More speed confusion

[k***@gmail.com]

As I said, light is affected the same as any other object by this
geometry.

Your model of your so-called geometry minimizes on the accumulated
spacetime, proper time, or whatever you want to call it. Any particle
massless or not moves from one fixed point in spacetime to another
also fixed in spacetime has its path uniquely identified by the
minimum amount of spacetime (than any other paths) it accumulates in
doing so. That is great until you include the photons themselves.
The photons always exist with a spacetime of exactly zero. Thus, it
is absolutely impossible to identify a unique path of trajectory for a
photon because any path you can trace between these two fixed points
in spacetime exactly accumulates a spacetime of very exactly zero.
Your model of geodesics must call out for uniqueness in light.
<shrug>

A light pulse has zero mass, and massless objects must move
with the symmetry speed of the manifold.

This is not true. A particle with zero rest mass (or
indistinguishable from zero) can simply travel at any speed under the
speed of light. In doing so, it becomes very difficult to detect.
One example is the neutrino. <shrug>

That's why we use the same
symbol for these two very different concepts

Do you mean ‘c’? If so, so what?

-- it can be confusing to
newbies and dilettantes, but not to people who understand the basics of
modern physics.

It looks like the geodesics are confusing the heck out of professors,
and that is no understatement. <shrug>

[Eric Gisse]

Post by k***@gmail.com

As I said, light is affected the same as any other object by this
geometry.

Your model of your so-called geometry minimizes on the accumulated
spacetime, proper time, or whatever you want to call it.  

Maximizes. Get it right.

[snip rest]

[Tom Roberts]

Post by Eric Gisse

Post by k***@gmail.com
Your model of your so-called geometry minimizes on the accumulated
spacetime, proper time, or whatever you want to call it.

Maximizes. Get it right.

Actually, this depends on one's choice of metric signature and the
character of the geodesic. For the signature -+++, a spacelike geodesic
minimizes it and a timelike geodesic maximizes it; roles are reversed
for the signature +---. A null geodesic does neither, but is a
stationary point of the integral (this does not uniquely determine the
path).

One can say "extremizes" for all cases.


Tom Roberts

[k***@gmail.com]

Post by Tom Roberts

Post by Eric Gisse
Maximizes. Get it right.

Actually, this depends on one's choice of metric signature and the
character of the geodesic.

Not really.

Post by Tom Roberts
For the signature -+++, a spacelike geodesic
minimizes it and a timelike geodesic maximizes it; roles are reversed
for the signature +---.

This is just not true. For the -+++ signature of spacetime, it is
nonsense because it allows objects to be indirectly identified to
travel beyond the speed of light by an observer. This is forbidden by
SR. For the +--- signature, geodesic model can call out for
minimizing the accumulated spacetime, local time (not to be confused
with proper time), or observed (coordinate) time. <shrug>

Post by Tom Roberts
A null geodesic does neither, but is a
stationary point of the integral (this does not uniquely determine the
path).

What are you talking about? The integral I take you mean is the
action of accumulating spacetime. It just does not exist because it
is always zero. So, being a stationary point of this integral does
not make any sense. <shrug>

There is no special law of physics regarding the null geodesics. Null
geodesics is a useless term to describe the geodesics of light.
Geodesics with minimum accumulated spacetime fails for light but not
the geodesics with minimum accumulated local or observed time.
<shrug>

Post by Tom Roberts
One can say "extremizes" for all cases.

Please don’t try to pull more mathemagic tricks out of the words
“extremize”. Study the calculus of variations thoroughly before you
come back for more. <shrug>

[Tom Roberts]

Post by k***@gmail.com

As I said, light is affected the same as any other object by this
geometry.

Your model of your so-called geometry minimizes on the accumulated
spacetime, proper time, or whatever you want to call it.

That is one way of defining geodesics, which as you point out does not
work for massless objects.

The better, more natural way to define geodesics is that they
parallel-transport their own tangent vector. This works for all
geodesics, and is expressed via the usual geodesic equation. This is
more natural, because it resides at a lower level of structure than the
metric -- one needs only a connection; if a metric is present (and in
physics there always is one) the two definitions are equivalent when
they are both well defined (as long as the connection is consistent with
the metric).

Post by k***@gmail.com
Your model of geodesics must call out for uniqueness in light.

And it does. The geodesic equation applies equally well to timelike,
spacelike, or null paths. A geodesic is UNIQUELY specified by giving a
point and a tangent vector at that point; the character of the initial
tangent vector (timelike, spacelike, or null) determines the character
of the entire geodesic path. (Other types of boundary conditions can be
used to solve that differential equation.)

