greywolf42 wrote:

Matthew Nobes wrote in message
...

Thank you for proving my point. (That was a lot of effort for nothing.)
Einstein 'fixed G by taking the Newtonian limit' is a statement
equivalent
to Einstein 'backfit his equation to Newton's equation.'

This is what I dispute. It's not a backfit, it's simply fixing an unknown
constant. This has nothing to do with the derivation of GR.

I say 'backfit', you say 'fixing an unknown constant'. We disagree on
terms.

And on the importance of fixing constants. You seem to regard fixing
a constant as "backfitting onto" an "equation". It's not. The *equation*
is V=1/r, that's the important part.

However, the determination of 'unknown constants' is very definitely
part of the derivation of 'GR'.

No it's not.

[snip most of the rest as it's just more of the same]

Hence to say GR was "backfit" onto Newton seems like, at best, a
bizzare way of putting it, or (more to the way I suspect you mean it) a
dishonest way of putting it, since it seems to imply that you somehow
need Newtonian mechanics to get to GR.

Well, yes, Newtonian mechanics are needed to get to GR (conservation of
energy and momentum).

Huh? Conservation of energy and momentum are concepts which are independant
of Newtonian mechanics. You don't need Newtonian mechanics to assume
them, all you need to assume is time and space translation invariance.

[snip]
--
Matthew Nobes
c/o Physics Dept. Simon Fraser University, 8888 University
Drive Burnaby, B.C., Canada
http://www.sfu.ca/~manobes

Matthew Nobes wrote in message
...
greywolf42 wrote:

Matthew Nobes wrote in message
...

Thank you for proving my point. (That was a lot of effort for
nothing.)
Einstein 'fixed G by taking the Newtonian limit' is a statement
equivalent
to Einstein 'backfit his equation to Newton's equation.'

This is what I dispute. It's not a backfit, it's simply fixing an
unknown
constant. This has nothing to do with the derivation of GR.

I say 'backfit', you say 'fixing an unknown constant'. We disagree on
terms.

And on the importance of fixing constants. You seem to regard fixing
a constant as "backfitting onto" an "equation". It's not. The *equation*
is V=1/r, that's the important part.

That is your opinion. But Einstein also threw out prior 'pretty' equations
becuase they didn't reduce to the form. When he found a method to return
the Newtonian equation, he also borrowed the Newtonian constant. Nothing
wrong with that.

However, the determination of 'unknown constants' is very definitely
part of the derivation of 'GR'.

No it's not.

LOL! We differ in philosopy, it seems. You feel that as soon as one has
chicken tracks on paper, that one is 'done.' I feel that one needs to have
the constants determined -- so that one can compare to the real universe
before one is 'done.'

[snip most of the rest as it's just more of the same]

Hence to say GR was "backfit" onto Newton seems like, at best, a
bizzare way of putting it, or (more to the way I suspect you mean it) a
dishonest way of putting it, since it seems to imply that you somehow
need Newtonian mechanics to get to GR.

Well, yes, Newtonian mechanics are needed to get to GR (conservation of
energy and momentum).

Huh? Conservation of energy and momentum are concepts which are
independant of Newtonian mechanics.

LOL!

You don't need Newtonian mechanics to assume
them, all you need to assume is time and space translation invariance.

If you assume time and space invariance, you have assumed energy and
momentum conservation. Energy and momentum conservation are ideas developed
by, for, and as a result of Newton mechanics. You may claim that you don't
*need* to derive them -- by elevating energy and momentum conservation to
additional 'principles.' But you should let people know when you do this.

[snip]

greywolf42
ubi dubium ibi libertas

Old Physics wrote:

If a massive shell of matter has the same gravity as a solid
sphere with the same number of atoms, would the collapse of the shell
result in an increase in mass,

Not according to general relativity. The gravitational field at a fixed
distance will remain he same, as long as you're looking at a point that
was always outside the shell and the collapse is spherically symmetric.

ie. the original mass plus the IR
radiation that results from the conversion of kenetic energy to heat?

If you want to think of it in these terms, the relevant energy you need
to look at is ``quasilocal energy,'' which includes a contribution
analogous to Newtonian gravitational potential energy. The change
in this potential energy piece balances the other energy changes;
the total quasilocal energy remains constant.

(Of course, some of the IR radiation you speak of will eventually
radiate out past the point at which you're measuring the
gravitational field. As that happens, the field at that point will
decrease.)

Steve Carlip

Esteemed Dr. Carlip,

In the simplest terms, did you not write that with "quasilocal
energy" added to the mass of the shell, it equals the mass of the
solid sphere plus the "energy mass" of the IR that is radiated. To
rephrase: "the mass of a shell with the same number of atoms at the
same temperature will be greater (when judged from a distance) than a
solid sphere".
If I have in anyway misinterpreted your statement, please correct
me.

Hopeing for an answer,
Stephen Kearney

Relativity posts no limit to the relative contraction- time
dilation an object can undergo. What would happen if two 10^57 GeV
protons were to collide? Would they form a BH? sk

(Old Physics) wrote in message . com...
Old Physics wrote:

If a massive shell of matter has the same gravity as a solid
sphere with the same number of atoms, would the collapse of the shell
result in an increase in mass,

Not according to general relativity. The gravitational field at a fixed
distance will remain he same, as long as you're looking at a point that
was always outside the shell and the collapse is spherically symmetric.

ie. the original mass plus the IR
radiation that results from the conversion of kenetic energy to heat?

If you want to think of it in these terms, the relevant energy you need
to look at is ``quasilocal energy,'' which includes a contribution
analogous to Newtonian gravitational potential energy. The change
in this potential energy piece balances the other energy changes;
the total quasilocal energy remains constant.

(Of course, some of the IR radiation you speak of will eventually
radiate out past the point at which you're measuring the
gravitational field. As that happens, the field at that point will
decrease.)

Steve Carlip

Esteemed Dr. Carlip,

In the simplest terms, did you not write that with "quasilocal
energy" added to the mass of the shell, it equals the mass of the
solid sphere plus the "energy mass" of the IR that is radiated. To
rephrase: "the mass of a shell with the same number of atoms at the
same temperature will be greater (when judged from a distance) than a
solid sphere".
If I have in anyway misinterpreted your statement, please correct
me.

Hopeing for an answer,
Stephen Kearney

Relativity posts no limit to the relative contraction- time
dilation an object can undergo. What would happen if two 10^57 GeV
protons were to collide? Would they form a BH? sk

The game should be "shoot this duck" not "duck this shot". sk