Where did the 8pi originally come from?
Perion
originally arrived at 8pi for the proportionality constant in G=8piT?
--
Thanks,
Perion
greywolf42
Perion <Razr...@hotmail.com> wrote in message
news:ks-dnchcNY_...@comcast.com...
> Can anyone describe (or point me to some information) how Einstein
> originally arrived at 8pi for the proportionality constant in G=8piT?
Quite simple. It was a backfit to Newton's equation of gravity -- in the
weak limit. That is, it was assumed by Einstein as one of the boundary
conditions in determining constants of GR.
greywolf42
ubi dubium ibi libertas
Perion
wasn't sure if Einstein derived it using the same method. I can't find the
online translated version of Einstens GR paper but I know it's out there
because I found it a month or two ago.
Regards,
Perion
"greywolf42" <min...@sim-ss.com> wrote in message
news:vm9on3l...@corp.supernews.com...
Tom Roberts
CGS/MKS units of course, but nowadays most authors use units with G=1 or
8piG=1; with the latter units one simply writes:
G = T
So the 8pi is not of major significance (except possibly historical
interest).
Tom Roberts tjro...@lucent.com
On 9/15/2003 8:31 AM, Perion wrote:
> Thanks. I saw how MTW did it by comparing Newton's mass density to R_00 but
> wasn't sure if Einstein derived it using the same method. I can't find the
> online translated version of Einstens GR paper but I know it's out there
> because I found it a month or two ago.
>
greywolf42
Tom Roberts <tjro...@Lucent.com> wrote in message
news:3F65C5F...@Lucent.com...
> On 9/15/2003 8:31 AM, Perion wrote:
> > "greywolf42" <min...@sim-ss.com> wrote in message
> > news:vm9on3l...@corp.supernews.com...
> >>Perion <Razr...@hotmail.com> wrote in message
> >>news:ks-dnchcNY_...@comcast.com...
> >>
> >>>Can anyone describe (or point me to some information) how Einstein
> >>>originally arrived at 8pi for the proportionality constant in G=8piT?
> >>
> >>Quite simple. It was a backfit to Newton's equation of gravity -- in
the
> >>weak limit. That is, it was assumed by Einstein as one of the boundary
> >>conditions in determining constants of GR.
> > Thanks. I saw how MTW did it by comparing Newton's mass density to R_00
but
> > wasn't sure if Einstein derived it using the same method. I can't find
the
> > online translated version of Einstens GR paper but I know it's out there
> > because I found it a month or two ago.
>
> The 8pi is merely a specific choice of units. Einstein used traditional
> CGS/MKS units of course, but nowadays most authors use units with G=1 or
> 8piG=1; with the latter units one simply writes:
>
> G = T
>
> So the 8pi is not of major significance (except possibly historical
> interest).
Wrong again, Tom. The 8 pi is not simply a unitary choice -- it follows
from the choice of units. It is not itself a choice of units. The strength
of the gravitational 'couple' was taken from Newton's equation. GR -- being
fundamentally a pure math theory -- requires a way to set the constants to
connect them to observations in the real universe.
The speed of light -- for example -- is physically the same... whether we
use units in mks, cgs, cubits per tic or whatever.
Dirk Van de moortel
"greywolf42" <min...@sim-ss.com> wrote in message news:vmc85pc...@corp.supernews.com...
>
> Tom Roberts <tjro...@Lucent.com> wrote in message
> news:3F65C5F...@Lucent.com...
[snip]
> > The 8pi is merely a specific choice of units. Einstein used traditional
> > CGS/MKS units of course, but nowadays most authors use units with G=1 or
> > 8piG=1; with the latter units one simply writes:
> >
> > G = T
> >
> > So the 8pi is not of major significance (except possibly historical
> > interest).
>
> Wrong again, Tom. The 8 pi is not simply a unitary choice -- it follows
> from the choice of units. It is not itself a choice of units.
Brilliant:
http://users.pandora.be/vdmoortel/dirk/Physics/Fumbles/Unitairy.html
Title: "About unitairy choices of units"
Dirk Vdm
greywolf42
Dirk Van de moortel <dirkvand...@ThankS-NO-SperM.hotmail.com> wrote in
message news:Xpq9b.22158$Wk4.1...@phobos.telenet-ops.be...
Hello again, coward. Still not willing to post any real physics?
Bye, bye, Dinky.
Perion
Perion
greywolf42
No reason to be sorry. Your question was a good one.
Dinky van der Mumble haunts the fringes of the newsgroups -- hoping that he
can shoot a spitwad when he thinks somebody's back is turned. But I hate to
just ignore him, he so obviously craves the attention. So I provide him a
minimum of what he apparently needs.
Dirk Van de moortel
"greywolf42" <min...@sim-ss.com> wrote in message news:vmgv9ol...@corp.supernews.com...
