Re: LIGO.


"Martin Hogbin" <goatREMOVETHIS123@xxxxxxxxxx> wrote in message news:auCdnYuj0KAcklPYnZ2dneKdnZydnZ2d@xxxxxxxxx

"cliff wright" <c.c.wright@xxxxxxxxxxxxxxx> wrote in message news:45cdc049$1@xxxxxxxxxxxxxxx
Martin Hogbin wrote:
"cliff wright" <c.c.wright@xxxxxxxxxxxxxxx> wrote in message news:45cd6bab$1@xxxxxxxxxxxxxxx

Well this is all very interesting but we still appear to have a non
functional, very expensive apparatus here!


Not yet functional! You have not responded to my latest
post about our bet. I want to place a serious bet. We need to
agree some basis on which the winner is decided otherwise it
could end up as an argument as to who has won. I will not
pay up unless I am sure that you would have paid up had you
lost.

Do you want to place a serious bet or shall we cal it off?


Michelson and Morley used an
old cellar and a realtively simple optical interfernometer, in fact they
had to cut their programme short because someone else needed the cellar.
Perhaps, it being in Dublin, a Guiness delivery was expected.
Strange, I always thought that Semantics were to do with the meaning
of language, but I suppose that mathematicians are running out of mames
for ever more abstruse calculations and logical operations.
None of this however more than partially answers my original question.
Though I see someone has phrased it quite well- In effect what are you
actually measuring and how does propagation speed enter the equation?
Electromagnetism had Maxwell, but can Einstein now join his illustrious
company or not?


Tom has carefully answered your question using the correct
technical language because that is the easiest way to do so.
Many words (such as 'energy' or 'momentum') have much more
precisely defined meanings in technical usage than in everyday
speech. You need to find out what the terms Tom has used mean
in order to get your answers.


Maxwell of course had the advantage of already knowing the approximate
velocity of electromagnetic radiation he did not have to assume it.
BTW how is the nature of the "space/time" positioning of the light paths
determined? Or is it assumed that space is substantially "flat" and
unstressed around the mirrors?
I presume that ant "directional" information depends on the time dealy
of signals and therefore the velocity of propagation, but I stand to be
corrected on that.


You are falling into the trap of expecting distance to be
a 'real' pre-defined thing. We can ultimately only define
distance by how we would measure it. Historically, different
methods have been used. In 1889 one metre was defined as
the distance between two marks on a platinum alloy bar kept
in Paris (this is the constant spacelike proper distance Tom
referred to). On this basis, LIGO would measure a variation
in the speed of light.

However, today one meter is defined as the distance travelled
by light in a specified time. In free space, away from gravitation
and other influences, this gives exactly the same result as using the
metal bar would. In the case of LIGO, because the speed of light
is now defined as a constant, we would now say that the length of
metalwork changes. It all depends on how you choose to define
'distance'.


I fully understand that Einstein's original work as regards
"gravitational radiation" has been much "worked on " since his death 50
years ago, but his name keeps coming up.


An quite rightly so. It is still his theory, unchanged, that is used.
It is just that more details have been worked out.

Martin Hogbin


Ok Martin. How about this? If both LIGO's can produce a signal which
correlates with the observation (using radio or optical techniques) of
some phenomenon. For example an especially close or powerful gamma ray
burst or supernova event. Then I will gladly stand corrected and pay
you the $50 US (about $74 NZ). However if by the end of 2011, an extra
year please note, no correlated signal which can be independently
checked is received then you owe me $50. The correlated event is
required based on the alleged signals detected by Weber (or was it
Wagner) back in the 1970's which turned out to be unrepeatable.
Does that seem fair to you?

I would prefer a generally accepted statement from the scientific
community that gravity waves have been detected. That I why I
suggest that we find an independent referee.

