I do not believe philosophy of time moved much forward since Reinchenbach and Grunbaum, as I gather from relatively new overview by Robert Rynasiewicz: SIMULTANEITY, CONVENTION, AND GAUGE FREEDOM.

There is only more and more maths added to the subject while underlying assumptions and interpretations still remain the same. This cannot produce a different outcomes. Just a new look of the old things.

Simultaneity as generally portrayed seems to be conventional while the one proposed by Einstein still conventional is superior to other conventions - to which I agree.

What I dont agree is that relative simultanity reflects the true nature of temporal coincidence as it skews it rather badly.

By conventional I mean arbitrary selected for a given purpose not much different in principle than convention to make clocks show 12 when the sun is in the highest point above the horizon (roughly) all across the globe.

Do you know a single convention of synchronisation which is inequivalent to Einstein's, while at the same time assuming Lorentz transformation? To the best of my knowledge there is not. This should somehow be relevant to the issue whether synchronisation is ``conventional''.

Dear François

There is no doubt Lorentz transformation is associated with a particular clock synchronisation method. No other synchronisation method will match Lorentz transformation whether you call it conventional or absolute. If one mentions absolute simultaneity, this on the surface may imply someone rejects Lorentz transformation. But this is not quite true. One needs to broaden the context in which the Lorentz transformation, clocks and temporal coincidence are considered.

One of the definition of absolute synchronisation is quite simple if not trivial. This is a synchronisation accomplished by means of an instantaneous signals. 

Surely such signals are in short supply so to speak, but not entirely unthinkable. Surely it is a blasphemy which might ruin anybody's career.  

As much as I do not see any signal that could instantaneously transport information from point to point, I do not see such limitation in remote clock synchronisation as it does not necessary require the transport of information from one clock to another. All I can say now is that I cannot rule out a synchronisation method which result will be equivalent to instantaneous synchronisation. And that is why I am interested what kind of impact of such method might have on philosophy of time.

Dear Andrew,

Surely you are right, in a sense. But an instantaneous signal is not a concept that is invariant under Lorentz transformation: there will be a set of reference frames in which the signal is instantaneous, another set in which it connects one event to a past or future event. So it would only be an instantaneous signal in a limited set of reference frames.

Personally, my favourite mode of synchronisation is slow clock transport. Two clocks are said to be synchronised iff when slowly brought close to one another, they are seen to give the same time. The slowness condition is required, since otherwise, if we accept Lorentz transform, the result of the synchronisation procedure depends on the path and on the velocities. But in the slow limit, no such problem arises. Now it can be shown that, if Lorentz transformations are the ones that connect reference frames in uniform rectilinear motion, then slow clock transport is equivalent to Einstein synchronisation. A broad class of other synchronisation procedures, essentially these that can be carried out in the reference frame itself, without appealing to other reference frames, can similarly be shown to be equivalent. In the light of the relativity principle, these may well have some claim on being more natural than such as require a special reference frame for their definition. These, surely, might well deserve the name of conventional.

Again, see Mansouri, R., and Sexl, R. U. . ``A test theory of special relativity: I. Simultaneity and clock synchronization'' General relativity and Gravitation, 8 (7), 497-513 (1977); ``A test theory of special relativity: II. First order tests'', General Relativity and Gravitation, 8(7), 515-524; ``A test theory of special relativity: III. Second-order tests'', General relativity and Gravitation, 8 (10), 809-814 (1977).

Dear François

The theoretical instantaneous signal represented by a vertical line on xt plot or horizontal one on Minkowski's diagrms would transform to a steep tilted one in the moving system. But the tilted line in the moving system shows how much the Einstein's synchronised clocks on the X' axis are shifted away from true simultaneity. Since the perception is that no experiment can detect an absolute frame we are left with clocks synchronised in the best possible way given circumstances. The vertical line in the moving system by the same token will transform to a tilted line in the stationary system indicating the same discrepancy. 

