Question from a non-physics person
robor...@msn.com
of near light speed travel (assuming we had knowledge to produce such
speeds): "How does your ship avoid getting pulverized by tiny grains in
space that would impact your ship with enormous energy?"
>From what I understand as your ship approaches the speed of light, its
mass would also increase to near infinite. These tiny objects would
not have enormous amounts of energy; the ship would, so the ship would
be the one doing the pulverizing.
There are everyday examples of this: Tornados can accelerate common hay
or dried grass to speeds of 300 mph, increasing their mass, and drive
them right through trees and telephone poles. If you accelerated a
tree or telephone pole to 300 mph, and shot it through a field of
hay, it would mow down the hay, not split into a thousand pieces.
So why do I continuously see this question posed as a problem of near
light speed travel? I understand larger objects that have mass more
equal to the near-light speed ship (comet, planet, etc.) would be a
danger, but not tiny particles. What am I not taking into
consideration? Thanks
sue jahn
<robor...@msn.com> wrote in message news:1124007916....@g49g2000cwa.googlegroups.com...
> A common question is posed when trying to find solutions to the problem
> of near light speed travel (assuming we had knowledge to produce such
> speeds): "How does your ship avoid getting pulverized by tiny grains in
> space that would impact your ship with enormous energy?"
It has no way to avoid this.
<< interstellar medium is the material which fills the space between the stars. Many people imagine outer space to be a complete
vacuum, devoid of any material. Although the interstellar regions are more devoid of matter than any vacuum artificially created on
earth, there is matter in space. These regions have very low densities and consist mainly of gas (99%) and dust. In total,
approximately 15% of the visible matter in the Milky Way is composed of interstellar gas and dust.>>
http://www-ssg.sr.unh.edu/ism/what1.html
>
> >From what I understand as your ship approaches the speed of light, its
> mass would also increase to near infinite.
No... a clock on your ship may give that apperarance to a
relative moving observer.
>These tiny objects would
> not have enormous amounts of energy; the ship would, so the ship would
> be the one doing the pulverizing.
<< A common analogy is the sonic boom of a supersonic aircraft or bullet.
The sound waves generated by the supersonic body do not move fast enough
to get out of the way of the body itself. Hence, the waves "stack up" and
form a shock front. Similarly, a speed boat generates a large bow shock
because it travels faster than waves can move on the surface of the water. >>
http://en.wikipedia.org/wiki/Cherenkov_effect
>
> There are everyday examples of this: Tornados can accelerate common hay
> or dried grass to speeds of 300 mph, increasing their mass, and drive
> them right through trees and telephone poles. If you accelerated a
> tree or telephone pole to 300 mph, and shot it through a field of
> hay, it would mow down the hay, not split into a thousand pieces.
>
> So why do I continuously see this question posed as a problem of near
> light speed travel?
To study the nature of matter these speeds are achieve in particle
accelerators.
http://www.bnl.gov/world/Default.asp
http://www.slac.stanford.edu/
http://www.fnal.gov/pub/now/index.html
>I understand larger objects that have mass more
> equal to the near-light speed ship (comet, planet, etc.) would be a
> danger, but not tiny particles.
That is correct. A soft sponge and some solvent will take care
of most bugs and even small birds. Anything larger that a 50cc scooter
is worth considering a detour off of the pavement to avoid. :o)
What am I not taking into
> consideration?
It sounds like you got it all
Sue...
Thanks
>
Androcles
You are and you are right.
That silly mass increase is garbage, though.
Androcles.
Androcles
The PoR is an axiom, not to be meddled with.
http://www.bartleby.com/173/7.html
Comments in square brackets are mine.
"Albert Einstein (1879-1955). Relativity: The Special and General
Theory. 1920.
The Apparent Incompatibility of the Law of Propagation of Light with the
Principle of Relativity.
THERE is hardly a simpler law in physics than that according
to which light is propagated in empty space
[except the PoR, a real simple law].
