Correct phrasing / use of vocabulary for SR

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Main Question or Discussion Point

This post is a continuation of my post
https://www.physicsforums.com/showpost.php?p=4041285&postcount=10
and
https://www.physicsforums.com/showthread.php?t=629655&page=2

PeterDonis and Harrylin are correct I better start a new thread for this.

I repeat my post here.

There is no claim about "optical illusions" but with disagreeing existential "is" statements one creates self contradictions - that's why. However, such a discussion about rather standard* phrasings is indeed off topic here; if you like you can start it as a topic - but please first search this site, it has been discussed already and perhaps one of the old threads is still open.

* you can even find "appear" (instead of "is") here:
http://www.fourmilab.ch/etexts/einstein/specrel/www/


Thanks for the link to Einstein's 1905 paper. The english translation. I hope you ever read the original german paper:
http://nausikaa2.mpiwg-berlin.mpg.de/cgi-bin/toc/toc.x.cgi?dir=Einst_Zurel_de_1905&step=thumb
I did it for you. I speak flemish which is close to german. That helps a lot.

Let me first show you the verbs in the english and german versions:

>>>>>>>>>>>>>>>>>>>
It is known that Maxwell's electrodynamics—as usually understood at the present time—when applied to moving bodies, leads to asymmetries which do not appear to be inherent in the phenomena.

Daß die Elektrodynamik Maxwells -- wie dieselbe gengen-
wärtig aufgefaßt zu werden pflegt -- in ihrer Anwendung auf
bewegte Körper zu Asymmetrien führt, welche den Phänomenen
nicht anzuhaften scheinen, ist bekannt.

-------
It might appear possible to overcome all the difficulties attending the definition of “time” by substituting “the position of the small hand of my watch” for “time.”

Es könnte scheinen, daß alle die Definition der ,,Zeit“ be-
treffenden Schwierigkeiten dadurch überwunden werden könnten,

------
Thus, whereas the Y and Z dimensions of the sphere (and therefore of every rigid body of no matter what form) do not appear modified by the motion, the X dimension appears shortened in the ratio

Während also die Y - und Z-Dimension der Kugel (also
auch jedes starren Körpers von beliebiger Gestalt) durch die Be-
wegung nicht modifiziert erscheinen, erscheint die X-Dimension
im Verhältnis

------
We still have to find the amplitude of the waves, as it appears in the moving system. If we call the amplitude of the electric or magnetic force A or A' respectively, accordingly as it is measured in the stationary system or in the moving system, we obtain

Wir haben nun noch die Amplitude der Wellen, wie
dieselbe im bewegten System erscheint, zu suchen. Nennt
man A bez. A' die Amplitude der elektrischen oder magne-
tischen Kraft im ruhenden bez. im bewegten System gemessen,
so erhält man

-----
It follows from these results that to an observer approaching a source of light with the velocity c, this source of light must appear of infinite intensity.

Es folgt aus den entwickelten Gleichungen, daß für einen
Beobachter, der sich mit der Geschwindigkeit V einer Licht-
quelle näherte, diese Lichtquelle unendlich intensiv erscheinen
müßte.

<<<<<<<<<<<<<<<<<<<<<<<<<<

You noticed that Einstein used two different verbs: 'scheinen' and 'erscheinen'. He doesn't mix these at random. They have different meanings:

'Sheinen' means: illusion - an appearance that does not correspond to reality - it appears so, but it may not be true - what you see is mere appearance - only outward show, things are not what they seem to be, etc. (Anschein= farce, sham, make-believe, pretence etc...)

'Erscheinen' is more: as it shows, come to light, as it is, etc.

