According to Einstein, it was not possible to distinguish between uniform acceleration and a gravitational field, whatever was the experiment, provided that you didn't look outside the laboratory. Then the EEP was reformulated and the requirements were more restrictive about which experiments could be performed.
Is it possible to distinguish between a real gravitational field and the accelerated configuration by using atomic clocks???
The answer is yes...because in the real gravitational field of earth there will Always be a time dilation between two oscillators situated at different gravitational potentials (not due to tidal effects) but no time dilation at all will be possible for equally accelerated clocks.
The extension of the equivalence principle performed by Einstein in a REAL gravitational field is unfortunately falsified by internal measurement, without looking outside.. And as some say, the principle of equivalence as applied by Einstein has to be considered just as an euristic tool.
Article A Falsification of the extension of the Equivalence Principle
Won't all test particles under uniform acceleration be uniformly directed (in paralell), whereas test particles being accelerted by a spherically symmetrical gravitational source be radially directed (eventually converging)?
Yes Johan, you are right about the speed of light. It regulates all the interactions and it is at the base of the time itself. So the question comes natural...what is the deeper reason why speed of light slows down in presence of matter-energy concentrations???
But here we are talking about the inapplicability of the equivalence principle in the way Einstein did it. He started from the simple thought that free fall cancels out the effects of gravitation, but later he realized that both the external (gravitational) curvature and the curvature determined by each particle cannot be cancelled out whatever the reference system.
Correct me if I am wrong.
I think gravity on edges of clock will be less compared to gravity at center of clock as edges are further from the center of mass attracting the clocks.
Hence there will be stress applied to the clocks horizontally.
If we can measure this stresses we could be able to say that clock is in gravitational field where as in normal acceleration there wont be any stresses applied on clocks.
It is not a matter of force. Curvature is not only orgin of force. Clocks respond to gravitational potential energy,in free space not the gravitational attraction.
@Eric:
"The simple answer is: curvature affects photons, therefore photons affect curvature. (Newton’s “action and reaction"....)"
So far the logic answer would seems yours, but I wonder in which way photons affect curvature......
@ Johan
About curvature and time I don't think I can agree with you. SInce you speak about variable speed of light this is anyway a fourth dimension of the Space-time and it is another way to conceive curvature at every point.
" IT HAS TO SLOW DOWN AS IT APPROACHES THE ELECTRON's REST-MASS ENERGY m*c^2, since it MUST STOP in its tracks to add to this mass-energy. Rest mass is stationary EM energy and the boundary conditions that trap this EM -energy is the gravitation-field around this mass "
I agree with you light is massless and not affected by time, time arises when the energy of light is condensed in an electron and becomes massive, becomes matter. The time arises in the Quantum Physical absorption of light which gets transformed from radiant to confined energy. I don't thnk rest mass is only stationary EM-energy anyway, leptons and quarks are not.
But anyway we are going out of the argument of the question which is the validity of the exstension of the WEP by Einstein.
@ Johan
Regarding the role of the variable speed of light I will have to populate another thread in another question, what do you think??
In the course of my research work for my theory of Physics in 5 Dimensions I came across the work of Rudolf Mössbauer and Pound & Snider - From section 13.3 of my book Photons treated as particles in the Mössbauer Effect:
Rudolf Mössbauer received the Nobel Prize in 1961 for his work on “Recoilless nuclear resonance absorption of gamma radiation” and the discovery of his effect was used by Pound & Snider in their experiment reported in the Physical Review[1] in 1965 that produced a very accurate result in agreement with the prediction of Einstein’s principle of equivalence.
Our interest in this subject is related to the use of the theory of physics in 5 dimensions in the case of the Mössbauer effect with its confirmed predictions associated with moving sources of photons, the Doppler Effect and the behaviour of photons as particles. In section 16.3 we look at the implications of the Mössbauer Effect in terms of the above mentioned Pound & Snider experiment and the relationship with the physical effects currently associated with gravity. The following text is an edited version of Mössbauer’s Nobel Lecture[2]..............
