Bill Hobba wrote:
the metric behaves exactly like
the potential in Newtonian gravity.

Not "exactly", but rather ANALOGOUSLY. In NG the gradient of the
potential give the gravitational force; in GR, certain combinations of
first derivatives of the metric give "gravitational force" (the
connection), but these derivatives are quite different in detail. The
coordinate dependence of the connection bars it from being of
fundamental significance in GR.


three assumptions lead to GR - no prior geometry, the metric
is a dynamic variable, and the principle of least action.

A fourth is needed -- that the equations involve no more than second
derivatives, and those appear at most quadratically in the Lagrangian
(so the equations of motion will be linear in second derivatives).
Without this restriction you could add terms like R^2 or R_ijkl*R^ijkl
to the Lagrangian, which would add additional terms to the Einstein
field equation and you would not have GR.

In QFT contexts this is called "the assumption of minimal coupling".


Tom Roberts

On Oct 28, 11:31 am, Laurent wrote:
On Oct 28, 1:22 am, PD wrote:





On Oct 27, 1:03 pm, Laurent wrote:

On Oct 27, 10:14 am, PD wrote:

Is empty space real? Yes.

Does it exist? No. It isn't matter, therefore can't exist... yet, it
is.

Can it be measured? No, since it isn't matter, it is unmeasurable.

It is empty because it is immaterial, but has physical qualities.

This is where language and preconceived ideas get in the way.
Apparently, you have in your head that only material things can be
said to physically exist.
And yet something that is not a material thing has physical
(measurable) properties.
This immediately leads to an apparent paradox. The common resolution
to this paradox is to insist that space must in fact be a material
thing, so that it can have measurable properties.
It hasn't occurred to you, apparently, that your premises are wrong,
and that the paradox is only an illusion fabricated from erroneous
premises.

PD

Being and existing are not synonymous. Being is not the same as
existing. To be, you don't need to be in a specific location, to
exist, you do.

That seems like a rather odd statement, especially since existence and
being are not carefully redefined physics terms, and so the dictionary
terms will suffice, and I'm pretty sure you will find existence in the
definition of "be" and being in the definition of "being".

I agree, those terms need clarification. That's what I'm doing,
clarifying things. Or not?

Dunno yet. Doesn't seem clear to me at all yet.

Furthermore, fields and waves and and extended entities are understood
to have existence in physics, but they don't have specific locations.
A field exists *everywhere*. Does the Earth's atmosphere exist? Where
is its specific location?

PD- Hide quoted text -

- Show quoted text -

Fields are made of particles

Not that have a definite location, no.

Fields have definite locations. You can determine where a given field
is.

Really? Where is the field, definitely, around a charged ping-pong
ball?

It is around the ping-pong ball... as you said.

At what point away from the ping-pong ball is there no more field?

which move according to lines of force

No, they don't. Double-slit experiment rules that out.

All particles in a field follow lines of force. If there were no lines
of force there wouldn't be any fields.

Sorry, your assertion is based apparently on misunderstanding. Fields
are real things. Lines of force are drawing exercises.

Wrong, particles in fields follow a path along these force lines.
Force lines are real.

determined at the aether level, therefore are matter. What is not
matter are the lines of force or the aether were they come from.

The Earth's atmosphere is located around it.

And what are the coordinates (the location) of "around it"? Or
alternatively, where are the boundaries between which you are certain
the atmosphere lies?

It is a gas, but it is not in Mars, it is on Earth.

Didn't answer the question. You see how hard it is to specify the
location of the atmosphere? Is "not around Mars, but instead around
Earth" close enough to a "definite location" for you? What does
"definite location" mean to you?

Why can't momentum and position of subatomic particles be measured at
the same time? What do we do? We use probability. We set boundaries.
We know they exist within a given region.

You seem to be having difficulty answering specific questions.

And you seem to think I was saying gases do not exist because their
molecules are not standing still, or becaue they are not solids.

