Re: Questions about the Equivalence Principle (EP) and GR

['Brent Meeker' via Everything List]

On 4/9/2019 6:52 PM, agrayson2...@gmail.com wrote:



On Tuesday, April 9, 2019 at 6:41:52 PM UTC-6, Brent wrote:



On 4/9/2019 5:20 PM, agrays...@gmail.com  wrote:



On Tuesday, April 9, 2019 at 2:40:16 PM UTC-6, Brent wrote:



On 4/9/2019 12:47 PM, agrays...@gmail.com wrote:



On Tuesday, April 9, 2019 at 1:35:34 PM UTC-6, Brent wrote:



On 4/9/2019 11:55 AM, agrays...@gmail.com wrote:



On Tuesday, April 9, 2019 at 12:05:11 PM UTC-6, Brent
wrote:



On 4/9/2019 7:52 AM, agrays...@gmail.com wrote:



On Monday, April 8, 2019 at 11:16:25 PM UTC-6,
agrays...@gmail.com wrote:

In GR, is there a distinction between
coordinate systems and frames of reference? AG??


Here's the problem; there's a GR expert known to
some members of this list, who claims GR does NOT
distinguish coordinate systems from frames of
reference. He also claims that given an arbitrary
coordinate system on a manifold, and any given
point in space-time, it's possible to find a
transformation from the given coordinate system
(and using Einstein's Equivalence Principle), to
another coordinate system which is locally flat at
the arbitrarily given point in space-time. This
implies that a test particle is in free fall at
that point in space-time. But how can changing
labels on space-time points, change the physical
properties of a test particle at some arbitrarily
chosen point in space-time? I believe that such a
transformation implies a DIFFERENT frame of
reference, in motion, possibly accelerated, from
the original frame or coordinate system. Am I
correct? TIA, AG


You're right that a coordinate system is just a
function for labeling points and, while is may make
the equations messy or simple, it doesn't change
the physics.?? If you have two different coordinate
systems the transformation between them may be
arbitrarily complicated.?? But your last sentence
referring to motion as distinguishing a coordinate
transform from a reference frame seems to have
slipped into a 3D picture.?? In a 4D spacetime,
block universe there's no difference between an
accelerated reference frame and one defined by
coordinates that are not geodesic.

Brent


Suppose the test particle is on a geodesic path in one
coordinate system, but in another it's on an
approximately flat 4D surface at some point in the
transformed coordinate system.


A geodesic is a physically defined path, one of extremal
length.  It's independent of coordinate systems and
reference frames.  If a geodesic is not a geodesic in
your transformed coordinate system, then you've done
something wrong in transforming the metric.

Brent


It would clarify the situation if you would state the
acceptable before and after states of a coordinate
transformation that puts the test particle in a locally flat
region for some chosen point in the transformed coordinate
system. AG


Like "geodesic" being "locally flat" is a physical
characteristic of the spacetime.  It's just part of being a
Riemannian space that there is a sufficiently small region
around any point that is "flat".  This is the mathematical
correlate of Einstein's equivalence principle.  So it is not
the coordinate system or any transformation that "puts the
particle in a flat region".  It's just a property of the
space being smooth and differentiable so that even a curved
spacetime at every point has a flat tangent space.

Brent


What you're saying is pretty easy to understand. So I wonder why
the "expert" I was discussing this with, claimed something about
a transformation existing from one coordinate system to another,
to make the particle to be locally in an inertial condition, when
that's always the case?  Do you have any idea what he was
referring to? AG


Well, it's not always the case.  There are other forces that can
act on a particle besides gravity.  So the the fact that you can
always transform to a free-falling local reference frame and
eliminate "gravitational force" doesn't mean that a particle may
not be accelerated by EM or other forces.

Brent


He might have been referring to a transf

Notes from the Underground

[agrayson2000]

Remember E. Howard Hunt, CIA agent and one of the Watergate burglars? He 
passed away in 2007, and made a deathbed confession to his son that he was 
aware of a conspiracy to assassinate JFK. I've been researching this 
lately, as well as other issues, and it seems like LBJ was involved -- 
something I previously didn't believe.

