I got stuck on Part II of Special Theory of Relativity (by Albert Einstein) textbook, please help
Albertito
My aim is to understand General Relativity Theory, but somebody
advised me to study Special Relativity before that GR attempt. So,
Here I am, stuck on Part II of Special Theory of Relativity by
Albert Einstein. It seems a blind alley to me. This Part II refers to
"The system of Co-ordinates". I have some 'naive' questions:
1. What is a rigid body?.
2. How can a system of co-ordinates be based on distances
through a rigid body, if you have not previously defined
rigorously what a rigid body is?.
3. Do rigid bodies actually exist in Nature?.
4. What would happen if you define a system of co-ordinates
based on the concept of non-rigid body?.
5. Is distance that what a ruler can measure?.
6. What would happen to a ruler's measurement if the ruler's
rigidity is slightly altered in some parts of it, in a manner
that
we cannot detect by means of any other ruler?.
Thanks in advance
Jeckyl
news:9f3df407-4417-4a08...@j20g2000hsi.googlegroups.com...
> Hi experts,
>
> My aim is to understand General Relativity Theory, but somebody
> advised me to study Special Relativity before that GR attempt.
Yeup .. its much simpler, and is a limiting case of GR
> So,
> Here I am, stuck on Part II of Special Theory of Relativity by
> Albert Einstein. It seems a blind alley to me. This Part II refers to
> "The system of Co-ordinates". I have some 'naive' questions:
>
> 1. What is a rigid body?.
It is something that anyone with any knowledge of physics, or eve of hte
English language (or the equivalent in German) would undersatnd. It is one
that doesn't distort (doesn't expand or contract in its own frame of
refernnce). There is no such think in reality .. everything can distort in
some sense .. but one can do some physics on the assumption that a body is
rigid (theories tend to be done in terms of ideals and then allowances made
for things like friction, no-rigidity etc)
> 2. How can a system of co-ordinates be based on distances
> through a rigid body, if you have not previously defined
> rigorously what a rigid body is?.
It was taken that any reasonable person would now what the word 'rigid'
means
> 3. Do rigid bodies actually exist in Nature?.
No .. not ones with any length at least :)
> 4. What would happen if you define a system of co-ordinates
> based on the concept of non-rigid body?.
A system of coordinates is always rigid, otherwise they aren't any use. And
as a system of coordinates is a concept only, it can indeed be truly rigid.
> 5. Is distance that what a ruler can measure?.
You can measure distance with a ruler (the absolute difference in spatial
coordinates between two events with the same time coordinate in a give
nframe of reference)
> 6. What would happen to a ruler's measurement if the ruler's
> rigidity is slightly altered in some parts of it, in a manner
> that
> we cannot detect by means of any other ruler?.
All rulers (like any other material object) are non-rigid .. which is why
when you want to measure things accurately, a ruler is not a good choice.
In general they are rigid enough for doing things like seeing how long a
piece of wood is (say).
Ockham
"Albertito" <albert...@gmail.com> wrote in message
news:9f3df407-4417-4a08...@j20g2000hsi.googlegroups.com...
|
| My aim is to understand General Relativity Theory, but somebody
| advised me to study Special Relativity before that GR attempt.
Good idea, GR is SR with knobs on. Same wooden horse but now
it has a wooden dick.
| So,
| Here I am, stuck on Part II of Special Theory of Relativity by
| Albert Einstein. It seems a blind alley to me. This Part II refers to
| "The system of Co-ordinates". I have some 'naive' questions:
|
| 1. What is a rigid body?.
Look it up in a dictionary.
If you want to nit-pick definitions to that level, first define "body".
| 2. How can a system of co-ordinates be based on distances
| through a rigid body, if you have not previously defined
| rigorously what a rigid body is?.
What is a system?
What is a coordinate?
What does "based" mean?
What are distances?
| 3. Do rigid bodies actually exist in Nature?.
No, they are mathematical entities.
| 4. What would happen if you define a system of co-ordinates
| based on the concept of non-rigid body?.
You get a system of co-ordinates based on the concept of non-rigid body.
| 5. Is distance that what a ruler can measure?.
What is a ruler and is it a rigid body?
| 6. What would happen to a ruler's measurement if the ruler's
| rigidity is slightly altered in some parts of it, in a manner
| that
| we cannot detect by means of any other ruler?.
|
Nit pick only those definitions that are falsifiable, there plenty
to chose from in SR. If Einstein says "assume" then you can be
certain he's about to lie through his teeth.
harry
"Albertito" <albert...@gmail.com> wrote in message
news:9f3df407-4417-4a08...@j20g2000hsi.googlegroups.com...