The main problem is that most people think Lorentz transformation is about time while it is only about clocks exactly as shown by Einstein in his 1905 work. I think that influenced by Minkowski, Einstein got carried away from his original idea, seduced by the concept of space-time which in my opinion is pure abstraction resulting from blending representation of real space distance measurement with time measurement combined in a neat set of linear equations that were chosen as being equivalent coordinates in the physical space of four dimensions.

There is no flaw in mathematics of special relativity only flaws in its understanding.

Dear Andrew,

Why, physically, should synchronisation be based on an absolute reference frame? It is not that I deny the logical possibility, rather, I ask for some kind of justification. If, as a large body of evidence indicates, all reference frames are physically equivalent, that is, if no measurement of fundamental properties is able to pick up a difference between the ``absolute'' reference frame and all others, then it surely seems to me to be highly conventional to choose one such reference frame in order to define synchronisation.

On the other hand, if I say ``two resting clocks are synchronised if, after being slowly brought together, we see them showing the same time'' this, I believe, is very much the common sense version of synchronisation. When synchronisation in this sense fails, you miss your appointments, because your friend will be at the appointed place when his clock shows the appointed time, whereas you will only be there when your clock does. So saying: clocks are desynchronised in that sense, is intrinsically important.

Now if an observer A decides to synchronise his clocks with respect to those of a reference frame B in motion with respect to B, A's clocks will be desynchronised in exactly that common sense meaning of the term.

Finally, I have often heard the claim that relativity should be about time, not clocks. I fail to understand the difference: clocks are the only way, or at least the only reliable way, we have to measure, and hence quantify, time. Clocks at rest with respect to each other are usually in good agreement. This gives us a standard for time. Let there now be two sets of clocks A and B, all clocks of A in uniform rectilinear motion with respect to those of B and viceversa, but all clocks of B at rest with respect to each other, and similarly all clocks of A at rest with respect to each other. Then all clocks of A agree, at least if they are first synchronised at a common position and then carried to their respective positions. The same happens for the B clocks. It then turns out that the A clocks and the B clocks do not show the same time when they are at the same position. That is an experimental fact, or at the very least, a consequence between a rather compelling mixture of theory and experiment.

I have no problem with agreeing to the fact that time and space are qualitatively different. But the Lorentz contraction does mix them, and it can be shown that the peculiar way in which it does so is the only possible one, apart from Galileo, if we are to stick with the symmetry requirements imposed by the relativity principle.

Dear François

Thank you for detailed reflections on the issue. I appreciate the time and quality of your response.

Why, physically, should synchronisation be based on an absolute reference frame?It is not that I deny the logical possibility, rather, I ask for some kind of justification

I think that they are intimately related. I can only derive it from the assumption of a prime reference frame. It is a fair assumption that it should be confirmed or contradicted. There is no way in between. I hope to justify it in not too distant future (or prove myself wrong which is also a good outcome)

The body of evidence you mention in my opinion is the evidence of ad- hock assumption. The evidence of CBR and experiments of Miller Cahill, Marinov seems to indicate something else. Paraphrasing Orwell's classic All frames are equivalent but some are more equivalent than others.

I am not prepared to discuss most  of clock synchronisation issues unless I know if absolute simultaneity exists. I know what people say at this point.

Finally, I have often heard the claim that relativity should be about time, not clocks. I fail to understand the difference

The difference is how you synchronise clocks. If you assume clock time between London and Paris changes linearly with longitude to account for 1 hour time zone offset you would see that the apparent time of travel for the same aircraft depends on direction while there is no difference for on board clock. You can convert all Newton dynamic to such defined time and it will be as good as the original but there will be a lot of unusual "effects". Similar effects arise with relative simultaneity, such as ever increasing distance of two identically moving uniformly accelerating points in the direction lateral to the moving inertial system which is a variation of Bell's spaceship paradox. Similar bizarre effects you will have without relativity if you take two clocks at two ends of a train and delay one with respect the other and connect position of the engine and last carriage as a function of the same t.(Example graph attached which shows the variation of the length of a perfectly normal fixed length train when you decide to present non simultaneous state as if they were just because clocks say so)

