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Dono
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 Posted: Wed Jul 16, 2008 3:13 pm Post subject: Re: Are SR effects real or not? Simplified case. |
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On Jul 16, 8:09 am, Uncle Ben <b...@greenba.com> wrote:
| Quote: |
This character who calls himself "Dano" says that he wrote the
Wikipedia article on Bell's
Paradox. He won't reveal his name, but from the character of the
exchange we have had over tha past two days, I am pretty sure I can
pick him out of the Discussion section of the Wikipedia article.
The Discussion section is many pages long if printed out. Participants
in the exchange get pretty heated and direct with each other. There
is one character there who seems to resist the suggestions of the
others. In one place, a senior member of the group accuses him of not
understanding relativity. Another accuses him of not accepting the
principle of the relativity of simulaneity, a familiar phrase from the
past few days. I don't really agree with these criticisms -- I think
he does understand -- but he has trouble grasping the writings of
others.
I won't out him here, but if you read the exchange we have had and
then read the Discussion (which takes a lot of patience), you may
agree with me as to which one is "Dano."
Uncle Ben
|
Ben,
Why don't you cut the BS and present your solution. |
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Uncle Ben
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| Posted: Wed Jul 16, 2008 3:39 pm Post subject: Re: Are SR effects real or not? Simplified case. |
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On Jul 16, 11:13 am, Dono <sa...@comcast.net> wrote:
| Quote: |
Ben,
Why don't you cut the BS and present your solution.- Hide quoted text -
- Show quoted text -
|
There's that reading problem again.
I never said I had a second solution.
I never said I had a second solution.
I never said I had a second solution.
I never said I had a second solution.
I never said I had a second solution.
Did I mention that I never said I had a second solution?
What I said was, that your reference to the "common frame of the space
ships", which is an accelerated frame, could be the basis of a correct
solution. But it is not the one I used.
First you say that my solution is wrong.
Then you say I got it from you.
Then you say it is trivial.
My one and only solution dates from 1967 when I was on the staff of
the Commission on College Physics. I enjoyed the company of several
distinguished physicists, some of which often disagreed with me over
the lunch table when we discussed interested bits of physics lore.
They never seemed to have the time to complete the analyses and
discover that I was right. So I adopted the strategy of betting them a
small but non-negligible amount of money, which in those days was 50
cents. That gave me the chance to establish myself as a reliable
source. Subsequently, when I offerred to bet fifty cents, they would
back down immediately.
One of those bets was on the string problem, which I had solved to my
own satisfaction by the argument I gave above, (July 15, 10:10 am).
The bet was with the director of the Commission. He never had the time
to do any analysis. But at one of our meetings at MIT, the editor of
the AJP was attending, and told us some of the history of the paper in
his journal that I had read and was fascinated by. He told us that
the paper had had to be reviewed several times before a concensus
could be formed to the effect that the paper was correct.
My director reached into his pocket and gave me the fifty cents.
Now almost half a century later, Mr. Dono accuses me of stealing his
solution. I don't care except that I would like to be known in the
group as a reliable source, not always right, but often so.
Uncle Ben |
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Daryl McCullough
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| Posted: Wed Jul 16, 2008 4:08 pm Post subject: Re: Are SR effects real or not? Simplified case. |
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Dono says...
| Quote: |
On Jul 15, 7:10=A0am, Uncle Ben <b...@greenba.com> wrote:
That is all we need. If the lead rocket fires first, it must stretch
the string.
This is not what happens in the Bell problem statement.If your problem
statement were correct, the problem would reduce to a trivial one. You
keep trying to peddle your reductionist view of the problem. What
happens in reality is presented here:
http://en.wikipedia.org/wiki/Bell%27s_spaceship_paradox#Analysis
|
What Uncle Ben said is completely in agreement with the wikipedia
article. I think you misunderstood Uncle Ben.
For simplicity, let's just consider two frames: (1) A frame
in which the rear rocket is at rest at time t=0, and (2) a frame
in which the rear is at rest at time t=1 second.