Every child at school knows, or believes he knows, that this
Harry Potter propagation takes place in straight lines with a
velocity c = 300,000 km./sec
[relative to the source, but cosmic muons can win that race by a mile,
literally. It seems that Einstein has forgotten light has infinite
velocity in his
theory.]
At all events we know with great exactness that this velocity is the
same for all colours, because if this were not the case [prisms would
split white light into different colours and we never see that, and ]
the minimum of emission would not be observed simultaneously for
different colours during the eclipse of a fixed star by its dark
neighbour
[except that Algol has no dark neighbour, John Goodricke forgot to
include the velocity of light into his calculations].
By means of similar considerations based on observations of double
stars,
[Sirius, 8 light years away with a period of 50 years, no other double
has ever been seen] the Dutch astronomer De Sitter was also able to show
that the velocity of propagation of light cannot depend on the velocity
of
motion of the body emitting the light [oh really? how? I see no
significant
velocity v from Sirius to add to c]. The assumption that this velocity
of
propagation is dependent on the direction "in space" is in itself
improbable [but
factually true. Real scientists don't deal in assumptions and
probables].
In short, let us assume [!!!!] that the simple law [because I say it
is]
of the constancy of the velocity of light c (in vacuum) is justifiably
believed by the child at school [who also believes in Santa Claus, but
not believed by thinking rational adults]. Who would imagine that this
simple law has plunged the conscientiously thoughtful physicist
[yes, that's Androcles] into the greatest intellectual difficulties
[and solved them, not being a peanut brain like Einstein]?
Let us consider how these difficulties arise [because I can
make up stories] ."
[Skip silly train story, or as Alan Schwartz would say,
snip crap. Idiot.]
"At this juncture the theory of relativity entered the arena.
As a result of an analysis of the physical conceptions of time and
space, [insert the 'analysis' in Einstein's own words] we establish by
definition that the "time" required by light to travel from A to B
equals the
"time" it requires to travel from B to A. [end insert] it became evident
that
[ I am lying through my teeth and ] in reality there is not the least
incompatibility between the principle of relativity and the law of
propagation of light [because I say so, its a LAW, stomp foot] and
that by
systematically holding fast to both these laws a logically [huh?]
rigid theory could be arrived at [such as the speed of light being
infinite].
This theory has been called the special theory of relativity [or the
special
theory of the exrement I produce] to distinguish it from the extended
theory,
with which we shall deal later. In the following pages we shall present
the fundamental ideas of the special theory of relativity [but
the conscientiously thoughtful physicist isn't taken in by it]."
Androcles.
dlzc1 D:cox T:net@nospam.com N:dlzc D:aol T:com (dlzc)
<robor...@msn.com> wrote in message
news:1124007916....@g49g2000cwa.googlegroups.com...
> A common question is posed when trying to find solutions to
> the problem of near light speed travel (assuming we had
> knowledge to produce such speeds):
We can and do for elementary particles. We even have accelerated
massive nucleii to very high speeds as well.
> "How does your ship avoid getting pulverized by tiny grains
> in space that would impact your ship with enormous energy?"
Very true. The hydrogen alone at 0.1c will quickly make the nose
of your ship highly radioactive.
>From what I understand as your ship approaches the speed
> of light, its mass would also increase to near infinite.
No. Its mass stays the same, but its energy and momentum
increase.
> These tiny objects would not have enormous amounts of
> energy;
They do with respect to your ship. Which is the point.
> the ship would, so the ship would be the one doing the
> pulverizing.
It isn't a bug splatting on a windshield. It is bombardment of
energetic elementary particles... aka. nuclear radiation.
> There are everyday examples of this: Tornados can
> accelerate common hay or dried grass to speeds of
> 300 mph, increasing their mass, and drive them right
> through trees and telephone poles.
The mass is not increased.
> If you accelerated a
> tree or telephone pole to 300 mph, and shot it through
> a field of hay, it would mow down the hay, not split into
> a thousand pieces.
