But What Does Einstein Mean - Really? [Relativity]

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From: Sue... on 2 Jun 2010 19:29

On Jun 2, 10:57 am, train <gehan.ameresek...(a)gmail.com> wrote:
> Much discussion has taken place about SRT, however much of it seems to
> alternate between what Einstein said, what he meant, what he is taken
> to have meant and modern interpretations of the Theory Of Special
> Relativity
>
> Going back to the original document written by AE at
>
> http://www.bartleby.com/173/7.html
>
> we may be able to discern what he said and what he meant, at least,
> and discuss the self - consistency of the theory from this point
>
> "THERE is hardly a simpler law in physics than that according to which
> light is propagated in empty space. Every child at school knows, or
> believes he knows, that this propagation takes place in straight lines
> with a velocity c = 300,000 km./sec"
>
> First question: What does he mean by 'empty space?' If space is empty
> there are no reference points against which to measure the speed of
> light. Should he not have said that the velocity of light between two
> points in empty space is c = 300,000 km /sec ?

The modern interpretation does not mean *empty*.

<< where epsilon_0 and mu_0 are physical constants which
can be evaluated by performing two simple experiments
which involve measuring the force of attraction between
two fixed charges and two fixed parallel current carrying
wires. According to the relativity principle, these experiments
must yield the same values for epsilon_0 and mu_0 in all
inertial frames. Thus, the speed of light must be the
same in all inertial frames. >>
http://farside.ph.utexas.edu/teaching/em/lectures/node108.html

"What is the Interstellar Medium?"
http://espg.sr.unh.edu/ism/what1.html

http://en.wikipedia.org/wiki/Impedance_of_free_space

Sue...

From: train on 2 Jun 2010 19:59

From: train on 2 Jun 2010 20:05

On Jun 3, 3:44 am, harald <h...(a)swissonline.ch> wrote:
> On Jun 2, 4:57 pm, train <gehan.ameresek...(a)gmail.com> wrote:
>
> > Much discussion has taken place about SRT, however much of it seems to
> > alternate between what Einstein said, what he meant, what he is taken
> > to have meant and modern interpretations of the Theory Of Special
> > Relativity
>
> > Going back to the original document written by AE at
>
> >http://www.bartleby.com/173/7.html
>
> That is a popular account. Here is a translation of his original
> document:
>
> http://www.fourmilab.ch/etexts/einstein/specrel/www/
>
> In case something isn't clear, you do well to compare those two; the
> second is a summary of the first.
>
> > we may be able to discern what he said and what he meant, at least,
> > and discuss the self - consistency of the theory from this point
>
> > "THERE is hardly a simpler law in physics than that according to which
> > light is propagated in empty space. Every child at school knows, or
> > believes he knows, that this propagation takes place in straight lines
> > with a velocity c = 300,000 km./sec"
>
> Yes.
>
> > First question: What does he mean by 'empty space?'
>
> The vacuum, in which light waves propagate - he referred to Maxwell's
> theory for stationary systems. At first he didn't think much of that
> but over time he changed his mind, as he explained here:
>
> http://www.tu-harburg.de/rzt/rzt/it/Ether.html
>
> > If space is empty
> > there are no reference points against which to measure the speed of
> > light. Should he not have said that the velocity of light between two
> > points in empty space is c = 300,000 km /sec ?
>
> What difference does that make? If a booklet in the seat pocket of an
> airplane states that its cruise speed is 900 km/h, do you need it to
> add "two points" in order to understand it? However, you do need to
> consider a material reference system relative to which you think you
> can define empty space -- as he next discusses.
>
> Note also that in 1905 he formulated it as follows:
>
> "light is always propagated in empty space with a definite velocity c
> which is independent of the state of motion of the emitting body."
>
> Harald

Also he states

"They suggest rather that, as has already been shown to the first
order of small quantities, the same laws of electrodynamics and optics
will be valid for all frames of reference for which the equations of
mechanics hold good.1 We will raise this conjecture (the purport of
which will hereafter be called the ``Principle of Relativity'') to the
status of a postulate, and also introduce another postulate, which is
only apparently irreconcilable with the former, namely, that light is
always propagated in empty space with a definite velocity c which is
independent of the state of motion of the emitting body."