That whole issue about rigidity is not essential for the theoretical
development: in practice, measurements must be repeatable and it helps a lot
if the rulers are sufficiently stiff, among other things. For example, you
could also define a system of coordinates on a length of rope but to be
accurate you should pull it straight with a well defined force. :-)
Cheers,
Harald
Sue...
> Hi experts,
>
> My aim is to understand General Relativity Theory, but somebody
> advised me to study Special Relativity before that GR attempt. So,
> Here I am, stuck on Part II of Special Theory of Relativity by
> Albert Einstein. It seems a blind alley to me. This Part II refers to
> "The system of Co-ordinates". I have some 'naive' questions:
>
> 1. What is a rigid body?.
> 2. How can a system of co-ordinates be based on distances
> through a rigid body, if you have not previously defined
> rigorously what a rigid body is?.
<< A classical rigid reference frame is the *imagined*
extension of a rigid body. For instance, the Earth
determines a rigid frame throughout all space,
consisting of all those points which remain
rigidly at rest relative to the Earth, and to
each other. >>
"The Relativity Principle"
http://farside.ph.utexas.edu/teaching/em/lectures/node108.html
Sue...
JanPB
> Hi experts,
>
> My aim is to understand General Relativity Theory, but somebody
> advised me to study Special Relativity before that GR attempt. So,
> Here I am, stuck on Part II of Special Theory of Relativity by
> Albert Einstein.
Don't read Einstein's original papers - they were written for experts.
Study from a good textbook instead - check the relativity FAQ (search
the Internet). It would also save you a _tremendous_ amount of time
and effort if you could find someone to teach you. There is nothing
like face to face contact in the early stages.
--
Jan Bielawski
Ockham
"JanPB" <fil...@gmail.com> wrote in message
news:2e04c6a0-fb6f-4361...@u10g2000prn.googlegroups.com...
| On Feb 1, 3:04 am, Albertito <albertito1...@gmail.com> wrote:
| > Hi experts,
| >
| > My aim is to understand General Relativity Theory, but somebody
| > advised me to study Special Relativity before that GR attempt. So,
| > Here I am, stuck on Part II of Special Theory of Relativity by
| > Albert Einstein.
|
| Don't read Einstein's original papers - they were written for experts.
And the polack monkey Jan Bielawski doesn't understand them.
Eric Gisse
> Hi experts,
>
> My aim is to understand General Relativity Theory, but somebody
> advised me to study Special Relativity before that GR attempt. So,
> Here I am, stuck on Part II of Special Theory of Relativity by
> Albert Einstein. It seems a blind alley to me. This Part II refers to
> "The system of Co-ordinates". I have some 'naive' questions:
You are studying the wrong sources. Modern presentations of both
theories are much more understandable, but still require that you have
about 5 more years of mathematics under your belt before you can fully
appreciate what is going on. You, at the very least, need calculus,
linear algebra, and a functional understanding of classical physics
along with the mathematics required for that.
>
> 1. What is a rigid body?.
A body in which the internal speed of sound is infinite.
> 2. How can a system of co-ordinates be based on distances
> through a rigid body, if you have not previously defined
> rigorously what a rigid body is?.
It is expected that you know this. Einstein wrote for other
physicists, not 16 yearolds with none of the required knowledge.
> 3. Do rigid bodies actually exist in Nature?.
No.
> 4. What would happen if you define a system of co-ordinates
> based on the concept of non-rigid body?.
Nothing. Coordinate do not determine physics.
> 5. Is distance that what a ruler can measure?.
Sometimes.
> 6. What would happen to a ruler's measurement if the ruler's
> rigidity is slightly altered in some parts of it, in a manner
> that
> we cannot detect by means of any other ruler?.
Too imprecise of a question.
>
> Thanks in advance
Jeckyl
news:b5f3cadd-eb07-45dc...@i7g2000prf.googlegroups.com...
><< A classical rigid reference frame is the *imagined*
>extension of a rigid body. For instance, the Earth
>determines a rigid frame throughout all space,
>consisting of all those points which remain
>rigidly at rest relative to the Earth, and to
>each other. >>
>"The Relativity Principle"
>http://farside.ph.utexas.edu/teaching/em/lectures/node108.html
>
> Sue...
My god .. you've actually replied with something on topic and relevant.
Miracles do happen :)
Eric Gisse
> "Sue..." <suzysewns...@yahoo.com.au> wrote in message
Stopped clock.
Everything that is in sight of relativity gets that reply from sue,
regardless of how worthless and off-topic it is.
Thomas Heger
"Albertito" <albert...@gmail.com> schrieb im Newsbeitrag
news:9f3df407-4417-4a08...@j20g2000hsi.googlegroups.com...