>
> So why do I continuously see this question posed as
> a problem of near light speed travel? I understand larger
> objects that have mass more equal to the near-light
> speed ship (comet, planet, etc.)
No.
> would be a danger, but not tiny particles. What am I
> not taking into consideration?
Velocity does not increase mass. The correct formula is:
E^2 = (pc)^2 + (mc^2)^2
... with p as momentum
An electron beam striking your body at 20+ eV can cause cancer.
This is hardly even fast, and much slower than the ones that
strike the phosphor on your CRT screen.
You are hay, and hay can penetrate hay. Analogies are really
poor ways of understanding reality.
... and now for the FAQ:
URL:http://hermes.physics.adelaide.edu.au/~dkoks/Faq/
David A. Smith
Autymn D. C.
> Velocity does not increase mass. The correct formula is:
> E^2 = (pc)^2 + (mc^2)^2
> ... with p as momentum
And what do you think momentum is made from?
Tom Roberts
> A common question is posed when trying to find solutions to the problem
> of near light speed travel (assuming we had knowledge to produce such
> speeds): "How does your ship avoid getting pulverized by tiny grains in
> space that would impact your ship with enormous energy?"
There are two basic approaches:
A. only move at such speeds in regions where the chance of hitting
such "grains" is negligible.
B. construct shields on the ship that can withstand these impacts;
it's not clear to me that this can be done.
Of course the current, more pratical approach is:
C. Don't move at speeds anywhere close to c (relative to such grains).
> From what I understand as your ship approaches the speed of idlight, its
> mass would also increase to near infinite. These tiny objects would
> not have enormous amounts of energy; the ship would, so the ship would
> be the one doing the pulverizing.
You must be careful to remember in which frame you are discussing
things. In the earth frame the grains move with speed <<c and the ship
(by your hypothesis) is moving with speed approaching c. Yes, the
collision of a small grain and a ship could well be catastrophic to both.
> There are everyday examples of this: Tornados can accelerate common hay
> or dried grass to speeds of 300 mph, increasing their mass,
The relativistic "mass increase" is negligible here -- on the order of 1
part per million. And this isn't really an increase in mass, it is
rather an increase in energy of ~1 ppm more than Newton's 0.5*m*v^2.
> and drive
> them right through trees and telephone poles.
Sure. But relativity is not needed to understand this. Straws can be
quite strong along their length -- in high school we could routinely
drive a paper drinking straw through a history book. But only ~1 in 100
attempts actually succeeded (lunchtime was boring (:-)). In a tornado,
it's clear that only an incredibly small fraction of the hay or grass
caught up by the storm is actually driven through trees or poles. The
impact must be EXACTLY along the straw's length....
> If you accelerated a
> tree or telephone pole to 300 mph, and shot it through a field of
> hay, it would mow down the hay, not split into a thousand pieces.
Sure. But to accelerate a tree to such a speed requires ENORMOUSLY more
energy thatn a piece of straw, or even a thousand pieces (which in
aggregate still weigh considerably less than the tree).
This is more a function of the total energy involved than any details of
hay, grass, straw, or tree. Note that in practice hurling a tree at a
field of hay would not mow any hay at all (it would bend, and some
ending up under the tree would be crushed, but little or none would be
mown [i.e. cut]).
> So why do I continuously see this question posed as a problem of near
> light speed travel? I understand larger objects that have mass more
> equal to the near-light speed ship (comet, planet, etc.) would be a
> danger, but not tiny particles.
If your spaceship actually achieved ~0.9c relative to the "grains", then
each grain would impace the front of the ship with enormous energy. I
doubt any material could withstand this for more than a handful of such
impacts, so you must select a region with very low density of such
grains. At some higher speed, nuclear reactions between grain and ship
would become likely....
Tom Roberts tjro...@lucent.com
Autymn D. C.