Post by k***@gmail.com

A light pulse has zero mass, and massless objects must move
with the symmetry speed of the manifold.

This is not true.

Yes, it is true in both SR and GR.

Post by k***@gmail.com
A particle with zero rest mass (or
indistinguishable from zero) can simply travel at any speed under the
speed of light.

Not true. In SR and GR a particle with zero mass must move at the
symmetry speed of the manifold, c. A particle with a small mass that is
indistinguishable from zero will move with a speed that is
indistinguishable from c.

Post by k***@gmail.com
In doing so, it becomes very difficult to detect.
One example is the neutrino.

Neutrinos are very difficult to detect because they interact only
weakly, not because they have such small masses. Proof: photons have
even less mass (zero) but are comparatively easy to detect -- because
they interact electromagnetically, not weakly. Electromagnetic
interactions are MUCH stronger than weak interactions at the energies
accessible to us.

Post by k***@gmail.com

That's why we use the same
symbol for these two very different concepts

Do you mean ‘c’?

Yes, of course.

Post by k***@gmail.com

-- it can be confusing to
newbies and dilettantes, but not to people who understand the basics of
modern physics.

It looks like the geodesics are confusing the heck out of professors,
and that is no understatement.

No. As always, YOU are confused, because you refuse to study modern physics.


Tom Roberts

[Steak]

Post by Tom Roberts

Post by k***@gmail.com

As I said, light is affected the same as any other object by this
geometry.

Your model of your so-called geometry minimizes on the accumulated
spacetime, proper time, or whatever you want to call it.

That is one way of defining geodesics, which as you point out does not
work for massless objects.
The better, more natural way to define geodesics is that they
parallel-transport their own tangent vector. This works for all
geodesics, and is expressed via the usual geodesic equation. This is
more natural, because it resides at a lower level of structure than the
metric -- one needs only a connection; if a metric is present (and in
physics there always is one) the two definitions are equivalent when
they are both well defined (as long as the connection is consistent with
the metric).

Post by k***@gmail.com
Your model of geodesics must call out for uniqueness in light.

And it does. The geodesic equation applies equally well to timelike,
spacelike, or null paths. A geodesic is UNIQUELY specified by giving a
point and a tangent vector at that point; the character of the initial
tangent vector (timelike, spacelike, or null) determines the character
of the entire geodesic path. (Other types of boundary conditions can be
used to solve that differential equation.)

Post by k***@gmail.com

A light pulse has zero mass, and massless objects must move
with the symmetry speed of the manifold.

This is not true.

Yes, it is true in both SR and GR.

Post by k***@gmail.com
A particle with zero rest mass (or
indistinguishable from zero) can simply travel at any speed under the
speed of light.

Not true. In SR and GR a particle with zero mass must move at the
symmetry speed of the manifold, c. A particle with a small mass that is
indistinguishable from zero will move with a speed that is
indistinguishable from c.

Post by k***@gmail.com
In doing so, it becomes very difficult to detect.
One example is the neutrino.

Neutrinos are very difficult to detect because they interact only
weakly, not because they have such small masses. Proof: photons have
even less mass (zero) but are comparatively easy to detect -- because
they interact electromagnetically, not weakly. Electromagnetic
interactions are MUCH stronger than weak interactions at the energies
accessible to us.

Post by k***@gmail.com

That's why we use the same
symbol for these two very different concepts

Do you mean ‘c’?

Yes, of course.

Post by k***@gmail.com

-- it can be confusing to
newbies and dilettantes, but not to people who understand the basics of
modern physics.

It looks like the geodesics are confusing the heck out of professors,
and that is no understatement.

No. As always, YOU are confused, because you refuse to study modern physics.
Tom Roberts

amazing to realise, that since i told you that todays
physics is all about modelling, your each 2nd sentence
is about models

and speaking the witch, you say you do so much modelling,
tell us what kinda models do you use, domains, boundary conditions,
numerical schemes, algorithms, constraints, error analysis,
validation, optimization, software and else

[Steak]

Post by Tom Roberts

Post by k***@gmail.com

As I said, light is affected the same as any other object by this
geometry.

Your model of your so-called geometry minimizes on the accumulated
spacetime, proper time, or whatever you want to call it.

That is one way of defining geodesics, which as you point out does not
work for massless objects.
The better, more natural way to define geodesics is that they
parallel-transport their own tangent vector. This works for all
geodesics, and is expressed via the usual geodesic equation. This is
more natural, because it resides at a lower level of structure than the
metric -- one needs only a connection; if a metric is present (and in
physics there always is one) the two definitions are equivalent when
they are both well defined (as long as the connection is consistent with
the metric).

