Tim88

So, does anybody know of a good simple video (History-tv-channel-education-level of a description) explaining the Ives-Stilwell apparatus (as there are simple videos for the Michelson-Morley apparatus)?

 

Thank you.

I don't know such. However, the basic idea is fairly straightforward. What is called "transverse Doppler" is a misnomer, it's just time dilation. That effect comes on top of the Doppler effect. Wikipedia explains it rather well, the Doppler equations are given; only some info about the set-up is lacking. The basic idea was that one can accurately determine the forward and the backward Doppler shifts, and these relate to each other for a given particle that is going at a certain speed at a given time. But due to time dilation the short wavelengths (high f) are longer than classically expected, and the long wavelengths (low f) are also longer than classically expected. Compared to the Doppler shifted wavelength they are thus both redshifted. And that creates an asymmetry in the frequency shifts that can be measured, as discussed in Wikipedia.

I'll now look up the details of the measurement set-up.

From reading through their paper I got the following understanding of their set-up.

Light coming out of the tube towards the detector consisted of:

- light emitted in the forward direction (to the right in your drawing)

- light emitted in the backward direction but next reflected by the mirror inside the tube.

That mirror is an important element that is lacking in the Wikipedia drawing.

- light from unaccelerated gas

All that light went through the slit (shown in the Wikipedia drawing) and was next focused on the spectrometer's metal-glass grating which reflected the light onto a photographic plate (with again a focusing lens). Thanks to the grating, the image of the slit is split in different bands depending on the emission frequency.

For classical theory there is only Doppler and for each rest frequency line there would be equal distance to the Doppler shifted lines. The deviation from that symmetry is a measure of the time dilation.

better question

What prevents the ball from going c?

Mass/Spacetime curvature. Not much distinction on geodesics. Just mass vs massless. What causes the ball or photon to have sufficient kinetic energy can be numerous.

 

PS what you call error is your opinion. I know no Lorentz ether is required to account for the geodesic relations of GR.

Quite frankly a good study of field theory quage groups under GR is more than enough to describe the above

Yes, that question is much better. However, spacetime curvature concerns the mathematics; and accounting is again math. I can think of two possibilities:

1. you either deny or can't understand the need for the existence of a physical cause for the math

2. you believe in a physical Spacetime (a 4D metaphysical entity), but you dislike the term "ether" as a label for such a causal entity.

Which is it?

What is your point ? we were discussing Lorentz ether not being needed. [..]

However as Einstein felt the ether was superfluos and not needed. Yet you seem to feel it is. Then you and Einstein disagree.

 

Quite frankly though I'll stick to Einsteins opinion over yours any day

No, and again no! Once more, this thread is a continuation in part of the thread http://www.scienceforums.net/topic/97105-is-space-time-a-physical-entity-or-a-mathematical-model. In that thread I explained why Einstein argued that "According to the general theory of relativity space without ether is unthinkable; for in such space there [...] would be no propagation of light".

This thread discussed two variant ether interpretations:

1) a "Lorentz" ether to which Einstein at that time adhered, and

2) a "Minkowski" "4D ether" to which he later tended, as it implies a form of immortality. Note however that it's not sure if that was really what Mnkowski had in mind.

By now interpretation 1) has been sufficiently clarified, but interpretation 2) remained, regretfully, a bit obscure. And strangely, my question about one aspect of interpretation 2 (posts #234 and #238) was repeatedly hijacked for more discussion of interpretation 1 as well as for discussion of the topic "is space-time a physical entity or a mathematical model" - which is not the topic of this continuation-in-part.

Once more: the speed of light is independent of the action of the source; in this thread we follow up on the insights of Einstein and consider that it's either a function of the properties of Space (interpretation 1) or of Spacetime (interpretation 2). If there is some constructive input about Spacetime as a physical entity and how it can be understood as governing the propagation of light, I will be interested. I'm not interested in more hijacking and I won't comment on such.

Hi Thales,

I suspect that you think that it's like the Michelson set-up; but it is totally different.