From the point of view of the first frame, the two rockets
launch simultaneously. From the point of view of the second
frame, the lead rocket fires first. So from the point of
view of the frame in which the string is at rest, the
string must be stretched.
--
Daryl McCullough
Ithaca, NY |
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Daryl McCullough
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| Posted: Wed Jul 16, 2008 4:18 pm Post subject: Re: Are SR effects real or not? Simplified case. |
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Dono says...
| Quote: |
On Jul 15, 6:47=A0pm, Uncle Ben <b...@greenba.com> wrote:
that is EXACTLY the
problem I stated and solved. =A0If you disagree, please explain.
Uncle Ben
You are contradicting your earlier post that says that you have no
interest in the original Bell paradox. Now, you claim that this is
exactly the problem that you solved (you didn't really solve
anything).
So, which one is true? Are you just trolling?
|
Why are you picking a fight? Those two statements are not
contradictory. Uncle Ben proposed a thought experiment
that was interesting in its own right, whether or not
it was the same as Bell's thought experiment. It turns
out it *was* the same as Bell's thought experiment.
And Uncle Ben did solve it correctly. You just misunderstood
his solution.
--
Daryl McCullough
Ithaca, NY |
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Daryl McCullough
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| Posted: Wed Jul 16, 2008 4:32 pm Post subject: Re: Are SR effects real or not? Simplified case. |
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Dono says...
| Quote: |
Then, your "solution" is plain wrong.
|
His solution is the same as that in the wikipedia article.
Let's make this more unambiguous by labeling events and frames.
Let F1 = the frame in which the two rockets are initially
at rest.
Let e1 = the event at which the rear rocket takes off.
Let e2 = the event at which the front rocket takes off.
Let e3 = the event at which the rear rocket is traveling
at 100 meters/second, relative to F1.
Let e4 = the event at which the front rocket is traveling
at 100 meters/second, relative to F1.
Let F2 = the frame in which the rear rocket is at rest at
event e3.
From the point of view of F1, e1 and e2 are simultaneous,
and e3 and e4 are simultaneous.
From the point of view of F2, e2 takes place before e1,
and e3 takes place before e4. So in frame F2, the lead
rocket launched first, and the distance between the
rockets has increased. So from the point of view of F2,
the string is stretched relative to its initial length.
F2 is the instantaneous rest frame of the string
(or at least the portion of the string attached
to the rear rocket). If the string is stretched
in this frame, then the string will break.
--
Daryl McCullough
Ithaca, NY |
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Daryl McCullough
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| Posted: Wed Jul 16, 2008 4:35 pm Post subject: Re: Are SR effects real or not? Simplified case. |
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Dono says...
| Quote: |
You ARE trolling.
The two rockets take off simultaneously in the launcher frame and also
in the common rocket frame since, at launch, the two frames are
coincident. Find another hobby.
|
I don't know how you are misunderstanding what Uncle Ben is saying,
but Ben is right.
--
Daryl McCullough
Ithaca, NY |
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Dono
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| Posted: Wed Jul 16, 2008 9:56 pm Post subject: Re: Are SR effects real or not? Simplified case. |
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On Jul 16, 8:39 am, Uncle Ben <b...@greenba.com> wrote:
| Quote: |
On Jul 16, 11:13 am, Dono <sa...@comcast.net> wrote:
Ben,
Why don't you cut the BS and present your solution.- Hide quoted text -
- Show quoted text -
There's that reading problem again.
I never said I had a second solution.
I never said I had a second solution.
I never said I had a second solution.
I never said I had a second solution.
I never said I had a second solution.
Did I mention that I never said I had a second solution?
What I said was, that your reference to the "common frame of the space
ships", which is an accelerated frame, could be the basis of a correct
solution. But it is not the one I used.
First you say that my solution is wrong.
Then you say I got it from you.
Then you say it is trivial.
My one and only solution dates from 1967 when I was on the staff of
the Commission on College Physics. I enjoyed the company of several
distinguished physicists, some of which often disagreed with me over
the lunch table when we discussed interested bits of physics lore.