No, that's not what I'm saying at all. You said that in order for
something to exist, it has to have a definite location. So I'm asking
you what the coordinates of the atmosphere are, or the boundaries that
the atmosphere definitely lies inside. In other words, what's the
definite location? A definite location is described either by a single
place which can be identified by coordinates, or a confined region
that can be identified by the location of its borders. So what's the
definite location of the atmosphere, or of the field surrounding a
charged ping-pong ball. If you can't answer the questions, then you
apparently don't know the definite location of either of these things,
yet you'd be hard pressed to say they don't exist. And so I'm
questioning the value of your definition.



I am talking about nonmaterial things.

You can be without existing, but can't exist without being.

--
Laurent





--
Laurent

PD- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -

On Oct 28, 5:57 pm, PD wrote:
On Oct 28, 11:31 am, Laurent wrote:





On Oct 28, 1:22 am, PD wrote:

On Oct 27, 1:03 pm, Laurent wrote:

On Oct 27, 10:14 am, PD wrote:

Is empty space real? Yes.

Does it exist? No. It isn't matter, therefore can't exist... yet, it
is.

Can it be measured? No, since it isn't matter, it is unmeasurable.

It is empty because it is immaterial, but has physical qualities.

This is where language and preconceived ideas get in the way.
Apparently, you have in your head that only material things can be
said to physically exist.
And yet something that is not a material thing has physical
(measurable) properties.
This immediately leads to an apparent paradox. The common resolution
to this paradox is to insist that space must in fact be a material
thing, so that it can have measurable properties.
It hasn't occurred to you, apparently, that your premises are wrong,
and that the paradox is only an illusion fabricated from erroneous
premises.

PD

Being and existing are not synonymous. Being is not the same as
existing. To be, you don't need to be in a specific location, to
exist, you do.

That seems like a rather odd statement, especially since existence and
being are not carefully redefined physics terms, and so the dictionary
terms will suffice, and I'm pretty sure you will find existence in the
definition of "be" and being in the definition of "being".

I agree, those terms need clarification. That's what I'm doing,
clarifying things. Or not?

Dunno yet. Doesn't seem clear to me at all yet.

Furthermore, fields and waves and and extended entities are understood
to have existence in physics, but they don't have specific locations.
A field exists *everywhere*. Does the Earth's atmosphere exist? Where
is its specific location?

PD- Hide quoted text -

- Show quoted text -

Fields are made of particles

Not that have a definite location, no.

Fields have definite locations. You can determine where a given field
is.

Really? Where is the field, definitely, around a charged ping-pong
ball?

It is around the ping-pong ball... as you said.

At what point away from the ping-pong ball is there no more field?

which move according to lines of force

No, they don't. Double-slit experiment rules that out.

All particles in a field follow lines of force. If there were no lines
of force there wouldn't be any fields.

Sorry, your assertion is based apparently on misunderstanding. Fields
are real things. Lines of force are drawing exercises.

Wrong, particles in fields follow a path along these force lines.
Force lines are real.

determined at the aether level, therefore are matter. What is not
matter are the lines of force or the aether were they come from.

The Earth's atmosphere is located around it.

And what are the coordinates (the location) of "around it"? Or
alternatively, where are the boundaries between which you are certain
the atmosphere lies?

It is a gas, but it is not in Mars, it is on Earth.

Didn't answer the question. You see how hard it is to specify the
location of the atmosphere? Is "not around Mars, but instead around
Earth" close enough to a "definite location" for you? What does
"definite location" mean to you?

Why can't momentum and position of subatomic particles be measured at
the same time? What do we do? We use probability. We set boundaries.
We know they exist within a given region.

You seem to be having difficulty answering specific questions.

And you seem to think I was saying gases do not exist because their
molecules are not standing still, or becaue they are not solids.

No, that's not what I'm saying at all. You said that in order for
something to exist, it has to have a definite location.

I said it needs to be in spacetime. It exists within the metric. How
you measure its location will depend on what type of matter we are
dealing with. Remember how Maxwell dealt with gases? He came up with
the distribution function.