Post by k***@gmail.com
Your model of geodesics must call out for uniqueness in light.

And it does. The geodesic equation applies equally well to timelike,
spacelike, or null paths. A geodesic is UNIQUELY specified by giving a
point and a tangent vector at that point; the character of the initial
tangent vector (timelike, spacelike, or null) determines the character
of the entire geodesic path. (Other types of boundary conditions can be
used to solve that differential equation.)

Post by k***@gmail.com

A light pulse has zero mass, and massless objects must move
with the symmetry speed of the manifold.

This is not true.

Yes, it is true in both SR and GR.

Post by k***@gmail.com
A particle with zero rest mass (or
indistinguishable from zero) can simply travel at any speed under the
speed of light.

Not true. In SR and GR a particle with zero mass must move at the
symmetry speed of the manifold, c. A particle with a small mass that is
indistinguishable from zero will move with a speed that is
indistinguishable from c.

Post by k***@gmail.com
In doing so, it becomes very difficult to detect.
One example is the neutrino.

Neutrinos are very difficult to detect because they interact only
weakly, not because they have such small masses. Proof: photons have
even less mass (zero) but are comparatively easy to detect -- because
they interact electromagnetically, not weakly. Electromagnetic
interactions are MUCH stronger than weak interactions at the energies
accessible to us.

Post by k***@gmail.com

That's why we use the same
symbol for these two very different concepts

Do you mean ‘c’?

Yes, of course.

Post by k***@gmail.com

-- it can be confusing to
newbies and dilettantes, but not to people who understand the basics of
modern physics.

It looks like the geodesics are confusing the heck out of professors,
and that is no understatement.

No. As always, YOU are confused, because you refuse to study modern physics.
Tom Roberts

or maybe you let your students to do the models

please ask them

in order for me to learn relativity much more !

[y***@gmail.com]

Post by Tom Roberts
Not true. In SR and GR a particle with zero mass must move at the
symmetry speed of the manifold, c. A particle with a small mass that is
indistinguishable from zero will move with a speed that is
indistinguishable from c.

A particle with a small mass (indistinguishable from zero but not
zero) mving at high velocity (indistinguishable from c but not c) can
(in principle) be chased and caught. At that tme, its velocity
(relative to the chaser) will be zero (which is distinguishable from
c).

Consequently A particle with a small mass that is "indistinguishable
from zero" will be moving with a speed that is *distinguishable* from
c.

Post by Tom Roberts

-- it can be confusing to
newbies and dilettantes, but not to people who understand the basics of
modern physics.

That's apparently not true.

Love,
Jenny

[Tom Roberts]

Post by y***@gmail.com

Post by Tom Roberts
Not true. In SR and GR a particle with zero mass must move at the
symmetry speed of the manifold, c. A particle with a small mass that is
indistinguishable from zero will move with a speed that is
indistinguishable from c.

A particle with a small mass (indistinguishable from zero but not
zero) mving at high velocity (indistinguishable from c but not c) can
(in principle) be chased and caught. At that tme, its velocity
(relative to the chaser) will be zero (which is distinguishable from
c).

You ave just described a situation for a particle with a mass
DISTINGUISHABLE from zero. If its mass were indistinguishable from zero,
you would not be able to catch up to it -- doing so is merely one way of
distinguishing its mass from zero.


Tom Roberts

[y***@gmail.com]

Post by Tom Roberts

Post by y***@gmail.com

Post by Tom Roberts
Not true. In SR and GR a particle with zero mass must move at the
symmetry speed of the manifold, c. A particle with a small mass that is
indistinguishable from zero will move with a speed that is
indistinguishable from c.

A particle with a small mass (indistinguishable from zero but not
zero) mving at high velocity (indistinguishable from c but not c) can
(in principle) be chased and caught. At that tme, its velocity
(relative to the chaser) will be zero (which is distinguishable from
c).

You ave just described a situation for a particle with a mass
DISTINGUISHABLE from zero. If its mass were indistinguishable from zero,
you would not be able to catch up to it -- doing so is merely one way of
distinguishing its mass from zero.

You were writing about a "small mass that is indistinguishable from
zero".

I was pointing out that, according to SR, there is no such animal.

A small mass cannot move at c, therefore it must move at zero relative
to something.

c is the only speed which is invariant.

You're getting confused.