The fact that clocks A and B are out of alignment is caused by the fact that you can synchronise clocks any way you desire and they no longer reflect the common passage of time. Not only their rates change (which I agree with) but they are also shifted in phase as a function of the distance. The shift is caused by the fact that you assume light speed equal in both direction because apparently there is no way to detect one way speed. To better understand this you need to assume God's eye view from the absolute frame and by the act of faith make it the only one with speed of light the same in all direction. You see then Lorentz transformations making the illusion of the same in any reference frame. But you know from down under what the truth is. But I think there is a better way than the act of faith to see the absolute frame.

I have no problem with agreeing to the fact that time and space are qualitatively different. But the Lorentz contraction does mix t

This is only because somebody's (Minkowski's)  view has dominated the world. There is more then one way to view things. Rather than spatializing time as the fourth dimension I can see it as a scalar parameter in  and introduce a fictitious spatial dimension w on the top of x,y,z and having all four vector component being a function of a scalar having value t everywhere. What is wrong with this view? Same equations different interpretation.

If the rate of processes change with speed is because the speed is locally affecting the container of the process which does not care how many coordinate systems keep the track of it. The best help is to assume that time does not exist only clocks change states under different influences and their internal mechanism.

Rene Descartes:

Of philosophy I will say nothing, except that when I saw that it had

been cultivated for many ages by the most distinguished men, and that

yet there is not a single matter within its sphere which is not still in

dispute, and nothing, therefore, which is above doubt, I did not presume

to anticipate that my success would be greater in it than that of others;

and further, when I considered the number of conflicting opinions

touching a single matter that may be upheld by learned men, while there

can be but one true, I reckoned as well-nigh false all that was only

probable.

As to the other sciences, inasmuch as these borrow their principles

from philosophy, I judged that no solid superstructures could be reared

on foundations so infirm; and neither the honor nor the gain held out by

them was sufficient to determine me to their cultivation: for I was not,

thank Heaven, in a condition which compelled me to make merchandise

of science for the bettering of my fortune;

@Andrew: ``This is only because somebody's (Minkowski's) view has dominated the world. There is more then one way to view things. Rather than spatializing time as the fourth dimension I can see it as a scalar parameter in and introduce a fictitious spatial dimension w on the top of x,y,z and having all four vector component being a function of a scalar having value t everywhere. What is wrong with this view? Same equations different interpretation.''

Indeed, there is nothing wrong with this. Indeed, I do not think the concept of a spatalized time really dominates physical thinking. It is more of an overinterpretation of some things Minkowski said. But physicists certainly do not view time and space as equivalent.

On the other hand, if you speak of a universal scalar t, then, from a combination of empirical data and logical work, it is seen that the quantity having units of time and measured by clocks is, in your notation, w/c. The quantity t will turn out to depend heavily on convention, at least if you assume that the laws of physics do transform according to the Lorentz transformation in your (x, y, z, w) variables.

As to your synchronisation example: of course, it is easy to cook up ludicrous examples. What I would like to see is a positive proposal: how do you plan to synchronise clocks in a way that is superior, say, to slow clock transport, the kind of synchronisation required in order not to miss your appointments. Clearly, if your clocks are on different time zones, and two people set up an appointment to meet at a given time, they will miss each other, so this is not a happy choice of synchronisation. 

Dear François

We can recalibrate physics to many synchronisation conventions. What is not conventional is that clocks once set progress in convention independent manner and the states of those clocks remain independent of any frame but their own. Additonally aĺl clocks tick simultaneously independent on what conventional procedures told them to indicate. There is only one temporal reality not many as relative simultaneity implies.

Dear Andrew,

``What is not conventional is that clocks once set progress in convention independent manner and the states of those clocks remain independent of any frame but their own''.