"The relevant microscopic information is not knowledge of the position
and velocity of every molecule at every instant of time, but just the
distribution function, that is to say, what percentage of the
molecules are in a certain part of the container, and what percentage
have velocities within a certain range, at each instant of time. For
a gas in thermal equilibrium, the distribution function is independent
of time. Ignoring tiny corrections for gravity, the gas will be
distributed uniformly in the container, so the only unknown is the
velocity distribution function."

Also see Brownia Motion.

"Brownian motion (named in honor of the botanist Robert Brown) is
either the random movement of particles suspended in a fluid or the
mathematical model used to describe such random movements, often
called a Wiener process.

The mathematical model of Brownian motion has several real-world
applications. An often quoted example is stock market fluctuations.
Another example is the evolution of physical characteristics in the
fossil record.[citation needed]

Brownian motion is among the simplest continuous-time stochastic
processes, and it is a limit of both simpler and more complicated
stochastic processes (see random walk and Donsker's theorem). This
universality is closely related to the universality of the normal
distribution. In both cases, it is often mathematical convenience
rather than the accuracy of the models that motivates their use."

http://en.wikipedia.org/wiki/Brownian_motion
http://galileo.phys.virginia.edu/cla...ic_theory.html


So I'm asking
you what the coordinates of the atmosphere are, or the boundaries that
the atmosphere definitely lies inside. In other words, what's the
definite location? A definite location is described either by a single
place which can be identified by coordinates, or a confined region
that can be identified by the location of its borders. So what's the
definite location of the atmosphere, or of the field surrounding a
charged ping-pong ball. If you can't answer the questions, then you
apparently don't know the definite location of either of these things,
yet you'd be hard pressed to say they don't exist. And so I'm
questioning the value of your definition.





I am talking about nonmaterial things.

You can be without existing, but can't exist without being.

--
Laurent

--
Laurent

PD-

"Tom Roberts" wrote in message
. net...
Bill Hobba wrote:
the metric behaves exactly like the potential in Newtonian gravity.

Not "exactly", but rather ANALOGOUSLY.

True.

In NG the gradient of the potential give the gravitational force; in GR,
certain combinations of first derivatives of the metric give
"gravitational force" (the connection), but these derivatives are quite
different in detail. The coordinate dependence of the connection bars it
from being of fundamental significance in GR.


three assumptions lead to GR - no prior geometry, the metric is a dynamic
variable, and the principle of least action.

A fourth is needed -- that the equations involve no more than second
derivatives, and those appear at most quadratically in the Lagrangian (so
the equations of motion will be linear in second derivatives).

True. But such is strongly suggested by classical field theory. Classical
field equations generally do not depend on more than the first derivative.
It is impossible to construct a covariant lagragngian containing only first
derivatives. If one goes to higher powers the divergence of its
Euler-Lagrange tensor density must vanish identically to have at the most
first derivatives in the field equations derived from the lagrangian. That
is enough to fix the form of the lagrangian. I know Tom knows this, but for
those interested, the relevant theorems can be found in Lovelock and Rund
page 305. The key theorem about the vanishing divergence is on page 313.
The key theorem establishing the form of the lagrangian is on page 321.

Without this restriction you could add terms like R^2 or R_ijkl*R^ijkl to
the Lagrangian, which would add additional terms to the Einstein field
equation and you would not have GR.

In QFT contexts this is called "the assumption of minimal coupling".


Tom Roberts

Thanks for clarifying my omissions.

Thanks
Bill

" Mdmeenken" wrote in message
...

"Bill Hobba" schreef in bericht
...

" Mdmeenken" wrote in message
...

"Bill Hobba" schreef in bericht
...

"Mdmeenken" wrote in message
. ..

"Bill Hobba" schreef in bericht
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"Mdmeenken" wrote in message
...

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...

"Laurent" wrote in message
ps.com...
Is empty space real? Yes.

Does it exist? No. It isn't matter, therefore can't exist... yet,
it
is.