In the english version 'sheinen' and 'erscheinen' are translated by one verb only: 'appear'. Strictly speaking the translation is not wrong (ask google to translate the english words and somehow you will find 'appear'), but the very important difference in meaning in german disappears in the english translation. Or at least 'might very well' get lost. I suppose that in english one can use the verb 'appear' in both meanings as long as the context makes clear what the semantics are. In the english 1905 paper translation that's not so obvious as in the original german text. Prove is that in thousands of texts dealing with SR the english 'appears' is often replaced by 'seems', which is a synonym of 'appears', but not the correct one to match the german significance. 'Seems' refers to 'scheins' (= illusion). [STRIKE]Dalespam's[/STRIKE] [edit: PeterDonis'] use of 'apparent' (= seeming, not proven real, illusive, illusory, likely, ostensible) is also prove of this, otherwise there would be no need to add that adjective. And his 'sense' of simultaneity is superb poetry, but no physics.
(The same mistake occurs in other translations, because a lot of them are translations of the/an english text. I will not go into that.)
Worse is that authors of those ambiguous texts (because of the use of 'appear' without proper explanation, or the word 'seem'), are probably not aware of the real significance of SR: trains ARE shorter, events ARE not simultaneous for one observer and ARE simultaneous for the other, meaning both observers ARE in different 3D worlds. etc. Those authors (not unlike many PF members) hide themselves in a type of Lorentz Ether Theory interpretation of the Lorentz Transformations as illusionary abstract calculations, because it matches perfectly the incorrect 'seems' interpretation of the german 'erscheins'. Unfortunately all those hundreds of thousands of people over the last 100 years are wrong. That's the most dreadfull and horrible scenario Einstein could ever imagine.
I hope I made my point clear why I get extremely nervous, with a sense of (to say the least) acute desperation, when I am confronted with a text using 'appear' vocabulary. (There is a tree in front of you. Nobody says that a tree appears in front of you. And for me a moving train is shorter, not appear shorter. A blitz of 10.000 volt shivers through my body. And make it a 20.000 volt when I read that the train 'seems' shorter.
And over the last 20 years it was (and still is) flabbergasting to read how people try to defend that false, erroneous approach of SR.
 
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Answers and Replies

  • #2
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No, because it helps to have *some* standard phrasing, even if it's clumsy.
Even if the clumsy one is wrong? What you write is wrong. 'Sense' of simultaneity is -no offence- ridiculous.
Do you know of a non-clumsy one?
Of course. Scrap all those ambiguous words. Easy cake. Talk about simultaneity, not the 'sense' of simultaneity. Moving trains are shorter, not 'appear' shorter, and definitely not 'seems' to get shorter (for reasons explained in my post). Is that so difficult? In his 1905 paper Einstein never uses 'sense' of simultaneity. Nor that time 'seems' to run slow, nor lengths that 'seem' to get shorter etc. So why are you guys using this vocabulary? Because everybody does? I said it elsewhere: people copy from everybody, even if what they copy is wrong. If enough people copy it becomes 'political correct' and even the only thruth. Even on a physics forum. That's dangerous for scientific evolution.

Face what Einstein found out and accept the consequences: block universe, even if you feel uncomfortable with the consequences (such as free will). I know that most people refuse to take that step. So they look for clumsy interpretations of SR or stick to Lorentz Transformations as illusions in LET...
.
 
  • #3
3,872
88
This post is a continuation of my post
https://www.physicsforums.com/showpost.php?p=4041285&postcount=10
and
https://www.physicsforums.com/showthread.php?t=629655&page=2

PeterDonis and Harrylin are correct I better start a new thread for this.

I repeat my post here.

Thanks for the link to Einstein's 1905 paper. The english translation. I hope you ever read the original german paper:
http://nausikaa2.mpiwg-berlin.mpg.de/cgi-bin/toc/toc.x.cgi?dir=Einst_Zurel_de_1905&step=thumb
I did it for you. I speak flemish which is close to german. That helps a lot.
Thanks for the elaboration. I speak Dutch which is extremely close to flemish :smile:
Let me first show you the verbs in the english and german versions:

>>>>>>>>>>>>>>>>>>>
It is known that Maxwell's electrodynamics—as usually understood at the present time—when applied to moving bodies, leads to asymmetries which do not appear to be inherent in the phenomena.

Daß die Elektrodynamik Maxwells -- wie dieselbe gengen-
wärtig aufgefaßt zu werden pflegt -- in ihrer Anwendung auf
bewegte Körper zu Asymmetrien führt, welche den Phänomenen
nicht anzuhaften scheinen, ist bekannt.

-------
It might appear possible to overcome all the difficulties attending the definition of “time” by substituting “the position of the small hand of my watch” for “time.”