Above references are:
[1] Effect of Gravity on Gamma Radiation, R.V. Pound and J.L. Snider, Physical Review Vol. 140, Number 3B, 3. November 1965
[2] Recoiless nuclear resonance absorption of gamma radiation, Nobel Lecture, December 11, 1961
I think that you will find that the Mössbauer Effect and the Pound & Snider experiment fully proves Einstein's principle of equivalence. If you use this link - http://www.physics-in-5-dimensions.com/keyword.html - and click on the Keyword search link, then enter "equivalence" in the "Google" box, you will see a selection of pages from the book on Physics in 5 Dimensions including page 402 with the above mentioned section 16.3 - so you can read some more about this subject there. Unfortunately section 13.3 is not free to be read via this link, but if you are interested I can send you more of this section if you would find this helpful. However the two references above take you to the core source of this topic. Both Nobel lectures are, or were, available via the web.
@ Johan: "You do not have to believe in the Voodoo of "wave-particle duality" and "complementarity".. I don't... it's a description that cannot convince.
" I do not believe that the actual physics of this gravitational interaction can be undrstood in terms of Einstein's principle of equivalence and space-time curvature".
Regarding the principle of Equivlance I agree that it is not a valid tool, regarding the curvature so far it explains a lot of things and I feel confortable with it.
It is quite difficult to explain everything in terms of Maxwell Equations....al the nuclear interactions matter and antimatter quarks which are the base of the single nucleon come to be quite difficult to have an explanation in terms of EM field.
What do you think about the Aharanov-Bohm effect???
@ Alan,
thanks for talking about the Mossbauer effect. I think that one and the gravitational light deflection are the way from the microscopic to the macroscopic realm , to understand the interaction between the photons and the space-time, or rather the behaviour of the SPACE-TIME.
The Einstein principle of Equivalence finds a relation which is not in agreement with GR. Photons don't lose energy in a Gravitational field. The process is only an apparent phenomenon. If you analize deeply the experiment of the Harvard Towers you find that some additional energy is provided in order for the photon to be absorbed by the above observer and the doppler shift provides it. This does not mean that the photon climbing loses its energy, but it means, according to the clock theory (exp. verified), that the absorpion property of the upper atom is changed compared to the lower one in a gravitational field. The higher atom has a higher absorption level due to its gravitational potential (actually due to the different light speed) and the radiation to be absorbed has to be rised in level. For this reason the above absorber has to move downward with a tiny, but not negligible speed in order to give the upcoming photon the sufficient energy to be absorbed.
I know this is a not easy thing to digest, and I thought the same as you till ten months ago...
Article Gravitation, photons, clocks
Article THE GRAVITATIONAL POTENTIAL ENERGY OF PHOTONS IS AGAINST THE...
Regarding the Mossbauer effect in itself I would suggest you to follow another thread of mine posing questions on it. And to analyze the point of view of Julian Schwinger about it.
Johan, that could be a good point....about the Aharanov Bohm effect.. I have doubts though that E and H exist separately in any way, it is only one field Since detecting E and H depends on the relative speed between the charges and the observer.
An accelerated frame of reference has the same acceleration throughout all space. The gravitational field of a finite body is not uniform. So it is possible to distinguish the two by measurements over a volume of space. But this is unrealistic since the apparatus has to be huge in order to detect the difference. However, measurements at a single point cannot differentiate between the two.
The remark by Prins above fails to distinguish between rest mass and mass equivalent of energy. He thus reaches incorrect conclusions.
All I am claiming is that the universe includes particles with mass that move with speeds less than c and massless particles that move with speed c. All these particles have energies. But the difference between particles with mass and massless particles is important and should be kept in mind. This difference is central to the special and general theories of relativity and to quantum mechanics.
There are other cases where "strong equivalence priple" doesn't seem to be correct. Consider an electric charge at rest in gravitational field and a uniformly accelerated electric charge. The second one radiates while the first one doesn't. (Or you can compare a free falling charge to a charge in a gravitation free portion of the space)
Yes I know, but this case is excluded, since it is sustained that the electric field extendig to infinity has not the local properties required by the equivalence principle, it is like having an observe which looks outside...