> A common question is posed when trying to find solutions to the problem
> of near light speed travel (assuming we had knowledge to produce such
> speeds): "How does your ship avoid getting pulverized by tiny grains in
> space that would impact your ship with enormous energy?"
That's easy. Put a bunch of bendy mirrors (NASA's too stupid to
understand amplification other than radio waves and matter exhaust.) in
orbit aimed at some carbon glass-carbon crustal solar sails strapped to
however heavy a craft one wants. Brake at the other end with a
swivelling crumbly radiator.
Use a Van Allen shield with forward-biased current to polarise debris
out of the way with an overlong overnarrow bulb of charges (likely the
doubled-up radiator). For the nastier bodies, hook up a magnetometer
to the solar driving elements and open the rear and fore shutters.
-Aut
I win.
Androcles
"Tom Roberts" <tjro...@lucent.com> wrote in message
news:aJPLe.264$hF1...@newssvr30.news.prodigy.com...
| robor...@msn.com wrote:
| > A common question is posed when trying to find solutions to the
problem
| > of near light speed travel (assuming we had knowledge to produce
such
| > speeds): "How does your ship avoid getting pulverized by tiny grains
in
| > space that would impact your ship with enormous energy?"
|
| There are two basic approaches:
| A. only move at such speeds in regions where the chance of hitting
| such "grains" is negligible.
| B. construct shields on the ship that can withstand these impacts;
| it's not clear to me that this can be done.
|
| Of course the current, more pratical approach is:
| C. Don't move at speeds anywhere close to c (relative to such
grains).
Egads! Roberts knows Galilean relativity!
Pity he believes and teaches
[quote]
we establish by definition that the "time" required by light 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/
|
|
| > From what I understand as your ship approaches the speed of idlight,
its
| > mass would also increase to near infinite. These tiny objects would
| > not have enormous amounts of energy; the ship would, so the ship
would
| > be the one doing the pulverizing.
|
| You must be careful to remember in which frame you are discussing
| things. In the earth frame the grains move with speed <<c and the ship
| (by your hypothesis) is moving with speed approaching c. Yes, the
| collision of a small grain and a ship could well be catastrophic to
both.
|
|
| > There are everyday examples of this: Tornados can accelerate common
hay
| > or dried grass to speeds of 300 mph, increasing their mass,
|
| The relativistic "mass increase" is negligible here -- on the order of
1
| part per million. And this isn't really an increase in mass, it is
| rather an increase in energy of ~1 ppm more than Newton's 0.5*m*v^2.
I'd edufart Roberts, but he's a stubborn fool.
|
|
| > and drive
| > them right through trees and telephone poles.
|
| Sure. But relativity is not needed to understand this.
Of course it is.
http://webexhibits.org/calendars/year-text-Galileo.html
| Straws can be
| quite strong along their length -- in high school we could routinely
| drive a paper drinking straw through a history book. But only ~1 in
100
| attempts actually succeeded (lunchtime was boring (:-)). In a tornado,
| it's clear that only an incredibly small fraction of the hay or grass
| caught up by the storm is actually driven through trees or poles. The
| impact must be EXACTLY along the straw's length....
|
|
| > If you accelerated a
| > tree or telephone pole to 300 mph, and shot it through a field of
| > hay, it would mow down the hay, not split into a thousand pieces.
|
| Sure. But to accelerate a tree to such a speed requires ENORMOUSLY
more
| energy thatn a piece of straw, or even a thousand pieces (which in
| aggregate still weigh considerably less than the tree).
|
| This is more a function of the total energy involved than any details
of
| hay, grass, straw, or tree. Note that in practice hurling a tree at a
| field of hay would not mow any hay at all (it would bend, and some
| ending up under the tree would be crushed, but little or none would be
| mown [i.e. cut]).
What if you burn the tree, use the heat to raise steam and harvest the
crop with a steam tractor?