They never seemed to have the time to complete the analyses and
discover that I was right. So I adopted the strategy of betting them a
small but non-negligible amount of money, which in those days was 50
cents. That gave me the chance to establish myself as a reliable
source. Subsequently, when I offerred to bet fifty cents, they would
back down immediately.
One of those bets was on the string problem, which I had solved to my
own satisfaction by the argument I gave above, (July 15, 10:10 am).
The bet was with the director of the Commission. He never had the time
to do any analysis. But at one of our meetings at MIT, the editor of
the AJP was attending, and told us some of the history of the paper in
his journal that I had read and was fascinated by. He told us that
the paper had had to be reviewed several times before a concensus
could be formed to the effect that the paper was correct.
My director reached into his pocket and gave me the fifty cents.
Now almost half a century later, Mr. Dono accuses me of stealing his
solution. I don't care except that I would like to be known in the
group as a reliable source, not always right, but often so.
Uncle Ben
|
So what's your "first solution" . Point to the post. Do you know how
to do that? |
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Dono
Guest
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| Posted: Wed Jul 16, 2008 10:00 pm Post subject: Re: Are SR effects real or not? Simplified case. |
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|
On Jul 12, 8:59 am, Uncle Ben <b...@greenba.com> wrote:
| Quote: |
-------------------------------
Proof:
1) According to Newton, the position of a ship under constant
acceleration is given by x=t*t in some units. In an obvious notation,
the equations of motion are
x1 = t*t + x0,
x2 = t*t,
so
x1-x2 = x0.
2) According to Einstein, the position of a ship under constant proper
acceleration is given by x=cosh(t). The equations of motion will be
x1 = cosh(t) + x0,
x2 = cosh(t).
so
x1-x2 = x0.
QED
-------------------------------
But what about the string? When the ships are moving at almost the
speed of light, the string must have tried to contract a lot. But it
is constrained to stay at a fixed length x0. Sooner or later it will
reach its breaking point and will snap!
Do you believe this? Does the string break or not? Is the Lorentz-
Fitzgerad contraction real or not real?
Uncle Ben
|
So, is this your "solution"? Where is the math? You "threatened" that
you will unveil the complete solution (what you have is nothing but a
bunch of trivial stuff). So , where is it? |
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Uncle Ben
Guest
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| Posted: Thu Jul 17, 2008 3:57 am Post subject: Re: Are SR effects real or not? Simplified case. |
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On Jul 16, 9:24 pm, Tom Roberts <tjroberts...@sbcglobal.net> wrote:
| Quote: |
PD wrote:
To put Tom's point more colloquially, an given ruler at any given
moment has got thousands of physical lengths, [...]
I wouldn't say that, either. To virtually everybody, "physical length"
means "proper length", and that's not what you mean.
Say "measured length", because that's what it is. And don't worry about
whether or not it's "real" -- that's hopelessly ambiguous, and is never
needed.
But more generally, don't try to make sound bites, as they are
invariably mis-interpreted by people who don't already understand SR,
and they are useless to people who do understand SR.
Uncle Ben said:
If you measure it, it is real.
Hmmm. But the "real length" of a ruler is quite clearly its proper
length. So you have a length that is "real" but that is not its "real
length". Yes, there are PUNS on "real" throughout that, and THAT IS THE
PROBLEM -- "real" is not precise enough to capture the nuances of what
is going on, and such sound bites are invariably misinterpreted (except
by people who already understand all this).
Go back to my analogy of the ladder and doorway. The "real length" of
the ladder quite clearly does not change with orientation. But you claim
the "length" of a moving ruler is "real" and does change with
orientation. In this case, it is the PROJECTED length of the ladder that
matters, and that also applies to what is measured for the moving ruler.
All you need to do is be more careful to avoid PUNs.
It is a cop-out to qualify cetain results in relativity as "apparent"
or "measured" as if measurement was a lesser way to truth.
No. It is no "cop-out" to say "measured length" when THAT IS WHAT IT IS.