Love isn't matter yet exists. Ideas aren't matter yet exist. You
need to learn what exists means. A good start is a dictionary '
Exist - to have being in a specified place or under certain
conditions; be found; occur: Hunger exists in many parts of the
world'


Can it be measured? No, since it isn't matter, it is unmeasurable.


IQ, force, data redundancy etc etc - all sorts of things that
aren't matter can be measured.

well Bill,

all nice and good,
but how is it,that something what is not matter, bend,as spactime
close to mass,

The same reason that something that is not matter - namely Euclidian
geometry, taught to 11-12 year olds hear in Australia, causes the
angles of material triangles made out of paper to add up to 180%. I
remember cutting them out in grade 7 and seeing them form a line i.e.
add to 180%. It is amazing that 11 year olds grasp the obvious that
seem to escape some adults. Or maybe they were asleep at school, but
nevertheless feel educated enough to post supposedly serious
questions, couched as a snide comment, whose answer in blindingly
obvious to those who were not asleep. That is assuming the question
was actually 'serious' - which I doubt.

is it now aussie logic ,or arrogance?,

anyway, hardly sufficient as a proper answer,
probably you have none,

einstein was a great man
but he knew very well the difference between a theorie and the real
thing,
i.e.,the difference between math and physics,
his theory is the best so far,and it stands every test so far ,and it
is logical,

Newton said once ,that he still did'nt understand how it is, that the
moon was attracted,

I had a couple of minutes to kill so decided to dig up Newtons exact
views on the issue.

To be specific Newton wrote:
"It is inconceivable that inanimate gross matter, without the mediation
of something immaterial, might affect some other matter with no mutual
contact, as it should happen if gravitation (in the sense proposed by
Epicurus) were essential and inherent to matter. This is one of the
reasons why I do not wish innate gravity to be attributed to me. For me
it is totally absurd that gravitation should be innate, inherent and
essential to matter, so that a body might act upon another body from a
distance, through vacuum, without the mediation of something else,
through which its action and force should be transported from one to
the other; it is so absurd that I believe no man with philosophical
questions in mind might believe it. Gravity must be caused by an agent
constantly acting according to certain laws; but I should let my
readers decide whether such agent is material or immaterial." (Newton
Optics, edition of 1717, Foreword)'

As Feynman said - if it can be conceived then it is not inconceivable.
And that is the entire answer to your initial question. Theories are
simply concepts. There has never been a requirement for all elements
of a theory to correspond with what we observe - only for those parts
that can resonably correpond to things we observe to be in accord with
the theory. This is not to slight Newton. The standards of what
constituted a reasonable argument in his time were different. While
space-time is immaterial, certain consequences are not eg for non
Euclidian geometry the angles of a triangle may not add up to 180% -
and such statements are testable. And that is what 11 year olds grasp
immediately about Euclidian geometry. Things like points and lines as
defined in Euclidian geometry do not actually exist eg points of
position and no size do not actually exist. But Euclidian geometry is
a theory about idealisations - which may or may not correspond to
observable objects, depending on your ability at physical insight. Few
would doubt that the points and lines drawn to justify the theorems of
Euclidian geometry are valid representations of the points and lines of
the theory. For those that do - then I am afraid they should take up
pursuits other than those that require 'applied math'.

mass dictates space time how to curve,and spacetime in his turn,
dictates mass how to move,

Attributable to Wheeler if I remember correctly.

famous words,
don't know whether einstein said that the first time,
but it says it all,
we have euclidan an non euclidian geometrie,as you so masterfull pointed
out,(f.i.a triangle on a sphere like earth does not add up to 180)
indeed ,indeed,
no comes the question, how come (as I thought that was clear the first
time),that mass causes spacetime to change from euclidian to non
euclidian,and that is apparently the case,