Yes I know but I think this is only an excuse to exclude this case easily. The greatest contribution to radiation comes from regions with greater electrical field strength namely from regions closer to a accelerated "point like charge". Namely from regions we can consider gravitation/acceleration as approximately constant over space.
@Johan,
theoretically any electric field gets 0 at infinity, so very far it has anyway some value. In such case the equivalence principle is not valid because there is no way to garantee that the charge does not interact with external bodies...
Einstein arrived at his theories (SR and GR) not by rigorous step-by-step logic but by imaginative musings that he called “thought experiments”. That was the way his mind worked. Once he had arrived at the final theories, he could express then in rigorous mathematical formulations. The elevator “thought experiment” simply demonstrates that an accelerated observer and an observer in a constant gravitational field will observe the same behaviour of falling bodies in his vicinity (which, incidentally, is true also in Newtonian mechanics) – it gave Einstein “food for thought”. It would be a mistake to regard it as a fundamental building block (an “axiom”) in a derivation of GR. Of course, once we have the final theory (the field equations and the geodesic “hypothesis”) it is of great interest to look back at the elevator thought experiment and see how far it can be pushed – to understand the limits of its validity. (Indeed, there is another fascinating RG discussion thread devoted to that.)
In terms of the final theory, the “equivalence principle” means simply that the very concepts of “inertial force” and “gravitational force” disappear – replaced by the metric of spacetime, which cannot be partitioned into an “inertial” part and a “gravitational” part. The elevator experiment was a pointer in that direction – nothing more.
Atilla ~
"Consider an electric charge at rest in a gravitational field and a uniformly accelerated electric charge. The second one radiates while the first one doesn't. (Or you can compare a free falling charge to a charge in a gravitation free portion of the space)"
The only theory we have for thinking about that question is GR in the presence of electromagnetism. According to the logic of that theory we would expect a freely falling charge to not radiate. On the other hand, an accelerated charge is under the influence of a (non-gravitational) force, and so is a charge in a gravitational field that is not falling (ie, the force that keeps it from falling). According to the logic of the theory, we should expect radiation in both cases, or in neither. If, indeed, it is true that a uniformly accelerated charge radiates but a non-falling charge in a gravitational field doesn't, then there is something very seriously wrong with our current theories.
There is a controversy in the literature (which I've not studied in detail) surrounding the question (in special relativity) "does a uniformly accelerated charge radiate?". Try googling it. I have neither the expertise nor the motivation to do the calculation myself but my intuition, based on the above argument, suggests to me that the answer is almost certainly "no" - that the radiation depends on the (proper-)time derivative of the acceleration.
@ Eric,
it is sure that an accelerating charge radiates.. it does not provoke a sinusoidal dipole radiation. dE/dt = (2/3) e2 g2 / c3 (erg/sec) where g is the acceleration of the charge.
It is enough a variation of the Electric field in order to provoke an EM wave.
@ Attilia,
"Yes I know but I think this is only an excuse to exclude this case easily. "
I agree, it might be an excuse. The effect of looking outside can be easily prevented by isolating the experiment within a (big) metal box the way the field remain confined in the box.
@ Johan,
"suggest an experiment that can prove that there is an electric-field around a charge"
I don't understand... the presence of the field can be detected by posing another charge and mesure the presence of a force according to the coulomb law.
Anyway, when you have problems with the equivalence principle, you are in good company. I quote from J.L Synge, Relativity: the general theory, p.IX-X:
``... I have never been able to understand this Principle. ... Does it mean that the effects of a gravitational field are indistinguishable from the effects of an observer's
acceleration? If so, it is false. In Einstein's theory, either there is a
gravitational field or there is none, according as the Riemann tensor does not
or does vanish. This is an absolute property; it has nothing to do with any
observer's world-line. Space-time is either flat or curved, and in several
places in the book I have been at considerable pains to separate truly
gravitational effects due to curvature of space-time from those due to
curvature of the observer's world-line (in most ordinary cases the latter
predominate). The equivalence principle performed the essential office of
midwife at the birth of general relativity, but, as Einstein remarked, the
infant would never have got beyond its long-clothes had it not been for
Minkowski's concept. I suggest that the midwife be now buried with appropriate
honours and the facts of absolute space-time faced.''