No real objection to that. In fact, I would say the states of the clock are independent of any frame.

``Additionally aĺl clocks tick simultaneously independent on what conventional procedures told them to indicate.'' If you refer to pairs of clocks at rest with respect to each other, fine and good. If you consider a moving clock, then, as it passes several clocks at rest, the clocks at rest will observe that the moving clock is ticking at a lower rate. That is, if clock B (moving) passes clock A1  (stationary, as are all other A clocks) at t=0, and both show t=0, then, if it passes A2 when A2 shows t=1, then B will show a reading of 1/gamma. So however you define the tick rate, it is not the same for B and A1 or A2. Those last two do have the same tick rate.

``There is only one temporal reality not many as relative simultaneity implies.'' If by that you mean that your idea of time is something that should be a Lorentz scalar, then all I can say is that such a time is not observable. The best devices we make to record something that behaves as time all record what you would call w/c, which transforms as predicted by the Lorentz transformation.

In my opinion, time cannot be described without making reference to physical systems that change as a function of it. Such physical systems are used to measure time and are called clocks. The crucial point is that any mechanical or atomic system showing some kind of regular behaviour as a function of time can be used to measure it, and it can be seen that the results between very different clocks are all equivalent.

Once we have defined time as what is indicated by the variation of some appropriate physical system, the experimental fact that processes that take place in a moving system are viewed, from a system at rest, to take longer time, must affect in some way our ideas about time. The easiest way is, in my opinion, to identify time with clock readings, and to use any of a number of not so conventional synchronisation procedures, such as slow transport.

Quote There is only one timelike reality Unquote

How would you then explain delayed choice experiments under that view? 

Not to mention a number of other issues having to do, variously, with the speed of light (a simple calculation shows that if time is the same everywhere, then the speed of light is infinite, which clearly is not the case), with the observed absence of bias in certain reactions involving the strong force (a bias which calculations show would be present in that case), and so on? All attempts to take a naive view of time have always failed, I believe for good reason.

Dear Chris,

Thank you for you answer.

"There is only one temporal reality" I said. I do not use word "timelike" because it is Orwellian "new speak"* designed to blend things that do not quite match in my opinion.

I respect your answer because it includes references to physical phenomena that might suggest your view is justified, but I would be careful calling absolute simultaneity or single temporal reality naive. 

I base my statements on the results of a long investigation. Starting with simultaneity, I have demonstrated why effect of relative simultaneity are not real - nothing much different than optical illusions which make things look different than they really are. 

This may not be convincing because what is mathematical must be real for most people. But I am in a position to demonstrate that absolute simultaneity is fully justified and remote absolute clock synchronisation possible in principle. And it is not "Standard Einstein Synchrony" Although the later is useful because of its simplicity. I cannot offer you more details at the moment because I must finish writing my paper. 

It is incorrect to say that "if time is the same everywhere, then the speed of light is infinite". The same time coordinate applies everywhere in whole space of an inertial system. And light line is at an angle to the fixed time coordinate line. The speed of light can be anything we want, To make it infinite it is enough to synchronise clocks by setting them consecutively to 0 on a light ray path

I am not sure how to explain the delayed choice experiment but if the approved interpretation is:

":a last-minute decision made on earth on how to observe a photon could alter a decision made millions or even billions of years ago."

I can say with confidence that:

"the photon changes its mind in the last moment"

But putting both these jokes aside, there are other interpretations that make more sense:

http://www.bbk.ac.uk/tpru/BasilHiley/DelayedChoice.pdf

We have to realise we are not special. People in the past could not explain simple things so they were giving bizarre explanations like phlogiston's negative weight. We have some model of the world that partially makes sense and partially does not. So instead of seeking answers we are often discouraged to investigate and become coerced to approve established truths.

“Once a structurally complete and closed system of opinions consisting of many details and relations has been formed, it offers enduring resistance to anything that contradicts it.”