If you think that then you do not understand GR correctly. In GR no
geometry at all is assumed. Your question, as far as I can determine its
meaning, is why is geometry itself dynamical? The answer is basically
that is the simplest way of it not having any particular geometry. Why
should nature single out one particular geometry over another - the
answer is it shouldn't. With greater detail, a number of approached to
GR exist, but the modern one is no-prior geometry. It starts by assuming
the most general framework that melds different geometries together.
That framework is pseudo Riemanian geometry. Assuming that alone, and
the idea that space and time must be on the same footing, dictates pseudo
Riemanian Minkowski geometry. Investigating geometries that have
infinitesimal curvature shows that a fundamental geometrical object - the
metric - behaves exactly like the potential in Newtonian gravity. This
leads to a bold conjecture - the metric is a dynamical variable. It also
follows heuristically from the principle of general covariance - the
reason I say heuristically is the principle of general covariance as
usually stated actually has no physical content - it is of heuristic
value only - but that is another issue. The principle of least action
then uniquely determines the Einstein field equations. So three
assumptions lead to GR - no prior geometry, the metric is a dynamic
variable, and the principle of least action. These imply that when
gravity is not present (the potential is zero) space-time is Minkowski
flat. So, in as far as you question has meaning, it boils down to why do
those principles hold. No one knows at our present level of
understanding. Nor is the lack of knowledge a problem, as any scientific
theory has unanswered questions. But the simplest answer to the question
of why should nature single out one geometry over another is that is
shouldn't That is the crux of GR - and why geometries change depending
on the stress-energy tensor (technical jargon that toughly translates to
mass being present) - it is the only way of having no prior geometry that
is consistent with well known physical principles like the principle of
least action.

thanks for your answer Bill,
see ya,

marten

You are most welcome. It is a pleasure dealing with someone actually
interested in answers. It is obvious I misunderstood your original post. I
thought you were making a snide comment about my post. I now think such is
not the case. I suspect English is not your first language and the way you
expressed yourself was taken out of context by me.

With Thanks
Bill


Bill


marten


Bill

by the earth over such a distance,
and he added, that he hoped that one time there would come somebody in
the future,
who could explain that,
that man came and was einstein,and newton would have liked his theory
,I am sure ,
because it is brilliant,

but does it answer all the questions,I am afraid , no,

marten








I don't really know,

Start by first by understanding what a mathematical model is. That
is after you have grasped the basics of Euclidian geometry.
http://en.wikipedia.org/wiki/Mathematical_model

Bill


marten

Rest snipped.

Bill

"shuba" wrote in message
...
Harald wrote:

"Aether drag" certainly is *not* part of Einstein's ether!

Nor is anything else. Repeatedly attempting to project your
worldviews on a dead man is silly. Here is a book giving
Einstein's perspective looking back at his career.

http://www.opencourtbooks.com/books_...ical_notes.htm

Search it in vain for "Einstein's ether", but do note what it
says about the physicality of spacetime. Sorry about that!

Since we have that information first-hand, it doesn't matter if a book omits
it. Attempts to falsify the past are becoming less successful - happily!

Cheers,
Harald

"Laurent" wrote in message
ups.com...
On Oct 26, 4:06 am, "harry"
wrote:
"Laurent" wrote in message

ps.com...

Is empty space real? Yes.

Does it exist? No. It isn't matter, therefore can't exist... yet, it
is.

Hmm.... see Bill's correction.

See me correcting Bill's correction.


Can it be measured? No, since it isn't matter, it is unmeasurable.

Same.

Same.


It is empty because it is immaterial, but has physical qualities. It
also lacks the property of motion, so it can't be described as
containing parts that follow a time line.

As Lorentz *did* do what according to Einstein here could not be done,
this
the part where IMO Einstein was either wrong or incomprehensible (which
is
for all practical purpose the same in physics).

The aether is one, it has no components. It is the space between
particles. It does not need motion, It is everywhere.

I'm afraid that I don't see the connection. With motion we usually mean
something relative. For example, when we say that sound has a speed of 340
m/s, this implies that the air has a speed of 340 m/s relative to the sound
wave. Do you disagree?

The universe is background
free and there is no fixed or absolute frameof reference, nor absolute
time.

Here the word "is" is suspect. And what is meant, really? For example, is
the ocean "background free" and "without absolute frame of reference"? A
lot
of this stuff depends on definitions, even more than the above ones that
are
less ambiguous.

