I guess you don't understand the consequences. What you are suggesting is that the speed of the waves would be 'c' relative to the Earth so for example when the radio signal from Cassini was passing Jupiter, its speed relative to that planet would vary by up to 30km/s depending on where Earth was in its orbit.

The same would be true for gamma rays from a GRB 10 billion light years away. You are suggesting they would have to vary their speed when passing a galaxy 8 billion light years away depending on where Earth was in its orbit, which is somewhat nonsensical since Earth didn't exist 8 billion years ago.

What you need to understand is that, other than transforms which specifically relate values in one frame to the equivalents in another, all physical equations link measurable values in one frame. If you put in numbers measured in the Cassini craft frame, you get out numbers in that same frame and can then transform those to the Earth frame (or Jupiter or any other) using the Lorentz transforms (ignoring gravity of course, we are talking SR).

 

[GeorgeDishman]

That's the key point, unlike LET, there are no physical changes involved in the object's rest frame.

This is another thing I stuggle with, but it relates to the question on the meaning of "at rest" which is the subject of a different thread - I might quote this in there, if that's alright?

That's easy, weld three mutally perpendicular rulers to the object. Something is "at rest relative to the object" or "in the object's rest frame" if its location measured by those rulers does not change over some finite period of time.

I can immediately tell I will struggle with the notion of "ripples of time".

Yes, and you will also need to have a grasp of "general covariance" and the effect of diffeomorphisms which is why I suggest keeping it separate.

 

[GeorgeDishman]

{p.s. You can say that it was the mistake of assuming 3D Euclidean space and time were separate rather than having a composite Reimann geometry that creates the illusion of effects described by LET.}

Presumably the same could be said in reverse though, that effects described by LET give the illision of a composite Reimann geometry?

You can but you then have a number of ad hoc and inexplicable effects conspiring to create one illusion. If you use the geometrical approach, you can also predict for example that mass will appear to increase with speed which can then be confirmed by experiment, another bizarre ad hoc effect in LET which again has no explanation. (In fact it is worse because mass no longer has the same value in different directions in LET, it is no longer a scalar quantity but becomes a tensor IIRC).

The biggest argument against taking that approach though is that it cannot be extended. By noting that energy (mass etc.) causes curvature of the geometry, Einstein explained gravity, and in particular gets the right result for a raft of observations where Newton's Law fails. If you take GR and let the masses become negligible, the result is the geometric model of SR.

It's your choice of course but if you prefer not to learn how the geometric model works, you can never move beyond the physics of pre-1917. YMMV but I think that benefit is worth the effort.

 

[Dale]

We seem to be talking at cross purposes here, probably because of the different interpretations associated with the term, RoS.

There is only one interpretation associated with the term RoS. You have failed to document that this confusion is anything other than a personal confusion unique to you and due entirely to your desire to invent some non-existent problem with SR by pretending that it is circular when it is not.

Again, I challenge you to provide any mainstream scientific reference supporting your use of the term "relativity of the time coordinate". In the absence of that, at least provide a pair of mainstream scientific references documenting that there are indeed two different uses of the term "relativity of simultaneity" which disagree with each other in the sense you are suggesting.

If you cannot find either of those then you must admit that the different interpretations associated with the term RoS are only in your mind and that such different interpretations are not part of the mainstream scientific literature.

I'm not claiming it as a scientific term, I'm using it as means of clarity in a discussion using the english language; it is more a literary technique than an attempt to define a scientific term. As far as I am aware, citations aren't required for every single english word used in the discussions here, nor for turns of phrase, so I can only presume that a citation isn't required for what is nothing more than an attempt to employ greater clarity of the english language, to faciliate the process of developing a greater understanding of Einsteinian relativity and reconciling issues that affect that understanding.

It is required when you are first claiming that such a discrepancy exists in the accepted use of the term "relativity of simultaneity" and second that this discrepancy leads to special relativity being circular. You cannot weasel out of it this way and pretend on one hand that it is only a literary technique while on the other hand claiming that this literary technique demonstrates an inconsistency or weakness in a scientific theory.

If it demonstrates a problem with a scientific theory then it must be a scientific term. If it is a literary technique then it cannot demonstrate a problem with a scientific theory. You are contradicting yourself in this attempt to avoid the issue, I can only assume it is because you know full well that there is no such reference and you are aware that you are inventing the supposed conflict for your own rhetorical purposes.

I will assert once again that $(\text{PoR} \cap \text{C}) \rightarrow (\text{TD} \cap \text{LC} \cap \text{RoS})$ as all of those terms are commonly understood in mainstream science with no circularity. (All referring to measurments only, I still am not interested in discussing non-scientific concepts like unmeasurable things here)

 

[GeorgeDishman]

I've reordered your response to try to address it more logically.

It's not so much the definition of simultaneous that is causing the problem, as it is the definition of time.

No, the main problem is that you are trying to use a new phrase for an old concept and then use the old phrase to mean something new. Swapping jargon terms without telling anyone what you mean will always cause confusion.

The common interpretation of RoS, that I have come across - the only one to be precise - is that events which are simultaneous in one reference frame are not necessarily, and absolutely, simultaneous across all reference frames. Meaning that the two concepts of simultaneity are incompatible.

I have highlighted two phrases which are the key to the confusion, there is and has only ever been one concept of simultaneity but you are trying to treat it as two. You have generated the problem in two parts, first by coining a new phrase, "relativity of time coordinates" and using that to mean what everyone else means by "relativity of simultaneity" and secondly by claiming that you have some new concept for which you re-use the existing term but without ever saying what you think it means.

Two events are classified as happening "simultaneously" if the times at which they occur are equal. To represent equality we use the symbol "=" and we say Ta=Tb if the numerical values of Ta and Tb are the same. Ta and Tb are of course the time coordinates of events A and B in some frame determined locally by using synchronised clocks. That method is the same for Newton's mechanics, LET and SR.

You have been asked several times to explain what alternative meaning you would give to "simultaneity" but have never offered any definition.

If are to apply it, then we need to come up with a term to distinguish the RoS of physical evetns from the RoS of time co-ordinates.

You have that the wrong way round. The term "relativity of simultaneity" is already taken and well defined, it means the equality of the times of the events allocated from syncronised local clocks. If you want to invent a new concept, what you need to do is first come up the scientific definition of that concept (i.e. how it can be measured) and secondly, to avoid the confusion you are currently creating, you need to find a new name for the new concept.

I think it is accurate enough to say that, in LET, time co-ordinates are provided by "local" clocks which give "local time";

Yes, in fact that is true in all the theories.

however, these time co-ordinates can differ but the events would still be absolutely simultaneous; which suggests that A and B above are not necessarily synonymous under LET.

Would that be fair enough?

No, it is wrong (but read on before replying).

That is, absolute simultaneity means that events that are simultaneous in one reference frame, absolutely, are simultaneous in all reference frames.

"Absolute" in this sense means "agreed by all" so "absolute simultaneity" means that, if one observer using local clocks which he considers are synchronised assigns the same time coordinate to two events, then the physics will ensure that any other observer moving relative to the first will also assign equal coordinates using clocks local to the events which he considers synchronised. That would happen if the transforms of Gallilean Relativity applied, it doesn't happen under the Lorentz Transforms. Newton's world model did exhibit absolute simultaneity, those of Lorentz and Einstein do not.