Es könnte scheinen, daß alle die Definition der ,,Zeit“ be-
treffenden Schwierigkeiten dadurch überwunden werden könnten,

------
Thus, whereas the Y and Z dimensions of the sphere (and therefore of every rigid body of no matter what form) do not appear modified by the motion, the X dimension appears shortened in the ratio

Während also die Y - und Z-Dimension der Kugel (also
auch jedes starren Körpers von beliebiger Gestalt) durch die Be-
wegung nicht modifiziert erscheinen, erscheint die X-Dimension
im Verhältnis

------
We still have to find the amplitude of the waves, as it appears in the moving system. If we call the amplitude of the electric or magnetic force A or A' respectively, accordingly as it is measured in the stationary system or in the moving system, we obtain

Wir haben nun noch die Amplitude der Wellen, wie
dieselbe im bewegten System erscheint, zu suchen. Nennt
man A bez. A' die Amplitude der elektrischen oder magne-
tischen Kraft im ruhenden bez. im bewegten System gemessen,
so erhält man

-----
It follows from these results that to an observer approaching a source of light with the velocity c, this source of light must appear of infinite intensity.

Es folgt aus den entwickelten Gleichungen, daß für einen
Beobachter, der sich mit der Geschwindigkeit V einer Licht-
quelle näherte, diese Lichtquelle unendlich intensiv erscheinen
müßte.

<<<<<<<<<<<<<<<<<<<<<<<<<<

You noticed that Einstein used two different verbs: 'scheinen' and 'erscheinen'. He doesn't mix these at random. They have different meanings:

'Sheinen' means: illusion - an appearance that does not correspond to reality - it appears so, but it may not be true - what you see is mere appearance - only outward show, things are not what they seem to be, etc. (Anschein= farce, sham, make-believe, pretence etc...)

'Erscheinen' is more: as it shows, come to light, as it is, etc. [...]
This is where knowing flemish/Dutch comes in handy, as you also said. However, despite that we both (should!) know the meaning of (Dutch) "schijnt" vs. "verschijnt", we come to almost contrary conclusions! :bugeye:

To make sure, I checked the dictionaries, both German and Dutch. I found that, just like in Dutch:
- Scheinen is mere appearance, but likely not real;
- Erscheinen is showing, appearing *

In a nutshell: I would translate "scheint" with "seems", and "erscheint" with "appears".

That fits perfectly with Einstein's use of the words: the first points to faulty appearance; and the second to measurement outcomes. As a reminder, I wrote (bold face added):

There is no claim about "optical illusions" but with disagreeing [..] "is" statements one creates self contradictions [..]

you can even find "appear" (instead of "is") here:
http://www.fourmilab.ch/etexts/einstein/specrel/www/[/QUOTE]


* ADDENDUM: the Dutch equivalent of the noun "Erscheinung" (verschijning) is correctly indicated by translate.google.com as appearance and even apparition. See : http://translate.google.com/#auto/en/erscheinung
http://translate.google.com/#auto/en/verschijning
 
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  • #4
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hope I made my point clear why I get extremely nervous, with a sense of (to say the least) acute desperation, when I am confronted with a text using 'appear' vocabulary. (There is a tree in front of you. Nobody says that a tree appears in front of you. And for me a moving train is shorter, not appear shorter.
I agree with you. I only like to use the word appear when I am talking about visual SR effects like Terrell rotation or Doppler shift or aberration. When I am talking about calculated effects, such as length contraction or time dilation or relativity of simultaneity, then I think that the word appear conveys the connotation that SR effects are optical illusions.

However, I think that more important than that is to emphasize the importance of specifying the frame for frame [STRIKE]invariant[/STRIKE] variant quantities. I.e. The spaceships length is meaningless, but the spaceships length wrt frame X has meaning.

EDIT: see below, I accidentally said invariant when I meant variant.
 
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  • #5
ghwellsjr
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However, I think that more important than that is to emphasize the importance of specifying the frame for frame invariant quantities. I.e. The spaceships length is meaningless, but the spaceships length wrt frame X has meaning.
Don't you mean "frame variant"?
 
  • #6
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Don't you mean "frame variant"?
Oops, yes, you are right.
 