Johan,
solitary electron emits nothing, no matter what is the frame.
Regards,
Eugene.
Johan,
let's stick to the experiment performed with atomic clocks. The Hafele and Keating experiment. In such experiment the twin atomic clocks started syncronised, looking at their gauges we read the same numbers. Bringing one in space and bringing it back and stopping them at once, one could read that the one which stayed on earth had a delay.
"Furthermore it is based on the concept of time-dilation on a "moving clock""
The concept is not the moving clock relatively to another in general. That does not make sense, it cannot be. Infact the relative movement of SR has to be replaced, the reference systems have to be replaced because they do not make really sense if they are not inertial. But what is an inertial system? In order to get rid of such ambiguity we have to get rid of the reference systems at all.
Special relativity does not explain such concept of time dilation. It is impossible to have a clue in SR. That is why GR comes about.
Dear Johan,
I reffered to Hafele and Keating but with the modern atomic clocks it is possible now to detect the time dilation in a gravitaitonal potential at a distance of less than a meter. And they did a lot of experiments about it. The HK experiment is only the oldest with lots of possible problems which you illustrated.
You spoke the other time about variable speed of light. It is the same as talking about time dilation. Where the speed of light slows down, the time dilates. It is a consequence of how we measure the time, since we measure it with clocks that way, clocks are affected by speed of light (atomic levels) and react accordingly.
Johan ~
“As you can see I do not believe that Einstein's General Theory of Relativity is correct.”
>> Science is not about “believing” it’s about trying to find out. “Believing” belongs in the realm of superstition and religion.
“Where I am sitting in front of my computer, time is "NOW"; and I live within a Universe which co-exist with me "NOW"”
>> What evidence do you have that your “NOW” is the same as the “NOW” of every other observer in the universe? You have none. Newtonian physics tacitly assumed that there is a universal “NOW”. Einstein’s Relativity denies it, and matches experiment and observation in situations where Newtonian physics does not.
“..Minkowski's concept of a 4D space-time manifold, which is mathematically impossible since x,y,z,t ARE NOT linearly independent coordinates…”
>> Of course they’re linearly independent coordinates! What on earth makes you say they aren’t??
“...the concept of time-dilation on a "moving clock", which is also impossible since it is absurd as many competent physicists, like, for example, Herbert Dingle [have] pointed out many times.”
>> 'Appeal to authority' is a dangerous way to try to win an argument. Even a competent physicist can occasionally be mistaken or even stupid – as for example was Herbert Dingle in this instance. See my final word on 'Dingle’s error' at https://www.researchgate.net/post/Is_there_a_solid_counter-argument_against_Dingles_old_objection_to_Relativity_Theory#view=543bea13d039b105258b465e
_________________________________________________
"Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason"
- Gautama (The Buddha)
LARMOR RELATION ABOUT UNIFORM ACCELERATING CHARGES
RADIATION
http://en.wikipedia.org/wiki/Larmor_formula
If the moving clock is analysed in SR framework, the concept of time dilation gets absurd. Who delays to who, who is in motion respect to whom or who is accelerated respect to whom. Only the relative motion is valid there, but since both the points of views don't have reason to be wrong, to remove such absurdity, it is necessary that there is no time dilation at all.
THe proper time concept is treated in GR so time dilation can be analysed in the framework of GRT .There is no need of reference systems and time dilation there makes sense and it is definite who is in delay respect to whom.
_____________________________
@Eric
"Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason"
- Gautama (The Buddha)
Beware, one's reason is oriented to tell that he is right... one's heart maybe not...
I think we have to arrange yet another sentence....
Johan,
it was not Einstein, it was Minkowski, who introduced Minkowski space. It was optimal mathematical formalism for physical (and philosophical) ideas of Einstein, formulated at that time. Futher development of theory is another question. All has it's limitations.
Regards,
Eugene.