1. the canal rays are explained in the Wikipedia article, inside the very text that accompanies the picture that you copied; and for a more elaborate explanation you should click with your mouse on the blue underlined "Canel rays" text.

2. These hydrogen ions emit light when they return (in flight) to a lower energy state.

Unfortunately a lot of people are hung up on the medium for light propagation. I've never really had a problem with that hurdle. Never really understood the hangup. Common reasoning seems to be sound requires a medium.

 

Yet one can simply ask. If I throw a ball do I require a medium for the ball to get from a to b ?

 

My physics instructor in grade 6 asked that to the class. Might have been what prevented me from getting caught on the same hangup.

 

[..]

You seem to think that neither Einstein or I ever thought about that. And again you bring it up in the wrong thread, as the error in your reasoning was already clarified in the mother thread (but even more elaborated in this thread, on p.12). Just one last question here to you: do you really pretend that the cause of the speed of the ball is the same as the cause of the speed of light?

Thats a useless argument. Any math definition states the number of independant variables is the number of dimensions. Thats basic math.

 

The number of independant variables =number of graph axis.

 

In Lorentz Ether you have 4 axis to graph

Not 3 hence spacetime diagrams. 3 dimensions of space with orthogonal axis+1 of time. Orthogonal simply means at 90 degrees to each other.

You continue to confound mathematics with physics.

Yes, Einstein and relativity is 'uncommon use of language' for laymen ;-)

You are mistaken: Einstein's relativity is characterized by the usage of common language. His writings are easy to understand, in my opinion (as I'm not a layman, I could of course overlook some parts that I think to be easy to understand for laymen while they are not!).

You are correct.

Conceptually, a 4 dimensional object cannot "exist" because to "exist" need time.

[..]

Well seen!

However, my point was merely that just because animals are living, that doesn't make them "4D objects". That's a misuse of language, a bit resembling of "Newspeak" - you know what I mean if you have read "1984".

In fact, space-time is 4D because space is 3D; and if we add force, then objects would be 5D in a space-time-force sense!

Instead of such Newspeak, I stick to normal language; and in normal language space is 3D - see also Einstein 1916.

Philosophically everyone has a right to have his own opinion, but it's not acceptable that jargon resulting from weird ideas of a minority should be imposed on the majority.

I won't further discuss such nonsense about nonstandard terminology here.

In other words, you would call clocks and animals "4 dimensional objects"?? To me that's highly uncommon use of language.

Your way of describing things risks to confuse people. Please understand that Newton's model also used x,y,z,t.

Moreover Lorentz ether is an interpretation of SR, and block universe is another interpretation of SR. Regretfully it remained a bit unclear what exactly the block universe interpretation means, but that's because we could not find a true "block" believer to explain it to us.

Your absolutely right it is a dead end.

 

What part about those calcs on those hyperlinks equate to Lorentz ether. Which is a 4d model not a 3d model Don't you understand?

 

I repeat you compared Galilean relativity to SR.

Not Lorentz ether to SR in that link.

 

[..]

I definitely explained Lorentz ether; you know very well that SR uses the math of Lorentz ether, and I explained in great detail how.

For completeness: I use the one way speed of light definition as in http://fourmilab.ch/etexts/einstein/specrel/www/

Thus the speed of light along x' of S' is c-v with respect to S' according to S.

Sorry obviously you can't show the difference mathematically otherwise you would. It is empirically impossible to seperate Lorentz ether and SR using the same transformation rules. Yet you yourself know this fact as you yourself mentioned this detail.

 

Yet you claim to be able to show a difference.[..]

I claim that their is no mathematical difference, and I elaborately demonstrated how the Lorentz ether works in not only creating a constant c for the return speed of light but also in obtaining invariance of c (note the continuing confusion between constant c and invariance; that's the origin of the lack of understanding).

 

[..] Thats funny Tim I haven't seen a single calculation from you in any of your threads in the philosophy forum.

That's funny indeed! Maybe you don't see calculations when you read them, or maybe you forgot to click on hyperlinks.