  • #7
ghwellsjr
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I agree with you. I only like to use the word appear when I am talking about visual SR effects like Terrell rotation or Doppler shift or aberration.
All visual effects are optical so of course "appear" is appropriate.
When I am talking about calculated effects, such as length contraction or time dilation or relativity of simultaneity, then I think that the word appear conveys the connotation that SR effects are optical illusions.
These calculated effects are not optical so the word "appear" is not appropriate. But how can something that is not optical be an optical illusion?

But it's not just that these non-optical effects are calculated, it's that they are based on a specific definition derived from the concept of a frame, which is the point you were making in the last part of your post.

The real issue from the previous thread for which this new thread is designed not to hijack the previous thread is the word "see". It's to the point now that when we want to use the word "see" to apply to optical effects, we have to say "actually see" to distinguish between the calculated effects for which the word "see" is also applied but not in an optical sense. I think a lot of people believe that these frame-dependent calculated effects are optical but since they depend on the frame, they are illusions.

I don't see how "appear" versus "seem" resolves this issue. It's always going to take phrases and extra commentary to clarify what we mean. [Notice how I just used the word "see" in a non-optical sense.]
 
  • #8
Nugatory
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Considering just length contraction, for the sake of definiteness:

The problem with "appears shorter" and similar words is that they suggest that the contraction is "not real", somehow an "illusion" or "just apparent".

The problem with the bald statement ("moving objects ARE shorter") is that it leads to endless confusion among people who haven't worked through the underlying math. Too many threads here start with someone asking "the faster I go the shorter and heavier I get, right?" with the unspoken assumption that this effect is experienced by the moving observer.

The best I've been able to come up with is "I will measure the length of an object to be less when it is moving relative to me".
 
  • #9
cepheid
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The problem with the bald statement ("moving objects ARE shorter") is that it leads to endless confusion among people who haven't worked through the underlying math. Too many threads here start with someone asking "the faster I go the shorter and heavier I get, right?" with the unspoken assumption that this effect is experienced by the moving observer.

The best I've been able to come up with is "I will measure the length of an object to be less when it is moving relative to me".
But the thing is, although such direct statements may cause this confusion, they shouldn't. And one need not work through a bunch of math to realize it. All one has to do is think about it carefully for a few seconds. I have a textbook on SR
That summarizes time dilation and length contraction as follows:

"Moving clocks run slow."

"Moving objects are shortened."

At first this succinct wording confused me, and I was tempted to add on the additional phrase, "as measured in the lab frame relative to which the objects are moving." But I eventually realized that this additional phrase is compleletly redundant. The idea that an observer who is moving along with a moving rod would see it shortened is inherently flawed, because in that case, the measurement is being done in the rest frame of the rod. So in that case, it wouldn't be a moving rod, would it? The same thing goes for time dilation. I'm never going to experience time as running more slowly than usual because, guess what? I'm not moving. That other guy is.

So in these direct ("bald") statements that you cautioned against, I think that the word "moving" says all that needs to be said.
 
  • #10
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Considering just length contraction, for the sake of definiteness:

The problem with "appears shorter" and similar words is that they suggest that the contraction is "not real", somehow an "illusion" or "just apparent". [..] The best I've been able to come up with is "I will measure the length of an object to be less when it is moving relative to me"
To me there is a big qualitative difference between "just apparent" (=seems) and "apparent" (= how it looks like at face value). "Apparent"/"appears" is the best word that I know in English as shorthand for "as measured by so-and-so", in order to differentiate from an absolute "is". Of course, we also commonly use "is" for the same whenever we assume that the reader will understand that we don't mean it in an absolute way. For example, most people understand that "the rod is moving" is only meant in a relative way.

So, I ended up using more or less the same kind of terminology as Einstein: frequently I use "is", but often I prefer more careful statements to stress that we discuss non-absolutes.
 
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  • #11
cepheid
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Okay I thought about it some more and realized that the confusion you (Nugatory) mention will arise for people who don't understand that all motion is relative, and who think they something can be "at rest", or "moving" in some absolute sense. So, when these people read about length contraction with the wording "moving objects ARE shortened," they will interpret it to mean that as long as the object is "moving" in this "universally agreed upon" sense, then all observers will perceive it to be shortened, even the observer who is himself the moving object.