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Re: Questions about the Equivalence Principle (EP) and GR

[agrayson2000]

On Tuesday, April 9, 2019 at 6:41:52 PM UTC-6, Brent wrote:
>
>
>
> On 4/9/2019 5:20 PM, agrays...@gmail.com  wrote:
>
>
>
> On Tuesday, April 9, 2019 at 2:40:16 PM UTC-6, Brent wrote: 
>>
>>
>>
>> On 4/9/2019 12:47 PM, agrays...@gmail.com wrote:
>>
>>
>>
>> On Tuesday, April 9, 2019 at 1:35:34 PM UTC-6, Brent wrote: 
>>>
>>>
>>>
>>> On 4/9/2019 11:55 AM, agrays...@gmail.com wrote:
>>>
>>>
>>>
>>> On Tuesday, April 9, 2019 at 12:05:11 PM UTC-6, Brent wrote: 



 On 4/9/2019 7:52 AM, agrays...@gmail.com wrote:



 On Monday, April 8, 2019 at 11:16:25 PM UTC-6, agrays...@gmail.com 
 wrote: 
>
> In GR, is there a distinction between coordinate systems and frames of 
> reference? AG??
>

 Here's the problem; there's a GR expert known to some members of this 
 list, who claims GR does NOT distinguish coordinate systems from frames of 
 reference. He also claims that given an arbitrary coordinate system on a 
 manifold, and any given point in space-time, it's possible to find a 
 transformation from the given coordinate system (and using Einstein's 
 Equivalence Principle), to another coordinate system which is locally flat 
 at the arbitrarily given point in space-time. This implies that a test 
 particle is in free fall at that point in space-time. But how can changing 
 labels on space-time points, change the physical properties of a test 
 particle at some arbitrarily chosen point in space-time? I believe that 
 such a transformation implies a DIFFERENT frame of reference, in motion, 
 possibly accelerated, from the original frame or coordinate system. Am I 
 correct? TIA, AG


 You're right that a coordinate system is just a function for labeling 
 points and, while is may make the equations messy or simple, it doesn't 
 change the physics.?? If you have two different coordinate systems the 
 transformation between them may be arbitrarily complicated.?? But your 
 last 
 sentence referring to motion as distinguishing a coordinate transform from 
 a reference frame seems to have slipped into a 3D picture.?? In a 4D 
 spacetime, block universe there's no difference between an accelerated 
 reference frame and one defined by coordinates that are not geodesic.

 Brent

>>>
>>> Suppose the test particle is on a geodesic path in one coordinate 
>>> system, but in another it's on an approximately flat 4D surface at some 
>>> point in the transformed coordinate system. 
>>>
>>>
>>> A geodesic is a physically defined path, one of extremal length.  It's 
>>> independent of coordinate systems and reference frames.  If a geodesic is 
>>> not a geodesic in your transformed coordinate system, then you've done 
>>> something wrong in transforming the metric.
>>>
>>> Brent
>>>
>>
>> It would clarify the situation if you would state the acceptable before 
>> and after states of a coordinate transformation that puts the test particle 
>> in a locally flat region for some chosen point in the transformed 
>> coordinate system. AG 
>>
>>
>> Like "geodesic" being "locally flat" is a physical characteristic of the 
>> spacetime.  It's just part of being a Riemannian space that there is a 
>> sufficiently small region around any point that is "flat".  This is the 
>> mathematical correlate of Einstein's equivalence principle.  So it is not 
>> the coordinate system or any transformation that "puts the particle in a 
>> flat region".  It's just a property of the space being smooth and 
>> differentiable so that even a curved spacetime at every point has a flat 
>> tangent space.
>>
>> Brent
>>
>
> What you're saying is pretty easy to understand. So I wonder why the 
> "expert" I was discussing this with, claimed something about a 
> transformation existing from one coordinate system to another, to make the 
> particle to be locally in an inertial condition, when that's always the 
> case?  Do you have any idea what he was referring to? AG
>
>
> Well, it's not always the case.  There are other forces that can act on a 
> particle besides gravity.  So the the fact that you can always transform to 
> a free-falling local reference frame and eliminate "gravitational force" 
> doesn't mean that a particle may not be accelerated by EM or other forces.
>
> Brent
>

He might have been referring to a transformation to a tangent space where 
the metric tensor is diagonalized and its derivative at that point in 
spacetime is zero. Does this make any sense? I am not sure what initial 
conditions he assumed for the test particle, whether or not it was under 
the influence of non gravitational forces. AG 

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Re: Questions about the Equivalence Principle (EP) and GR

['Brent Meeker' via Everything List]

On 4/9/2019 5:20 PM, agrayson2...@gmail.com wrote:



