"greywolf42" wrote in message ...

Thomas Clarke wrote in message
news:6d744b161b1785aa74e6b4cc9e568c52.128340@mygat e.mailgate.org...
"greywolf42" wrote in message

[snip]


It sounds like the way real science is conducted by real people.

If you define "science" by what brown-nosing grant-chasers in academia do, I
concur. But it in no way resembles the scientific method.

What do you think constitutes a valid scientific critique?

One that conforms to the scientific method. (Avoid ad hominem attacks,
character assassination, straw men, and the rest of the panopaly of
pseudo-science.)

Title: "Avoid ad hominem attacks, character assassination..."
http://users.pandora.be/vdmoortel/di...les/Avoid.html
One for the road.

Dirk Vdm

Matthew Nobes wrote in message
...
Thomas Clarke wrote:
"greywolf42" wrote in message
[snip]
Einstein found a mathematical set of equations that had the properties
that
he desired. However, Einstein had to determine the constants of that
mathematics. All the math is is symbols. In order to determine one
set of
boundary conditions, Einstein decided (wisely so) to make the
weak-field
solution (almost) equal to Newton's gravitational equation. (That's
the 8
pi part.) It was a very explicit backfit.

There is a constant G in all formulations of gravity.
Newton got their first so that G was defined in terms of
Newton's F=GmM/r^2 on the basis of observation.
If somehow GR had been invented before
inverse square gravity, then G might have been determined
from observation with the 8-pi absorbed into it.

But to call this "backfit" is to me an overstatement.

It's more than that, it's essentially wrong. The *important* thing about
GR is that it reduces to an inverse square law in the weak field limit.

Plus a constant speed of gravity equal to 'c'. (In GR, the speed of gravity
varies between 'c' at the weak-field limit and increases to infinity at the
strong-field limit.)

The constant G (or G/8pi) is merely a unit convention, relativists use
G=1 all the time.

It is not just a unitary convention. The units used for the symbols MUST
match some real-world system of measure when the mathematical scrawls are
compared to reality.

GR was not in any way "backfit" onto Newtonian gravity.

Well, at least you seem to accept that Einstein's 'relativity' was a
'variation' on Newtonian 'relativity.'

greywolf42
ubi dubium ibi libertas

Thomas Clarke wrote in message
news:18365b6488c7b05e5c1bd44a29d1debf.128340@mygat e.mailgate.org...
"greywolf42" wrote in message
Thomas Clarke wrote in message
.....
Does "ring true" the criterion for valid scientific
critique?

It sounds like the way real science is conducted by real people.

If you define "science" by what brown-nosing grant-chasers in academia
do, I
concur. But it in no way resembles the scientific method.

Below you called something I wrote understated.
I would call that statement overstated, vastly overstated.

You may have met different academicians than I did. I've met darned few
scientists, and a lot of Machiavellian schemers. But I did a lot of work
with the National Laboratories (sic).

What do you think constitutes a valid scientific critique?

One that conforms to the scientific method. (Avoid ad hominem attacks,
character assassination, straw men, and the rest of the panopaly of
pseudo-science.)

What do you think constitutes the scientific method?

See:
http://groups.google.com/groups?q=g:...=&ie=UTF-8&sel
m=pmr67.28286%24ot3.1637161%40nntp1.onemain.com

...........
OK, let's discuss:

"Einstein's variation on Newtonian relativity (special relativity)"

"Relativity" was described by both Galileo and -- more formally -- by
Newton.

I usually associate the term "relativity" with Galileo but
Newton is more or less the same era.

OK.

According to Newton, the velocities of importance in physical
interactions are the relative velocities of the objects undergoing
interaction. This is an "object-centered" viewpoint. Einstein's
variation
was to disconnect the basis of measuring velocity from the object and
attach
it to the "observer."

You can call it a variation if you like. But that is an
overstatement.

We disagree. Einstein (in his first paragraph of his 1905 work wrote)

"... The observable phenomenon here depnds only on the relative motion of
the conductor and the magnet, whereas the customary view draws a sharp
distinction between the two cases in which either the one or the other of
these bodies is in motion. ... " This reasoning precedes Einstein's only
passing inference to the Michelson-Morely experiment.