>
[snip]
>
> Dinky van der Mumble haunts the fringes of the newsgroups -- hoping that he
> can shoot a spitwad when he thinks somebody's back is turned. But I hate to
> just ignore him, he so obviously craves the attention. So I provide him a
> minimum of what he apparently needs.
http://users.pandora.be/vdmoortel/dirk/Physics/Fumbles/Avoid.html
Dirk Vdm
Ken S. Tucker
> Gee... sorry I brought it up ;-)
> Perion
Gee, is that a pun...
Check out Dover's "Principle of Relativity",
go to Eq. (69) in GR and find,
kappa = 8 pi K / c^2
This refs back to Poisson's Eq. on pg 148
Nabla^2 phi = 4 pi kappa density
Ken S. TUcker
Steve Carlip
This is right, for a sufficiently loose definition of ``backfit.''
You should first as the question of where Newton's constant G
came from in Newton's law of gravity, F=GMm/r^2. (Warning:
I'm using G to mean Newton's constant, *not* the Einstein
tensor.) The answer is that given a system of units for mass,
length, and time, G was an undetermined coupling constant,
that had to be fixed by measurement. Note that this did not
significantly weaken the predictive power of Newtonian gravity:
one careful laboratory measurement determines G, and that
value can then be used to predict the results of millions of other
measurements.
Now write the Einstein field equations as G_{ab} = kT_{ab}. The
constant k is again an unknown coupling constant, which has
to be measured. One can again set up a laboratory experiment
like the Cavendish experiment to make this measurement. The
main difference is that you now need to know the GR prediction
for the result of such an experiment. In principle, you can just
sit down with the field equations and work out the answer, to
whatever accuracy you need.
In practice, it's easier to go via the Newtonian limit. The Einstein
field equations predict that for weak fields (and a careful definition
of coordinates, time, etc.) a pair of masses behave as if there were
a Newtonian gravitational attraction F = kc^4Mm/8 pi r^2, where
c is the speed of light. By comparing this to Newton's expression,
you can read off the value k=8 pi G/c^4. You can think of this as
``backfitting'' to Newton's equation, but it's probably better to
think of it as fitting a single instance of Nwton's equation -- say,
Newton's equation applied to a particular Cavendish experiment.
As in Newtonian gravity itself, once the constant k is fixed by one
experiment, you have no more freedom left.
Why the pi? Basically because the Einstein field equations are
differential equations. If you write Newton's gravitational force
law as a differential equation, the Poisson equation, you'll find
that the right-hand side is not just density, but 4pi(density).
This is the same 4pi you get when you go from Coulomb's law
to Gauss's. If you trace it back far enough, it comes from the
area of a sphere.
Finally, note that k, like G, is a dimensionful constant, that is, it
depends on your choice of units. In Newtonian gravity, you could,
in principle, decide to use meters and seconds and to set G=1;
this would then simply determine what units you were using to
measure mass. In this sense, the whole 8pi G/c^4 can also be
viewed as defining a choice of units.
Steve Carlip
AndroclesInEngland
but it IS an accurate description.
A couple of years ago I described him as a puppy trying to run with the
hounds after the fox, yapping as he went along - he certainly has nothing to
say for himself.
Well put, greywolf.
Dirk Van de moortel
"AndroclesInEngland" <jp006...@blueyonder.co.uk> wrote in message news:FJbab.1606$sj....@news-binary.blueyonder.co.uk...
[snip]
> Well put, greywolf.
Careful, Mingst is a true believer in time dilation and
length contraction. You guys are highly incompatible.
He's not your kind of puppy.
Dirk Vdm
AndroclesInEngland
Androcles
Perion
"Steve Carlip" <car...@dirac.ucdavis.edu> wrote in message
news:bk7rqr$7p4$4...@woodrow.ucdavis.edu...
Excellent reply - thank you.
Best wishes,
Perion
Dirk Van de moortel
"AndroclesInEngland" <jp006...@blueyonder.co.uk> wrote in message news:Bfgab.5291$sj....@news-binary.blueyonder.co.uk...
I fully agree on the fact that you do have a lot in common.
No question about that.
Dirk Vdm
greywolf42
By the way, Dinky, I haven't thanked you before for posting that 'fumble.'
Perhaps when you get to junior high reading comprehension, you'll
understand.
greywolf42
Even your memory's going, Dinky. I favor Lorentz Electrodynamic Theory.
There is no 'time dilation' at all. And there is no 'length contraction.'
Material objects contract. Not 'length.'
greywolf42
>
> > Perion <Razr...@hotmail.com> wrote in message
> > news:ks-dnchcNY_...@comcast.com...
> >> Can anyone describe (or point me to some information) how Einstein
> >> originally arrived at 8pi for the proportionality constant in G=8piT?
>
> > Quite simple. It was a backfit to Newton's equation of gravity -- in
the
> > weak limit. That is, it was assumed by Einstein as one of the boundary
> > conditions in determining constants of GR.
>
> This is right, for a sufficiently loose definition of ``backfit.''
>
> You should first as the question of where Newton's constant G
> came from in Newton's law of gravity, F=GMm/r^2. (Warning:
> I'm using G to mean Newton's constant, *not* the Einstein
> tensor.)
