Link between dark matter and baryonic matter

[there were some strange characters in the quoted message. I've
replaced them with =, but if that wasn't what was intended, I may
have misunderstood the point.]

In article ,
dlzc writes:
I think they are discussing only one mass, namely:
mass = rest mass = inertial mass = gravitational mass =
relativistic mass,

The first two would be the same thing in modern parlance. The last
three, if used at all, would now be considered synonyms for "energy."
In general they are not equal to rest mass. That's physics, not
terminology. Taylor & Wheeler used what is now obsolete terminology,
but they had the physics right.

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Dear Steve Willner:

On Tuesday, November 29, 2016 at 1:26:53 PM UTC-7, Steve Willner wrote:
[there were some strange characters in the quoted
message. I've replaced them with =, but if that
wasn't what was intended, I may have misunderstood
the point.]

That is the case. =/= was intended to mean "not equal to". Sometimes represented as #, or .

I think they are discussing only one mass, namely:
mass = rest mass = inertial mass = gravitational mass
relativistic mass,

The first two would be the same thing in modern
parlance.

.... and the second two Eotvos has shown to be the same as the first two.

The last three, if used at all, would now be
considered synonyms for "energy."

False.

In general they are not equal to rest mass.

Still false, as Eotvos has shown.

That's physics, not terminology. Taylor &
Wheeler used what is now obsolete terminology,
but they had the physics right.

On that last bit we agree.

David A. Smith

In article ,
dlzc writes:
That is the case. =/= was intended to mean "not equal to".

I still don't know where you used = and where =/=. That's a problem
with using non-ASCII character sets.

A quote from Taylor and Wheeler p. 256 may help:
The source of our difficulty is some confusion between two quite
different concepts: (1) energy, the time component of the
momentum-energy 4-vector, and (2) mass, the magnitude of this
4-vector.

Nowadays, physicists avoid confusion by using "energy" when they mean
(1). Terms used in the past for this concept include "relativistic
mass," "inertial mass," "gravitational mass," and most regrettably,
sometimes just "mass." (T&W did this, though it's usually clear in
context which concept they meant.) Nowadays the term "mass" is
reserved for (2), but "rest mass" or "proper mass" can be used if
there's any chance of confusion.

If you want to discuss physics, please be careful to use unambiguous
terminology. In particular, be careful to keep straight the two
concepts T&W described.

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Help keep our newsgroup healthy; please don't feed the trolls.
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Dear Steve Willner:

On Thursday, December 1, 2016 at 12:01:32 PM UTC-7, Steve Willner wrote:
In article ,
dlzc writes:
That is the case. =/= was intended to mean "not equal to".

I still don't know where you used = and where =/=.
That's a problem with using non-ASCII character
sets.

Sorry, but I *only* used ASCII character sets. I just presented it in a format you did not expect / decipher.

I said these things are exactly the same:
mass, rest mass, inertial mass, gravitational mass.
(you correct this more clearly below.)

I said this was not the same as mass:
relativistic mass (which Einstein said not to teach).

A quote from Taylor and Wheeler p. 256 may help:
The source of our difficulty is some confusion
between two quite different concepts: (1)
energy, the time component of the momentum-
energy 4-vector, and (2) mass, the magnitude
of this 4-vector.

Nowadays, physicists avoid confusion by using
"energy" when they mean (1). Terms used in the
past for this concept include "relativistic
mass," "inertial mass," "gravitational mass,"
and most regrettably, sometimes just "mass."
(T&W did this, though it's usually clear in
context which concept they meant.) Nowadays the
term "mass" is reserved for (2), but "rest mass"
or "proper mass" can be used if there's any
chance of confusion.

And is tantamount to a religious argument, with those that find no issue slinging relativistic mass around. Ignoring that it an infinite number for different scalar values, depending on in which axis a tiny bit of momentum might be applied, in relation to its line of motion.

If you want to discuss physics, please be
careful to use unambiguous terminology. In
particular, be careful to keep straight the two
concepts T&W described.

I find this harder and harder to do. Thanks.

David A. Smith

In article ,
dlzc writes:
I said these things are exactly the same:
mass, rest mass, inertial mass, gravitational mass.

