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Definition of "Lorentz Transformation"



 
 
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  #1  
Old September 27th 03 posted to sci.physics.relativity
Pmb
external usenet poster
 
Posts: 779
Default Definition of "Lorentz Transformation"

Alas there is more misinformation being passed around. This time regarding
the precise definition of "Lorentz Transformation." The misinformation is
that, for example, a transformation from frame S which has spherical spatial
coordinates (t,r,theta,phi) to another frame S' moving relative to S and
having coordinates (t',r',theta',phi') is a Lorentz transformation. That is
incorrect. While there most certainly exists transformations as suich and
which leave the spacetime interval ds^2 invariant they are not refered to as
"Lorentz Transformations." That term has a very specific meaning.

Let S have coordinates X = (t,x,y,z) and S' have coordinates X' =
(t',x',y',z'). These coordinates are often refered to as "Lorentz
Coordinates" or "Minkowski Coordinates." Let n = Minkowski metric =
diag(1,-1,-1,-1). The correct, precise, definition of a Lorentz
transformation is as follows

Definition: A transformation L from X to X', i.e. X' = LX, is a
transformation for which n'LL = n.

Such transformations include rotations, reflections and boosts. This
definition is found in most decent texts on relativity and tensor analysis.

Sources -
From Thorne and Blanchard's new text --
http://www.pma.caltech.edu/Courses/p...p01/0201.2.pdf - page 28

"Introducing Einstein's Relativity," D'Inverno, Oxford Univ. Press, (1992),
page 109-111
"Tensors, Differential Forms, and Variational Principles," Lovelock & Rund,
Dover Pub., (1989), page 53
"Electrodynamics and Classical Theory of Fields and Particles," Barut, Dover
Pub., (1980), Chapter 1

Pmb


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  #3  
Old September 27th 03 posted to sci.physics.relativity
Martin Hogbin
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Posts: 365
Default Definition of "Lorentz Transformation"


"Pmb" wrote in message ...
Alas there is more misinformation being passed around. This time regarding
the precise definition of "Lorentz Transformation." The misinformation is
that, for example, a transformation from frame S which has spherical spatial
coordinates (t,r,theta,phi) to another frame S' moving relative to S and
having coordinates (t',r',theta',phi') is a Lorentz transformation. That is
incorrect. While there most certainly exists transformations as suich and
which leave the spacetime interval ds^2 invariant they are not refered to as
"Lorentz Transformations."


What are they referred to as?

Martin Hogbin


  #4  
Old September 27th 03 posted to sci.physics.relativity
Pmb
external usenet poster
 
Posts: 779
Default Definition of "Lorentz Transformation"


"Martin Hogbin" wrote in message
...

"Pmb" wrote in message

...
Alas there is more misinformation being passed around. This time

regarding
the precise definition of "Lorentz Transformation." The misinformation

is
that, for example, a transformation from frame S which has spherical

spatial
coordinates (t,r,theta,phi) to another frame S' moving relative to S and
having coordinates (t',r',theta',phi') is a Lorentz transformation. That

is
incorrect. While there most certainly exists transformations as suich

and
which leave the spacetime interval ds^2 invariant they are not refered

to as
"Lorentz Transformations."


What are they referred to as?


They don't have a name.

Pmb


  #6  
Old September 28th 03 posted to sci.physics.relativity
Pmb
external usenet poster
 
Posts: 779
Default Definition of "Lorentz Transformation"


"Martin Hogbin" wrote in message
...

"Pmb" wrote in message

...
Alas there is more misinformation being passed around. This time

regarding
the precise definition of "Lorentz Transformation." The misinformation

is
that, for example, a transformation from frame S which has spherical

spatial
coordinates (t,r,theta,phi) to another frame S' moving relative to S and
having coordinates (t',r',theta',phi') is a Lorentz transformation. That

is
incorrect. While there most certainly exists transformations as suich

and
which leave the spacetime interval ds^2 invariant they are not refered

to as
"Lorentz Transformations."


What are they referred to as?

Martin Hogbin


Moller wrote a general relation between the spatial vector and the time in
his text "The Theory of Relativity." This relation is found in many places
such as Goldstein's "Classical Mechanics" - But that is not exactly a
"coordinate transformation" since it has little, if nothing, to do with
coordinates. In fact you don't even need to write coordinates down in that
relation. In that view you're changing frames of reference rather changing
coordinate systems - a subtle difference

Pmb


  #8  
Old September 28th 03 posted to sci.physics.relativity
Bilge
external usenet poster
 
Posts: 13,439
Default Definition of "Lorentz Transformation"

Pmb:
[...]
incorrect. While there most certainly exists transformations as suich
and which leave the spacetime interval ds^2 invariant they are not
refered to as "Lorentz Transformations." That term has a very specific
meaning.


Lorentz transforms are transforms which preserve inertial frames.

Let S have coordinates X = (t,x,y,z) and S' have coordinates X' =
(t',x',y',z'). These coordinates are often refered to as "Lorentz
Coordinates" or "Minkowski Coordinates." Let n = Minkowski metric =
diag(1,-1,-1,-1). The correct, precise, definition of a Lorentz
transformation is as follows

Definition: A transformation L from X to X', i.e. X' = LX, is a
transformation for which n'LL = n.


Thats obviously incorrect. The rotation:

[ cos(A) -sin(A) ]
X' = [ ] X
[ sin(A) cos(A) ]

Doesn't satisfy the relation you've written, since LL = L^2 != 1.
Multiply it out. You also might try actually writing the equations
out instead of trying to use notational shortcuts that only let you
shoot yourself in the foot.

Such transformations include rotations, reflections and boosts.


Unfortunately, your definition only gives reflections, since the
operator LLX only equals X for L = +/- 1.

This definition is found in most decent texts on relativity and
tensor analysis.


Sources -
From Thorne and Blanchard's new text --
http://www.pma.caltech.edu/Courses/p...p01/0201.2.pdf - page 28


Which doesn't agree with you. What they have written is:

q_uv L^u_a L^v_b = g_ab

L^u_a and L^v_b are inverses of each other. That is not what you have
written. In particular, rotations are orthogonal transformations and
an orthogonal transformation is defined by a matrix for which the
transpose is equal to the inverse. Also, note the example they give at
the top of the next page (29).

Furthermore, the relations given don't _define_ lorentz transforms.
What your reference says is that a transform which satisfies those
relations is a lorentz transform. But, that's strictly because the
transforms were derived in order to preserve the scalar product
under the assumption of the minkowski metric. To wit, your reference
defines the transforms by first defining X and X' as inertial frames.
In order to find a transform between them, the transformation has to
preserve inertial frames.


  #9  
Old September 28th 03 posted to sci.physics.relativity
Martin Hogbin
external usenet poster
 
Posts: 365
Default Definition of "Lorentz Transformation"


"Pmb" wrote in message ...

"Martin Hogbin" wrote in message
...

"Pmb" wrote in message

...
Alas there is more misinformation being passed around. This time

regarding
the precise definition of "Lorentz Transformation." The misinformation

is
that, for example, a transformation from frame S which has spherical

spatial
coordinates (t,r,theta,phi) to another frame S' moving relative to S and
having coordinates (t',r',theta',phi') is a Lorentz transformation. That

is
incorrect. While there most certainly exists transformations as suich

and
which leave the spacetime interval ds^2 invariant they are not refered

to as
"Lorentz Transformations."


What are they referred to as?


They don't have a name.


I would have thought that calling them 'the Lorentz
transformations in spherical polar coordinates' would
make everyone happy.

Martin Hogbin



 




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