Or to say "projected length" when that is what it is. But "real length"
would CLEARLY be wrong for the measured length of a moving ruler, or for
the length relevant to the ladder fitting through the doorway.
It simply does not make sense to claim the length of a moving ruler is
"real", but is not its "real length" -- yet that's what your ambiguous
usages do.
It is
because the writer is still not quite accepting the results as real
in the back of his mind, or he thinks the reader wont accept it and he
is hedging his bets.
No. It is (at least in my case) because the writer does not want to use
an inappropriate PUN, and wants to specify what he/she is talking about.
Yes, the measurement of a projected length can have real, physical
consequences. But it is not the "real length" of a moving ruler, just
like the length of the ladder projected onto the doorway is not the
"real length" of the ladder.
There is no ambiguity at all in the "real length" of the ladder. But you
introduce ambiguity into "real length" of a moving rod. Those cases are
directly analogous, and it's silly to use the language differently for them.
That is why I always state it outright that, for example, the length
w.r.t. frame f "IS" so-and-so, not "appears to be".
That usage is OK, because you DID specify what you meant. The problem is
that you repeatedly use similar words and DON'T specify what you mean,
leaving your ambiguous words to be interpreted by the reader -- THAT is
the problem I'm trying to get you to understand. And it is a problem,
especially around here.
Length is defined
relative to a frame of reference.
To you, perhaps. But not necessarily to everybody else. When
communicating you must share definitions of words with your reader, or
it is hopeless. Do not count on "length" being defined that way to
everybody else, because it isn't: "length" and "real" are simple, basic
words, and you cannot possibly prevent people from applying their
simple, basic meanings. In the way you use those words, those basic
meanings are WRONG. You have no control over your readers, so you should
avoid such words, and use the correct terminology from the technical
vocabulary -- that's why it was invented. There are no shortcuts, and
sound bites are invariably misinterpreted.
Nobody will misinterpret "proper length", "measured length", or
"projected length", and there's no excuse not to use those phrases WHEN
THAT IS WHAT YOU MEAN.
Tom Roberts
|
Tom, I appreciate what you are trying to say, but I fundamentally
disagree with you. You said a lot, but the key is this quote:
| Quote: |
Length is defined
relative to a frame of reference.
To you, perhaps. But not necessarily to everybody else.
|
But the student should learn to say it this way. Because that is what
Einstein teaches.
If they don't believe it, they should still be able to say, "Einstein
teaches that length is relative to a frame of reference." The
beginning of understanding is first to know what is being claimed,
even if it ultimately is proved to be false.
It is not called the Theory of Relativity for nothing. Length is
relative, time is relative, mass is relative, atomic number is not
relative, rest mass is not relative, proper length is not relative,
etc., where relative means "is defined relative to an inertial frame
of reference."
If somebody is reluctant to say what Einstein says, he is not using
SR. The "paradoxes" and proofs of the "falsity" of SR are possible
because people cannot bring themselves to adopt this idea of what
relativity means, or they simply reject it. If they reject it, we just
have to leave them behind.
The fastest way for someone to grasp relatativity, in my humble
opinion, is to CONFRONT this fundamental teaching of Einstein and
accept it, at least tentatively, long enough to be able to understand
the tests of SR and, if they cannot find a better explanation of the
experimental facts, finally to acknowledge that it is as close to the
truth as we can get at this time.
Best wishes,
Ben |
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Uncle Ben
Guest
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| Posted: Thu Jul 17, 2008 3:59 am Post subject: Re: Are SR effects real or not? Simplified case. |
|
|
On Jul 16, 6:00 pm, Dono <sa...@comcast.net> wrote:
| Quote: |
On Jul 12, 8:59 am, Uncle Ben <b...@greenba.com> wrote:
-------------------------------
Proof:
1) According to Newton, the position of a ship under constant
acceleration is given by x=t*t in some units. In an obvious notation,
the equations of motion are
x1 = t*t + x0,
x2 = t*t,
so
x1-x2 = x0.