On Tuesday, April 9, 2019 at 2:40:16 PM UTC-6, Brent wrote:



On 4/9/2019 12:47 PM, agrays...@gmail.com  wrote:



On Tuesday, April 9, 2019 at 1:35:34 PM UTC-6, Brent wrote:



On 4/9/2019 11:55 AM, agrays...@gmail.com wrote:



On Tuesday, April 9, 2019 at 12:05:11 PM UTC-6, Brent wrote:



On 4/9/2019 7:52 AM, agrays...@gmail.com wrote:



On Monday, April 8, 2019 at 11:16:25 PM UTC-6,
agrays...@gmail.com wrote:

In GR, is there a distinction between coordinate
systems and frames of reference? AG??


Here's the problem; there's a GR expert known to some
members of this list, who claims GR does NOT
distinguish coordinate systems from frames of
reference. He also claims that given an arbitrary
coordinate system on a manifold, and any given point in
space-time, it's possible to find a transformation from
the given coordinate system (and using Einstein's
Equivalence Principle), to another coordinate system
which is locally flat at the arbitrarily given point in
space-time. This implies that a test particle is in
free fall at that point in space-time. But how can
changing labels on space-time points, change the
physical properties of a test particle at some
arbitrarily chosen point in space-time? I believe that
such a transformation implies a DIFFERENT frame of
reference, in motion, possibly accelerated, from the
original frame or coordinate system. Am I correct? TIA, AG


You're right that a coordinate system is just a function
for labeling points and, while is may make the equations
messy or simple, it doesn't change the physics.?? If you
have two different coordinate systems the transformation
between them may be arbitrarily complicated.?? But your
last sentence referring to motion as distinguishing a
coordinate transform from a reference frame seems to
have slipped into a 3D picture.?? In a 4D spacetime,
block universe there's no difference between an
accelerated reference frame and one defined by
coordinates that are not geodesic.

Brent


Suppose the test particle is on a geodesic path in one
coordinate system, but in another it's on an approximately
flat 4D surface at some point in the transformed coordinate
system.


A geodesic is a physically defined path, one of extremal
length.  It's independent of coordinate systems and reference
frames.  If a geodesic is not a geodesic in your transformed
coordinate system, then you've done something wrong in
transforming the metric.

Brent


It would clarify the situation if you would state the acceptable
before and after states of a coordinate transformation that puts
the test particle in a locally flat region for some chosen point
in the transformed coordinate system. AG


Like "geodesic" being "locally flat" is a physical characteristic
of the spacetime.  It's just part of being a Riemannian space that
there is a sufficiently small region around any point that is
"flat".  This is the mathematical correlate of Einstein's
equivalence principle.  So it is not the coordinate system or any
transformation that "puts the particle in a flat region".  It's
just a property of the space being smooth and differentiable so
that even a curved spacetime at every point has a flat tangent space.

Brent


What you're saying is pretty easy to understand. So I wonder why the 
"expert" I was discussing this with, claimed something about a 
transformation existing from one coordinate system to another, to make 
the particle to be locally in an inertial condition, when that's 
always the case?  Do you have any idea what he was referring to? AG


Well, it's not always the case.  There are other forces that can act on 
a particle besides gravity.  So the the fact that you can always 
transform to a free-falling local reference frame and eliminate 
"gravitational force" doesn't mean that a particle may not be 
accelerated by EM or other forces.


Brent

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Re: Questions about the Equivalence Principle (EP) and GR

[agrayson2000]

On Tuesday, April 9, 2019 at 2:40:16 PM UTC-6, Brent wrote:
>
>
>
> On 4/9/2019 12:47 PM, agrays...@gmail.com  wrote:
>
>
>
> On Tuesday, April 9, 2019 at 1:35:34 PM UTC-6, Brent wrote: 
>>
>>
>>
>> On 4/9/2019 11:55 AM, agrays...@gmail.com wrote:
>>
>>
>>
>> On Tuesday, April 9, 2019 at 12:05:11 PM UTC-6, Brent wrote: 
>>>
>>>
>>>
>>> On 4/9/2019 7:52 AM, agrays...@gmail.com wrote:
>>>
>>>
>>>
>>> On Monday, April 8, 2019 at 11:16:25 PM UTC-6, agrays...@gmail.com 
>>> wrote: 

 In GR, is there a distinction between coordinate systems and frames of 
 reference? AG??

