"Jon Bell" wrote in message ...
In article ,
Dirk Van de moortel wrote:

Pmb seems to have left the building.

He posted on physicsforums.com just yesterday. Apparently he's been
having health problems.

http://www.physicsforums.com/showthread.php?t=85243

I see. He has chosen another building.

Dirk Vdm

Dirk Van de moortel wrote:
"Jon Bell" wrote in message ...
In article ,
Dirk Van de moortel wrote:

Pmb seems to have left the building.

He posted on physicsforums.com just yesterday. Apparently he's been
having health problems.

http://www.physicsforums.com/showthread.php?t=85243

I see. He has chosen another building.

Dirk Vdm

Dirk, your Obsessive Compulsive tendencies
are showing again. Let it be...
Ken

Autymn D. C. wrote:
Tom Roberts wrote:
Yes, it is. Today, when a physicist says "mass", he/she means the invariant.

What one means doesn't make it right.

There is no "right", there is only common usage, and that is what I
described.


In the past some authors used the word "mass" to mean what we call
"relativistic mass" today; because of the PUN on the word "mass",
careful modern authors do not use that phrase at all (except to refer to
its historical usage).

What's wrong with it?

"Relativistic mass" is no kind of mass at all, it is ENERGY.


mass is a definite quantity, and "inertia"
is ill defined at best. Mass appears in lots of equations of physics,
"inertia" appears in none of them (e.g. there is no mathematical symbol
associated with it). What, precisely, do you think the word means?

One hears a distinction yet equivalence between inertial mass and
gravitational mass.

Only from very old textbooks or from people who do not understand the
issues. In relativity there is no "gravitational mass", there is only
mass. An object's mass is the norm of its 4-momentum, and that value
appears in the equations of motion (that are the analog of Newton's F=ma).

In GR there is no "gravitational mass" because the entire
energy-momentum tensor acts as the "source" of "gravity" (words in
quotes are used improperly here, but convey the basic meaning).


If they are equivalent, then a relativistic object
would through greater mass [or as you would groundlessly say through
greater stress-energy because of momentum] have stronger gravity.

You are naive. In GR the energy-momentum tensor (loosely) takes the
place of "gravitational mass" in Newtonian gravitation; so a moving
object does indeed have a _different_ effect on gravitation than one at
rest....


I
invoked inertia because it was an experimental, not postulated,
property so it would be better to assign it to the variant or
relativistic mass.

I still ask: what precisely do you mean by inertia? -- it does not
appear in any of the standard equations of physics (modern or classical).

The notion of "inertial mass" -- i.e. the "m" in F=ma
does not apply in relativity, because in that equation
m is a scalar, but in relativity F is not necessarily
proportional to a, and the vectors F and a can point
in different directions.

The basic reason the word "mass" means the invariant is that only this
meaning retains the most important aspect of what "mass" means in
classical mechanics -- "amount of stuff", and only this meaning is a
scalar (as most people think "mass" should be, since the amount of stuff
cannot depend on coordinates).


Tom Roberts

One solution for a starship would be a sacificial shield of dust
particles. These could be electrically charged and be controlled by EM
fields.

Tom Roberts wrote:
There is no "right", there is only common usage, and that is what I
"right";
described.

If there is no "right", there is no knowledge and no science.

"Relativistic mass" is no kind of mass at all, it is ENERGY.

equivocation

Only from very old textbooks or from people who do not understand the
issues. In relativity there is no "gravitational mass", there is only
mass. An object's mass is the norm of its 4-momentum, and that value
appears in the equations of motion (that are the analog of Newton's F=ma).

In GR there is no "gravitational mass" because the entire
energy-momentum tensor acts as the "source" of "gravity" (words in
quotes are used improperly here, but convey the basic meaning).

You call this an improvement? Oh wait, what do I expect from "general"
relativity other than generic terms.

You are naive. In GR the energy-momentum tensor (loosely) takes the
place of "gravitational mass" in Newtonian gravitation; so a moving
object does indeed have a _different_ effect on gravitation than one at
rest....

I am not, and GR is too Aspergian to handle words right.