Consequently you even get your facts wrong, for everyone to see:

 

As a matter of fact I am the only poster that even covered the math involved.

This topic came to a dead end.

In order to do that you have to define what you mean by 'substantial', 'real' etc.

Go for it, I'm all ears.

In my previous post I already asked you to define what you mean by 'physical'.

No I don't, for, once more, that question was elaborate in the mother thread: http://www.scienceforums.net/topic/97105-is-space-time-a-physical-entity-or-a-mathematical-model/

And if you can't explain light propagation that's also OK; it would just have helped to make block universe more convincing.

For the record modern tests have tested isotropy of light to an accuracy of 10^-19. Wiki has 10^-17 but this came out later than the last reference test on wiki.

http://www.google.ca/url?q=https://arxiv.org/pdf/1412.6954&sa=U&ved=0ahUKEwjwmaGj99jQAhVDwVQKHVxlAJEQFggUMAE&usg=AFQjCNEhZHeTyLlenVD-Xem4V95RFXRR8A

Which just goes to show that you still don't understand my question; but we already knew that. Only this is worse, for it also means that you don't even understand that the speed of light is made isotropic by means of Einstein synchronization. Explaining that belongs not to this philosophy forum but to the physics forum (note that my calculation examples imply that fact and that Einstein specifically clarified that already in 1907; if you still have questions about it, start a topic in the relativity forum). It could be that that is the reason why you did not understand my question, as my question concerned the "true" one-way speed of light according to "block" in contrast to the "apparent" one-way speed of light as operationally defined in SR.

And you suddenly asked me questions about the Lorentz ether of which I can't make any sense; in particular:

 

how did you mathematically show Lorentz ether as having a different result than SR

To the contrary, this topic is based on the assumption that a theory cannot give results that differ from its mathematics, and my examples were meant to demonstrate that fact!

Anyway, I have clarified as much as I could; and it appears that -currently- nobody else here is willing or capable of further explaining either the Lorentz ether interpretation or the block universe interpretation by means of clarifying examples. I thus consider this topic from here on to be "on standby".

Thanks for the discussions, which made this topic not only more interesting for onlookers but also for me!

[..] Light propagation doesn't need a medium/ether to be physical. Movement is reading successive events, all frozen and co-existing in 4D block universe. We don't know yet why we experience ourselves as a 3D being evolving in time, but part of our 4D existence, part of the block universe events. We don't know why we experience evolving time. That's for further generations to sort out.

Co-existing events is all you need. 'Real/physical' 3D space/world is section through 4D block universe.

[..]

Light is isotropic in 4D block universe, each observer measures with real/physical clocks and rulers. They all consider light propagation c physical/real.

I think you don't understand how block universe works.

Thanks VanD, I see that you make a serious attempt to explain the block inverse.

You are certainly right that I don't fully understand how the block universe can work as a substantial entity, as opposed to a mere mathematical tool.

Now, by claiming that the 4D "block" is not some kind of a medium, you seem to deviate from other defenders of that interpretation and that you make it less substantial - for what is it then? If you claim that it is nothingness, then this is the wrong thread for you: the starting assumption or postulate of this thread is that there is something substantial (either "Space" or "Spacetime") that we assume in order to explain and make sense of it all, and this thread is discussing two of those interpretations that we can choose from. If you want to argue that neither Space nor Spacetime have substantial existence, then you should continue the discussion in the mother thread.

Is there anyone who can explain with block universe interpretation how and relative to what, light truly isotropically propagates at speed c?

[..] you don't want the math and if your understanding of metaphysics is ignore the math then I have no interest. [..]

That's nonsense, as I demonstrated how the 3D + time interpretation perfectly matches the math and how it makes perfect sense metaphysically. I also explained how light propagation is understood with that interpretation; no need to repeat what I already elaborated one page back (page 12, post # 223). My demand for those who are promoting the 4D space interpretation (any variant of it), is to do the same, and ducking the issue doesn't bring anything.