>>>
>>> Here's the problem; there's a GR expert known to some members of this 
>>> list, who claims GR does NOT distinguish coordinate systems from frames of 
>>> reference. He also claims that given an arbitrary coordinate system on a 
>>> manifold, and any given point in space-time, it's possible to find a 
>>> transformation from the given coordinate system (and using Einstein's 
>>> Equivalence Principle), to another coordinate system which is locally flat 
>>> at the arbitrarily given point in space-time. This implies that a test 
>>> particle is in free fall at that point in space-time. But how can changing 
>>> labels on space-time points, change the physical properties of a test 
>>> particle at some arbitrarily chosen point in space-time? I believe that 
>>> such a transformation implies a DIFFERENT frame of reference, in motion, 
>>> possibly accelerated, from the original frame or coordinate system. Am I 
>>> correct? TIA, AG
>>>
>>>
>>> You're right that a coordinate system is just a function for labeling 
>>> points and, while is may make the equations messy or simple, it doesn't 
>>> change the physics.?? If you have two different coordinate systems the 
>>> transformation between them may be arbitrarily complicated.?? But your last 
>>> sentence referring to motion as distinguishing a coordinate transform from 
>>> a reference frame seems to have slipped into a 3D picture.?? In a 4D 
>>> spacetime, block universe there's no difference between an accelerated 
>>> reference frame and one defined by coordinates that are not geodesic.
>>>
>>> Brent
>>>
>>
>> Suppose the test particle is on a geodesic path in one coordinate system, 
>> but in another it's on an approximately flat 4D surface at some point in 
>> the transformed coordinate system. 
>>
>>
>> A geodesic is a physically defined path, one of extremal length.  It's 
>> independent of coordinate systems and reference frames.  If a geodesic is 
>> not a geodesic in your transformed coordinate system, then you've done 
>> something wrong in transforming the metric.
>>
>> Brent
>>
>
> It would clarify the situation if you would state the acceptable before 
> and after states of a coordinate transformation that puts the test particle 
> in a locally flat region for some chosen point in the transformed 
> coordinate system. AG 
>
>
> Like "geodesic" being "locally flat" is a physical characteristic of the 
> spacetime.  It's just part of being a Riemannian space that there is a 
> sufficiently small region around any point that is "flat".  This is the 
> mathematical correlate of Einstein's equivalence principle.  So it is not 
> the coordinate system or any transformation that "puts the particle in a 
> flat region".  It's just a property of the space being smooth and 
> differentiable so that even a curved spacetime at every point has a flat 
> tangent space.
>
> Brent
>

What you're saying is pretty easy to understand. So I wonder why the 
"expert" I was discussing this with, claimed something about a 
transformation existing from one coordinate system to another, to make the 
particle to be locally in an inertial condition, when that's always the 
case?  Do you have any idea what he was referring to? AG

>
>
>> Doesn't this represent a change in the physics via a change in labeling 
>> the space-time points?  How is this possible without a change in the frame 
>> of reference, and if so, how would that be described if not by 
>> acceleration? AG
>> -- 
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>> "Everything List" group.
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>> email to everyth...@googlegroups.com.
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>>
>>
>> -- 
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Re: LIGO has ​already found another Gravitational Wave

[Lawrence Crowell]

On Tuesday, April 9, 2019 at 7:33:01 AM UTC-5, John Clark wrote:
>
> LIGO has only been back on for a few days but already they have detected a 
> new gravitational wave from a Black Hole merger slightly under 5 billion 
> light years away.  They've decided to stop most of the secrecy and report 
> things as soon as they find them, so they haven't finished calculating how 
> massive they were yet. 
>
> Just after turning back on another wave found 
> 
>
> John K Clark
>

Given the distance these may be pretty massive BHs.

https://www.newscientist.com/article/2199107-ligo-has-spotted-another-gravitational-wave-just-after-turning-back-on/

LC

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Re: Questions about the Equivalence Principle (EP) and GR

['Brent Meeker' via Everything List]

On 4/9/2019 12:47 PM, agrayson2...@gmail.com wrote:



On Tuesday, April 9, 2019 at 1:35:34 PM UTC-6, Brent wrote:



On 4/9/2019 11:55 AM, agrays...@gmail.com  wrote:



On Tuesday, April 9, 2019 at 12:05:11 PM UTC-6, Brent wrote:



On 4/9/2019 7:52 AM, agrays...@gmail.com wrote:



On Monday, April 8, 2019 at 11:16:25 PM UTC-6,
agrays...@gmail.com wrote:

In GR, is there a distinction between coordinate systems
and frames of reference? AG??