Lotsa people here think that you understand what you're writing about.

Please be more precise in what you write.

Love,
Jenny

[Tom Roberts]

Post by y***@gmail.com
You were writing about a "small mass that is indistinguishable from
zero".
I was pointing out that, according to SR, there is no such animal.

Nonsense. There is ALWAYS some measurement resolution. For instance, at
present the upper bound on the mass of a photon is 6*10^-17 eV/c^2 -- a
mass we generally consider to be zero. The upper bound on the masses of
neutrinos is 2 eV/c^2, and there is now a lower bound that is on the
order of a fraction of an eV/c^2 -- this used to be considered to be
zero, but now we know it isn't. These represent the experimental
resolutions of the best experiments that measure these masses.

Post by y***@gmail.com
A small mass cannot move at c, therefore it must move at zero relative
to something.

But that frame may well be completely unaccessible to human
experimenters. And even so, the object may be completely unobservable as
it moves (which is the case for both photons and neutrinos, but for
different reasons: the photon can only interact once, and the neutrino
interacts extremely weakly with a cross-section proportional to its energy).

This is about ACTUAL MEASUREMENTS, not abstract concepts and principles.


Tom Roberts

[y***@gmail.com]

Post by Tom Roberts

Post by y***@gmail.com
You were writing about a "small mass that is indistinguishable from
zero".
I was pointing out that, according to SR, there is no such animal.

Nonsense.

Nonsense back at you.

As I wrote:
_____________________
A particle with a small mass (indistinguishable from zero but not
zero) moving at high velocity (indistinguishable from c but not c) can
(in principle) be chased and caught. At that tme, its velocity
(relative to the chaser) will be zero (which is distinguishable from
c).
______________________

Note the use of the words "in principle".

In what way does what I wrote conflict with SR?

Post by Tom Roberts
But that frame may well be completely unaccessible to human
experimenters. And even so, the object may be completely unobservable as
it moves (which is the case for both photons and neutrinos, but for
different reasons: the photon can only interact once, and the neutrino
interacts extremely weakly with a cross-section proportional to its energy).
This is about ACTUAL MEASUREMENTS, not abstract concepts and principles.

I was replying to what you wrote:
________________
A particle with a small mass that is
indistinguishable from zero will move with a speed that is
indistinguishable from c.
________________


What you wrote *does* conflict with SR, which is why I jumped in.

You were making a statement that is wrong *in principle*, as I
claimed.

You did *not* write:
________________
A particle with a small mass that is
indistinguishable from zero will move with a speed that is
very difficult to measure
________________

Please don't try to rewrite history.

How you measure these things was never the issue.


Love,
Jenny

[Tom Roberts]

Post by y***@gmail.com
How you measure these things was never the issue.

When I wrote "indistinguishable", I meant experimentally. So how you
measure these things was always an issue, as it always is in physics.


Tom Roberts

[y***@gmail.com]

Post by Tom Roberts

Post by y***@gmail.com
How you measure these things was never the issue.

When I wrote "indistinguishable", I meant experimentally. So how you
measure these things was always an issue, as it always is in physics.

Distinguishable:

to perceive a difference in : mentally separate

Perceive:

to attain awareness or understanding of

I can distinguish (perceive a world of a difference) between light
speed and not light speed in SR.

If you can't then you don't truly understand SR.

Light speed is invariant and not light speed is not invariant.

The're the 2 kinds of speed we have in SR.

Most physicists (not including you, apparently) consider the above
statements to be experimentally well substantiated.

Massless objects must move with the symmetry speed of the manifold
massive objects mustn't. That hasn't been experimentally confirmed for
infinitesimal masses, but is taken to be true in SR -- it can be
confusing to newbies and dilettantes, but not to people who understand
the basics of modern physics.

The title of this thread was well chosen.

Love,
Jenny

[k***@gmail.com]

Post by Tom Roberts

Post by k***@gmail.com
Your model of your so-called geometry minimizes on the accumulated
spacetime, proper time, or whatever you want to call it.

That is one way of defining geodesics, which as you point out does not
work for massless objects.

There is actually no other way. Any geodesic models must work for
particles with mass >= 0. If not, it is just wrong. <shrug>

Post by Tom Roberts
The better, more natural way to define geodesics is that they
parallel-transport their own tangent vector.

What makes you think your definition of geodesics is valid without any
mathematics backing it up?

Post by Tom Roberts
This works for all
geodesics, and is expressed via the usual geodesic equation.

