Re: Doubts about relativity 'dogmas'

"Tom Roberts" <tjroberts137@xxxxxxxxxxxxx> writes:

[Roberts]: I'm only going to respond to the outrageously wrong statements.

But finding none of those, I see you argued with some correct
statements instead. J

[tvf]: Two problems got geometric GR falsified precisely because of its
lack of forces, which means it has no cause to initiate 3-space motion.

[Roberts]: You REALLY need to learn about GR. This is just plain false.

I see. It is false because you say it is false. And all of us
should take your word for that because, after all, you are TOM ROBERTS. And
all those years I studied GR and relativistic celestial mechanics to the
doctoral level, and years of researching the subject and publishing in
mainstream journals on precisely this matter, have still no doubt left me
far behind your knowledge of GR. I was told (apparently falsely) that being
granted a Ph.D. in a field qualified me to go beyond present knowledge and
to learn and publish new things about my fields of training. Can I still get
my money back for this false claim? (Of course, my doctorate was from Yale,
which probably explains exactly what went wrong to all the Harvard graduates
on this forum. :-)

I did list two reasons and one citation to back up my statement.
And you did have the courtesy to comment on the first of those (next below),
although only after changing the meaning of my words.

[tvf]: Curvature alone, in the absence of a force, cannot initiate such
motion.

[Roberts]: Sure it can, because it is curvature in spaceTIME.

I said repeatedly that I was speaking in a Euclidean 3-space
context, because that is the frame in which the GR equations of motion
apply, where all the observations are made, and where GR is tested. I said
specifically that "force" is defined as "the time rate of change of 3-space
momentum". So how can you read my statement as applying to 4-space when I
made clear I meant curvature and forces in 3-space? Of what possible
relevance is curvature in 4-space or 17-space to the force of gravity? No
cause exists in 4-space able to initiate motion in *3-space*, and there is
no source in 4-space for the new 3-space momentum received by target bodies.
Geometric GR cannot survive those two challenges despite it being "just
marvelous" (Feynman's words).

Also relevant is that "spacetime" for time-like geodesic paths
is a pseudonym for proper time, simply expressed in space-like units of
measurement by multiplying it by c. It is normal to speak of curvature in
space. But it is not normal to speak of the "curvature of time", even if it
is proper time. That is just one of the several confusions introduced by
geometric GR that I hope will soon be purged from all textbooks. Those
interested in a clearer explanation of this point in a relativity context
may find it better explained at
http://metaresearch.org/cosmology/gravity/spacetime.asp.

[tvf]: In math, you don't need to ask "why" bodies follow geodesic paths,
but in physics you do.

[Roberts]: Hmmm. Asking "why" the world is what it is is outside the
province of physics.

No, you can't hijack the word "physics" for your own private
meaning and expect others to follow. Physics is all about answering "why"
questions. Why does light have colors? Why does sound have different
pitches? Why do planets orbit? Why do like charges repel? "Why" is outside
the province of mathematics because mathematics doesn't have constraints
such as the principles of physics. (See
http://metaresearch.org/cosmology/PhysicsHasItsPrinciples.asp for some
examples.) But it is very much the province of physics.

[Roberts]: GR predicts that _small_ objects will follow geodesic paths
through spacetime because that's what the field equation says.

However, our universe is not run by mathematics, and we are
continually improving our equations as we learn more about nature. Physics
drives mathematic, not vice versa. And physics is in large measure about
"why". At some future date (some would say we're already there now), we will
have a quantum gravity theory, and the Einstein equations will have to be
changed to accommodate that new knowledge.

[tvf]: Without that force, all bodies would follow straight line paths
through Euclidean 3-space.

[Roberts]: You may, if you wish, interpret the connection components as
"forces" when projected onto a specific foliation of spacetime into a
Euclidean 3-space and a time coordinate. But that has no fundamental
standing, and is directly coordinate dependent. Moreover, such "forces"
are inherently fictitious, and that meaning of "force" is not the closest
analogy to what the word means in older theories.

You have obviously never compared theory to observations, or
computed orbits for practical applications. For such purposes, the metric
equations are useless and equations of motion in Euclidean 3-space are
essential. It would apparently rock your world if you had to do the simplest
2-body solution in relativistic celestial mechanics. It's all about 3-space
forces.

[Roberts]: In relativity, the most relevant meaning of "force" is a
4-vector. For a small object in freefall, the 4-force on the object is
identically zero and it follows a geodesic path through spacetime. This
includes all the familiar effects of gravity.

Most practical work with gravity involves calculating orbits or
paths through Euclidean 3-space. You can't derive even the simplest 2-body
orbit in 3-space without equations of motion or their equivalent (such as
forming a Lagrangian or a Hamiltonian). Solutions to the field equations may
tell you about proper time, but they contain no dynamics. You must start
taking partial derivatives to get some dynamics from them. But only
instantaneous partials with no retardation will give correct equations of
motion. That is where the speed of gravity goes to infinity in GR,

[tvf]: You might wish to argue that space is curved, but that is false
because a taut rope between any two points along an orbit shows a
shorter, uncurved path.

[Roberts]: The curvature is in spaceTIME. It's outrageous that you write
so much about gravity and yet don't know the first thing about GR.

It should have been obvious that I was again speaking of
curvature in Euclidean 3-space, not curvature in spacetime. It is outrageous
that you write so much about GR yet know nothing about 3-space equations of
motion or how to get ordinary orbits out of GR.

[Roberts]: The moon's path around the earth (neglecting everything else)
is approximately a helix with axis along the earth's time coordinate
having radius ~1.3 light-seconds and period ~29 light-days. It is
orthogonal to the spatial direction perpendicular to the plane of the
orbit. That is less than one part per million away from a straight line
through spaceTIME.

Minkowski diagrams aren't of any practical value that I know of.
But because you raise the example, let's use it to show the problem that you
seem to be ignoring. Suppose the Moon is initially at rest in 3-space so
that its path on your diagram is a straight line parallel to Earth's world
line. Where is the force that will start the Moon moving off that linear
geodesic path?

[tvf]: But since when do approximations [the equations of motion] not
represent the theories they approximate?

[Roberts]: Just read what you wrote and apply basic English:
approximations only APPROXIMATE the theories they come from.

They approximate them, but do not then represent them? That
seems nonsensical. Please spell out what you mean so it doesn't look as if
you are using semantics to avoid admitting a mistake.

[Roberts]: Those APPROXIMATE equations [the equations of motion] are used
because the actual equations of GR are too difficult to solve for most
practical situations, and that APPROXIMATION is more than good enough.
Physicists have been making approximations since Newton, and it is
outrageous that you don't understand this.

I'd have to agree that it is becoming clear whose ignorance is
outrageous. It is starting to seem invincible too. Take my Moon example,
What starts a body on a linear world line falling toward Earth? Just point
to that initial impulse in the field or metric equations. No need to solve
anything. But you can't use gradients (3-space forces) or equations of
motion in your answer because you claim they are not representative of GR,
and you certainly don't want to admit outrageous ignorance.

Surely there is not a simpler application I can ask you about to
show you understand the dynamics of GR. I eagerly await your answer. -|Tom|-


Tom Van Flandern - Sequim, WA - see our web site on replacement astronomy
research at http://metaresearch.org


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