What is wrong or right with this characterization?:

Relativity is a measurement theory.

**************************

Patrick

"Patrick Reany" wrote in message
om...
What is wrong or right with this characterization?:

Relativity is a measurement theory.

**************************

For a starter, "relativity" is too generic, several theories ( SRT and
LET -and eventually some variants-) can be put under that same label.

Harald

Patrick Reany:
What is wrong or right with this characterization?:

Relativity is a measurement theory.

What's wrong with that statement is that relativity is _not_ a
measurement theory.

"Harry" wrote in message ...
"Patrick Reany" wrote in message
om...
What is wrong or right with this characterization?:

Relativity is a measurement theory.

**************************

For a starter, "relativity" is too generic, several theories ( SRT and
LET -and eventually some variants-) can be put under that same label.

Harald

By what definition do you claim that LET is a relativistic theory?
What makes a theory "relativistic" to you? Do you have a definition of
a "measurement theory"?

Patrick

For kriz sakes Patrick, YOU are the one that asked whether relativity is
a "measurement theory". It is incumbent upon YOU to define "measurement
theory", otherwise you are just trolling.

"Patrick Reany" wrote in message
om...
"Harry" wrote in message
...
"Patrick Reany" wrote in message
om...
What is wrong or right with this characterization?:

Relativity is a measurement theory.

**************************

For a starter, "relativity" is too generic, several theories ( SRT and
LET -and eventually some variants-) can be put under that same label.

Harald

By what definition do you claim that LET is a relativistic theory?
What makes a theory "relativistic" to you? Do you have a definition of
a "measurement theory"?

Any theory that takes into account Poincare's Principle of Relativity can be
said to be "relativistic".
Lorentz presented in 1927 SRT as his own theory (laws based on the PoR) -
despite his extreme modesty and although his interpretation was LET.

I don't have a definition for "measurement theory". But I can suggest one:
A theory that only consists of laws and principles, that is, it predicts
what will be measured under certain conditions, without functional model or
physical explanation.

According to such a definition, SRT as proposed by Lorentz, Poincare and
Einstein would be a measurement theory, only giving the principle and laws
but avoiding or disagreeing about the explanation (and, according to you,
even disagreeing about the meaning of "PoR").

Anyone who knows about the Principia of Newton? I think he did more than
just give laws, but I'm not sure, I only know his laws, and one opinion he
gave in a letter about the way gravitation is transmitted.

Harald

Oh, I just think about this:

Isn't officially quantum mechanics a "measurement theory"?

Harald

(Bilge) wrote in message ...
Patrick Reany:
What is wrong or right with this characterization?:

Relativity is a measurement theory.

What's wrong with that statement is that relativity is _not_ a
measurement theory.

Well, I can't say just yet because I don't know what it means. It's
just that I've never heard or read the phrase "measurement theory."
But recently it's being used on this NG like it's common knowledge.
Certainly every good physical theory has some measurement content, so
it can't be as simple as that. What does the phrase mean to you?

Patrick

"Harry" wrote in message ...
"Patrick Reany" wrote in message
om...
"Harry" wrote in message
...
"Patrick Reany" wrote in message
om...
What is wrong or right with this characterization?:

Relativity is a measurement theory.

**************************

For a starter, "relativity" is too generic, several theories ( SRT and
LET -and eventually some variants-) can be put under that same label.

Harald

By what definition do you claim that LET is a relativistic theory?
What makes a theory "relativistic" to you? Do you have a definition of
a "measurement theory"?

Any theory that takes into account Poincare's Principle of Relativity can be
said to be "relativistic".
Lorentz presented in 1927 SRT as his own theory (laws based on the PoR) -
despite his extreme modesty and although his interpretation was LET.

Please give the quote and reference for this claim of yours about
Lorentz.

But this notion of yours of "relativistic" goes against the historical
and philosophical basis of what is meant by relative vs absolute
spaces in the controversy of how to find an adequate foundation to all
of physics. I doubt that Poincare, Lorentz, or Einstein would accept
your definition of being relativistic by being based on equation
covariance alone. I'd bet that they would all agree that LET is NOT a
relativistic theory simply because it uses an absolute velocity space,
and that Newtonian mechanics and SR are relativistic simply because
they do NOT use an absolute velocity space in the foundations to those
theories.


I don't have a definition for "measurement theory". But I can suggest one:
A theory that only consists of laws and principles, that is, it predicts
what will be measured under certain conditions, without functional model or
physical explanation.