The observer is not necessarily involved in the
actual interaction of two physical objects. Einstein himself based his
initial work on Newton and Maxwell.

Well since Newton and Maxwell are incompatible, it was a bit
more than "based...on"

I would consider this statement of yours completely untrue. Maxwell derived
"Maxwell's equations" using Newton's equations of motion with a fluid aether
model. Maxwell's equations are typical examples of fluid medium
equations -- which is to say, motion within the fluid is important.

Since relativity has been known for
hundreds of years, I call special relativity a variation on Newtonian
relativity.

An overstatement.

You apparently think this because you seem to be unaware that Maxwell used a
Newtonian analysis to get "his" equations.



"GR was backfit onto Newton's force equation"

One of the reasons that I admire Einstein is that he was willing to
propose
unusual paths to get to a desired point. But also willing to abandon
roads
that didn't seem to be going anywhere ("That fellow Einstein. Every
year he
throws out what he did the year before." -- A. Einstein). GR took him
many
years of effort and false starts. However, he was always willing to
modify
what didn't work. In the reference below, for example, Einstein states:
"It
will also be obvious that the principle of the constancy of the speed of
light IN VACUO must be modified..." Hence, SR is not contained withing
GR.
In GR there IS a preferred frame.

Einstein found a mathematical set of equations that had the properties
that
he desired. However, Einstein had to determine the constants of that
mathematics. All the math is is symbols. In order to determine one set
of
boundary conditions, Einstein decided (wisely so) to make the weak-field
solution (almost) equal to Newton's gravitational equation. (That's the
8
pi part.) It was a very explicit backfit.

There is a constant G in all formulations of gravity.
Newton got their first so that G was defined in terms of
Newton's F=GmM/r^2 on the basis of observation.
If somehow GR had been invented before
inverse square gravity, then G might have been determined
from observation with the 8-pi absorbed into it.

But to call this "backfit" is to me an overstatement.

The G or "8 pi" is not just a unitary convention. The units used for the
symbols MUST match some real-world system of measure when the mathematical
scrawls are compared to reality.


And it's not the "questionable" aspect that makes the slime site
unacceptable. It is the fact that the slime site makes egregious
distortions about the work of a third party. And won't identify
who's
doing
the attacking.

The mathpages site seems to be a compendium of works from various
usenet sites over the years. It would be better if it had sources
indicated more clearly.

Understated, but we agree on your last point.

You should try understatement, greywolf42.

I prefer clarity to understatement.

greywolf42
ubi dubium ibi libertas

greywolf42 wrote:

Matthew Nobes wrote in message
...
Thomas Clarke wrote:
"greywolf42" wrote in message
[snip]

[snip mangled stuff]

There is a constant G in all formulations of gravity.
Newton got their first so that G was defined in terms of
Newton's F=GmM/r^2 on the basis of observation.
If somehow GR had been invented before
inverse square gravity, then G might have been determined
from observation with the 8-pi absorbed into it.

But to call this "backfit" is to me an overstatement.

It's more than that, it's essentially wrong. The *important* thing about
GR is that it reduces to an inverse square law in the weak field limit.

Plus a constant speed of gravity equal to 'c'.

No. In the weak field limit, c doesn't enter into it. Plus c=1.

(In GR, the speed of gravity
varies between 'c' at the weak-field limit and increases to infinity at the
strong-field limit.)

That's not true, gravitational waves propagate at c, no matter how strong
they are. Please don't tell me that you're still trying to tell Steve
Carlip what he "really meant" in his Speed of Gravity paper.

The constant G (or G/8pi) is merely a unit convention, relativists use
G=1 all the time.

It is not just a unitary convention.

Well, yes it is.

G = 6.672 x 10^(-11) Nm^2/kg^2 = 66.72 pNm^2/kg^2

Look at that, I just changed G by 11 orders of magnitude.

The units used for the symbols MUST
match some real-world system of measure when the mathematical scrawls are
compared to reality.

Sure, but the choice of units in the "mathematical scrawls" cannot affect
the predictions. Hence the units are arbitary. Hence G=1 (and c=1) is fine
for understanding the important *physics* of GR.