So, your model does not satisfy the variational principle, and that is
really, really bad. <shrug>

Post by Tom Roberts
This is
more natural, because it resides at a lower level of structure than the
metric

This is nonsense if you really have understood the fundamental issues
involved with the geodesics. The variational principle manifests the
parallel, vertical, side-ways, or whatever tangential transports.
<shrug>

Post by Tom Roberts
-- one needs only a connection;

You really do not understand the subject well. The variational
principle allows you to identify these connections. <shrug>

Post by Tom Roberts
if a metric is present (and in
physics there always is one) the two definitions are equivalent when
they are both well defined (as long as the connection is consistent with
the metric).

The connections are always consistent with the metric under the
variational principle. <shrug> Please discuss physics with
mathematics instead of word salad.

Post by Tom Roberts

Post by k***@gmail.com
Your model of geodesics must call out for uniqueness in light.

And it does. The geodesic equation applies equally well to timelike,
spacelike, or null paths. A geodesic is UNIQUELY specified by giving a
point and a tangent vector at that point; the character of the initial
tangent vector (timelike, spacelike, or null) determines the character
of the entire geodesic path. (Other types of boundary conditions can be
used to solve that differential equation.)

Your model does not work, and you are trying to weasel your way out of
it. What you are talking about makes no mathematical sense. <shrug>

Post by Tom Roberts
A light pulse has zero mass, and massless objects must move
with the symmetry speed of the manifold.

Post by k***@gmail.com
This is not true.

Yes, it is true in both SR and GR.

Well, I am not objecting to the first half of that sentence. It is
the second half that is false. <shrug>

Post by Tom Roberts

Post by k***@gmail.com
A particle with zero rest mass (or
indistinguishable from zero) can simply travel at any speed under the
speed of light.

Not true. In SR and GR a particle with zero mass must move at the
symmetry speed of the manifold, c. A particle with a small mass that is
indistinguishable from zero will move with a speed that is
indistinguishable from c.

Massless object must moves at the speed of light if it has non-zero
energy or momentum what is a special case. Massless objects can very
well move under the speed of light and offer no momentum and
observable energy. This is all in the mathematics of GR and SR where
SR agrees with the mathematical foundations of the Voigt transform in
this aspect as well. <shrug>

Post by Tom Roberts

Post by k***@gmail.com
In doing so, it becomes very difficult to detect.
One example is the neutrino.

Neutrinos are very difficult to detect because they interact only
weakly, not because they have such small masses. Proof: photons have
even less mass (zero) but are comparatively easy to detect -- because
they interact electromagnetically, not weakly. Electromagnetic
interactions are MUCH stronger than weak interactions at the energies
accessible to us.

You can kid kindergarten kids with that one. Photons are easy to
detect because it has a very high observed (relativistic) mass even
though the rest mass is zero. According to the Standard Model,
neutrinos are detectable when they are traveling near the speed of
light and with a lot of energy. Your definition of mass is preventing
you from understanding this. It is much easier to accept any mass as
an observed quantity even though “rest” mass can be zero. <shrug>

Post by Tom Roberts

Post by k***@gmail.com

That's why we use the same
symbol for these two very different concepts

Do you mean ‘c’?

Yes, of course.

Hmmm... I have already forgotten what these two very different
concepts. I hope it is not Alzheimer.

Post by Tom Roberts

Post by k***@gmail.com
It looks like the geodesics are confusing the heck out of professors,
and that is no understatement.

No. As always, YOU are confused, because you refuse to study modern physics.

I am ever more convinced that the geodesics are confusing the heck out
of professors, and that is no understatement.

As I have said, the geodesic model where the unique path follows the
one with the least accumulated spacetime fails miserably for light.
However, not affecting the result of the field equations under GR, the
geodesic model calling out for the unique path being the one with the
least amount of accumulated local or observed (coordinate) time allows
light to propagate with twice the deflection of Newtonian result.

You just cannot handwave to sow massed particles under one model and
massless particles under the other model together and call that blah,
blah, blah transports. Only Dr. Frankenstein is allowed to do that.
<shrug>

And once again, <CHECKMATE>

[G. L. Bradford]

You are aware a zero-mass photon is probably no spherical-, or bubble- or
ball-, or point-like particle observationally or measureably multi-sided or
multiplex, but is probably the simplest two-dimensional single-sided
membrane-like tissue only (strictly frontside photo-face only, thus strictly
2-dimensional!). It has no tangible, or even intangible, backside (which
would make it a 3-d object) to ever catch up to, much less surpass. Move
around from front to back to try to observe it, there is nothing there to
it, it does not exist.

GLB

============================