So that's a misconception that needs to be addressed first.
 
  • #12
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[..] These calculated effects are not optical so the word "appear" is not appropriate.
"Erscheint" is just as "optical" as "appears"; what is no doubt meant here, is that it is not an absolute truth (an invariant) but a matter of observation of measurement instruments, and which differs from one reference system to another (a variant). I would expect that after one century of using such terminology, this would be understood - not?!
[..] I don't see how "appear" versus "seem" resolves this issue. It's always going to take phrases and extra commentary to clarify what we mean. [Notice how I just used the word "see" in a non-optical sense.]
Good one! :smile:
"Appear" is merely a succinct part of such extra commentary.
 
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  • #13
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Of course. Scrap all those ambiguous words. Easy cake. Talk about simultaneity, not the 'sense' of simultaneity. Moving trains are shorter, not 'appear' shorter, and definitely not 'seems' to get shorter (for reasons explained in my post). Is that so difficult? In his 1905 paper Einstein never uses 'sense' of simultaneity. Nor that time 'seems' to run slow, nor lengths that 'seem' to get shorter etc. So why are you guys using this vocabulary? Because everybody does? I said it elsewhere: people copy from everybody, even if what they copy is wrong. If enough people copy it becomes 'political correct' and even the only thruth. Even on a physics forum. That's dangerous for scientific evolution.
Agreed. The reality of physics is what's measured/observed.
 
  • #14
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88
Even if the clumsy one is wrong? What you write is wrong. 'Sense' of simultaneity is -no offence- ridiculous.

Of course. Scrap all those ambiguous words. Easy cake. Talk about simultaneity, not the 'sense' of simultaneity. [..]
Hmm ... simultaneity can be understood in an absolute way - and that's not at all what is meant. Insisting on scrapping of "ambiguous words" that were included to clarify the meaning is not helpful. And this has nothing to do with "truth", more with free speech! :rolleyes:
Face what Einstein found out and accept the consequences: block universe, even if you feel uncomfortable with the consequences (such as free will). I know that most people refuse to take that step. So they look for clumsy interpretations of SR or stick to Lorentz Transformations as illusions in LET...
Do I smell here an attempt to philosophical (non-scientific) indoctrination? I certainly think so!
 
  • #15
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Agreed. The reality of physics is what's measured/observed.
Modern physics is concerned with (and limited to!) describing what is really measured, and not what "truly is" - is that what you mean? That certainly is what Einstein meant when he used "appears" ("erscheint") instead of "is".

But if you meant to make a claim about unmeasured "reality", then that goes beyond the physics ("meta physics") and you can't prove it scientifically.
 
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  • #16
ghwellsjr
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[..] These calculated effects are not optical so the word "appear" is not appropriate.
"Erscheint" is just as "optical" as "appears"; what is no doubt meant here, is that it is not an absolute truth (an invariant) but a matter of observation of measurement instruments, and which differs from one reference system to another (a variant). I would expect that after one century of using such terminology, this would be understood - not?!
Please don't take me out of context. I was specifically referring to the calculated effects that DaleSpam just mentioned:
When I am talking about calculated effects, such as length contraction or time dilation or relativity of simultaneity, then I think that the word appear conveys the connotation that SR effects are optical illusions.
These effects are not "a matter of observation of measurement instruments". An observer cannot optically observe these effects either with his naked eyes or with the help of instruments because they are always, because they involve moving objects, remote observations and we have to factor out the time delay caused by the propagation of light which always involves an arbitrary assumption about how long that takes and then a calculation. You need a well-defined frame with coordinates to discuss those three non-optical effects.
 
  • #17
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Modern physics is concerned with (and limited to!) describing what is really measured, and not what "truly is" - is that what you mean? That certainly is what Einstein meant when he used "appears" ("erscheint") instead of "is".

But if you meant to make a claim about unmeasured "reality", then that goes beyond the physics ("meta physics") and you can't prove it scientifically.
The quoted part in my reply is the context.

Yes it is limited to what is observed/measured. Which makes it odd that it's an "issue" i.e. terming length contraction / time dilation as appearances / illusions or "seems to".