This thread has shown that terminology can be a problem, so I'm not
sure what actual quantity you mean by each of those terms. Let's
leave aside "mass," which is surely ambiguous. I think nearly
everyone (but possibly not you) takes "rest mass" to refer to the
invariant magnitude of the energy-momentum 4-vector. The point of
Taylor & Wheeler's discussion on pp 254ff is that gravitational
acceleration is related to the time component of the 4-vector.
That's what I'd mean by "gravitational mass," though I'd usually use
the term "energy."

The physical point to be made is that there are two different
quantities involved, and "rest mass" (meaning the invariant magnitude
of the 4-vector) is not the one directly related to gravity or
inertia.

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Help keep our newsgroup healthy; please don't feed the trolls.
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Dear Steve Willner:

On Friday, December 2, 2016 at 2:58:23 PM UTC-7, Steve Willner wrote:
In article ,
dlzc writes:
I said these things are exactly the same:
mass, rest mass, inertial mass, gravitational mass.

This thread has shown that terminology can be
a problem, so I'm not sure what actual quantity
you mean by each of those terms. Let's leave
aside "mass," which is surely ambiguous. I
think nearly everyone (but possibly not you)
takes "rest mass" to refer to the invariant
magnitude of the energy-momentum 4-vector. The
point of Taylor & Wheeler's discussion on pp
254ff is that gravitational acceleration is
related to the time component of the 4-vector.
That's what I'd mean by "gravitational mass,"
though I'd usually use the term "energy."

The physical point to be made is that there are
two different quantities involved, and
"rest mass" (meaning the invariant magnitude
of the 4-vector) is not the one directly related
to gravity or inertia.

OK, so in this thread, we are talking about all the photons currently wending their way outward, centered more-or-less on the center of a spiral galaxy, but inboard of your position in said galaxy. They originated as more lower-mass atoms, being fused into fewer higher-mass atoms plus light sprayed in all directions (on average).

So you'd say that the photons represent "energy" or "gravitational mass" until they pass your position (Newton's shells).

How does that differ from some tiny amount of "rest mass" or "proper mass" disappearing (magic required of course), and "changes in the gravitational field" propagating outwards past your position at c (classical speed of gravity)?

And note one immediate difference is some light is absorbed and scattered by a medium (dust, gas) that is warmer than the CMBR, and located inboard of your position...

Again, this is far smaller than the amount of Dark Matter "orbiting a spiral galaxy", and probably could be entirely ignored.

David A. Smith

In article ,
dlzc writes:
OK, so in this thread, we are talking about all the photons
currently wending their way outward, centered more-or-less on the
center of a spiral galaxy, but inboard of your position in said
galaxy.

So you'd say that the photons represent "energy" or "gravitational
mass" until they pass your position (Newton's shells).

They represent energy (and "gravitational mass" if you want to use
that term) regardless of their position. The gravitational effect
they have depends on position; to the extent the photons form a
spherically symmetric distribution, the ones outside "your position"
won't have any net effect.

How does that differ from some tiny amount of "rest mass" or
"proper mass" disappearing (magic required of course),

As you pointed out (and I snipped), the photons originated from
proper mass "disappearing" by being converted to energy. The effect
(again assuming spherical symmetry) is a gradual decrease in
centripetal attraction as photons (on balance) fly past one's
position. That is, the fact that photons have energy gives them
exactly the same gravitational effect as the rest mass they replaced.
All that changes is the location; the photons move around faster than
does mass.

And note one immediate difference is some light is absorbed and
scattered by a medium (dust, gas) that is warmer than the CMBR,
and located inboard of your position...

Energy is still conserved (in a suitable reference frame), and energy
translates to gravitational mass.

Again, this is far smaller than the amount of Dark Matter "orbiting
a spiral galaxy", and probably could be entirely ignored.

Oh indeed, the gravitational effect of radiation is utterly trivial
in every context I can think of in today's universe. It was
important, however, for some seconds after the Big Bang, when the
universe was radiation-dominated.

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Steve Willner Phone 617-495-7123
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