2) According to Einstein, the position of a ship under constant proper
acceleration is given by x=cosh(t). The equations of motion will be
x1 = cosh(t) + x0,
x2 = cosh(t).
so
x1-x2 = x0.
QED
-------------------------------
But what about the string? When the ships are moving at almost the
speed of light, the string must have tried to contract a lot. But it
is constrained to stay at a fixed length x0. Sooner or later it will
reach its breaking point and will snap!
Do you believe this? Does the string break or not? Is the Lorentz-
Fitzgerad contraction real or not real?
Uncle Ben
So, is this your "solution"? Where is the math? You "threatened" that
you will unveil the complete solution (what you have is nothing but a
bunch of trivial stuff). So , where is it?- Hide quoted text -
- Show quoted text -
|
Dono, fugeddaboutit.
Love, Ben |
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Dono
Guest
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| Posted: Thu Jul 17, 2008 4:18 am Post subject: Re: Are SR effects real or not? Simplified case. |
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|
On Jul 16, 8:59 pm, Uncle Ben <b...@greenba.com> wrote:
| Quote: |
On Jul 16, 6:00 pm, Dono <sa...@comcast.net> wrote:
On Jul 12, 8:59 am, Uncle Ben <b...@greenba.com> wrote:
-------------------------------
Proof:
1) According to Newton, the position of a ship under constant
acceleration is given by x=t*t in some units. In an obvious notation,
the equations of motion are
x1 = t*t + x0,
x2 = t*t,
so
x1-x2 = x0.
2) According to Einstein, the position of a ship under constant proper
acceleration is given by x=cosh(t). The equations of motion will be
x1 = cosh(t) + x0,
x2 = cosh(t).
so
x1-x2 = x0.
QED
-------------------------------
But what about the string? When the ships are moving at almost the
speed of light, the string must have tried to contract a lot. But it
is constrained to stay at a fixed length x0. Sooner or later it will
reach its breaking point and will snap!
Do you believe this? Does the string break or not? Is the Lorentz-
Fitzgerad contraction real or not real?
Uncle Ben
So, is this your "solution"? Where is the math? You "threatened" that
you will unveil the complete solution (what you have is nothing but a
bunch of trivial stuff). So , where is it?- Hide quoted text -
- Show quoted text -
Dono, fugeddaboutit.
Love, Ben
|
I did, you have nothing. This is how I tell the crackpots, when the
chips are down and they are asked to put down the math , they
"fugeddaboutit". |
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PD
Guest
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| Posted: Thu Jul 17, 2008 5:03 am Post subject: Re: Are SR effects real or not? Simplified case. |
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On Jul 16, 8:24 pm, Tom Roberts <tjroberts...@sbcglobal.net> wrote:
| Quote: |
PD wrote:
To put Tom's point more colloquially, an given ruler at any given
moment has got thousands of physical lengths, [...]
I wouldn't say that, either. To virtually everybody, "physical length"
means "proper length", and that's not what you mean.
Say "measured length", because that's what it is. And don't worry about
whether or not it's "real" -- that's hopelessly ambiguous, and is never
needed.
|
Well, with all respect, I disagree. The problem philosophically and
pedagogically with assigning "physical length" to "proper length" is
that it singles out a reference frame. While this is not a unique
frame in the sense of some pervasive ether that sets it, it is only a
half a step behind, implying that there is something special about the
rest frame of an object, and that the true "physical" property of an
object is what we measure when it is at rest. I find it distasteful,
and I believe Einstein would too, to think that "physical" length can
only be accessed directly by measurement in one reference frame. The
whole point of the principle of relativity is to convey that there is
nothing *physically* different or unique about measurements made in
one frame as opposed to any other.
I agree with Uncle Ben that "length" is physical insofar as it is the
result of a measurement and is in fact *defined* by a measurement
procedure, which happens to rely on simultaneity. If you insist that
length becomes "physical length" only in one frame, then this also
suggests that the simultaneity invoked in the measurement made in that
frame is somehow more "real" than what is simultaneous in other
frames, and again I think most would think this off the mark.