Be patient, Johan. Nobody tries to insult You.
We are argueing about nothing, because, actually, notion of "time" is not defined. In this situation everyone is correct, if he does not logical mistakes.
Regards,
Eugene.
Dear Johan,
sorry if I seemed rude, but I didn't mean.
But if there is no curvature, where is the GRT??
So what is left valid is Special Relativity..
Johan ~
I attempted to initiate an intelligent discussion with you about the differences in our views about physics. You took offence when no offence was intended. You misinterpreted the meaning of almost everything I said. You attribute opinions to me which I do not hold, and attack them. I give up - I'm unable to cope with people who's only mode of discussion is an an inflexible "I'm right and you're wrong".
Best wishes
~ Eric (-:
@ Eric.
You are right nobody here wants to offend anybody. We are here to discuss interesting things with open minds.
Johan ~
Mathematically, the study of Minkowskian four-dimensional space is nothing more than the study of a homogeneous quadratic form in four independent variables that is not positive definite. It belongs to a respectable and important class of abstract geometrical entities with interesting properties that are well-understood by mathematicians. There is nothing wrong with it mathematically. We understand that you have reason to suspect that it is not relevant as a model of space and time in physics. That is a separate issue. If you are willing to present your views rationally without resorting to words such as 'impossible mathematics', 'absurd nonsense', 'voodoo' and 'claptrap', we will be willing to pay attention.
Johan,
You are using Newtonian views on time. It is your axiom. Axioms can not be proved or disproved. But all the others use Einsteinian (it is also axiom). If You want to remain in Newtonian frames, You must remake all the contemporary physics. May be You first solve more simple problem?
Let me first say that I share some of Johan's worries. I, too, am not fond of Minkowski and Riemann space formulations. But at the same time I realize that the relativity theories have a considerable domain of application. Many experiments are well-described by means of RT, and I know of no other theory doing this equally well. I understand that Eugene is just challenging to come up with a theory that does so. In my view he is perfectly justified to do so. It does not make sense to quarrel about which theory is true, and which is false. Up till now we never had any true theory. Also classical mechanics is thoroughly falsified. Neverthless we are happy to use it within its domain of application. We have no reason to assume that this will be different with RT.
Willem de Muynck
Johan ~
I’m sure you realise that you are battling against the majority view. I respect you for that. Generations of theoretical physicists (including myself) have been trained to think of space and time in terms of Einstein’s special relativity. As a mathematician I can assure you that there is no irrationality in the mathematics of it - incorrect as physics it may be (as you assert), but it’s not mathematically irrational.
You accuse Einstein of assuming t and t’ to be two “simultaneously different times”. I very much doubt that he did. He went to great lengths to convince himself that “simultaneity” is not a valid concept (recall his “thought experiment” with the train and the lightening…).
We are in agreement that “it is impossible for the time-rate to be different within two inertial reference frames moving relative to one another”. I do not regard the t and t’ in the Lorentz transformations as referring to different time rates in two different inertial frames. I regard t and t' simply as as convenient coordinates, not "clock times". If the two clocks of two inertial observers are identically constructed, and by hypothesis all physical laws are identical in the two inertial frames, then of course they cannot run at different rates. The catch is that two inertial observers can only meet once, if at all, so they have no means of comparing time rates. That is true even in Newtonian mechanics. However, if one of them is not an inertial observer, they can meet twice and compare their clock measurements of total time elapsed. In the Newtonian case they agree, according to Einstein’s SR the do not. That is the true meaning of "time dilation" according to Einstein’s theory, not the t and t’ in the Lorentz transformation. Experiment confirms the Einstein prediction (eg, Hafele-Keeting 1971, Ives-Stilwell 1941, Rossi & Hall 1941, and the innumerable high-energy physics experiments in which SR is routinely and successfully employed to interpret the results). How do you account for that?
I am somewhat puzzled that you appear to accept the Lorentz transformations and yet you reject the full theory (Special Relativity). As far as I can see, the full theory is an inevitable logical consequence of the Lorentz transformations.