Unmeasured could be as simple as what the some other observer measures, not at all beyond physics, just beyond what is measurable. (i.e. i can't measure your proper time/length, just my own, generally speaking)
 
  • #18
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Please don't take me out of context. I was specifically referring to the calculated effects that DaleSpam just mentioned: [length contraction or time dilation or relativity of simultaneity]

These effects are not "a matter of observation of measurement instruments". An observer cannot optically observe these effects either with his naked eyes or with the help of instruments because they are always, because they involve moving objects, remote observations and we have to factor out the time delay caused by the propagation of light which always involves an arbitrary assumption about how long that takes and then a calculation. You need a well-defined frame with coordinates to discuss those three non-optical effects.
Effects that are predicted but not measurable (or at least, that cannot be demonstrated) in principle are not part of modern physics. Physics is an empirical science and those effects have been demonstrated by means of measurements, although not yet entirely to the satisfaction of all.

But indeed, those measurements very much depend on the setting of the instruments. We are not describing physical reality of what is being measured but instead, we describe our perception of physical reality as affected by our chosen perspective. If you know a better word for that than "appears", please provide us with it! :tongue2:

Note: while we seem to disagree about words, I have the impression that we basically say the same!
 
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  • #19
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[..] Unmeasured could be as simple as what the some other observer measures, not at all beyond physics, just beyond what is measurable. (i.e. i can't measure your proper time/length, just my own, generally speaking)
Sorry, I meant unmeasurable in principle. It sounded as if you perhaps made a statement about "what truly is", and not about what our instruments show, partly due to our assumptions (see also my foregoing post).
 
  • #20
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Sorry, I meant unmeasurable in principle. It sounded as if you perhaps made a statement about "what truly is", and not about what our instruments show, partly due to our assumptions (see also my foregoing post).

Well if you subscribe to what is measurable/observed is your physical reality I kinda did make a statement about "what truly is", just that "what truly is" isn't absolute in the exact same sense as simultaneity isn't absolute.
 
  • #21
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Thanks for the elaboration. I speak Dutch which is extremely close to flemish :smile:
Prima, maar daarmee is het probleem helaas nog niet opgelost...;)
This is where knowing flemish/Dutch comes in handy, as you also said. However, despite that we both (should!) know the meaning of (Dutch) "schijnt" vs. "verschijnt", we come to almost contrary conclusions! :bugeye:
(In a dutch translation even 'vertoond' is used). But in Dutch you have the same problem. (I'll keep it short for our english speakers). Your 'schijnt' and 'verschijnt' are correct but you should know what happens in dutch literature: instead of 'verschijnt' rather 'lijkt' is used: de trein 'lijkt' korter te worden, de tijd 'lijkt trager te lopen' (the equivalent of 'seems'...). That's wrong. In my post I do not state that 'appear' is 100 % wrong, but it will be interpreted wrong by most of the readers. Definitely laymen.
To make sure, I checked the dictionaries, both German and Dutch. I found that, just like in Dutch:
- Scheinen is mere appearance, but likely not real;
- Erscheinen is showing, appearing *

In a nutshell: I would translate "scheint" with "seems", and "erscheint" with "appears".
It's not 100% wrong, but you play with fire.
That fits perfectly with Einstein's use of the words: the first points to faulty appearance; and the second to measurement outcomes.
No, it does not fit 'perfectly'. The reader can interpret it as 'not as it is'.
As a reminder, I wrote (bold face added):

There is no claim about "optical illusions" but with disagreeing [..] "is" statements one creates self contradictions [..]

you can even find "appear" (instead of "is") here:
http://www.fourmilab.ch/etexts/einstein/specrel/www/

* ADDENDUM: the Dutch equivalent of the noun "Erscheinung" (verschijning) is correctly indicated by translate.google.com as appearance and even apparition. See : http://translate.google.com/#auto/en/erscheinung
http://translate.google.com/#auto/en/verschijning
I know. I never said in my post that 'appear' is a completely wrong translation. But using 'appears' has big consequences. Most people read is as 'seems' (or dutch 'lijkt'). That's wrong. And why do all those authors in thousands of articles and books writing 'seems' (or 'lijkt')? because they interpret 'appear' wrongly, or do not understand what SR is all about.
 