Newton's constant was derived by application of the calculus to Kepler's
observational "laws" of planetary motion. Newton determined the equation of
force necessary to duplicate Kepler's laws. The formula F= GMm/r^2 resulted
from this analysis. This is why Newton never attempted to explain 'why' his
gravitational equation was what it was ("Hypothesis non fingo.")
> The answer is that given a system of units for mass,
> length, and time, G was an undetermined coupling constant,
> that had to be fixed by measurement. Note that this did not
> significantly weaken the predictive power of Newtonian gravity:
> one careful laboratory measurement determines G, and that
> value can then be used to predict the results of millions of other
> measurements.
The *VALUE* of the constant, G, is given by the laboratory measurements
(because we can use known masses). The equation of gravitational attraction
and the identification of the constant G, however, was derived elsewhere.
> Now write the Einstein field equations as G_{ab} = kT_{ab}. The
> constant k is again an unknown coupling constant, which has
> to be measured. One can again set up a laboratory experiment
> like the Cavendish experiment to make this measurement. The
> main difference is that you now need to know the GR prediction
> for the result of such an experiment. In principle, you can just
> sit down with the field equations and work out the answer, to
> whatever accuracy you need.
>
> In practice, it's easier to go via the Newtonian limit. The Einstein
> field equations predict that for weak fields (and a careful definition
> of coordinates, time, etc.) a pair of masses behave as if there were
> a Newtonian gravitational attraction F = kc^4Mm/8 pi r^2, where
> c is the speed of light. By comparing this to Newton's expression,
> you can read off the value k=8 pi G/c^4. You can think of this as
> ``backfitting'' to Newton's equation, but it's probably better to
> think of it as fitting a single instance of Nwton's equation -- say,
> Newton's equation applied to a particular Cavendish experiment.
> As in Newtonian gravity itself, once the constant k is fixed by one
> experiment, you have no more freedom left.
But Einstein didn't do that ("Foundation of the General Theory of
Relativity," 1916, section 21). Adding additional constants (8, pi, c) to
the mix only changes the units. Not the strength of the interaction
(obviously). Einstein explicitly adjusted to the Newtonian *equation*. Not
to an arbitrary experiment.
And the experiments were first done prior to GR, so the issue was moot.
Experiments don't care if you're using GR to analyse the data or Newton.
> Why the pi? Basically because the Einstein field equations are
> differential equations. If you write Newton's gravitational force
> law as a differential equation, the Poisson equation, you'll find
> that the right-hand side is not just density, but 4pi(density).
> This is the same 4pi you get when you go from Coulomb's law
> to Gauss's. If you trace it back far enough, it comes from the
> area of a sphere.
>
> Finally, note that k, like G, is a dimensionful constant, that is, it
> depends on your choice of units. In Newtonian gravity, you could,
> in principle, decide to use meters and seconds and to set G=1;
> this would then simply determine what units you were using to
> measure mass. In this sense, the whole 8pi G/c^4 can also be
> viewed as defining a choice of units.
Correct. The choice of units does not determine the physical strength of
the constant (or couple).
FrediFizzx
How about if the 8pi comes from rotation?
FrediFizzx
Gregory L. Hansen
>
> > Perion <Razr...@hotmail.com> wrote in message
> > news:ks-dnchcNY_...@comcast.com...
> >> Can anyone describe (or point me to some information) how Einstein
> >> originally arrived at 8pi for the proportionality constant in G=8piT?
>
> > Quite simple. It was a backfit to Newton's equation of gravity -- in the
> > weak limit. That is, it was assumed by Einstein as one of the boundary
> > conditions in determining constants of GR.
>
> This is right, for a sufficiently loose definition of ``backfit.''
>
> You should first as the question of where Newton's constant G
> came from in Newton's law of gravity, F=GMm/r^2. (Warning:
> Why the pi? Basically because the Einstein field equations are
> differential equations. If you write Newton's gravitational force
> law as a differential equation, the Poisson equation, you'll find
> that the right-hand side is not just density, but 4pi(density).
> This is the same 4pi you get when you go from Coulomb's law
> to Gauss's. If you trace it back far enough, it comes from the
> area of a sphere.
In Newton's law, the 1/4*pi term is conspicuously absent. But what
about the extra factor of 2 in Einstein's equations? Is that just
because g_0i = g_i0?
greywolf42
FrediFizzx <fredi...@hotmail.com> wrote in message
news:bkda75$gb0e$1...@ID-185976.news.uni-berlin.de...
> "greywolf42" <min...@sim-ss.com> wrote in message
> news:vmk2u9k...@corp.supernews.com...
> |
> | Steve Carlip <car...@dirac.ucdavis.edu> wrote in message
> | news:bk7rqr$7p4$4...@woodrow.ucdavis.edu...
> | > greywolf42 <min...@sim-ss.com> wrote:
> | >
> | > > Perion <Razr...@hotmail.com> wrote in message
> | > > news:ks-dnchcNY_...@comcast.com...