It means there are no landmarks, no place from where to take a
reference measurement.

That is the case for an ocean. However, there is a subtle but important
distinction between what Newton's definition of "absolute" (= for the
working of physics), and what you call "absolute" (= for observation). It
has been (and still is) generally accepted that we can only observe relative
measures. But of course, nature doesn't care if we observe it or not.

Isn't empty space all pervading, that which is between and inside
particles, like the aether? Isn't it eternal? Isn't it real? Isn't
empty space what Einstein described as the gravitational aether, a
continuos field, in that now famous 1920 essay? Aether (empty space),
like Einstein said, is not comprised of particles or components that
follow a time line. Motion is not one of its properties. You know why?
Because it is everywhere.

What do you mean with "particles", "time line", "motion", and
"everywhere"?

heheh, please...

No, I wasn't joking! As you are deeply diving into philosophy, sharp
definitions of words become more important.

Empty space is the origin, a plenum, also known as the aether. That's
where field properties, like propagation speed and direction, or force
lines, are determined, and that's why it is physical but immaterial,
because even though it isn't matter it can act on matter.

Like I said, empty space is like a point, dimensionless, yet, it
contains the universe.

Look, it's really simple. Empty space was, then came the universe.

So you don't include physical space with the everything ("universe")?

Empty space is the sit of the field, therefore the universe.

There can be empty space without a universe, but not a universe
without empty space... just like there can't be matter without
causality. Reduce yourself to a size smaller than the smallest
particle and what you get? More empty space. Empty space that, like
Einstein said, has physical properties.

Einstein's aether - which is the aether I mostly talk about - isn't
bound by time , but by topolgical properties, a set of ratios
determined at the aether scale; frame independent constants.

Maybe you're the first person on this NG who thinks to understand
Einstein's
ether! :-)
Constants are math. To what kind of physical entities do you think they
relate?

All.

I'm afraid that that's too vague to be useful for me.

[...]

To measure aether drag all you need to do is measure the momentum of a
moving object.

"Aether drag" certainly is *not* part of Einstein's ether!

[no comment]

At least that seems to be settled. :-)

Cheers,
Harald

Harald wrote:

"shuba" wrote in message

http://www.opencourtbooks.com/books_...ical_notes.htm

Search it in vain for "Einstein's ether", but do note what it
says about the physicality of spacetime. Sorry about that!

Since we have that information first-hand, it doesn't matter if a book omits
it. Attempts to falsify the past are becoming less successful - happily!

Omit it? Hardly. The book not only discusses the ether, but puts
it perfectly in perspective. You should read it. Tee hee. It may
even prompt you to change the presentation of some of your
preferred revisionist history, which, as you hint, has been a
completely unsuccessful endeavor.


---Tim Shuba---

"shuba" wrote in message
...
Harald wrote:

"shuba" wrote in message

http://www.opencourtbooks.com/books_...ical_notes.htm

Search it in vain for "Einstein's ether", but do note what it
says about the physicality of spacetime. Sorry about that!

Since we have that information first-hand, it doesn't matter if a book
omits
it. Attempts to falsify the past are becoming less successful - happily!

Omit it? Hardly. The book not only discusses the ether, but puts
it perfectly in perspective. You should read it. Tee hee. It may
even prompt you to change the presentation of some of your
preferred revisionist history, which, as you hint, has been a
completely unsuccessful endeavor.

It may be a correct presentation, but it may also be just a reflection of
your preferred revisionist history. Anyway it doesn't matter much since we
still have the original papers.

Harald

Harald wrote:

It may be a correct presentation, but it may also be just a reflection of
your preferred revisionist history. Anyway it doesn't matter much since we
still have the original papers.

I forgot about that. You (plural) have "the original papers",
hence your (plural) opinions and interpretations of "the original
papers" have more validity about what Einstein believed than
anything in the book I mentioned. Very well then, I guess you
(all) have shown me a thing or two. Hahaha! It slipping away, but
I'm glad there's still some humor left on usenet.


---Tim Shuba---