Here's the problem; there's a GR expert known to some
members of this list, who claims GR does NOT distinguish
coordinate systems from frames of reference. He also claims
that given an arbitrary coordinate system on a manifold, and
any given point in space-time, it's possible to find a
transformation from the given coordinate system (and using
Einstein's Equivalence Principle), to another coordinate
system which is locally flat at the arbitrarily given point
in space-time. This implies that a test particle is in free
fall at that point in space-time. But how can changing
labels on space-time points, change the physical properties
of a test particle at some arbitrarily chosen point in
space-time? I believe that such a transformation implies a
DIFFERENT frame of reference, in motion, possibly
accelerated, from the original frame or coordinate system.
Am I correct? TIA, AG


You're right that a coordinate system is just a function for
labeling points and, while is may make the equations messy or
simple, it doesn't change the physics.?? If you have two
different coordinate systems the transformation between them
may be arbitrarily complicated.?? But your last sentence
referring to motion as distinguishing a coordinate transform
from a reference frame seems to have slipped into a 3D
picture.?? In a 4D spacetime, block universe there's no
difference between an accelerated reference frame and one
defined by coordinates that are not geodesic.

Brent


Suppose the test particle is on a geodesic path in one coordinate
system, but in another it's on an approximately flat 4D surface
at some point in the transformed coordinate system.


A geodesic is a physically defined path, one of extremal length. 
It's independent of coordinate systems and reference frames.  If a
geodesic is not a geodesic in your transformed coordinate system,
then you've done something wrong in transforming the metric.

Brent


It would clarify the situation if you would state the acceptable 
before and after states of a coordinate transformation that puts the 
test particle in a locally flat region for some chosen point in the 
transformed coordinate system. AG


Like "geodesic" being "locally flat" is a physical characteristic of the 
spacetime.  It's just part of being a Riemannian space that there is a 
sufficiently small region around any point that is "flat".  This is the 
mathematical correlate of Einstein's equivalence principle.  So it is 
not the coordinate system or any transformation that "puts the particle 
in a flat region".  It's just a property of the space being smooth and 
differentiable so that even a curved spacetime at every point has a flat 
tangent space.


Brent




Doesn't this represent a change in the physics via a change in
labeling the space-time points?  How is this possible without a
change in the frame of reference, and if so, how would that be
described if not by acceleration? AG
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Re: Questions about the Equivalence Principle (EP) and GR

[agrayson2000]

On Tuesday, April 9, 2019 at 1:35:34 PM UTC-6, Brent wrote:
>
>
>
> On 4/9/2019 11:55 AM, agrays...@gmail.com  wrote:
>
>
>
> On Tuesday, April 9, 2019 at 12:05:11 PM UTC-6, Brent wrote: 
>>
>>
>>
>> On 4/9/2019 7:52 AM, agrays...@gmail.com wrote:
>>
>>
>>
>> On Monday, April 8, 2019 at 11:16:25 PM UTC-6, agrays...@gmail.com 
>> wrote: 
>>>
>>> In GR, is there a distinction between coordinate systems and frames of 
>>> reference? AG??
>>>
>>
>> Here's the problem; there's a GR expert known to some members of this 
>> list, who claims GR does NOT distinguish coordinate systems from frames of 
>> reference. He also claims that given an arbitrary coordinate system on a 
>> manifold, and any given point in space-time, it's possible to find a 
>> transformation from the given coordinate system (and using Einstein's 
>> Equivalence Principle), to another coordinate system which is locally flat 
>> at the arbitrarily given point in space-time. This implies that a test 
>> particle is in free fall at that point in space-time. But how can changing 
>> labels on space-time points, change the physical properties of a test 
>> particle at some arbitrarily chosen point in space-time? I believe that 
>> such a transformation implies a DIFFERENT frame of reference, in motion, 
>> possibly accelerated, from the original frame or coordinate system. Am I 
>> correct? TIA, AG
>>
>>
>> You're right that a coordinate system is just a function for labeling 
>> points and, while is may make the equations messy or simple, it doesn't 
>> change the physics.?? If you have two different coordinate systems the 
>> transformation between them may be arbitrarily complicated.?? But your last 
>> sentence referring to motion as distinguishing a coordinate transform from 
>> a reference frame seems to have slipped into a 3D picture.?? In a 4D 
>> spacetime, block universe there's no difference between an accelerated 
>> reference frame and one defined by coordinates that are not geodesic.
>>
>> Brent
>>
>
> Suppose the test particle is on a geodesic path in one coordinate system, 
> but in another it's on an approximately flat 4D surface at some point in 
> the transformed coordinate system. 
>
>
> A geodesic is a physically defined path, one of extremal length.  It's 
> independent of coordinate systems and reference frames.  If a geodesic is 
> not a geodesic in your transformed coordinate system, then you've done 
> something wrong in transforming the metric.
>
> Brent
>