> | > >> Can anyone describe (or point me to some information) how Einstein
> | > >> originally arrived at 8pi for the proportionality constant in
G=8piT?
{snip to comments pertaining to 8 pi and rotation}
If one likes the units, 4 pi comes from the solid angle of integration, and
the factor of 2 comes from the "equations of motion of the material point
according to the Newtonian theory." (Einstein, section 21, 1916.) Rotation
does not enter into it.
FrediFizzx
"Solid *angle* of integration"? Doesn't this imply some kind of rotation?
Well, I am really talking out my ass here since I have not studied GR that
much yet. The only reason I mention it because of a parallel I was getting
between EM energy and gravitonic energy. I highly suspect a spin 1 photon
has a 4pi rotation overall in free space. So if we get this from photonic
energy, then a spin 2 graviton as a "particle" of gravitonic energy might
have an 8pi rotation?
FrediFizzx
Steve Carlip
> Steve Carlip <car...@dirac.ucdavis.edu> wrote in message
> news:<bk7rqr$7p4$4...@woodrow.ucdavis.edu>...
[...]
>> Why the pi? Basically because the Einstein field equations are
>> differential equations. If you write Newton's gravitational force
>> law as a differential equation, the Poisson equation, you'll find
>> that the right-hand side is not just density, but 4pi(density).
>> This is the same 4pi you get when you go from Coulomb's law
>> to Gauss's. If you trace it back far enough, it comes from the
>> area of a sphere.
> In Newton's law, the 1/4*pi term is conspicuously absent. But what
> about the extra factor of 2 in Einstein's equations? Is that just
> because g_0i = g_i0?
No, it's because of the 1/2 in the connection,
\Gamma^a_{bc} = 1/2 g^{ad}(\partial_b g_cd} + ...)
This means that in the weak field approximation of the geodesic
equation, you have a term of (1/2)\partial_i g_{tt}, so g_{tt} looks
like twice the Newtonian potential.
Steve Carlip
Old Physics
Dr. Carlip,
My question is off this thread but I want to make sure that I have
been given the correct answer by others. Would a train two units in
length, in the rest frame of a "barrel roll" track one unit in
circumference, fit on the track if it were traveling in excess of
86.6% the SoL? Could straight sections of track be put in and still
maintain this ratio?
With greatest respect,
Stephen Kearney
shuba
> Would a train two units in
> length, in the rest frame of a "barrel roll" track one unit in
> circumference, fit on the track if it were traveling in excess of
> 86.6% the SoL?
Relativity isn't about explaining contrived gedankens, rather it's
about explaining observations. Rigidity is frame dependent. See
the FAQ. Read a book. Post something interesting.
> Could straight sections of track be put in and still
> maintain this ratio?
Yes, and although it's consistently denied by card-carrying
members of the mainstream physics establishment, both gay and
bisexual sections of the track will generally maintain an even
more flexible ratio.
---Tim Shuba---
Perion
> Relativity," 1916, section 21). Adding additional constants (8, pi, c)
to
> the mix only changes the units. Not the strength of the interaction
> (obviously). Einstein explicitly adjusted to the Newtonian *equation*.
Not
> to an arbitrary experiment.
>
hunting for an online english translation of that paper - any idea where I
can get it?
Perion
Perion
with it? I'd like to know what (mathematically and physically) he struggled
with to deal with arriving at k in G_uv = - kT_uv. I understand it was a
"retrofit" to Newton "in the weak field limit". Did he, at that point know
anything about "the weak field limit"???
Perion
Dirk Van de moortel
"Perion" <Razr...@hotmail.com> wrote in message news:G6acnSKCfqH...@comcast.com...
This scanned version might help:
http://www.alberteinstein.info/gallery/gtext3.html
Enjoy...
Dirk Vdm
greywolf42
I'd also recommend the Dover edition of "The Principle of Relativity." It's
a compendium of early seminal papers in the field, including FGTR. Cheap
and easily available.
Dirk,
Thanks for providing some useful input to the group.
greywolf42
Yes, since he was defining it.
What Einstein said was (Einstein, "The Foundation of the General Theory of
Relativity," section 21, 1916.):
"... (W)e suppose the gravitational field to be a quasi-static field, by
confining ourselves to the case where this motion of the matter generating
the gravitational field is but slow (in comparison with the velocity of the
propagation of light), we may neglect on the right-hand side
differentiations with respect to the time in comparison with those with
respect to the space co-ordinates, so that we have
d^2 x / dt^2 = - 1/2 partial g44/partial x (tau = 1, 2, 3) {eq 67}
"This is the equation of motion of the material point according to Newton's
theory, in which 1/2 g44 plays the part of the gravitational potential."
greywolf42
No. A 'solid angle' identifies the 'exposure' of a point to the surrounding
3D space. The '2' above is from the standard linear equations of motion.