Like I said, the important *physical* result of the weak-field expansion
of GR is that it shows that

V(r) ~ 1/r

the constant out front expresses the choice of units, it can be 10^{-11} or 10
or 1 or anything really. It's the 1/r part that's important.

GR was not in any way "backfit" onto Newtonian gravity.

Well, at least you seem to accept that Einstein's 'relativity' was a
'variation' on Newtonian 'relativity.'

While I would call that a strong statement, it is a defensible position.
The idea that time could be relative too was definately a big leap though.
(Of course others had this idea too, not just Einstein).

--
Matthew Nobes
c/o Physics Dept. Simon Fraser University, 8888 University
Drive Burnaby, B.C., Canada
http://www.sfu.ca/~manobes

Matthew Nobes wrote in message
...
greywolf42 wrote:

Matthew Nobes wrote in message
...
Thomas Clarke wrote:
"greywolf42" wrote in message
[snip]

[snip mangled stuff]

'Mangled stuff?'

There is a constant G in all formulations of gravity.
Newton got their first so that G was defined in terms of
Newton's F=GmM/r^2 on the basis of observation.
If somehow GR had been invented before
inverse square gravity, then G might have been determined
from observation with the 8-pi absorbed into it.

But to call this "backfit" is to me an overstatement.

It's more than that, it's essentially wrong. The *important* thing
about
GR is that it reduces to an inverse square law in the weak field limit.

Plus a constant speed of gravity equal to 'c'.

No. In the weak field limit, c doesn't enter into it.

LOL! So sorry, but you are incorrect. In the weak field limit, the speed
of gravity is 'c.' The speed of gravity tends to infinity as the field
approaches the strong limit. See Steve Carlip's paper,
http://arXiv.org/abs/gr-qc/9909087.

Plus c=1.

LOL! Whether you call it 3.0E8 mps or 3.0E10 cps or 1 light-unit it's the
same thing. A finite speed of gravity, intially determined by Paul Gerber,
17 years prior to Einstein.

(In GR, the speed of gravity
varies between 'c' at the weak-field limit and increases to infinity at
the
strong-field limit.)

That's not true, gravitational waves propagate at c, no matter how strong
they are. Please don't tell me that you're still trying to tell Steve
Carlip what he "really meant" in his Speed of Gravity paper.

I don't think even Steve will disagree that the point of his paper was that
the speed of gravity can be 'c', without any ill effects. Steve disagreed
with my taking his paper and demonstrating that Steve's logic applies to
other finite-speed theories -- not just GR. But here's Steve's conclusion:

"In particular, while the observed absence of aberration is consistent with
instantaneous propagation (with an extra interaction somehow added on to
explain the gravitational radiation reaction), it is also consistent with
the speed-of-light propagation predicted by general relativity."

The constant G (or G/8pi) is merely a unit convention, relativists use
G=1 all the time.

It is not just a unitary convention.

Well, yes it is.

G = 6.672 x 10^(-11) Nm^2/kg^2 = 66.72 pNm^2/kg^2

Look at that, I just changed G by 11 orders of magnitude.

What a pathetic attempt. You didn't change G. By any chance were you in
charge of that Mars lander a couple of years ago? The 'values' were the
same. But one was in newtons and the other in pounds......

The units used for the symbols MUST
match some real-world system of measure when the mathematical scrawls
are
compared to reality.

Sure, but the choice of units in the "mathematical scrawls" cannot affect
the predictions. Hence the units are arbitary.

LOL! Tell that to the Mars lander!!!

Hence G=1 (and c=1) is fine
for understanding the important *physics* of GR.

But not for comparing to the real world.

Like I said, the important *physical* result of the weak-field expansion
of GR is that it shows that

V(r) ~ 1/r

the constant out front expresses the choice of units, it can be 10^{-11}
or 10
or 1 or anything really. It's the 1/r part that's important.

The 'weak field' expansion also includes a finite 'c'. That's also
important, because it leads to the NNPA of Mercury.

GR was not in any way "backfit" onto Newtonian gravity.

Well, at least you seem to accept that Einstein's 'relativity' was a
'variation' on Newtonian 'relativity.'