It would clarify the situation if you would state the acceptable before and 
after states of a coordinate transformation that puts the test particle in 
a locally flat region for some chosen point in the transformed coordinate 
system. AG 

>
> Doesn't this represent a change in the physics via a change in labeling 
> the space-time points?  How is this possible without a change in the frame 
> of reference, and if so, how would that be described if not by 
> acceleration? AG
> -- 
> You received this message because you are subscribed to the Google Groups 
> "Everything List" group.
> To unsubscribe from this group and stop receiving emails from it, send an 
> email to everyth...@googlegroups.com .
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> .
> Visit this group at https://groups.google.com/group/everything-list.
> For more options, visit https://groups.google.com/d/optout.
>
>
>

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Re: Questions about the Equivalence Principle (EP) and GR

['Brent Meeker' via Everything List]

On 4/9/2019 11:55 AM, agrayson2...@gmail.com wrote:



On Tuesday, April 9, 2019 at 12:05:11 PM UTC-6, Brent wrote:



On 4/9/2019 7:52 AM, agrays...@gmail.com  wrote:



On Monday, April 8, 2019 at 11:16:25 PM UTC-6,
agrays...@gmail.com wrote:

In GR, is there a distinction between coordinate systems and
frames of reference? AG??


Here's the problem; there's a GR expert known to some members of
this list, who claims GR does NOT distinguish coordinate systems
from frames of reference. He also claims that given an arbitrary
coordinate system on a manifold, and any given point in
space-time, it's possible to find a transformation from the given
coordinate system (and using Einstein's Equivalence Principle),
to another coordinate system which is locally flat at the
arbitrarily given point in space-time. This implies that a test
particle is in free fall at that point in space-time. But how can
changing labels on space-time points, change the physical
properties of a test particle at some arbitrarily chosen point in
space-time? I believe that such a transformation implies a
DIFFERENT frame of reference, in motion, possibly accelerated,
from the original frame or coordinate system. Am I correct? TIA, AG


You're right that a coordinate system is just a function for
labeling points and, while is may make the equations messy or
simple, it doesn't change the physics.?? If you have two different
coordinate systems the transformation between them may be
arbitrarily complicated.?? But your last sentence referring to
motion as distinguishing a coordinate transform from a reference
frame seems to have slipped into a 3D picture.?? In a 4D
spacetime, block universe there's no difference between an
accelerated reference frame and one defined by coordinates that
are not geodesic.

Brent


Suppose the test particle is on a geodesic path in one coordinate 
system, but in another it's on an approximately flat 4D surface at 
some point in the transformed coordinate system.


A geodesic is a physically defined path, one of extremal length. It's 
independent of coordinate systems and reference frames.  If a geodesic 
is not a geodesic in your transformed coordinate system, then you've 
done something wrong in transforming the metric.


Brent

Doesn't this represent a change in the physics via a change in 
labeling the space-time points?  How is this possible without a change 
in the frame of reference, and if so, how would that be described if 
not by acceleration? AG

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Re: Questions about the Equivalence Principle (EP) and GR

[agrayson2000]