  • #22
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All visual effects are optical so of course "appear" is appropriate.

These calculated effects are not optical so the word "appear" is not appropriate. But how can something that is not optical be an optical illusion?

But it's not just that these non-optical effects are calculated, it's that they are based on a specific definition derived from the concept of a frame, which is the point you were making in the last part of your post.

The real issue from the previous thread for which this new thread is designed not to hijack the previous thread is the word "see". It's to the point now that when we want to use the word "see" to apply to optical effects, we have to say "actually see" to distinguish between the calculated effects for which the word "see" is also applied but not in an optical sense. I think a lot of people believe that these frame-dependent calculated effects are optical but since they depend on the frame, they are illusions.

I don't see how "appear" versus "seem" resolves this issue. It's always going to take phrases and extra commentary to clarify what we mean. [Notice how I just used the word "see" in a non-optical sense.]
I quite agree with this. The context should be clear and most of the time it's not.
I didn't mention the 'see' problem you mention, but indeed that too is a risk. The time dilation en length shortening are no 'optical effects' nor optical illusions'', but yes we see them slower and shorter. I know it's confusing, therefore one should be very careful using certain vocabulary. But on PF I do not see (sic) any problems with the 'see' aspect.
 
  • #23
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Considering just length contraction, for the sake of definiteness:

The problem with "appears shorter" and similar words is that they suggest that the contraction is "not real", somehow an "illusion" or "just apparent".

The problem with the bald statement ("moving objects ARE shorter") is that it leads to endless confusion among people who haven't worked through the underlying math. Too many threads here start with someone asking "the faster I go the shorter and heavier I get, right?" with the unspoken assumption that this effect is experienced by the moving observer.

The best I've been able to come up with is "I will measure the length of an object to be less when it is moving relative to me".
That's a good start, although I have come across some reactions stipultaring that " Oh, you MEASURE the train shorter; but the train IS not shorter... " Gotcha.

There's a way to get around that.
IF one writes that you measure the train shorter he should also have written that he measures the immobile not shorter. But if you write: the train is 100 m long, but when he moves I measure him 80m long, then I get nervous... Beter: is ... is . OR: measure .... measure.
 
  • #24
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But the thing is, although such direct statements may cause this confusion, they shouldn't. And one need not work through a bunch of math to realize it. All one has to do is think about it carefully for a few seconds. I have a textbook on SR
That summarizes time dilation and length contraction as follows:

"Moving clocks run slow."

"Moving objects are shortened."

At first this succinct wording confused me, and I was tempted to add on the additional phrase, "as measured in the lab frame relative to which the objects are moving." But I eventually realized that this additional phrase is compleletly redundant. The idea that an observer who is moving along with a moving rod would see it shortened is inherently flawed, because in that case, the measurement is being done in the rest frame of the rod. So in that case, it wouldn't be a moving rod, would it? The same thing goes for time dilation. I'm never going to experience time as running more slowly than usual because, guess what? I'm not moving. That other guy is.

So in these direct ("bald") statements that you cautioned against, I think that the word "moving" says all that needs to be said.
You got it right.
One normally does not say that an immobile clock 'appears' to run normal. Or a immobile train 'appears' 100 m long.
So why doing it for the moving clock or trains?
There is no reason fo doing it!
"Moving clocks run slow." "Moving objects are shortened."
You got it!
 
  • #25
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To me there is a big qualitative difference between "just apparent" (=seems) and "apparent" (= how it looks like at face value). "Apparent"/"appears" is the best word that I know in English as shorthand for "as measured by so-and-so", in order to differentiate from an absolute "is". Of course, we also commonly use "is" for the same whenever we assume that the reader will understand that we don't mean it in an absolute way. For example, most people understand that "the rod is moving" is only meant in a relative way.

So, I ended up using more or less the same kind of terminology as Einstein: frequently I use "is", but often I prefer more careful statements to stress that we discuss non-absolutes.
Why use 'appearent' or 'appears' if one normally does not say that an immobile clock 'appears' to run normal or is apparent running normal? Do you say that an immobile train has an apparent length of 100 m long? So why doing it for the moving clock or trains?
 

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