While I would call that a strong statement, it is a defensible position.

OK.

The idea that time could be relative too was definately a big leap though.
(Of course others had this idea too, not just Einstein).

Einstein's redefinition of time (to 'common time') and space is unavoidable
after his tying the motion to observers, then creating his synchronization
procedure. The function of Einstein's 'synchronization' procedure is to
shield the assumption that c = constant from disproof. Thus, it is not a
big leap. It is a crutch. And -- if Einstein was right about c=constant to
the observer -- it wouldn't really be necessary. 'Normal' synchronization
would work. And time and space would not be modified.

greywolf42
ubi dubium ibi libertas

greywolf42 wrote:

Matthew Nobes wrote in message
...
greywolf42 wrote:

Matthew Nobes wrote in message
...

[snip mangled stuff]

'Mangled stuff?'

Yes, stuff pushed over an 80 character width, which my newsreader
renders in a most unpleasant way.

Restoring it is more trouble than it's worth, so I've snipped
it.

It's more than that, it's essentially wrong. The *important* thing
about
GR is that it reduces to an inverse square law in the weak field limit.

Plus a constant speed of gravity equal to 'c'.

No. In the weak field limit, c doesn't enter into it.

LOL! So sorry, but you are incorrect. In the weak field limit, the speed
of gravity is 'c.'

You're thinking of the *next* term in the series. The lowest order effect
(i.e. a *really* weak field) gives the Newtonian theory, and nothing
else.

The speed of gravity tends to infinity as the field
approaches the strong limit. See Steve Carlip's paper,
http://arXiv.org/abs/gr-qc/9909087.

This is untrue in GR. Nothing in Dr. Carlip's paper says that
the speed of gravity is infinite in the strong field limit.

From the final paragraph

"The Einstein Field Equations contain a single parameter c_g, which
describes both the speed of gravitational waves and the ``speed of
gravity'' occuring in the expression for abberation [...]."

and

"The success of the theory in explaining the orbital decay of binary
plusars implies that c_g=c at the 1% level or better."

Plus c=1.

LOL! Whether you call it 3.0E8 mps or 3.0E10 cps or 1 light-unit it's the
same thing.

My point exactly. The *physics* of GR/SR doesn't depend on what units you
use.

A finite speed of gravity, intially determined by Paul Gerber,
17 years prior to Einstein.

Whatever. I'm not discussing history.

[snip]
That's not true, gravitational waves propagate at c, no matter how strong
they are. Please don't tell me that you're still trying to tell Steve
Carlip what he "really meant" in his Speed of Gravity paper.

I don't think even Steve will disagree that the point of his paper was that
the speed of gravity can be 'c', without any ill effects.

No. That's not the point. The point is in GR the speed of gravity is c and
that's it. How hard is that to understand? Read the final paragraph.

Steve disagreed
with my taking his paper and demonstrating that Steve's logic applies to
other finite-speed theories -- not just GR. But here's Steve's conclusion:

"In particular, while the observed absence of aberration is consistent with
instantaneous propagation (with an extra interaction somehow added on to
explain the gravitational radiation reaction), it is also consistent with
the speed-of-light propagation predicted by general relativity."

I'm not disputing that. I'm addressing your claim that GR was "backfit"
onto Newton's theory. I have no problem believing that a different, *non-GR*
theory could explain some things.

The constant G (or G/8pi) is merely a unit convention, relativists use
G=1 all the time.

It is not just a unitary convention.

Well, yes it is.

G = 6.672 x 10^(-11) Nm^2/kg^2 = 66.72 pNm^2/kg^2

Look at that, I just changed G by 11 orders of magnitude.

What a pathetic attempt. You didn't change G.

Sure I did. What you really mean is that I didn't change the physics
which is my point. Einstein showed that his theory reduced to a
1/r potential, i.e. that it had the *SAME*PHYSICS* as Newton's. The
constant out front is just a choice of units, hence GR was not "backfit".

By any chance were you in
charge of that Mars lander a couple of years ago? The 'values' were the
same. But one was in newtons and the other in pounds......