The simplest way of deriving the Lorentz transformations [the full group of transformations (x, y, z, t) → (x’, y’, z’, t’)] is to accept that Maxwell's theory should be the same in all inertial frames. That of course incidentally assures that the speed of light will be the same for all inertial observers. The result is the group SO(3, 1), which is the group of transformations that preserve “Minkowskian” geometry!
I’m sorry if I seemed “pompous and patronizing”. I can assure you I’m not like that. What you probably detected in my tone was irritation at seeing my understanding of Einstein’s theories and my years of exploring them summarily dismissed as nonsense! You will succeed better in getting people to listen to you if you show more respect for others' opinions.
Why would you say "The person who deserve scorn is not Dingle, but rather Peter Higgs"? That's a thoroughly unpleasant remark and totally uncalled for. I knew Peter. He is charming, unassuming and rather shy; embarrassed, I would guess, by all the attention.
@ Eric, Johan and Eugene
it seems you are right about the fact that an Electric charge under a constant acceleration does not radiate,
a charge does radiate if
a) it is constantly accelerated in an electric field
b) it is accelerated by an electric field (X rays)
c) the acceleration is not constant
In the absence of another electric field the charge radiates only in the presence of the not null third derivative of the space coordinate.
This explains why such fact cannot be a counter example to EEP. In order to radiate, the constantly accelerated charge has to be immersed into an Electric field. This fact is like looking outside the system.
@ Johan,
you wrote
"In fact the concept of time-dilation is not just wrong it is obviously, patently absurd. The same event cannot simultaeously occur at different times: It is insane to believe this"
In fact it is not this which is described to happen, the events are central, the events are not under discussion. But at one gravitational potential it is needed for example 10^6 oscillations of an atom of Kripton between two energy levels to cover the interval between two events, at another gravitational potential for example 10^6 + 2 oscillation of the same atom are needed in order to cover the same interval. Because this is the only way for us to measure something which we call time...and this comes out...
Dear Johan,
but the experience says that same oscillators had different numbers of ticks in the same interval of events. This experience is made every day with modern atomic clocks very accurate machines, they are put one on the top of the other at 1 meter distance in the gravitational field of Earth. How do you explain such experience??
Johan ~
Haven’t much time just now to answer in detail. I’ll try to find time later. For now, I’ll just answer this:
“..in both cases the laws within the two reference frames are the same and therefore in both cases the times will be the same unless there were other factors involved that slowed the one clock down relative to one another. In the special theory of relativity there are not any other factors involved at all.”
The rate of clocks of two inertial observers is the same because the laws of physics are the same for both. If one of them is not an inertial observer SR nowhere asserts that the laws are the same. An accelerating frame is subject to forces – so there are other factors involved. I don’t see why you feel so strongly that the passage of time cannot be influenced at all, under any circumstances. I agree that Einstein often expressed himself badly – but we shouldn’t be misled by his verbal explanations - it may even be true that he himself was sometimes misled about what his theory implies. We need to look at the theories in their completed form and figure out for ourselves what they imply. Which is what you are doing.
As for the idea that Minkowski space is crazy, I won’t argue any more. Consult a mathematician or a good textbook dealing with different kinds of geometries. The four coordinates are not linearly dependent. A "null vector" has zero length. But it can still locates a unique point.
Dear Johan,
"Why do you claim that this means that time passes at another rate. When the oscillator is electronic the frequency becomes lower, and when the oscillator is mechanical, like a pendulum, the frequency becomes higher. "
Why should then the frequency become lower for an electronic device?
Dear Johnan,
the pendulum dipends actually on the acceleration, so if you bring it under the earth's surface it will tick slower, as it is brought over the surface of earth. It is not a function of the potential like the atomic clock. So who is wrong the pendulum or the atomic clock??
Dear Johan ~
Agreed: "clocks" are not 'the passage of time" and do not "create" time. They are the only means we have of measuring the passage of time. Cesium clock experiments have established that there is a phenomenon that can be called "time dilation". Quite apart from Einstein's theories (even if those theories didn't exist) those results of observation needs to be explained.
