Dear Israel
''You seem to overlook Newton's words, I quote them again to remark their deep meaning. "And so, instead of absolute places and motions, we use relative ones". Notice how he was aware that for practical matters we use relative places and motions. Notice also how he was relating motion not only to reference bodies but also to space.''
Agreed. Newton takes absolute space for granted. Classical mechanics is tremendoulsy powerful. However, notice that the statements of Newton´s mechanics
can never be classified as true or false (because F=ma and ''a'' is defined in the absolute space frame which cannot be seen, so there´s no way we can verify the theory). We must choose an object to become ou reference frame, so that we measure distances upon it (x,y,z). Now if this frame is inertial,
-(grad V)=ma.So we could almost see absolute space, except that we still could never measure absolute position and velocity. Again, any problem with that? Well, we know classical mechanics is incredibly useful. But that is because we take the ''distant stars'' as a substitute for absolute frame, and that is very practical and as precise as we need for everyday engineering. But if we can create a theory WITHOUT unobservable data and which lead to the same (and/or new) verified results, then shouldn´t we prefer it? So why did it take so long for someone to find a substitute for Newton´s classical mechanics which didn´t have unobservable statements? The general belief that it could not be created. Let´s move on.
'' I agree with you that is difficult (or may be impossible) to put a material object at rest relative to the ZPF, but despite that one cannot reject its existence. In my entry I replied to you and discussed how the principle of relativity should be understood. I would be glad if you take a look at it and answer the questions I raised there in relation to the rejection of the PSR.''
Okay, I see you have written new arguments there, I will definitely take a look.
''As far as I can see you do not get the usefulness as I do, and so you conclude that, as absolute newtonian space, my arguments are devoid of utility.''
That´s not the case actually. With the snapshot argument I tried to remark that the ZPF by itself cannot be identified with a PSR. But PSR have utility. For instance, as far as I know, string theory is a backgound dependet theory. So if in the end it proves to be correct, we see that there would be a PSR, even though symmetries of the theory would make it become unobservable. But strictly at the classical level, I think relational formulations have clear advantages as I explained above and in other replies.
''This is not the case. In my last replied to you I provided a counter example in allusion to the measurement of the one-way speed of light. So far, no experiment has ever measured it, but despite this, as we all have witnessed, the special relativity has been quite successful for physics. ''
It really does not break your argument, but anyway, you will find interesting that a guy has filmed light moving! Video link. I agree that we may have unobservable data in physical theories. Maybe they are inevitable. Who knows? But don´t you think we should get rid of them if we can?
''The case is similar with the ZPF, despite that the absolute position of an object relative to ZPF could not be determined I find the assumption elucidating and helpful for the construction of a strong and coherent theory.''
That´s the point. If it is REALLY useful, yes, I agree we should take the PSR proposal. But then we must always bear in mind that such a theory would provide us unobservable data (like newton´s mechanics). Nevertheless, it is a way to conceive motion. There may be others as well. The point of my essay is to study all these possible conceptions systematically.
''Just because fields (gravitational, electromagnetic) cannot be seen by the senses, this does not mean that they do not exist.''
They can be seen, where by ''seen'' I mean detected. This is different form PSR.
'' Similarly occurs with the ZPF. Despite that it cannot be perceived by the senses we know it is there (do you deny this?), just recall the Casimir effect.''
Yes, it is there. But we cannot use it (as far as I know, please correct me if I´m wrong) to define a preferred position. So it is as invisible as absolute space (this is where the snapshot argument comes in).
''So, I can assume it as a continuous fluid because this will help me to explain the body of observations. Moreover, the existence of this omnipresent field allows us to assume the PSR (...)''
don´t agree that the existence of ZPF allows us to assume PSR, because PSR can´t be used to define a preferred position. Same aguments as before.
''(...), again, despite the fact that (as Newton argued) we only had access to relative measurements. The ZPF and the PSR has to be considered, above all, because light, seen as a wave, demands it (as a photon the explanation becomes faint). ''
I don´t see why this is so. We can easily imagine electromagnetic waves without ether. Instead of saying an eletric field E=E(x,y,z,t) is a pertubation of some invisible ether it can be seen as telling you that the measurements of that quantity you call eletric field in the position (x,y,z,t) as seen by an observer has the value E. The wave would be a compact way of telling us operational procedures. Above all, what I´m trying to say is that there is no strictly LOGICAL need for a medium where electromagnetic waves would propagate. In more advanced theories like string theory, the vibrating strings would produce the waves and even space-time itself.
''Because its speed is defined relative to the ZPF, not relative to the source or any other material body.''
As far as I know, no one has ever measured the speed of light against the background of ZPF (and I still argue that the ZPF cannot provide a background, snapshot argument). The speed of light is always measured against a material, visible object. What empirical experiences say is that, no matter what object you choose as reference, the speed value is always ''c''.
''Light does not travel relative to the empty space as Newton contended, but relative to the ZPF. If you have understood this, I ask you to provide any objection to the motion of light. According to you, with respect to what physical entity do light move? What physical entity defines the speed of light waves?''
As argued above, you can choose any physical entity as reference, when the speed of light is measured the value is always ''c''.
''In addition to these arguments, I pointed out another paradox in relation to the isotropy of the speed of light (see my reply to you in my entry). To avoid the paradox, it is necessary to assume the PSR.''
Once again, I will take a look. If the PSR solves any paradox, we have a strong reason to consider it, even though that would render unobservable statemets. Bt again, if these paradox can be solved by a theory without unobservable statements, we should prefer this theory.
''You say: if we can do mechanics without invisible concepts, why not do it? Because if do not introduce the PSR we arrive at several paradoxes.''
Again, this is the good point. Now our discussion should turn to this paradoxes.
''Furthermore, if a theory A assuming a PSR explains the same amount of observations as another theory B in which there is no PSR, I would chose theory A, because theory A would be free from paradoxes. ''
Again, these paradoxes should now be the center of our discussion.
''You: You should discuss these points more thoroughly with Julian Barbour, he´s the author of Shape Dynamics and strongly advocates Machian philosophy.
As I explained, Newton was also relational contrary to the customary view. The material objects we used as reference systems are in space, but one has be careful in how we conceive space. From my perspective, Mach misconceived the deep meaning of Newton conceptions because Mach thought of space as an empty vessel not as a massive fluid, this is why he claimed that the stars, and not space, were playing the major role in defining inertia and centrifugal forces.
Best Regards''
Once again, this massive fluid (that you identify with ZPF) must be able to define a preferred position, so that (x,y,z) can be meaningful even without any material object. If we could identify this ZPF field values with absolute space, then we could finally see absoulte space. But the existence of this field by itself does not (see snapshot argument again) entail that the PSR is any more reasonable then in the classical case.
Now, let´s turn to the paradoxes in your entry.
Best regards
Daniel