OK, what's a "functional model" and what's a "physical explanation"?
(Sounds to me like your non-"measurement theory" is Einstein's
"constructive" theory.)


According to such a definition, SRT as proposed by Lorentz, Poincare and
Einstein would be a measurement theory, only giving the principle and laws
but avoiding or disagreeing about the explanation (and, according to you,
even disagreeing about the meaning of "PoR").

I'd say that your definition of a "measurement theory" is very much
like Einstein's definition of a "principle theory." Einstein
considered LET a constructive theory, which has explanations in
speculative "physical" terms. Seems to me that this is just one more
example of why all this stuff to should be taught to all students
before they graduate from high school.

Lorentz, Poincare, and Einstein would never agree with you that LET
and SR are the same theory.

The pure and simple form of the PoR is stated as a negative principle
(i.e., in the form of an impossibility) is this:

It is impossible to perform any ________________ experiment that can
determine one's _____________ reference frame's absolute
_________________ .

As an example, I'll state the form for SR:

It is impossible to perform any mechanical, optical,
or electrodynamical experiment that can determine one's
inertial reference frame's absolute velocity.

And GR goes much further:

It is impossible to perform any experiment that can
determine one's reference frame's absolute velocity
or absolute acceleration.

Now, it's a simple argument to go from the PoR to equational form
invariance, since if it were not true, then the laws we develop in
different frames of reference would not be generally the same. The
view was that the explanation for that difference would lie in the
absolute motion of the frame of reference, and hence that some means
could be invented to exploit that difference to reverse-engineer the
absolute velocity of the frame. This would be a particularly simple
task of reverse-engineering if that law took a form in one's reference
frame which is explicitly dependent on the frame's absolute velocity
in some simple way. The MMX was designed along these theoretic lines.
But this goes immediately to the question of what one means by a "law"
in the first place. In relativity, one is only interested in those
"laws" which are in a form which is covariant under at least Lorentz
transformations (locally). Einstein called such laws "general" and --
I think -- sloppily introduced the term implicitly by his statement of
the PoR.

The general laws of nature are covariant with
respect to Lorentz transformations.
This is a definite mathematical condition
that the theory of relativity demands of a natural
law, and in virtue of this, the theory becomes a
valuable heuristic aid in the search for general
laws of nature.
---- Relativity, the Special and General Theory,
Crown Publisher, p 43.



The general principle of relativity requires that all these
[reference] molluscs can be used as reference bodies
with equal right and equal success in the FORMULATION
OF THE GENERAL LAWS OF NATURE; the laws themselves must
be quite independent of the choice of the mollusc.
The GREAT power possessed by the general principle
of relativity lies in the comprehensive limitation which
is imposed on the laws of nature in consequence of
what we have seen.
[Found in: Albert Einstein's Theory of General Relativity,
reprinted Albert Einstein, Relativity, p. 91-92, emphasis mine.]

I know of no place where Einstein defined what he meant by a "general
law," hence these claims he made on their behalf amount to an implicit
definition of what "general law" means to him; after that, the claims
have heuristic value to the theorist.

Now, equational form invariance is not quite true spacetime
covariance, which is not only that equational form invariance holds,
but that it holds under a group of spacetime transformations between
any two frames. The justification for this is in two parts: 1) it is
true of Galilean-Newtonian relativity, and 2) Einstein's relativity is
a generalization of Galilean-Newtonian relativity. The upshot being
that a generalization of a spacetime-transformation-invariant law must
also be a spacetime-transformation-invariant law. In other words, the
"general" laws of mechanics generalized to "general" laws of SR, based
on the Principle of the Harmony of Nature that Einstein believed in so
dearly. So, the commitment to form a new theory as a generalization of
some other successful theory is a very powerful heuristic indeed!

Patrick

Harry:
Oh, I just think about this:

Isn't officially quantum mechanics a "measurement theory"?

No, "measurement theory" is a measurement theory. Officially,
quantum mechanics is a theory in which the classical variables
like p and E become operators like p = -i\hbar\grad and
E = i\hbar d/dt and then reinserted into classical mechanics:

E = p^2/2m + U is the schroedinger equation

Quantum mechanics just looks different because it's more natural to use
the poisson bracket formalism of classical mechanics in quantum mechanics
and calling the poisson bracket a commutator. The physicists who developed
quantum mechanics understood classical mechanics very well. Today, people
regard possion brackets as the classical analogue of commutators rather
than the other way around, mainly because they don't see poisson brackets
much until after they've seen quantum mechanics.