I think the Victorians thought of that.
| > So why do I continuously see this question posed as a problem of
near
| > light speed travel? I understand larger objects that have mass more
| > equal to the near-light speed ship (comet, planet, etc.) would be a
| > danger, but not tiny particles.
|
| If your spaceship actually achieved ~0.9c relative to the "grains",
then
| each grain would impace the front of the ship with enormous energy. I
| doubt any material could withstand this for more than a handful of
such
| impacts, so you must select a region with very low density of such
| grains. At some higher speed, nuclear reactions between grain and ship
| would become likely....
|
| Tom Roberts tjro...@lucent.com
Yes, the grains would impace the front of the ship with enormous
energy.
E = 1/2mv^2 much. And m is? (I'm nt to surw about "imapace!)
Androcles
Dirk Van de moortel
"Autymn D. C." <lysd...@sbcglobal.net> wrote in message news:1124058832.3...@g44g2000cwa.googlegroups.com...
You probably have 'relativistic mass'
M = m / sqrt(1-v^2/c^2)
in mind.
See also
http://hermes.physics.adelaide.edu.au/~dkoks/Faq/Relativity/SR/mass.html
If mass is defined as 'invariant rest mass', then momentum is
'made from' mass and velocity.
Velocity increases momentum as in
p = m v / sqrt(1-v^2/c^2)
and obviously does not increase mass.
Together with
E = m c^2 / sqrt(1-v^2/c^2)
this gives
E^2 = (p c)^2 + (m c^2)^2
or better and more relevantly:
(m c^2)^2 = E^2 - (p c)^2
which is the invariant squared magnitude of the energy-momentum
four-vector with components (E, c px, c py, c pz ) and where
p = sqrt( px^2 + py^2 + pz^2 )
Dirk Vdm
Autymn D. C.
make it the distinction between mass and inertia?
Dirk Van de moortel
"Autymn D. C." <lysd...@sbcglobal.net> wrote in message news:1124131584.9...@g43g2000cwa.googlegroups.com...
> Mass isn't defined as invariant rest mass.
Apparently it usually is nowadays, whether you like it or not.
Dirk Vdm
Ken S. Tucker
Autymn D. C. wrote:
> Mass isn't defined as invariant rest mass.
Yes, it's oxymoronic to say a relative quantity
like "mass" is invariant in one Frame, picking
the arbituary "rest frame".
Dirk will never understand that, we've tried.
He's stuck in 1905 SR.
> Though maybe one should
> make it the distinction between mass and inertia?
In GR, you have 3 components for "mass" given by,
p^0, p , p_0 , where "p_0" is the "rest mass" and
is NOT invariant.
Ken
Tom Roberts
> Mass isn't defined as invariant rest mass.
Yes, it is. Today, when a physicist says "mass", he/she means the invariant.
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).
The meaning of this word has CHANGED over time. In this
newsgroup there will probably be a storm of replies claiming
other than what I said above. And there will also be replies
from people without a clue (e.g. Ken S. Tucker's below).
I am describing how the word is actually used by physicists
working in the field, TODAY.
> Though maybe one should
> make it the distinction between mass and inertia?
OF COURSE one must do so -- 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?
This is physics; being "precise" means writing an equation.
Ken S. Tucker wrote:
> Yes, it's oxymoronic to say a relative quantity
> like "mass" is invariant in one Frame, picking
> the arbituary "rest frame".
This is false (and confused). Mass is indeed invariant (meaning
independent of coordinate system or "frame"), in both SR and GR. This is
basic and fundamental -- an object's mass is the norm of its 4-momentum.
Tom Roberts tjro...@lucent.com
Dirk Van de moortel
"Tom Roberts" <tjro...@lucent.com> wrote in message news:ddr0tk$7...@netnews.net.lucent.com...
> Autymn D. C. wrote:
> > Mass isn't defined as invariant rest mass.
>
> Yes, it is. Today, when a physicist says "mass", he/she means the invariant.
>
> 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).
>
> The meaning of this word has CHANGED over time. In this
> newsgroup there will probably be a storm of replies claiming
> other than what I said above. And there will also be replies
> from people without a clue (e.g. Ken S. Tucker's below).