Okay, everybody has to use the same units. But you're missing the point.
Surely you're not claiming that the laws of physics were different
in the two different systems of units?

The units used for the symbols MUST
match some real-world system of measure when the mathematical scrawls
are
compared to reality.

Sure, but the choice of units in the "mathematical scrawls" cannot affect
the predictions. Hence the units are arbitary.

LOL! Tell that to the Mars lander!!!

*sigh* Tell me something, do you think that the choice of units affects
the fact that weak field GR reduces to a 1/r potential? Would you dispute
the fact that it's the 1/r part that's important, not the SPECIFIC numerical
value for G?

Hence G=1 (and c=1) is fine
for understanding the important *physics* of GR.

But not for comparing to the real world.

Sure, if two groups use the same units.

Like I said, the important *physical* result of the weak-field expansion
of GR is that it shows that

V(r) ~ 1/r

the constant out front expresses the choice of units, it can be 10^{-11}
or 10
or 1 or anything really. It's the 1/r part that's important.

The 'weak field' expansion also includes a finite 'c'. That's also
important, because it leads to the NNPA of Mercury.

That's the first correction from GR. The leading term is Newton, and has
no c. Why do you think they call it the POST-newtonian approximation?

[snip stuff that has nothing to do with wether GR was "backfit" or not]

--
Matthew Nobes
c/o Physics Dept. Simon Fraser University, 8888 University
Drive Burnaby, B.C., Canada
http://www.sfu.ca/~manobes

Matthew Nobes wrote in message
...
greywolf42 wrote:

Matthew Nobes wrote in message
...
greywolf42 wrote:

Matthew Nobes wrote in message
...

[snip mangled stuff]

'Mangled stuff?'

Yes, stuff pushed over an 80 character width, which my newsreader
renders in a most unpleasant way.

Restoring it is more trouble than it's worth, so I've snipped
it.

Not sure whose reader did that, but OK.

It's more than that, it's essentially wrong. The *important* thing
about
GR is that it reduces to an inverse square law in the weak field
limit.

Plus a constant speed of gravity equal to 'c'.

No. In the weak field limit, c doesn't enter into it.

LOL! So sorry, but you are incorrect. In the weak field limit, the
speed
of gravity is 'c.'

You're thinking of the *next* term in the series. The lowest order effect
(i.e. a *really* weak field) gives the Newtonian theory, and nothing
else.

The 'weak limit' is as the field goes to zero (mass tends to zero). Not
'really, really zero.' It would be interesting to see the math that has a
speed of propagation 'c' as mass goes to zero .... but just before it gets
there it zooms to infinity (just like at 'infinite' mass).

The speed of gravity tends to infinity as the field
approaches the strong limit. See Steve Carlip's paper,
http://arXiv.org/abs/gr-qc/9909087.

This is untrue in GR. Nothing in Dr. Carlip's paper says that
the speed of gravity is infinite in the strong field limit.

You are correct that Dr. Carlip's paper does not refer to the strong limit
of GR. The reference to Dr. Carlip's paper was for the weak field limit
(which was much clearer before my paragraph was split.) You are incorrect
in claiming that the speed of gravity does not tend to infinity at
'infinite' mass.

From the final paragraph

"The Einstein Field Equations contain a single parameter c_g, which
describes both the speed of gravitational waves and the ``speed of
gravity'' occuring in the expression for abberation [...]."

and

"The success of the theory in explaining the orbital decay of binary
plusars implies that c_g=c at the 1% level or better."

What's the point of this quote? It seems to support my point (c_g = 'c' in
the weak limit).

Plus c=1.

LOL! Whether you call it 3.0E8 mps or 3.0E10 cps or 1 light-unit it's
the
same thing.

My point exactly. The *physics* of GR/SR doesn't depend on what units you
use.

??? That was my point. A unit change doesn't affect the physics. So your
'c=1' was amusing.

3.0E8 mps = 1 light-unit. Same speed.

A finite speed of gravity, intially determined by Paul Gerber,
17 years prior to Einstein.

Whatever. I'm not discussing history.

[snip]


That's not true, gravitational waves propagate at c, no matter how
strong
they are. Please don't tell me that you're still trying to tell Steve
Carlip what he "really meant" in his Speed of Gravity paper.