> Hi experts,
>
> My aim is to understand General Relativity Theory, but somebody
> advised me to study Special Relativity before that GR attempt.
the stupid questions arise from the mixture of newton-like space and
lorentz-transform. In fact you have to think of spacetime as
four-dimensional.
> So,
> Here I am, stuck on Part II of Special Theory of Relativity by
> Albert Einstein. It seems a blind alley to me. This Part II refers to
> "The system of Co-ordinates". I have some 'naive' questions:
>
> 1. What is a rigid body?.
This issue is an other example of confusing the relation between modell and
reality. The same confusion leads to the statement, clocks on a mountain are
slower. In relativity is important to choose the right view. Relativity is
about the conversion of one view into the other one. Coordinates are a
modell of someone (the observer) to measure relations of type lenght. He
will certainly use the most rigid thing around to define those lenghtses.
In practis they use clocks for this purpose.
Now you want to think, what defines coordinates, if not even rigid bodies
are really rigid. This is misleading. First it is not true, that clock run
slower for a local observer. There is no slower, cause time is defined as
what a clock says. Simmilar the lenght. You do not get stretched, because a
distant object pacing by see you lenght-contracted.
PD
Just a couple of comments:
1. I don't actually recommend that you *start* to read about
relativity starting with Einstein's writings. People have figured out
how to explain it better since then. I suggest you start with Taylor
and Wheeler's "Spacetime Physics" and Geroch's "General Relativity
from A to B". Both are low-cost paperbacks available used on Amazon.
2. Since you are having difficulty grasping basic physics concepts, I
suggest you slog through a book on basic mechanics and electrodynamics
before you tackle subjects that assume you have grounding in the
basics. I know it's not as much fun as going directly to the fun
stuff, but you see that you will frustrate yourself by not
understanding some things that simply won't be explained again in a
book on relativity. There is no shortcut. You really do have to jump
from A to B to C to D, and if you jump directly from A to D you will
only jump short and get wet.
3. You came into the group critiquing relativity, and now it appears
you were doing it *before* attempting to learn the subject. This is
*always* a foolhardy move. I'm glad to see now that you are working to
correct that mistake, but I do hope that you take that as a lesson
learned for the future in other subject areas. Likewise, if you want
to learn something about neurophysiology, you're going to have to read
a basic book in biology FIRST.
PD
Mike Fontenot
>
> On Feb 1, 2:04 am, Albertito <albertito1...@gmail.com> wrote:
> > Hi experts,
> >
> > My aim is to understand General Relativity Theory, but somebody
> > advised me to study Special Relativity before that GR attempt. So,
> > Here I am, stuck on Part II of Special Theory of Relativity by
> > Albert Einstein. It seems a blind alley to me. This Part II refers to
> > "The system of Co-ordinates". I have some 'naive' questions:
>
> You are studying the wrong sources. Modern presentations of both
I disagree (although I concede that your opinion is the majority
opinion). It's true that the modern presentations are much more
elegant mathematically, and they add value in their consiseness,
economy, and better generalizability to general relativity. But
I think they also LOSE something: they lose a lot of the feel for
Einstein's motivation and intuition, that led him to arrive at
special relativity. And I think an appreciation for Einstein's
thought processes is very helpful for a student new to special
relativity. I read a quote somewhere that Einstein said, a few
years after his first SR paper was published, that "After the
mathematicians got through with it, I could barely recognize my
own theory" (or some similar quote). One of the mathematicians
he was probably refering to was Minkowski, who said of Einstein
(before he published that first SR paper) that "He is lazy, and
will never amount to anything" (again, I'm paraphrasing here).
Mike Fontenot
Eric Gisse
Minkowski saw the error of his ways, but it's too bad he didn't live
long enough to see the development of GR or quantum theory. I imagine
he would have been a major contributor.
I do see your point - by moving away from Einstein's original works,
we lose his motivations. A part of the problem, though, is that the
theory /has/ changed since 1905. We don't use light clocks anymore,
and the geometry of the theory has a stronger emphasis. Also, his
motivations [Maxwell's equations] are less-than-transparent to someone
who doesn't know what Maxwell's equations are.
Furthermore, the original paper was written for other physicists and
not people with a minimum of education in the subject. That isn't a
criticism, that's just a fact of life.
>
> Mike Fontenot
Mike Fontenot
>
> [...] Also, his
> motivations [Maxwell's equations] are less-than-transparent to someone
> who doesn't know what Maxwell's equations are.
>
> Furthermore, the original paper was written for other physicists and
> not people with a minimum of education in the subject.
I'm hoping that the OP was referring to Einstein's popularization,
"Relativity" (Crown Publishers). It's actually fairly accessible
to non-physicists, although some familiarity with Newtonian physics
is helpful. You're right that Einstein's original 1905 paper wouldn't
be a good place to start.
Mike Fontenot