It's clear that you and I will never find common ground on which we can agree. That's all I've tried to do. You appear to have made no real efforts to find out what "Minkowskian geometry" means to a mathematician. If you had you would know that it is a self-consistent construct whose rules are not those of Euclidean geometry. Yet when I point you in that direction I'm a "pompous ass" engaged in "insulting patronization". You accuse me of "personal insults". I have never insulted you, Johann. You say, without the least shred of evidence, "I have probably read more of these books than you have, and I believe that I am a better mathematician than you will ever be!" Which of us is the one behaving like a "pompous ass" throwing "personal insults" about?
That's all, Johann. I cannot waste any more time. I leave you to carry on discussing your ideas with others - hopefully without any more ridiculous non-scientific terminology such as "absolutely absurd", "metaphysical claptrap", "baboons playing with their navels", etc., etc.
Dear Johan,
It is a pity that you make discussion with you a bit difficult by reacting the way you did above. As I see it, you have a certain point. But it needs more to make it than the way you scorn Einstein like this: ``Unfortunately, my hero, Einstein also contributed to this absurd legacy wth his absurd concepts of "time-dilation" and "length contraction"''. I agree that Einstein was not always reliable, but not in the way you suggest. In 1905 his intention was to free physics at least from `Lorentz contraction' rather than introducing ``absurd concepts of "time-dilation" and "length contraction" ''.
It is true that Einstein during his physical career shifted more and more from his initial empiricist/operationalist approach to a more realist one, in this way at last seemingly complying with the methodology of classical mechanics (aspiring at an absolutely true `theory of everything'). But it is not impossible (and probably even necessary) to abide with the young Einstein, and realize that the operational way in which he defined simultaneity by means of propagation of electromagnetic signals is the basis of his derivation of the Lorentz transformations, and consequently, of the whole of the mathematical formalism of the special theory of relativity.
It is probable that Einstein not always has kept his operationalist attitude. This does not mean, however, that we are required to do the same. It is very well possible to deal with so-called length contraction and time dilation in an operationalist way (rather than in a classically realist way) by introducing a concept of non-ideal measurement into RT, more or less analogous to the way this is possible in quantum mechanics (see for this latter issue my book Willem M. de Muynck, Foundations of quantum mechanics, an empiricist approach, Kluwer, 2002, or my website http://www.phys.tue.nl/ktn/Wim/muynck.htm ).
Then Lorentz contraction and time dilation, as derivable from the mathematical formalism, can be seen not to refer to `reality as it is', but as `reality as seen in measurements valid within the domain of application of SRT', taking full account of the influence such measurements may have on the relation between `what we see' and `what there iis' (see, for instance, http://www.phys.tue.nl/ktn/Wim/advrel20011.pdf, where it is made plausible that Lorentz contraction is just a property of a certain way of carrying out a length measurement).
Willem de Muynck
P.S This is a message from a new and booming Eindhoven
@ Johan,
there is a thing for which I certainly agree, time flows regardless the presence of clocks, or somebody who is there to measure it... unless somebody would dare to come out and say, since time is our definition, doesn't really exist if it is not measured, but then fantasy is fantasy...
@ Eugene,
stricly talking about experimental method I agree, since a measure has to be provided.
Anyway the initial question was about the equivalence principle...
we derailled from the original path...
It is not evident that time flows regardless the presence of clocks, Johan.
Stefano,
imagine, You have only two systems, accelerated one from other. How can You determine, which of them is inertial?
If I don't see apparent forces appearing internally, that one is inertial.
If I'm on one of the systems and have the possibility to measure apparenf forces, if I don't detect any I say it is inertial.
From external Only if one is connected to a very massive body respect to the other one, is the inertial system.
And how do You distinguish between internal and external forces, Stefano?
Eugene, I'm here to ask questions...
If there is something wrong on the text of my question about the EP tell.
Stefano ~
"If I'm on one of the systems and have the possibility to measure apparenf forces, if I don't detect any I say it is inertial."
Agreed! Put another way: If I observe that Newton's first law is valid in my immediate vicinity, then I conclude I'm an inertial observer.
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