> Well, I am really talking out my ass here since I have not studied GR that
> much yet. The only reason I mention it because of a parallel I was
getting
> between EM energy and gravitonic energy. I highly suspect a spin 1 photon
> has a 4pi rotation overall in free space. So if we get this from photonic
> energy, then a spin 2 graviton as a "particle" of gravitonic energy might
> have an 8pi rotation?
Neither GR nor Maxwell's equations were developed from quantum effects or
concepts like 'photons.' So the characteristics of quantum entities won't
affect the results.
greywolf42
What Einstein said was (Einstein, "The Foundation of the General Theory of
Relativity," section 21, 1916.):
"... (W)e suppose the gravitational field to be a quasi-static field, by
confining ourselves to the case where this motion of the matter generating
the gravitational field is but slow (in comparison with the velocity of the
propagation of light), we may neglect on the right-hand side
differentiations with respect to the time in comparison with those with
respect to the space co-ordinates, so that we have
d^2 x / dt^2 = - 1/2 partial g44/partial x (tau = 1, 2, 3) {eq 67}
"This is the equation of motion of the material point according to Newton's
theory, in which 1/2 g44 plays the part of the gravitational potential."
greywolf42
ubi dubium ibi libertas
Old Physics
> Stephen Kearny wrote:
>
> > Would a train two units in
> > length, in the rest frame of a "barrel roll" track one unit in
> > circumference, fit on the track if it were traveling in excess of
> > 86.6% the SoL?
>
> Relativity isn't about explaining contrived gedankens, rather it's
> about explaining observations. Rigidity is frame dependent. See
> the FAQ. Read a book. Post something interesting.
Contrived "thought experiments" are a proud tradition in
developing experiments and explaining relativity. The train and
lightning bolts of Einstein's gedanken are still used in modern
physics literature. I did not see a reference to this peculiar
version, with linear track added. Perhaps you could direct me to a
text or site that addresses this scenario.
>
> > Could straight sections of track be put in and still
> > maintain this ratio?
>
> Yes, and although it's consistently denied by card-carrying
> members of the mainstream physics establishment, both gay and
> bisexual sections of the track will generally maintain an even
> more flexible ratio.
>
>
> ---Tim Shuba---
I take that Yes to be a "Yes". This leads to a problem. If a
pole 40ft long is traveling with the train it will physically be
contracted to fit in a barn 20.1 ft in length that is stationary to
the track. That from the pole's FoR the closing of the barn doors
appear not to be simultaneous, is in consequence of the light having a
fixed speed in a medium. If the track, with its atoms also made of
wave energy, were moving WRT the aether, then the train would be more
physically contracted on the side where its velocity is added to the
tracks motion. The Lorentz transform would apply as Lorentz intended.
I prefer a linear answer, but any answer is sure to be
interesting.
Thanks,
Stephen Kearney
FrediFizzx
Well of course not. But we are pretty certain that the Universe is
composed entirely of "quantum objects". Taking that into consideration,
then GR should probably be defined by *all* the quantum objects in the
Universe. So I would think the "true" source of the 8pi might be quantum
mechanically related to the spin of gravitonic energy. If this *is* the
case, then quantum objects *are* affecting the results indirectly.
FrediFizzx
Perion
Perion
Perion
>
> By the way, Dinky, I haven't thanked you before for posting that 'fumble.'
> Perhaps when you get to junior high reading comprehension, you'll
> understand.
>
> greywolf42
perion
Steve Carlip
[on the value of k in G=kT]
> Sure that's why - now - in retrospect. But, is that why Einstein came up
> with it? I'd like to know what (mathematically and physically) he struggled
> with to deal with arriving at k in G_uv = - kT_uv. I understand it was a
> "retrofit" to Newton "in the weak field limit". Did he, at that point know
> anything about "the weak field limit"???
Yes, certainly. Newtonian gravity was a highly successful theory;
the ``zeroeth test'' of GR, long before light deflection or Mercury's
perihelion, was that it would reduce to Newtonian gravity in an
appropriate approximation.
(In the same way, someone who wants to propose a replacement
for GR had better show that the new theory reduces to GR in an
appropriate approximation).
Steve Carlip
shuba
> Contrived "thought experiments" are a proud tradition in
> developing experiments and explaining relativity. The train and
> lightning bolts of Einstein's gedanken are still used in modern
> physics literature. I did not see a reference to this peculiar
> version, with linear track added. Perhaps you could direct me to a
> text or site that addresses this scenario.
I already did. See the FAQ entry about the rotating disk.
Perfect rigidity is incompatible with relativity. You can look
up Ehrenfest's paradox as well.
[..]
> I prefer a linear answer, but any answer is sure to be
> interesting.
If you want a linear answer, learn some linear algebra. You'll
even see why the result you expect from your airliner experiment
is inconsistent with both SR and LET.
---Tim Shuba---
greywolf42
news:bkqhqf$2p5$1...@woodrow.ucdavis.edu...
Since the only GR tests are in the weak-field limit, then all they have to
do is reproduce the weak-field limit of GR -- not GR proper.
