Real Lorentz–FitzGerald contraction

  • #76
Ich
Science Advisor
1,931
1
Einstein's principle of covariance explicitly states that anything that can be altered by a change of coordinates ( eg LT) is not a real physical effect !
Length contraction is not a changing component of a covariant quantity like a vector (time dilatation is). It is the comparison of the length of two different vectors. These vectors really have different length, but I don't think that it's appropriate to speak of one and the same thing really contracting.
Nothing contracts, one simply compares different things, depending on the reference frame.
 
  • #77
jtbell
Mentor
15,618
3,650
There was a young fellow named Bob,
Who was eating a shami kebab.
His twin, on a trip, in a fast rocket ship
Saw the shami contracted, by jeepers!
Gotta make the rhyme come out right... hmmm... last line:

Saw the kabab had shrunk to a knob!

Not quite up to the one about the fellow named Fisk, but it will do.
 
  • #78
Hans de Vries
Science Advisor
Gold Member
1,089
23
Thanks Hans de Vries. I've already cited your delicious book at #28 and #45.
Hi, Helder.

Special Relativity is generally teached first using only space and time and the
postulate that the laws of physics should be the same independent of the boost
or rotation of the reference frame. Live as we know would be quite unlikely if
this wasn't the case. So, somehow nature manages to create the conditions
we need.

In my book I work the other way around. The aim is to derive the postulates, as
well as the invariance under boosts and rotation from the relativistic wave equations.

Interesting is that the symmetry isn't perfect. Physics isn't the same under parity
inversion. The world we see in the mirror can not physically exist in each and every
detail because the electroweak force is not the same in a mirrored world.

But then, we don't need this symmetry to survive. We can rotate, we can change
velocity but as long as we don't mirror our self we can't get problems because of
different laws of physics. Nature does a wonderful job in creating the necessary
symmetries but it doesn't care about the ones we don't need.


Regards, Hans
 
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  • #79
30,025
6,419
All relativistic wave equations exhibit physical Lorentz contraction. ... The proof can't hardly be any simpler.
It is a very simple proof that I like very much except for one thing. You have not defined the word "physical" so it is unclear to me that you have proved physicality. For example, the same proof would be valid for a computer simulation of the relativistic wave equation, would that imply that the computer simulation is physical? Or, you could do the exact same proof for waves in other dimensions, would those then be physical?

You have certainly derived length contraction in a particularly pleasing and elegant way, and you have therefore shown that any system which obeys the relativistic wave equation will demonstrate length contraction. But without a solid definition of the word "physical" you cannot say that you have proven that length contraction is physical.

By the way, unlike "real" I do have a definition of "physical" which I like:
Physical - of or pertaining to physics.

Length contraction pertains to physics so it is physical. (my proof is even simpler)
 
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  • #80
252
0
...
I do have a definition of "physical" which I like:
Physical - of or pertaining to physics.

Length contraction pertains to physics so it is physical.
circular definition. is not a definition at all (pt- tautologia, en - ??)

how could you, mr. Dalespam, have such a profound misunderstanding of 'real' versus 'frame dependent', artifact,... since the begining of this discussion?

I use the Poincaré version of 'measuring' that I quoted above.
'rigid rods' are dead, I beleived since GR , but I found that Poincare' did it sooner.
-----------------

mr. Hans de Vries : Einstein paper has a move where a symetry appears, it was when he made psi(V)=psi(-V)=1, and ... ,a generalized lorentz contraction with some nuances, ...can appear someday
 
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  • #81
30,025
6,419
circular definition. is not a definition at all (pt- tautologia, en - ??)
My definition of physical is not circular.
how could you, mr. Dalespam, have such a profound misunderstanding of 'real' versus 'frame dependent', artifact,... Since the begining of this discussion?
If you believe that you have a good definition of "real" then I would be glad to hear it and thereby clear up my profound misunderstanding.
 
  • #82
252
0
To those that do not know the concept of circular definition, see: http://en.wikipedia.org/wiki/Circular_definition" [Broken], (tautology , from greek)

The concept of 'real' is a philosophical concern. Plato, Kant, Berkeley ...
It is a never ending story if you wish to adress those issues. I skip.
I am a simple minded one and can use the sketch/art work at post #2 to understand the level of reality I meant.
---------------------------------------------------

In post #59 I've said "OK, there is no way to distinguish experimentally the existence of an 'absolute referential'.
By the rules of this forum I will not try to show you differently.
But the its existence is a different issue and, in another thread, having the time, I will try to show why I consider it mandatory."

Mr. A.T. in post #61 replied : "Then it is not physics. " to the sentence "...no way to distinguish experimentally..."
and replied "In physics it is the same." to the sentence "But the its existence is a different issue".

I'will focus my attention to clarify what I meant in post #59 and to show that it is a misconception the usual perception that it is fruitless and not meaningful the pursue of 'absolute rest frame'.
I remember that it is extremelly difficult IMO, unreasonable, to maintain sentences that deny some outcome at 'the end of a path' without actually explore the 'path'.
 
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  • #83
5,428
291
Length contraction is not a changing component of a covariant quantity like a vector (time dilatation is). It is the comparison of the length of two different vectors. These vectors really have different length, but I don't think that it's appropriate to speak of one and the same thing really contracting.
Nothing contracts, one simply compares different things, depending on the reference frame.
Thanks, Ich.
 
  • #84
30,025
6,419
The concept of 'real' is a philosophical concern. Plato, Kant, Berkeley ...
It is a never ending story if you wish to adress those issues. I skip.
I completely agree with this.

However, now I have a hard time understanding why you chose to place a thread entitled "Real Lorentz–FitzGerald contraction" in the physics sub-forum when you seem to agree that it fits better in the philosophy sub-forum. I also do not understand your previous rather dismissive comment about me having "a profound misunderstanding of 'real'" when it turns out that not only do I correctly understand the issue but you share my understanding.

Your present statement seems wholly at odds with your entire previous approach.
 
  • #85
252
0
copy/paste from post #72

"REAL"
Quoting Poincaré (1906) On the dynamics of the electron:
"How do we go about measuring?
The first response will be: we transport objects considered to be invariable solids, one on top
of the other. But that is no longer true in the current theory if we admit the Lorentzian
contraction. In this theory, two lengths are equal, by definition, if they are traversed by
light in equal times.
"

Can I presume that no important paper can be presented against the "Real Lorentz-Fitzgerald-Poincaré' length contraction, nor experiment?
 
  • #86
30,025
6,419
That is a definition of "length", not a definition of "real". How can you possibly have evidence either for or against "real Lorentz contraction" if you cannot even define "real"?
 
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