― Ludwik Fleck

"Evidence conforms to conceptions just as often as conceptions conform to evidence."

Ludwik Flec

https://en.wikipedia.org/wiki/Newspeak

Just a note - I normally eschew 'temporal' because the first definition of that particular word is 'transitory, temporary, provisional', rather than 'relating to time'.

Timelike is much narrower in meaning, and exclusively means relating to time or along the time axis. Thus,  If you are to explore, like Itzhak Bars, Paul Davies et al., that there could be several dimensions or time, or universes with a time signature higher than 1 within a wider multiverse, then the word 'timelike' is far less ambiguous and precise than 'temporal' which seems to imply only one existing dimension of time.

BTW, spatial, meaning 'relating to space', is far more interchangeable with 'spacelike'.

Dear Andrew:

On your remark, “There is only more and more maths added to the subject while underlying assumptions and interpretations still remain the same. This cannot produce a different outcomes. Just a new look of the old things.” I cannot agree more.  I believe that moving on is not good advice, unless churning the same butter is a waste of time or it complicates the process, which in this case is very debatable.  Science cannot be cast in stone.

Having said that, let me describe to you my attempt at resolving the philosophical problems with SR —including simultaneity— by re-stating the underlying assumptions posed by Einstein, as follows:

1.      There exists an absolute frame of reference.

2.      Time is not a dimension but the manifestation of an orthogonal (Hermitian) process.

3.      The constant c, —which has been interpreted as the speed of light— is part of the Lorentz transformation equations as a scale constant in the spatial/temporal manifestation process and not the speed of anything.

Based on the above I have been able to derive three types of relativities —one of which is Einstein’s SR— as follows:

Reciprocal Relativity.  This set of equations consider moving object A or B, whose property values are being observed from each other’s moving reference frames.  This is Einstein’s SR.  I found this case to result in true but misleading (unphysical) observance of property values that lead to apparent paradoxes.

Comparative Relativity.  This is the set of equations for moving object A or B, whose properties are being observed compared to each other’s, from an absolute (static) reference frame.  This case leads to real (physical) conclusions, albeit I found this case to be useful for understanding and resolving paradoxes but impractical for direct measurement.

Absolute Relativity.  Not an oxymoron, once explained, this is the set of equations for moving object B’s properties being observed from object A’s static (absolute) reference frame or vice versa.  This case leads again to real conclusions without any conflicts, but also impractical for direct measurement.

The above cases may not satisfy current empirical science but they helped me immensely in understanding SR and its apparent consequences without contradicting it, as well as, providing feedback and insight for future theoretical development on my proposed Infophysical Spacetime Model.

You are welcome to download my RG monograph on relativity, if you haven’t done so yet, and help me find where I may have gone astray.

Regards,

Bernardo.

Dear Chris,

There is indeed some ambiguity in the world "temporal" as well as the association with "temporary". My foreground notion is as the first line in most dictionaries: "related to time". My temporal lobes are in pain when I see about four other meanings of the same word.

This is however not chosen ad hock. We have a formal "temporal logic"  It is used in a composite term  "spatiotemporal" referring to space and time together. Finally Max Jammer uses this term frequently in the meaning "related to time" and provides broader description of simultaneity as the “temporal coincidence of events.” which is  very wise choice.

But surely we can have our preferences.

Dear Bernardo,

I think concurrent models of relativity make sense. Likewise I see that STR is not complete in some respect, and I do not mean General Relativity.

A lot of people will be fuming at this point thinking of Enstein Minkowski theory as the ultimate achievement of human thought.

My purpose in life is to establish the clear status of absolute simultaneity which currently is denied as a valid concept. I am on the right track now and after I finish my project I might look at your work in detail.

I don't think that Philosophy of Science and Philosophy of Time are prepared for such a task, since, after 100 years, we are still have debates about general relativity, special relativity and many "ghost predictions" of them, that have never been revealed.