Firstly, the fact that it does not matter if the magnet or the wire is
moving, as long as they are moving wrt each other, does not support
the leap to 'all frames of reference' here we are concerned with two
only the magnet frame and the wire frame of reference

Curiously, in order to specify that light is propagated independent of
the motion of the emitting body, he is admitting that the velocity of
the emitting body is to be measured and compared to the velocity of
light. But if space is empty, where is our reference point? If space
is not empty, hydrogen molecules and all, there is a reference point
ie 'light is always propagated at c with respect to the hydrogen
molecules situated in empty space' which is absurd don't you think? Is
it because he lived in the early 1900s that he had this limited view?

From: Inertial on 2 Jun 2010 20:11

"train" <gehan.ameresekere(a)gmail.com> wrote in message
news:ca4c6bdf-6ac7-4239-adc9-b81cd5d9dc83(a)v29g2000prb.googlegroups.com...
> Much discussion has taken place about SRT, however much of it seems to
> alternate between what Einstein said, what he meant, what he is taken
> to have meant and modern interpretations of the Theory Of Special
> Relativity

This is due to lack of study. and lack of effort, on the part of posters

> Going back to the original document written by AE at
>
> http://www.bartleby.com/173/7.html

Usually the paper referred to is his 1905 paper

> we may be able to discern what he said and what he meant, at least,
> and discuss the self - consistency of the theory from this point
>
> "THERE is hardly a simpler law in physics than that according to which
> light is propagated in empty space. Every child at school knows, or
> believes he knows, that this propagation takes place in straight lines
> with a velocity c = 300,000 km./sec"
>
> First question: What does he mean by 'empty space?' If space is empty
> there are no reference points against which to measure the speed of
> light.

Doesn't matter .. it can go through empty space BETWEEN reference points

> Should he not have said that the velocity of light between two
> points in empty space is c = 300,000 km /sec ?

Its exactly the same thing

From: Inertial on 2 Jun 2010 20:13

"train" <gehan.ameresekere(a)gmail.com> wrote in message
news:2508a8e3-32ab-436d-a0e8-ede9837c96a9(a)q39g2000prh.googlegroups.com...
> On Jun 3, 3:44 am, harald <h...(a)swissonline.ch> wrote:
>> On Jun 2, 4:57 pm, train <gehan.ameresek...(a)gmail.com> wrote:
>>
>> > Much discussion has taken place about SRT, however much of it seems to
>> > alternate between what Einstein said, what he meant, what he is taken
>> > to have meant and modern interpretations of the Theory Of Special
>> > Relativity
>>
>> > Going back to the original document written by AE at
>>
>> >http://www.bartleby.com/173/7.html
>>
>> That is a popular account. Here is a translation of his original
>> document:
>>
>> http://www.fourmilab.ch/etexts/einstein/specrel/www/
>>
>> In case something isn't clear, you do well to compare those two; the
>> second is a summary of the first.
>>
>> > we may be able to discern what he said and what he meant, at least,
>> > and discuss the self - consistency of the theory from this point
>>
>> > "THERE is hardly a simpler law in physics than that according to which
>> > light is propagated in empty space. Every child at school knows, or
>> > believes he knows, that this propagation takes place in straight lines
>> > with a velocity c = 300,000 km./sec"
>>
>> Yes.
>>
>> > First question: What does he mean by 'empty space?'
>>
>> The vacuum, in which light waves propagate - he referred to Maxwell's
>> theory for stationary systems. At first he didn't think much of that
>> but over time he changed his mind, as he explained here:
>>
>> http://www.tu-harburg.de/rzt/rzt/it/Ether.html
>>
>> > If space is empty
>> > there are no reference points against which to measure the speed of
>> > light. Should he not have said that the velocity of light between two
>> > points in empty space is c = 300,000 km /sec ?
>>
>> What difference does that make? If a booklet in the seat pocket of an
>> airplane states that its cruise speed is 900 km/h, do you need it to
>> add "two points" in order to understand it? However, you do need to
>> consider a material reference system relative to which you think you
>> can define empty space -- as he next discusses.
>>
>> Note also that in 1905 he formulated it as follows:
>>
>> "light is always propagated in empty space with a definite velocity c
>> which is independent of the state of motion of the emitting body."
>>
>> Harald
>
> Thanks for the 'original' document. Now again he is using the terms
> 'at rest' and 'in motion' rather loosely

Not really .. he defines quite clearly in his example which system he will
call the rest system

> "For if the magnet is in motion and the conductor at rest, there
> arises in the neighbourhood of the magnet an electric field with a
> certain definite energy, producing a current at the places where parts
> of the conductor are situated."

Nothing loose about that.

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