Or show where GR is contradicted by experiment.
Perion
>
It seemed like such a simple question. Heh.
I found the k in that in MTW's treatment and with Poisonn's equation - just
as some wise soul told me earlier.
Sorry - didn't mean to create a stirr,
Perion
greywolf42
>
> "greywolf42" <min...@sim-ss.com> wrote in message
> news:vmp3aj5...@corp.supernews.com...
> >
> It seemed like such a simple question. Heh.
Simple, but instructive.
> I found the k in that in MTW's treatment and with Poisonn's equation -
just
> as some wise soul told me earlier.
>
> Sorry - didn't mean to create a stirr,
No problem. The 'stirring' comes from those who have created a religion
from Einstein's work. And who can't accept the simple, mundane method that
Einstein used to match his math to the universe. GR is good work, but
certain types react violently to anyone who doesn't intone the currently
accepted mantra -- even if one simply quotes Einstein.
car...@nospam.dirac.ucdavis.edu
> Steve Carlip <car...@nospam.dirac.ucdavis.edu> wrote in message
> news:bkqhqf$2p5$1...@woodrow.ucdavis.edu...
>> for GR had better show that the new theory reduces to GR in an
>> appropriate approximation).
> Since the only GR tests are in the weak-field limit, then all they have to
> do is reproduce the weak-field limit of GR -- not GR proper.
The binary pulsar tests are strong field tests.
> Or show where GR is contradicted by experiment.
``And,'' not ``or.'' The point is that if GR is eventually contradicted
by an experiment, it's *not* enough to just manage to get the right
answer for that experiment; you also have to explain the cases where
GR agrees with experiment. You don't get to say, ``Look, I can explain
this new result'' without *also* saying ``and I can explain the old
results, too.''
Steve Carlip
greywolf42
news:bl2e8a$gbm$1...@woodrow.ucdavis.edu...
> greywolf42 <min...@sim-ss.com> wrote:
> > Steve Carlip <car...@nospam.dirac.ucdavis.edu> wrote in message
> > news:bkqhqf$2p5$1...@woodrow.ucdavis.edu...
>
> >> (In the same way, someone who wants to propose a replacement
> >> for GR had better show that the new theory reduces to GR in an
> >> appropriate approximation).
>
> > Since the only GR tests are in the weak-field limit, then all they have
> > to do is reproduce the weak-field limit of GR -- not GR proper.
>
> The binary pulsar tests are strong field tests.
They would have been -- if the masses of the pulsars had not first been
determined by assuming GR. In short, that particular observation is
circular.
> > Or show where GR is contradicted by experiment.
>
> ``And,'' not ``or.'' The point is that if GR is eventually contradicted
> by an experiment, it's *not* enough to just manage to get the right
> answer for that experiment; you also have to explain the cases where
> GR agrees with experiment. You don't get to say, ``Look, I can explain
> this new result'' without *also* saying ``and I can explain the old
> results, too.''
Once one has disproved GR by experiment (whenever and wherever this
happens), then one no longer has to match even consider 'matching' any part
of GR. What one then has to match is experiments -- not GR.
For example, there conceivably might arise a theory that explains the
experiment that disproves GR, but can't be applied to one of the 'cases
where GR agrees with experiment'. The new theory would then be better than
GR (one can't-answer vs. one wrong-answer).
Aside from the quibbling, the point is the same. One does not have to
reduce to "GR" -- one has to reduce to the part(s) of GR that are
experimentally verified (i.e. only the weak-field limit portion of GR).
Explaining the pulsar decay would be nice, too. But one can settle for
being consistent -- just like GR is.
greywolf42
> "greywolf42" <min...@sim-ss.com> wrote in message
> news:vmp3agr...@corp.supernews.com...
> |
> | FrediFizzx <fredi...@hotmail.com> wrote in message
> | news:bkfcad$1621r$1...@ID-185976.news.uni-berlin.de...
> | > "greywolf42" <min...@sim-ss.com> wrote in message
> | > news:vml5frp...@corp.supernews.com...
> | > |
{snip higher levels}
That would contradict cosmology. Unless the 'space' is itself a quantum
object. Of course, current relativisitic cosmological theory is based on
GR.
> Taking that into consideration,
> then GR should probably be defined by *all* the quantum objects in the
> Universe. So I would think the "true" source of the 8pi might be quantum
> mechanically related to the spin of gravitonic energy. If this *is* the
> case, then quantum objects *are* affecting the results indirectly.
The *true* source of the 8 pi is a historical fact. 4 pi from geometry and
a factor of 2 from Newton's equations.
Keep in mind that GR is a mathematical map -- not a physically-derived
theory.
FrediFizzx
Huh? What else is there other than quantum objects? If the Universe is a
closed system, we only have quantum objects in it. There is nothing else.