I don't think even Steve will disagree that the point of his paper was
that
the speed of gravity can be 'c', without any ill effects.

No. That's not the point. The point is in GR the speed of gravity is c
and
that's it. How hard is that to understand? Read the final paragraph.

Sigh. If the speed of gravity = c in GR (and 'that's it'), then the speed
of gravity is 'c' in the weak limit. NOT infinity.

Steve disagreed
with my taking his paper and demonstrating that Steve's logic applies to
other finite-speed theories -- not just GR. But here's Steve's
conclusion:

"In particular, while the observed absence of aberration is consistent
with
instantaneous propagation (with an extra interaction somehow added on to
explain the gravitational radiation reaction), it is also consistent
with
the speed-of-light propagation predicted by general relativity."

I'm not disputing that. I'm addressing your claim that GR was "backfit"
onto Newton's theory. I have no problem believing that a different,
*non-GR* theory could explain some things.

Whoa! I think we've come 'round Robin Hood's barn, here.

The immediate point I was discussing was that general relativity contains a
finite speed of gravity -- even in the weak limit. Specifically, your claim
was:

"In the weak field limit, c doesn't enter into it."

Which you clarified as:

"You're thinking of the *next* term in the series. The lowest order effect
(i.e. a *really* weak field) gives the Newtonian theory, and nothing else."

I.O.W. an essentially infinite speed of gravity. Are we confusing each
other?


The constant G (or G/8pi) is merely a unit convention, relativists
use
G=1 all the time.

It is not just a unitary convention.

Well, yes it is.

G = 6.672 x 10^(-11) Nm^2/kg^2 = 66.72 pNm^2/kg^2

Look at that, I just changed G by 11 orders of magnitude.

What a pathetic attempt. You didn't change G.

Sure I did. What you really mean is that I didn't change the physics
which is my point. Einstein showed that his theory reduced to a
1/r potential, i.e. that it had the *SAME*PHYSICS* as Newton's. The
constant out front is just a choice of units, hence GR was not "backfit".

I think I see a glimmer of the misunderstanding. When I said "8 pi" was
selected, I meant that Einstein selected a constant that returned Newton's
equation (except for finite speed-of-gravity). I did not mean that he
selected a specific set of units.


By any chance were you in
charge of that Mars lander a couple of years ago? The 'values' were the
same. But one was in newtons and the other in pounds......

Okay, everybody has to use the same units. But you're missing the point.
Surely you're not claiming that the laws of physics were different
in the two different systems of units?

No. I believe you misunderstood my use of the term '8 pi' (see above).

The units used for the symbols MUST
match some real-world system of measure when the mathematical scrawls
are
compared to reality.

Sure, but the choice of units in the "mathematical scrawls" cannot
affect
the predictions. Hence the units are arbitary.

LOL! Tell that to the Mars lander!!!

*sigh* Tell me something, do you think that the choice of units affects
the fact that weak field GR reduces to a 1/r potential? Would you dispute
the fact that it's the 1/r part that's important, not the SPECIFIC
numerical
value for G?

I consider the specific, experimental value (regardless of units used)
important. But the 1/r is only PART of the equation that I consider
important in the GR weak-field limit. The other part is the finite speed of
propagation.


Hence G=1 (and c=1) is fine
for understanding the important *physics* of GR.

But not for comparing to the real world.

Sure, if two groups use the same units.

They can use different units -- so long as after a day the effect has
travelled 24 light-hours, 1 light-day, etc.

Like I said, the important *physical* result of the weak-field
expansion
of GR is that it shows that

V(r) ~ 1/r

the constant out front expresses the choice of units, it can be
10^{-11}
or 10
or 1 or anything really. It's the 1/r part that's important.

The 'weak field' expansion also includes a finite 'c'. That's also
important, because it leads to the NNPA of Mercury.

That's the first correction from GR. The leading term is Newton, and has
no c. Why do you think they call it the POST-newtonian approximation?

I'm not discussing the PPN or an 'approximation' to GR. I'm discussing the
theoretical weak-field limit of GR.