Now, between any two events in spacetime, there is an invariant
interval, and if that interval is spacelike, then there is a reference
frame in which that 4D interval numerically coincides with the 3D
length. But again, there is nothing *physically* special about that
frame, anymore than there is something physically special about the
choice of coordinate axes that makes the 2D length of a line segment
numerically coincide with its projection on the x-axis.
So I agree that the point is to use the word "measured", but if you
do, then you should abstain from using the term "physical length" at
all, because it is just as ambiguous as using the adjective "real".
| Quote: |
But more generally, don't try to make sound bites, as they are
invariably mis-interpreted by people who don't already understand SR,
and they are useless to people who do understand SR.
Uncle Ben said:
If you measure it, it is real.
Hmmm. But the "real length" of a ruler is quite clearly its proper
length. So you have a length that is "real" but that is not its "real
length". Yes, there are PUNS on "real" throughout that, and THAT IS THE
PROBLEM -- "real" is not precise enough to capture the nuances of what
is going on, and such sound bites are invariably misinterpreted (except
by people who already understand all this).
Go back to my analogy of the ladder and doorway. The "real length" of
the ladder quite clearly does not change with orientation. But you claim
the "length" of a moving ruler is "real" and does change with
orientation. In this case, it is the PROJECTED length of the ladder that
matters, and that also applies to what is measured for the moving ruler.
All you need to do is be more careful to avoid PUNs.
It is a cop-out to qualify cetain results in relativity as "apparent"
or "measured" as if measurement was a lesser way to truth.
No. It is no "cop-out" to say "measured length" when THAT IS WHAT IT IS.
Or to say "projected length" when that is what it is. But "real length"
would CLEARLY be wrong for the measured length of a moving ruler, or for
the length relevant to the ladder fitting through the doorway.
It simply does not make sense to claim the length of a moving ruler is
"real", but is not its "real length" -- yet that's what your ambiguous
usages do.
It is
because the writer is still not quite accepting the results as real
in the back of his mind, or he thinks the reader wont accept it and he
is hedging his bets.
No. It is (at least in my case) because the writer does not want to use
an inappropriate PUN, and wants to specify what he/she is talking about.
Yes, the measurement of a projected length can have real, physical
consequences. But it is not the "real length" of a moving ruler, just
like the length of the ladder projected onto the doorway is not the
"real length" of the ladder.
There is no ambiguity at all in the "real length" of the ladder. But you
introduce ambiguity into "real length" of a moving rod. Those cases are
directly analogous, and it's silly to use the language differently for them.
That is why I always state it outright that, for example, the length
w.r.t. frame f "IS" so-and-so, not "appears to be".
That usage is OK, because you DID specify what you meant. The problem is
that you repeatedly use similar words and DON'T specify what you mean,
leaving your ambiguous words to be interpreted by the reader -- THAT is
the problem I'm trying to get you to understand. And it is a problem,
especially around here.
Length is defined
relative to a frame of reference.
To you, perhaps. But not necessarily to everybody else. When
communicating you must share definitions of words with your reader, or
it is hopeless. Do not count on "length" being defined that way to
everybody else, because it isn't: "length" and "real" are simple, basic
words, and you cannot possibly prevent people from applying their
simple, basic meanings. In the way you use those words, those basic
meanings are WRONG. You have no control over your readers, so you should
avoid such words, and use the correct terminology from the technical
vocabulary -- that's why it was invented. There are no shortcuts, and
sound bites are invariably misinterpreted.
Nobody will misinterpret "proper length", "measured length", or
"projected length", and there's no excuse not to use those phrases WHEN
THAT IS WHAT YOU MEAN.
Tom Roberts |
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Tom Roberts
Guest
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| Posted: Thu Jul 17, 2008 6:15 am Post subject: Re: Are SR effects real or not? Simplified case. |
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|
Uncle Ben wrote:
| Quote: |
Theorem: Given two events that are simultaneous w.r.t. a given
inertial frame, they are non simultaneous w.r.t. any other inertial
frame not at rest w.r.t. the first frame.
|
Nope. Counterexamples abound. You forgot to specify that they are
separated by a spatial interval that has nonzero projection on the
frames' relative velocity.