Space-time *has* to be defined by the quantum objects including the ones
in the vacuum. Especially the quantum objects in the vacuum.
| > Taking that into consideration,
| > then GR should probably be defined by *all* the quantum objects in the
| > Universe. So I would think the "true" source of the 8pi might be
quantum
| > mechanically related to the spin of gravitonic energy. If this *is*
the
| > case, then quantum objects *are* affecting the results indirectly.
|
| The *true* source of the 8 pi is a historical fact. 4 pi from geometry
and
| a factor of 2 from Newton's equations.
My point being that the 4 pi from geometry is from geometry that quantum
objects are defining. IOW, what is creating this "geometry" in the first
place? It has to be mostly vacuum quantum objects. There is nothing
else. If not the quantum objects in the universe, then the geometry would
have to be being created by "forces" outside of our universe. If that is
the case, then we have to extend our universe to include those "forces"
anywise. And what would be creating these outside "forces"? Probably
quantum objects.
| Keep in mind that GR is a mathematical map -- not a physically-derived
| theory.
Yes, but it has to be based in some kind of reality or it wouldn't make
predictions that work.
FrediFizzx
greywolf42
> "greywolf42" <min...@sim-ss.com> wrote in message
> news:vne7p1p...@corp.supernews.com...
> |
> | FrediFizzx <fredi...@hotmail.com> wrote in message
> | news:bkifpr$1n38b$1...@ID-185976.news.uni-berlin.de...
> | > "greywolf42" <min...@sim-ss.com> wrote in message
> | > news:vmp3agr...@corp.supernews.com...
{snip higher levels}
> | > | Neither GR nor Maxwell's equations were developed from quantum
> effects
> | > or
> | > | concepts like 'photons.' So the characteristics of quantum entities
> | > won't
> | > | affect the results.
> | >
> | > Well of course not. But we are pretty certain that the Universe is
> | > composed entirely of "quantum objects".
> |
> | That would contradict cosmology. Unless the 'space' is itself a quantum
> | object. Of course, current relativisitic cosmological theory is based
> | on GR.
>
> Huh? What else is there other than quantum objects? If the Universe is a
> closed system, we only have quantum objects in it. There is nothing else.
> Space-time *has* to be defined by the quantum objects including the ones
> in the vacuum. Especially the quantum objects in the vacuum.
Spacetime is not defined by quantum objects. Regardless of your desire for
them. See Einstein, 1916.
You are welcome to spin your own theories. But don't project them onto GR
or Einstein.
> | > Taking that into consideration,
> | > then GR should probably be defined by *all* the quantum objects in the
> | > Universe. So I would think the "true" source of the 8pi might be
> quantum
> | > mechanically related to the spin of gravitonic energy. If this *is*
> the
> | > case, then quantum objects *are* affecting the results indirectly.
> |
> | The *true* source of the 8 pi is a historical fact. 4 pi from geometry
> and
> | a factor of 2 from Newton's equations.
>
> My point being that the 4 pi from geometry is from geometry that quantum
> objects are defining.
You are incorrect in historical fact. There are no quantum objects in the
development of GR.
> IOW, what is creating this "geometry" in the first place?
Humans create geometry. That's what the word means. Earth measurement.
Keyword being "measurement."
> It has to be mostly vacuum quantum objects. There is nothing
> else.
You are welcome to your personal fantasy.
> If not the quantum objects in the universe, then the geometry would
> have to be being created by "forces" outside of our universe.
Geometry is created solely in the minds of humans.
> If that is
> the case, then we have to extend our universe to include those "forces"
> anywise. And what would be creating these outside "forces"? Probably
> quantum objects.
But that is not the case, so your logic fails.
> | Keep in mind that GR is a mathematical map -- not a physically-derived
> | theory.
>
> Yes, but it has to be based in some kind of reality or it wouldn't make
> predictions that work.
Incorrect. It is a map. Not a fundamental theory. It was picked *because*
it can be used to map experimental results. It was not based on any
'reality.' But a couple of postulates that Einstein thought were likely to
be the case. He threw out many otherwise 'pretty' theories because they
didn't map properly to the real universe. Call it guided trial-and-error.
FrediFizzx
This has nothing to do with Einstein. This has to do with fundamental
definitions. If you don't think the quantum objects in the universe are
defining spacetime, then what would be your guess? AFAIK, there is nothing
else to use for the definition. This is just plain common sense.
| > | > Taking that into consideration,
| > | > then GR should probably be defined by *all* the quantum objects in
the
| > | > Universe. So I would think the "true" source of the 8pi might be
| > quantum
| > | > mechanically related to the spin of gravitonic energy. If this *is*
| > the
| > | > case, then quantum objects *are* affecting the results indirectly.
| > |
| > | The *true* source of the 8 pi is a historical fact. 4 pi from
geometry
| > and
| > | a factor of 2 from Newton's equations.
| >
| > My point being that the 4 pi from geometry is from geometry that quantum
| > objects are defining.
|
| You are incorrect in historical fact. There are no quantum objects in the
| development of GR.