"Gerber was lucky enough to come up with the combination that, in
retrospect, we can recognize as the weak field approximation of general
relativity." *

*Quote from Dr. Steve Carlip
From: (Steve Carlip)
Date: 1998/05/26
Message-ID:
Newsgroups: sci.physics.relativity

And Gerber -- of course -- had a finite speed of gravity. Which he
determined to be 'c'.

[snip stuff that has nothing to do with wether GR was "backfit" or not]

greywolf42
ubi dubium ibi libertas

greywolf42 wrote:
If the speed of gravity = c in GR (and 'that's it'), then the speed
of gravity is 'c' in the weak limit. NOT infinity.

This is not true. In order to obtain the Newtonian limit of GR, one must
have:
a) weak fields
b) velocities small compared to c
c) Newtonian-like coordinates

(b) is equivalent to taking the limit c-infinity.... That is, of
course, also the relationship between the Lorentz transform and the
Galilean transform....

Of course in our everyday lives, c is indistinguishable from
infinity. Newtonian mechanics was invented at a time when
everyday experience was all they had. GR's Newtonian limit
could not possibly reproduce this very accurately unless
it, too, had an infinite speed of light and of gravity.
[See my post in the thread "Einstein GR approximation" for
what I mean by "speed of gravity".]

An approximation to GR is not GR. shrug


Tom Roberts

Tom Roberts wrote in message
...
greywolf42 wrote:
If the speed of gravity = c in GR (and 'that's it'), then the speed
of gravity is 'c' in the weak limit. NOT infinity.

This is not true. In order to obtain the Newtonian limit of GR, one must
have:
a) weak fields
b) velocities small compared to c
c) Newtonian-like coordinates

Nobody is talking about the 'Newtonian' approximation, Tom. We're
discussing the weak-field limit of GR.

(b) is equivalent to taking the limit c-infinity.... That is, of
course, also the relationship between the Lorentz transform and the
Galilean transform....

Of course in our everyday lives, c is indistinguishable from
infinity.

In your life, maybe. It's very evident to those who work with telephony,
radar, GPS, piloting, computer hardware, travel, .....

Newtonian mechanics was invented at a time when
everyday experience was all they had.

Horsefeathers. The Greeks measured the circumference of the Earth (accurate
to within 10%) with a single straight stick.

GR's Newtonian limit
could not possibly reproduce this very accurately unless
it, too, had an infinite speed of light and of gravity.

Horsefeathers again. All that was needed was that the speed of the planets
was significantly smaller than the speed of gravity.

[See my post in the thread "Einstein GR approximation" for
what I mean by "speed of gravity".]

And it was a pathetic game of counting angels on pinheads, there.


An approximation to GR is not GR. shrug

Precisely my point. No one was talking about an approximation to GR. We
were discussing the weak-field limit (which is not an approximation).

greywolf42
ubi dubium ibi libertas

greywolf42 wrote:

Tom Roberts wrote in message
...
greywolf42 wrote:
If the speed of gravity = c in GR (and 'that's it'), then the speed
of gravity is 'c' in the weak limit. NOT infinity.

This is not true. In order to obtain the Newtonian limit of GR, one must
have:
a) weak fields
b) velocities small compared to c
c) Newtonian-like coordinates

Nobody is talking about the 'Newtonian' approximation, Tom. We're
discussing the weak-field limit of GR.

Umm, when you neglect *all* terms that go like 1/c they're one and the same.
That's the case *I* was talking about when disputing your claim that GR
was "backfit". I'll try to be really clear here,

*If* you *neglect* *all* terms that go like 1/c then GR reduces to a
*1/r* potential. Hence there is no "backfit" onto Newtonian gravity.

[snip]
Precisely my point. No one was talking about an approximation to GR. We
were discussing the weak-field limit (which is not an approximation).

Yes it is. You keep terms up to some power of 1/c and throw the rest
away. If you neglect *all* terms of order 1/c and higher you get
Newtonian gravity, hence there was no "backfit".

--
Matthew Nobes
c/o Physics Dept. Simon Fraser University, 8888 University
Drive Burnaby, B.C., Canada
http://www.sfu.ca/~manobes