Pmb seems to have left the building.
I wonder when Tucker will follow.
Dirk Vdm
Bill Hobba
>> Mass isn't defined as invariant rest mass.
>
> Yes, it is. Today, when a physicist says "mass", he/she means the
> invariant.
>
> 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).
>
> The meaning of this word has CHANGED over time. In this
> newsgroup there will probably be a storm of replies claiming
> other than what I said above. And there will also be replies
> from people without a clue (e.g. Ken S. Tucker's below).
> I am describing how the word is actually used by physicists
> working in the field, TODAY.
And I suspect it has been that way for some time. Landau does not even
define it in the Classical Theory of Fields.
Thanks
Bill
Ken S. Tucker
> Ken S. Tucker wrote:
> > Yes, it's oxymoronic to say a relative quantity
> > like "mass" is invariant in one Frame, picking
> > the arbituary "rest frame".
What Tom is about to write is...
> false (and confused). Mass is indeed invariant (meaning
> independent of coordinate system or "frame"), in both SR and GR. This is
> basic and fundamental -- an object's mass is the norm of its 4-momentum.
> Tom Roberts tjro...@lucent.com
Ok, that's what I said about "p" , in agreement with Autymn, he's
accurate.
Define the momentum components p^0 , p , p_0 and while your
at it define the spatials p^i , p_i for us, consistent with GR.
In GR, spacetime is nonorthogonal, meaning the component
p^u =/= p_u.
As a simple example using association,
p_0 = g_00 p^0 .
In a g-field, recall g_00 =/=1, hence the geometry fractures by
the imposition of energy in the near-field and g_00 =/= g^00.
Ok, define, define, define.
I think Tom can do it, I'm listening...
Ken
Ken S. Tucker
Do the math. $1 billion of taxpayers money is
wrapped in GP-b, that's a lot, so be less
arrogant.
In one definition it works, in the other it
doesn't.
We have missile upstairs that will, properly
determined, set forth the theoretical agenda
for the next few decades and more possibly a
century.
Anyone who can contribute is invited to remark,
but shut the fuckin idiot remarks out, we're
flyin' high and data is eminent, for the future
generation of physicists, have respect as would
to those who have given their lives to make
theses missions possible.
Ken S. Tucker
Jon Bell
Dirk Van de moortel <dirkvand...@ThankS-NO-SperM.hotmail.com> 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
--
Jon Bell <jtb...@presby.edu> Presbyterian College
Dept. of Physics and Computer Science Clinton, South Carolina USA
Autymn D. C.
> Yes, it is. Today, when a physicist says "mass", he/she means the invariant.
What one means doesn't make it right.
> 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?
> OF COURSE one must do so -- 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. 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. 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.
-Aut
Dirk Van de moortel
"Jon Bell" <jtb...@presby.edu> wrote in message news:dds33p$bon$1...@jtbell.presby.edu...
> In article <ys8Me.170337$Ar6.9...@phobos.telenet-ops.be>,
> Dirk Van de moortel <dirkvand...@ThankS-NO-SperM.hotmail.com> 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
Ken S. Tucker
Dirk Van de moortel wrote:
Dirk, your Obsessive Compulsive tendencies
are showing again. Let it be...
Ken
Tom Roberts
> 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 tjro...@lucent.com
ianpa...@gmail.com
particles. These could be electrically charged and be controlled by EM
fields.
Autymn D. C.
> There is no "right", there is only common usage, and that is what I
> 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
Ken S. Tucker
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?!?
Ken S. Tucker
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 tjro...@lucent.com
"amount of stuff"
Googled "stuff", 158,000,000 hits, which one defines mass?
Ken
gau...@hotmail.com
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
Androcles
<gau...@hotmail.com> wrote in message
news:1126093931.0...@g49g2000cwa.googlegroups.com...
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.
gau...@hotmail.com
*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