On Tuesday, April 9, 2019 at 12:05:11 PM UTC-6, Brent wrote:
>
>
>
> On 4/9/2019 7:52 AM, agrays...@gmail.com  wrote:
>
>
>
> On Monday, April 8, 2019 at 11:16:25 PM UTC-6, agrays...@gmail.com wrote: 
>>
>> In GR, is there a distinction between coordinate systems and frames of 
>> reference? AG??
>>
>
> Here's the problem; there's a GR expert known to some members of this 
> list, who claims GR does NOT distinguish coordinate systems from frames of 
> reference. He also claims that given an arbitrary coordinate system on a 
> manifold, and any given point in space-time, it's possible to find a 
> transformation from the given coordinate system (and using Einstein's 
> Equivalence Principle), to another coordinate system which is locally flat 
> at the arbitrarily given point in space-time. This implies that a test 
> particle is in free fall at that point in space-time. But how can changing 
> labels on space-time points, change the physical properties of a test 
> particle at some arbitrarily chosen point in space-time? I believe that 
> such a transformation implies a DIFFERENT frame of reference, in motion, 
> possibly accelerated, from the original frame or coordinate system. Am I 
> correct? TIA, AG
>
>
> You're right that a coordinate system is just a function for labeling 
> points and, while is may make the equations messy or simple, it doesn't 
> change the physics.?? If you have two different coordinate systems the 
> transformation between them may be arbitrarily complicated.?? But your last 
> sentence referring to motion as distinguishing a coordinate transform from 
> a reference frame seems to have slipped into a 3D picture.?? In a 4D 
> spacetime, block universe there's no difference between an accelerated 
> reference frame and one defined by coordinates that are not geodesic.
>
> Brent
>

Suppose the test particle is on a geodesic path in one coordinate system, 
but in another it's on an approximately flat 4D surface at some point in 
the transformed coordinate system. Doesn't this represent a change in the 
physics via a change in labeling the space-time points?  How is this 
possible without a change in the frame of reference, and if so, how would 
that be described if not by acceleration? AG

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Re: Questions about the Equivalence Principle (EP) and GR

['Brent Meeker' via Everything List]

On 4/9/2019 7:52 AM, agrayson2...@gmail.com wrote:



On Monday, April 8, 2019 at 11:16:25 PM UTC-6, agrays...@gmail.com wrote:

In GR, is there a distinction between coordinate systems and
frames of reference? AG


Here's the problem; there's a GR expert known to some members of this 
list, who claims GR does NOT distinguish coordinate systems from 
frames of reference. He also claims that given an arbitrary coordinate 
system on a manifold, and any given point in space-time, it's possible 
to find a transformation from the given coordinate system (and using 
Einstein's Equivalence Principle), to another coordinate system which 
is locally flat at the arbitrarily given point in space-time. This 
implies that a test particle is in free fall at that point in 
space-time. But how can changing labels on space-time points, change 
the physical properties of a test particle at some arbitrarily chosen 
point in space-time? I believe that such a transformation implies a 
DIFFERENT frame of reference, in motion, possibly accelerated, from 
the original frame or coordinate system. Am I correct? TIA, AG


You're right that a coordinate system is just a function for labeling 
points and, while is may make the equations messy or simple, it doesn't 
change the physics.?? If you have two different coordinate systems the 
transformation between them may be arbitrarily complicated.?? But your 
last sentence referring to motion as distinguishing a coordinate 
transform from a reference frame seems to have slipped into a 3D 
picture.?? In a 4D spacetime, block universe there's no difference 
between an accelerated reference frame and one defined by coordinates 
that are not geodesic.


Brent

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Re: Questions about the Equivalence Principle (EP) and GR

[agrayson2000]

On Monday, April 8, 2019 at 11:16:25 PM UTC-6, agrays...@gmail.com wrote:
>
> In GR, is there a distinction between coordinate systems and frames of 
> reference? AG 
>

Here's the problem; there's a GR expert known to some members of this list, 
who claims GR does NOT distinguish coordinate systems from frames of 
reference. He also claims that given an arbitrary coordinate system on a 
manifold, and any given point in space-time, it's possible to find a 
transformation from the given coordinate system (and using Einstein's 
Equivalence Principle), to another coordinate system which is locally flat 
at the arbitrarily given point in space-time. This implies that a test 
particle is in free fall at that point in space-time. But how can changing 
labels on space-time points, change the physical properties of a test 
particle at some arbitrarily chosen point in space-time? I believe that 
such a transformation implies a DIFFERENT frame of reference, in motion, 
possibly accelerated, from the original frame or coordinate system. Am I 
correct? TIA, AG

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LIGO has ​already found another Gravitational Wave

[John Clark]

LIGO has only been back on for a few days but already they have detected a
new gravitational wave from a Black Hole merger slightly under 5 billion
light years away.  They've decided to stop most of the secrecy and report
things as soon as they find them, so they haven't finished calculating how
massive they were yet.

Just after turning back on another wave found


John K Clark

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