Actually you know I have quite a lot of background in practical Physics
even though my degree was in the history of Technology. I spent most of
my career as an electronics design engineer, and I am an active Amateur
astronomer.
I have most defintely tried NOT to fall into the "trap of distance"
problem. However since Einstein and Quantum mechanics fail to agree on
so many points I get a definite inkling that this whole experiment might
be falling into difficulties beacause of the difference between "macro"
real world conditions and the behaviour of the universe at a quantum level.
At a macroscopic level it is patently absurd to suggest that distance is
not "real".

Perhaps 'real' is not the right term to use.

Perhaps you listen to Humpty Roberts.

"Tom Roberts" <tjroberts@xxxxxxxxxx> wrote in message
news:hG3Sf.54263$H71.9335@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
| GSS wrote:
| > Tom Roberts wrote:
| >> I repeat: that is not really "speed".
| > Let us elaborate this point.
|
| Imagine a train leaving one city at 12:00 and arriving in a city 60
| miles to its west at 12:01. Do you really think that train traveled
| 3,600 miles per hour? Of course not! This example used two _different_
| coordinate systems for "time", the two timezones of those two cities. To
| obtain the speed you _must_ use a single coordinate system; then you'll
| realize it traveled just under 60 miles per hour.
|
|
| > If a time interval *dt* is measured by using UTC (or TAI) time
| > standards in reference frames K1, K2, K3 etc. in relative motion within
| > our solar system, will you regard this time interval as real or not
| > real?
|
| "real" has nothing to do with it.
|
|
| > If a distance interval *ds* is measured by using a standard meter rod
| > as per SI standards in reference frames K1, K2, K3 etc. in relative
| > motion within our solar system, will you regard this distance interval
| > as real or not real?
|
| "Real" has nothing to do with it.
|
| To obtain a speed, you must divide the distance traveled by the travel
| time, and _all_ quantities _must_ be measured in a single coordinate
| system. In Newtonian mechanics and SR, the coordinate system must be
| inertial, using standard clocks and rulers. In GR (or other coordinate
| systems) this merely yields coordinate speed.
|
| _Nothing_ else is speed. Because that is what we mean by the word. <shrug>
|
|
| Tom Roberts tjroberts@xxxxxxxxxx




"The Magpie" <usenet@xxxxxxxxxxxxxxxxxxxx> wrote in message
news:e0u2ol$2e8$1$8300dec7@xxxxxxxxxxxxxxxxxxx
| Hexenmeister wrote:
| > "The Magpie" <usenet@xxxxxxxxxxxxxxxxxxxx> wrote in message
| > news:e0qpkh$8ba$1$830fa17d@xxxxxxxxxxxxxxxxxxx
| > | No it is not. Space is space, time is time. Together they form a
| > | four-dimensional continuum of which and within which the universe
| > | exists. They are by no means equivalent or similar.
| >
| > Yep. But as the shithead relativist Roberts says:
| > "Real" has nothing to do with it.
| >
| SO who mentioned "real"? Not me.

That's ok. You can say whatever you like in
sci.physics.relativity,sci.physics

as long as it isn't connected to, related to or involves reality. Most do.
You were getting might close to reality with that "four-dimensional
continuum", "universe" and "exists".
Perhaps you don't mean "exist". Shrugging Humpty Roberts doesn't mean
the words he uses either.

Humpty Roberts in Wonderland:-
| Tom Roberts tjroberts@xxxxxxxxxx

Newsgroups: sci.physics.relativity
From: Tom Roberts <tjrobe...@xxxxxxxxxx> - Find messages by this
author
Date: Sat, 17 Sep 2005 17:57:18 GMT
Local: Sat, Sep 17 2005 6:57 pm
Subject: Re: Does the 'Curvature of Spacetime' cause gravity?


"Yes, tests of strong fields are few and far between, but there are
some:
the binary pulsars, and observations of accretion disks near black
holes

`I don't know what you mean by "observations",' Alice said.