Why would we 'invent' time if it wasn't already there? Are we that clever and to 'invent' time dilation when things don't quite fit in with our temporal picture? Do animals know the time and thus know when to mate, which is often just a very specific window in the calender, or are they induced by the cyclic behaviour of their environment?

In a way "time" is already there, as what we call "time" is based on the cyclic behaviour of the environment. However it's still our choice to call a certain aspect of what we see in nature "time".

Time can only be what we think it is. [..]

Taken without my elaboration here above, your two statements here are self contradictory - except if you think that nature doesn't exist outside of our fantasy!

[..] The majority of the terminology used in GR/SR regardless of model is rooted in differential geometry. Yet it seems you don't wish to understand the mathematical basis behind the key terminologies.

 

[..]

 

Your right I am not using metaphysics arguments to answer this but the math behind the physics. [..]

The terminology of physics must be rooted in physics; and the issue I raised has nothing to do with geometry but the physical model behind the physics -thus metaphysics. If you are commenting physics terminology with geometric terminology, then indeed no useful discussion is possible.

 

As light is invariant to all observers. Then light [propagation] is obviously symmetric and isotropic. [..]

Here you confound invariance of reference systems with isotropic media! As I elaborated thrice already, if you are a ground observer and according to you light propagates isotropically at speed c relative to you, then according to you it propagates at c-v and c+v relative to the moving car. How do you explain light propagation?

Let me phrase the issue differently, with a reminder with the starting point of this thread. The 3D Space and 4D Spacetime views of reality resulted, among other considerations, from the realisation (as earlier discussed here) that the speed c ("the speed of light in vacuum") must be a characteristic of some kind of medium - either 3D ("Lorentz ether") or 4D ("block universe"). It isn't a characteristic of the emitter or the receiver or of the state of motion of either, and it can't be a characteristic of the observer.

However, "space" and "time" are definitely not substantially of the same nature. 4D Spacetime can therefore not provide a truly homogeneous medium for isotropic light propagation.

Well ,what about my journey to a fixed destination?

 

Say, Alpha Centauri ,4 light years hence I believe.

 

One expedition travels there and back at a speed of c/2 and the other does the journey there and back at a different speed ,say c/10.

 

When they return do they exhibit an identical discrepancy vis a vis the clock they left behind at departure?

 

I can obviously see that ,f they do not then the difference in time dilation(correct term for the aging twin effect?) between the two expeditions must be a function of their speed.

 

 

[..]

They do not; time dilation is a function of speed, as already explained by Einstein in 1905, here in section §4.

The effect of acceleration is indirect, as it can change speed.

Mordred, I'm sorry as you clearly put time and effort in this, but it's hopeless as I'm not talking about anything that you discussed in your last two replies; but I'm hardly surprised, as metaphysics isn't really your thing.

- No, I'm not asking about Lorentz ether

- No, I'm not asking about symmetry of transformation equations

- No, I'm not asking about the Doppler effect

- No, I'm not asking about a "preferred frame"

Instead, I am questioning a serious apparent defect of the block universe interpretation. Maybe someone else who adheres to the block universe interpretation and reads my posts #234 and 236, may be able to answer my question.

And no doubt you are currently on the right side of a revolutionary paradigm. I didn't say "scientists" I said "science"; I was speaking of the the overarching principle of this discipline; the change to the new padradigm still occurs regardless of the feelings of any individual....this is the wonderful thing about science... it doesn't give a shit about ones feelings.

Science happens to be the averaging out of opinions of scientists. As you indicated, those are sometimes in error. Also a new paradigm may be revolutionary but still incorrect; science is just as much affected by fashion as scientists.

In the long term of course much of that is ironed out, simply because generations of scientists die out and are replaced by new ones (that's a paraphrase, not originating with me, but I forgot who said that first).

 

I'm really sorry, I tried looking for the rules but couldn't find them, I have found them now though. I'll be sure to provide a summary next time.

 

Yeah I know scientists are wrong often, and that it's part of the job (I study sciences myself), I just thought it would be fun to make a video about the biggest (interesting) mistakes scientists have made (in recent history). [..]