Dear Andrew:

I did not mean to imply that there are three “concurrent models of relativity”, what I have come up with are three different sets of equations that describe the same physical world from three different points of observation (points of view).  One of those points of view is our presently known point of view, which has the same results as Einstein’s STR, that which I call Reciprocal Relativity.

Obviously STR is not wrong, but it is misleading, because it considers both the observer and the observed object properties are moving.  Also, by postulating time as a dimension, the concepts of spatial (dimension) contraction and temporal (dimension) dilation are introduced, which I believe are wrong interpretations of length (wavelength) contraction and frequency (temporal frequency) increase, thus mass and energy increase with increasing relative velocity.

STR has been confirmed without doubt because we have measured its predictions of length contraction and mass/energy increase, but that does not mean that its interpretation of spatial contraction and temporal dilation have been verified as Minkowsky spacetime predicts.  Because of the dimensional construct (Minkowsky), STR also denies the concept of an absolute frame of reference and with it, the concept of absolute simultaneity.  Yet… on second thought, I think that STR “ignores” these concepts, more than “denies” them.

I don’t believe anyone should be “fuming at this point thinking of Enstein Minkowski theory…”, we should all be relieved instead, if and when we can get rid of it.

By the way, one of the meanings of the word temporal is “of or relating to time”, as you pointed out, which I believe should be unambiguous in our context.

Thanks for your comments,

Bernardo.

Dear Demetris,

I think from my perspective of rather superficial knowledge of the whole philosophy of time, There is a kind of saturation where all conceivable ideas about time has already been presented and there is no conclusive evidence either way. And I think by the overwhelming influence of relativistic physics the idea of absolute simultaneity has been basically ridiculed following Bergson's humiliation. There is nowhere to go. From that comes my question: If absolute simultaneity has been proven a valid and practically realisable, which way the philosophy of time would go? And as I have mentioned in the preamble, this is not a rhetorical question.

It seems no one is interested in answers. Its the journey that seems to matter in philosophy but not the destination. 

I have tried to get a few philosophers to comment on my concepts with no effect whatsoever. I think if at least one had said its a complete rubbish, al least it would mean something. 

I am stunned that logical apparatus used in philosophy cannot distinguish fictions from facts. And here comes a question: What is fact? What is fiction? What is real? then What is a question?.....

Dear Francois

Thanks for reference to Mansouri&Saxl. Great overview confirming absolute simultaneity not contradictory to SR. There is a lack of final presentation of absolute simultaneous clock synchronization at a distance from local measurement without a help of infinitely fast signals.

Dear Andrew,

It should perhaps be appreciated that the main thrust of Mansouri-Sexl is to look at what happens when the principle of relativity is violated. When it is not, as they show, slow clock transport and Einstein synchronisation are equivalent. In fact, I believe one can show that all internal synchronisation procederes are equivalent when relativity holds. When relativity fails, that is, when there is a physically distinguished frame, then slow clock transport generally differs from Einstein synchronisation. The experimental fact that clocks can equivalently be synchronised either way can be used as quantitative evidence that the alpha parameter is close to its relativistic value.

As far as your interests go, it seems to me to say that synchronisation is not that conventional if relativity holds. Sure, you can have absolute simultaneity if you synchronise, say, with respect to the CBR frame. But if relativity holds, this frame has no particular properties singling it out. So such a definition of simuitaneity would indeed deserve the name of conventional. On the other hand, since most natural choices of synchronisation procedures are equivalent under the hypothesis of relativity, the claim that Einstein synchronisation is conventional loses much of its cogency. Add to this the fact that experimentally slow clock transport and Einstein synchronisation are to a high level of accuracy equivalent, and one has, in my opinion, a satisfactory situation for SRT.

Dear Amrit

I agree with you about the necessity of the concept of common "Now". This means the concept of absolute simultaneity common to all inertial frames is not a fantasy. But people seem to be unprepared for this. In contrast they demonstrate "relative simultaneity" of clocks without understanding what it really is.