Humpty Roberts smiled contemptuously. `Of course you don't -- till I tell
you.
I meant "there's a nice knock-down argument for you!"' <shrug>

`But "observations" doesn't mean "a nice knock-down argument",' Alice
objected.

`When I use a word,' Humpty Roberts said, in rather a scornful tone,
<shrug>,
`it means just what I choose it to mean -- neither more nor less.' <shrug>

`The question is,' said Alice, `whether you can make words mean so many
different things.'

`The question is,' said Humpty Roberts, `which is to be master -- that's
all.' <shrug>

Alice was too much puzzled to say anything; so after a minute Humpty Roberts
began again. `They've a temper, some of them -- particularly verbs: they're
the proudest -- adjectives you can do anything with, but not verbs --
however,
I can manage the whole lot of them! Impenetrability! That's what I say!'
<shrug>

"And you never responded to how a 2-d surface in a flat 4-d spacetime can
have nonzero curvature, and why that shows that the curvature of such
2-d surfaces is useless in "describing" the geometry of the 4-d
manifold...." he
droned on.

"If you say that the curvature of 2-d surfaces is useless in
"describing" the geometry of the 4-d manifold....I am willing to agree
with you. But I just wanted you people to help me visualize the
intrinsic curvature of 3-d Schw. space. I was told that the Gaussian
curvature of certain 2-d surfaces will represent the intrinsic
curvature of 3-d Schw. space. When I wanted these 2-d surfaces to be
identified, Jan PB had given some interesting suggestions. But now you
say it is *useless*....." said Alice.

"_SOME_ 2-d surfaces can be useful in describing the geometry of 4-d
spacetime, in particular those spanned by a 2-d vector space of
geodesics. But you were discussing 2-d surfaces defined by coordinates,
and _those_ are useless because coordinates are completely arbitrary,
and introducing that arbitrariness destroys their usefulness" replied Humpty
Roberts.

"That means the notion of intrinsic curvature of space is either too
complex that it cannot be visualized or it is just invalid." exclaimed
Alice.

"No. But in many cases using a ball of dust particles is a better
visualization tool than 2-d surfaces.", said Humpty Roberts, teetering
on his wall.

"Mathematically it is good enough to state that in Riemannian geometry
the Riemann tensor is non-zero. Where is the necessity of associating
it with a cooked up fictitious term 'curvature of space'? " asked Alice,
thinking of the cooked up egg she had for breakfast.

"Mathematicians and physicists are human. We share the common desire to
communicate with each other easily, accurately, and concisely -- that's
why technical vocabularies were invented." said Humpty Roberts scornfully
and pretending he is human by saying "we".

Alice pondered this for moment, then asked "Was it required to fool and
mislead the 'layman'?"

"Your problem, not mine", said Humpty Roberts, then realizing his
Freudian slip, he was pretending to be human, added "(ours).
But this technical vocabulary is not secret or unfathomable, it just
takes _STUDY_. <shrug>"

Alice then went back to say "The term *curvature* basically applies to
the bending of curves and 2-d surfaces."

Ho ho, thought Humpty Roberts, "Not in differential geometry or GR.
The term "curvature" was borrowed by analogy with 2-d surfaces, and
has come to mean the Riemann curvature tensor. That is, a manifold of
_any_ dimension with nonzero Riemann tensor is said to be curved."
and he shrugged like this :- "<shrug>"

Alice asked "Why *said* to be curved when it is actually not curved?"

Humpty Roberts let out a great sigh.
" <sigh>", he said.
"The nuances of English. I was discussing the usage of words and
not the concepts they represent."
-- Tom Humpty Roberts tjroberts@xxxxxxxxxx
news:ZDmYf.51582$2O6.5573@xxxxxxxxxxxxxxxxxxxxxxxxxx
The end.
With thanks to Lewis Carroll.

The reader should take careful note here.
Humpty Roberts is not discussing the concepts words represent, he is
discussing the meaning of words. The rest of us use a dictionary.

Professor Androcles.



|


.

Loading