Better do so, for now the thread is freewheeling on its own, since we don't know which examples you find most interesting.

I think that you are confounding two different experiments by M-M; but sorry, I'm not talking about MM in particular, and neither am I talking about time transformations. Note also that a true one way test (i.e. revealing "true" one-way speed of light) cannot be done, as that would break the relativity principle. However that is not the topic of discussion here. If you don't believe me, please start it as a question in the relativity forum.

I am talking about the physical interpretation of light propagation. If light propagates through a 3D ether, that is without conceptual problems, as I explained earlier on this page.

Already with the car example, the speed of light relative to the car according to a ground observer (the "closing speed") is anisotropic. Thus I asked: how is propagation of light interpreted with the 4D Spacetime (block universe/evolving block) models? What are their "hidden reality" views? Surely the interpretation can't be that light propagation is both truly isotropic and anisotropic! Light can not be truly moving at c relative to an arbitrarily chosen 3D reference system, as that would be self contradictory.

An obvious explanation attempt would be a literal 4D ether, made up of "space and "time". However, for light propagation to be truly isotropic, "time" and "length" should be of the same substance. And we know that this is not true; clocks measure time, and rulers measure length. Thus my question stands.

Mordred I suspect that such a discussion has more chance to take off when it is presented in the relativity forum, as more people are likely to see it.

Meanwhile I suddenly thought of a rather basic issue that has not yet been discussed, and which is directly related to relativity of simultaneity: the isotropy of light propagation.

With 3D Space (Lorentz ether) that's easy to picture: light propagates at c through the ether, the same in all directions. By means of a "local" reference system one can make it appear as if instead the light propagates at c relatively to that reference system. I explained this in detail in post #223 example 4.

It may be useful to point out that the consequence of making light propagation appear to be isotropic relative to the chosen reference system (("closing velocity"), is that it then appears to be anistropic relative to other, "moving" reference systems, such as with for example a "moving" Michelson interferometer. From the perspective that the apparatus is moving, along an arm that is oriented along the direction of motion, the light appears to take more time to traverse it in one direction than in the opposite direction.

How is propagation of light interpreted with the 4D Spacetime (block universe/evolving block) models? What is their "hidden reality" view? Surely the interpretation can't be that light propagation is both truly isotropic and anisotropic!

PS I had not seen your earlier comment which looks very wrong, and probably that's also what swansont referred to (I marked it in red):

[..]
Why more experiments, for more accuracy, when the experiment is wrong?
The more accurate link you gave me earlier, #2, maintains the same wrong geometry.
http://www.relativitycalculator.com/Albert_Michelson_Part_II.shtml
The dotted line path is wrong,
& the incident ray should land (hitting perpendicularly, straight up) at C
(instead of diagonally to the right at C'),
but to do that the mirror C must be much longer to the left
(not even a millimeter experimentally),
(in order to advance (to the) right to the C' position
while getting hit perpendicularly at C).
Is that clear for you?
The reflection at C is based on a (circular) Huygens wavefront.
The incident angle is 90 degrees,
but the reflected angle is double the professor's.
E.g. Michelson allowed himself half of that (correct angle)
split onto both angles, which is wrong,
because 90 degrees (incident) does not exist (in his sketch)
although his experiment is so (=90 degrees, even while moving).
Most calculations don't use Huygen's principle
& so they get the wrong answer.

[..]

You are right that one should use the Huygens principle. If you do it correctly, you will find that the error is much smaller than you claim, and in the other direction. Correct use of that principle with a moving mirror implies that you account for the position of each point of the mirror at the time that the wavefront reaches that point.

By the way, at first also Michelson got that one wrong in his first publication. If I correctly remember, he was corrected by Lorentz.

As a matter of fact, indeed: https://en.wikisource.org/wiki/On_the_Relative_Motion_of_the_Earth_and_the_Luminiferous_Ether

- As corrected by Lorentz, and also (without going in details):

 

It may be remarked that the rays ba_/ and ca_/, do not now meet exactly in the same point a_/, though the difference is of the second order; this does not affect the validity of the reasoning.