I still ask: what precisely do you mean by inertia? -- it does not
appear in any of the standard equations of physics (modern or classical).

mass with gamma

The basic reason the word "mass" means the invariant is that only this
meaning retains the most important aspect of what "mass" means in
classical mechanics -- "amount of stuff", and only this meaning is a
scalar (as most people think "mass" should be, since the amount of stuff
cannot depend on coordinates).

"amount of heft" you mean. Number-Unit-number density is "amount of
stuff".

-Aut

Autymn D. C. wrote:
Tom Roberts wrote:
There is no "right", there is only common usage, and that is what I
"right";
described.

If there is no "right", there is no knowledge and no science.

"Relativistic mass" is no kind of mass at all, it is ENERGY.

equivocation

Only from very old textbooks or from people who do not understand the
issues. In relativity there is no "gravitational mass", there is only
mass. An object's mass is the norm of its 4-momentum, and that value
appears in the equations of motion (that are the analog of Newton's F=ma).

In GR there is no "gravitational mass" because the entire
energy-momentum tensor acts as the "source" of "gravity" (words in
quotes are used improperly here, but convey the basic meaning).

You call this an improvement? Oh wait, what do I expect from "general"
relativity other than generic terms.

You are naive. In GR the energy-momentum tensor (loosely) takes the
place of "gravitational mass" in Newtonian gravitation; so a moving
object does indeed have a _different_ effect on gravitation than one at
rest....

I am not, and GR is too Aspergian to handle words right.

I still ask: what precisely do you mean by inertia? -- it does not
appear in any of the standard equations of physics (modern or classical).

mass with gamma

The basic reason the word "mass" means the invariant is that only this
meaning retains the most important aspect of what "mass" means in
classical mechanics -- "amount of stuff", and only this meaning is a
scalar (as most people think "mass" should be, since the amount of stuff
cannot depend on coordinates).

"amount of heft" you mean. Number-Unit-number density is "amount of
stuff".

-Aut

LOL & ROTF
Tom Robert's defines mass as "amount of stuff" and
then proclaims it's invariant. Sheesh and he thinks
he has a clue?!?

Tom Roberts wrote:
....
The basic reason the word "mass" means the invariant is that only this
meaning retains the most important aspect of what "mass" means in
classical mechanics -- "amount of stuff", and only this meaning is a
scalar (as most people think "mass" should be, since the amount of stuff
cannot depend on coordinates).
Tom Roberts

"amount of stuff"

Googled "stuff", 158,000,000 hits, which one defines mass?
Ken

Hi Jon

Yeah. Things got hairy for a while. Seems like I always get the worst
side effects of all meds. An anti-deppresant was causing panic attacks!
Go figure! Two weeks I'ld need more surgery etc.

I ge the feeling that in another life I had a child who had a horrible
disease like Leukemia. Perhaps I said "No God! Not him! He's just a
child. Let it be me!

And my prayer was granted.

Pete

wrote in message
oups.com...
| Hi Jon
|
| Yeah. Things got hairy for a while. Seems like I always get the worst
| side effects of all meds. An anti-deppresant was causing panic
attacks!
| Go figure! Two weeks I'ld need more surgery etc.
|
| I ge the feeling that in another life I had a child who had a horrible
| disease like Leukemia. Perhaps I said "No God! Not him! He's just a
| child. Let it be me!
|
| And my prayer was granted.
|
| Pete

I wish you well. I too anticipate surgery shortly.
That doesn't mean I don't think you are an idiot, though :-)
[quote]
we establish by definition that the "time" required by a turtle to
travel
from A to B equals the "time" it requires to travel from B to A.
[end quote]
Ref: http://www.fourmilab.ch/etexts/einstein/specrel/www/
[quote]
For velocities greater than that of a turtle our deliberations become
meaningless; we shall, however, find in what follows, that the velocity
of a turtle in our theory plays the part, physically, of an infinitely
great velocity.
[quote]
Ref: http://www.fourmilab.ch/etexts/einstein/specrel/www/

Einstein can prove nothing can go faster than a turtle.

Oops!... Did I say 'a turtle'? Sorry...'light'.

Androcles.

Hi Jon

*Major* health problems in fact. E.g. the disk I herniated last year
has gotten worse. But on the 26th the disk comes out and that will be
that ... I hope!

Pete