I never said there was QO's in the development of GR. But it ultimately has
to reduce to quantum objects, doesn't it? There is nothing else besides
quantum objects. I guess you think spacetime is an entity of its own? How
does it get its properties then?
| > IOW, what is creating this "geometry" in the first place?
|
| Humans create geometry. That's what the word means. Earth measurement.
| Keyword being "measurement."
|
| > It has to be mostly vacuum quantum objects. There is nothing
| > else.
|
| You are welcome to your personal fantasy.
Let's hear what your fantasy is then. GR just is? Without any underlying
fundamental principle.
| > If not the quantum objects in the universe, then the geometry would
| > have to be being created by "forces" outside of our universe.
|
| Geometry is created solely in the minds of humans.
Baloney. The earth is round is not created soley in the minds of humans.
Where are you getting that malarkey from?
| > If that is
| > the case, then we have to extend our universe to include those "forces"
| > anywise. And what would be creating these outside "forces"? Probably
| > quantum objects.
|
| But that is not the case, so your logic fails.
Let's hear your case then.
| > | Keep in mind that GR is a mathematical map -- not a physically-derived
| > | theory.
| >
| > Yes, but it has to be based in some kind of reality or it wouldn't make
| > predictions that work.
|
| Incorrect. It is a map. Not a fundamental theory. It was picked
*because*
| it can be used to map experimental results. It was not based on any
| 'reality.' But a couple of postulates that Einstein thought were likely
to
| be the case. He threw out many otherwise 'pretty' theories because they
| didn't map properly to the real universe. Call it guided trial-and-error.
Well, I think a lot of our "fundamental" theories were created this way if
not most of them.
FrediFizzx
greywolf42
> "greywolf42" <min...@sim-ss.com> wrote in message
> news:vnh7mu...@corp.supernews.com...
> | FrediFizzx <fredi...@hotmail.com> wrote in message
> | news:bl7drp$8nnon$1...@ID-185976.news.uni-berlin.de...
> | > "greywolf42" <min...@sim-ss.com> wrote in message
> | > news:vne7p1p...@corp.supernews.com...
> | > |
> | > | FrediFizzx <fredi...@hotmail.com> wrote in message
> | > | news:bkifpr$1n38b$1...@ID-185976.news.uni-berlin.de...
> | > | > "greywolf42" <min...@sim-ss.com> wrote in message
> | > | > news:vmp3agr...@corp.supernews.com...
> |
{snip higher levels}
> | > | > Well of course not. But we are pretty certain that the Universe
But quantum theory isn't itself common sense.
To test GR, they use the CMBR field as a measure of the local standard of
rest.
{snip}
> | You are incorrect in historical fact. There are no quantum objects in
the
> | development of GR.
>
> I never said there was QO's in the development of GR. But it ultimately
has
> to reduce to quantum objects, doesn't it?
No.
> There is nothing else besides quantum objects.
Continuing to repeat the bald claim changes nothing.
> I guess you think spacetime is an entity of its own? How
> does it get its properties then?
'Spacetime' is merely a mathematical map. It gets its properties from
physical reality.
> | > IOW, what is creating this "geometry" in the first place?
> |
> | Humans create geometry. That's what the word means. Earth measurement.
> | Keyword being "measurement."
> |
> | > It has to be mostly vacuum quantum objects. There is nothing
> | > else.
> |
> | You are welcome to your personal fantasy.
>
> Let's hear what your fantasy is then. GR just is? Without any underlying
> fundamental principle.
The underlying fundamental principles of GR are metaphysical and/or
philosophical. Historically. See Einstein, 1916.
> | > If not the quantum objects in the universe, then the geometry would
> | > have to be being created by "forces" outside of our universe.
> |
> | Geometry is created solely in the minds of humans.
>
> Baloney. The earth is round is not created soley in the minds of humans.
> Where are you getting that malarkey from?
"The Earth is round" is a description of an ideal. A generalization. Not a
cause. Geometrey is a measurement. Saying the 'geometry would have to be
created' is like saying the 'ruler would have to be created.' Objects have
lengths and properties even before we measure them.
> | > If that is
> | > the case, then we have to extend our universe to include those
"forces"
> | > anywise. And what would be creating these outside "forces"? Probably
> | > quantum objects.
> |
> | But that is not the case, so your logic fails.
>
> Let's hear your case then.
I've given you my 'case.' Einstein, 1916, is the source for where things
came from in GR.
> | > | Keep in mind that GR is a mathematical map -- not a
> | > | physically-derived theory.
> | >
> | > Yes, but it has to be based in some kind of reality or it wouldn't
make
> | > predictions that work.
> |
> | Incorrect. It is a map. Not a fundamental theory. It was picked
> | *because* it can be used to map experimental results. It was not
> | based on any 'reality.' But a couple of postulates that Einstein
> | thought were likely to be the case. He threw out many otherwise
> | 'pretty' theories because they didn't map properly to the real universe.
> | Call it guided trial-and-error.
>
> Well, I think a lot of our "fundamental" theories were created this way if
> not most of them.
That would also disprove your claim that one of those theories (GR) required
fundamental quantum objects.