Actually, the MM experiment falsified a static aether. Other experiments disprove a dragged aether.

 

[..]

Surely you know better than that! The MMX falsified Newton's mechanics, in particular the Galilean transformations; this was solidly established by Lorentz and Einstein. Maxwell and MM assumed their validity, which seemed at the time so natural that they didn't even mention that assumption. However, the point of the discussion is the calculations, which all of us (except Capiert) hold to be essentially correct, insofar as they were based on that faulty assumption.

[..] That (now) voice_like impression

indicated (=pointed to)

from the (experiment's) sketch in my mind

to look at the experiment('s setup, comparing)

look for its errors (differences).

Do you see any differences

between the sketch & the experiment setup?

Then I noticed on the 2nd arm (=path),

if that was suppose to be a 90 degrees angle to the mirror (b),

why wasn't it so in the diagram fig. 2 (1887)?

Then I thought, uh?

How is that possible?

How can you make a 90 degrees (angle into) not 90 (degrees).

[..]

OK, so if the M&M experiment has a (serious math error (flaw)

& it's not being discussed

& made public,

then what is the reason (=purpose)

for the coverup?

 

Why is it still being promoted?

(To promote relativity? Who knows?)

[..]

 

Sorry but it's unclear to me what error you perceive.

There is a little issue with the reflection angle, and that was discussed in the literature of the time; is that perhaps what you mean? I can dig up one of the old publications next week if you like. For a null result one has to assume length contraction; that also fixes the issue with the reflection angles (that's a detail that is rarely mentioned).

There is no cover-up; only a simplification. While MMX played a motivating role in the development of SR, it was just one of many experiments that led to it.

From a modern perspective however, you can approach the question much more simply.

The Kennedy-Thorndike experiment demonstrated the reality of Lorentz contraction in case of time dilation; and time dilation by the Lorentz factor has been established by means of a number of experiments since then.

When you make a drawing taking that into account, you should find that you will predict a perfect null result for MMX.

PS I see that now the Wikipedia article on this, while still flawed, is much improved, and the issue with the mirror is discussed as well:

https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment#Mirror_reflection

I have a number of those papers at work. I'll check next week; will message you if I find something!

Note: I have no reprints, just copies of a number of his papers.

Apart of one detail, further answering to your points here would just continue the infinite loop, and some of what you try to make me understand happens to be what I already told you. But in a nutshell: SR contains no metaphysics, and physics is concerned with verifiable phenomena.

The detail: I don't ignore what I actually verified myself. It's straightforward to verify the step from Lorentz-1904 (the transformations of Lorentz) to Poincare-1905 (the modern "Lorentz transformations"). If you don't know how, please start it as a topic in the physics section.

We'll no doubt meet again in a future thread.

The purpose of the Lorentz ether was to model and understand electromagnetic phenomena, as a guide for theoretical development (which was extremely successful). Without it, the second postulate is pure magic; or, as Einstein phrased it in 1920: "space without ether is unthinkable; for in such space there [..] would be no propagation of light".

Also, the name "Lorentz transformations" was introduced by Poincare in 1905, and they were first presented by him in their symmetric form.

And I forgot to comment on another remark in your post #99: you wrote "Einstein showed a preferred frame is unnecessary". Well of course, no such assumption was needed for the derivation (from the second postulate!); but may I remind you, the starting point of this discussion happened to be the choice between either a 3D Absolute Space or a 4D Absolute Spacetime, so it's misleading to pretend that the 3D Space concept implies a superfluous entity compared to the alternative.

I discovered thanks to these discussions that it's quite the inverse: as one cannot avoid a form of presentism (to be reasonable one must include the observation of present time, be it by means of "presentism" or by means of "evolving block"), one has with "evolving block" an additional metaphysical entity ("eternal time") that 3D Space can do without.

But now the conversation is really drifting.

I'll abstain from more if it doesn't further contribute to the topic.