Tom Roberts |
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Tom Roberts
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| Posted: Thu Jul 17, 2008 6:24 am Post subject: Re: Are SR effects real or not? Simplified case. |
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PD wrote:
| Quote: |
To put Tom's point more colloquially, an given ruler at any given
moment has got thousands of physical lengths, [...]
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I wouldn't say that, either. To virtually everybody, "physical length"
means "proper length", and that's not what you mean.
Say "measured length", because that's what it is. And don't worry about
whether or not it's "real" -- that's hopelessly ambiguous, and is never
needed.
But more generally, don't try to make sound bites, as they are
invariably mis-interpreted by people who don't already understand SR,
and they are useless to people who do understand SR.
Uncle Ben said:
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If you measure it, it is real.
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Hmmm. But the "real length" of a ruler is quite clearly its proper
length. So you have a length that is "real" but that is not its "real
length". Yes, there are PUNS on "real" throughout that, and THAT IS THE
PROBLEM -- "real" is not precise enough to capture the nuances of what
is going on, and such sound bites are invariably misinterpreted (except
by people who already understand all this).
Go back to my analogy of the ladder and doorway. The "real length" of
the ladder quite clearly does not change with orientation. But you claim
the "length" of a moving ruler is "real" and does change with
orientation. In this case, it is the PROJECTED length of the ladder that
matters, and that also applies to what is measured for the moving ruler.
All you need to do is be more careful to avoid PUNs.
| Quote: |
It is a cop-out to qualify cetain results in relativity as "apparent"
or "measured" as if measurement was a lesser way to truth.
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No. It is no "cop-out" to say "measured length" when THAT IS WHAT IT IS.
Or to say "projected length" when that is what it is. But "real length"
would CLEARLY be wrong for the measured length of a moving ruler, or for
the length relevant to the ladder fitting through the doorway.
It simply does not make sense to claim the length of a moving ruler is
"real", but is not its "real length" -- yet that's what your ambiguous
usages do.
| Quote: |
It is
because the writer is still not quite accepting the results as real
in the back of his mind, or he thinks the reader wont accept it and he
is hedging his bets.
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No. It is (at least in my case) because the writer does not want to use
an inappropriate PUN, and wants to specify what he/she is talking about.
Yes, the measurement of a projected length can have real, physical
consequences. But it is not the "real length" of a moving ruler, just
like the length of the ladder projected onto the doorway is not the
"real length" of the ladder.
There is no ambiguity at all in the "real length" of the ladder. But you
introduce ambiguity into "real length" of a moving rod. Those cases are
directly analogous, and it's silly to use the language differently for them.
| Quote: |
That is why I always state it outright that, for example, the length
w.r.t. frame f "IS" so-and-so, not "appears to be".
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That usage is OK, because you DID specify what you meant. The problem is
that you repeatedly use similar words and DON'T specify what you mean,
leaving your ambiguous words to be interpreted by the reader -- THAT is
the problem I'm trying to get you to understand. And it is a problem,
especially around here.
| Quote: |
Length is defined
relative to a frame of reference.
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To you, perhaps. But not necessarily to everybody else. When
communicating you must share definitions of words with your reader, or
it is hopeless. Do not count on "length" being defined that way to
everybody else, because it isn't: "length" and "real" are simple, basic
words, and you cannot possibly prevent people from applying their
simple, basic meanings. In the way you use those words, those basic
meanings are WRONG. You have no control over your readers, so you should
avoid such words, and use the correct terminology from the technical
vocabulary -- that's why it was invented. There are no shortcuts, and
sound bites are invariably misinterpreted.
Nobody will misinterpret "proper length", "measured length", or
"projected length", and there's no excuse not to use those phrases WHEN
THAT IS WHAT YOU MEAN.
Tom Roberts |
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