| Topic: |
Sociology > Depression |
| User: |
"Indigo Moon Man" |
| Date: |
20 Nov 2003 11:30:00 PM |
| Object: |
Taglines |
I love collecting taglines and so I thought I would share a few...
Under capitalism man exploits man; under socialism the reverse is true.
Always remember you're unique, just like everyone else.
Give me ambiguity or give me something else.
186,000 miles/sec. It's not just a good idea, it's the law.
This reading lamp hasn't uttered a single word since I bought it!
BREAKFAST.COM Halted! Cereal port not responding.
Borg Spreadsheet: Locutus 1-2-3
What can we do about ignorance and apathy? Who knows? Who cares?
--
Our Daily Bread Devotional:
http://www.gospelcom.net/rbc/odb/odb.shtml
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| User: "Don Quixote" |
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| Title: Re: Taglines |
21 Nov 2003 09:49:31 PM |
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Indigo Moon Man might have said:
186,000 miles/sec. It's not just a good idea, it's the law.
Isn't that off a little? ISTR a flame war over this. Uh, not here,
and I thought it was funny 'cause someone .sig'd to the actual number
for a bit.
Which I can't recall.
At any rate http://www.why-is-the-sky-blue.tv/speed-of-light.htm is
also funny.
--
Looking for some conversation? Bored? Another facet of support and friendship:
IRC- Undernet.org 6667 #freeasd
There are occasional moments of silence, but if you say hello, someone else will
too. Usually. We all must sleep, and have our own bad days. But we like you!
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| User: "old coyote" |
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| Title: Re: Taglines |
22 Nov 2003 10:01:47 PM |
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Don Quixote <spambait@whitehouse.gov.invalid> wrote in
news:ihmtrvs5nlmlgo8662076hks6jmjsn9n2i@fishead.news.meowkitty.com:
Indigo Moon Man might have said:
186,000 miles/sec. It's not just a good idea, it's the law.
Isn't that off a little? ISTR a flame war over this. Uh, not here,
and I thought it was funny 'cause someone .sig'd to the actual number
for a bit.
Which I can't recall.
At any rate http://www.why-is-the-sky-blue.tv/speed-of-light.htm is
also funny.
http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/speed_of_ligh
t.html
Updated 1997 by Steve Carlip.
Original by Philip Gibbs 1996.
Is The Speed of Light Constant?
There are a number of senses to the meaning of this question and so there
are a number of different answers. Firstly . . .
Does the speed of light change in air or water?
Yes. Light is slowed down in transparent media such as air, water and
glass. The ratio by which it is slowed is called the refractive index of
the medium and is always greater than one*. This was discovered by Jean
Foucault in 1850.
When people talk about "the speed of light" in a general context they
usually mean "the speed of light in a vacuum". This quantity is also
referred to as c.
Is the c, speed of light in vacuum, constant?
At the 1983 Conference Generale des Poids et Mesures the following SI
(Systeme International) definition of the metre was adopted:
The metre is the length of the path travelled by light in vacuum during a
time interval of 1/299 792 458 of a second.
This defines the speed of light in vacuum to be exactly 299,792,458 m/s.
This provides a very short answer to the question "Is c constant": Yes, c
is constant by definition!
However, this is not the end of the matter. The SI is based on very
practical considerations. Definitions are adopted according to the most
accurate known measurement techniques of the day and are constantly
revised. At the moment you can measure macroscopic distances most
accurately by sending out laser light pulses and timing how long they take
to travel using a very accurate atomic clock. (The best atomic clocks are
accurate to about one part in 1013.) It therefore makes sense to define
the metre unit in such a way as to minimise errors in such a measurement.
The SI definition makes certain assumptions about the laws of physics. For
example, they assume that the particle of light, the photon, is massless.
If the photon had a small rest mass, the SI definition of the metre would
become meaningless because the speed of light would change as a function of
its wavelength. They could not just define it to be constant. They would
have to fix the definition of the metre by stating which colour of light
was being used. Experiments have shown that the mass of the photon must be
very small if it is not zero (see the FAQ: What is the mass of the
photon?). It is certainly too small to have any practical significance for
the definition of the metre in the foreseeable future but it cannot be
shown to be exactly zero even though currently accepted theories indicate
that it is. If it wasn't zero, the speed of light would not be constant
but from a theoretical point of view we would then take c to be the upper
limit of the speed of light in vacuum so that we can continue to ask if c
is constant.
Previously the metre and second have been defined in various different ways
according to the measurement techniques of the time. They could change
again in the future. If we look back to 1939, the second was defined as
1/84,600 of a mean solar day and the metre as the distance between two
scratches on a bar of platinum-iridium alloy held in France. We now know
that there are variations in the length of a mean solar day as measured by
atomic clocks. Standard time is adjusted by adding or subtracting a leap
second from time to time. There is also an overall slowing down of the
Earth's rotation by about 1/100,000 of a second per year due to tidal
forces between the Earth, Sun and Moon. There may have been even larger
variations in the length or the metre standard caused by metal shrinkage.
The net result is that the value of the speed of light as measured in m/s
was slowly changing at that time. Obviously it would be more natural to
attribute those changes to variations in the units of measurement than to
changes in the speed of light itself, but by the same token it is nonsense
to say that the speed of light is now constant just because the SI
definitions of units define its numerical value to be constant.
But the SI definition highlights the point that we need to first be very
clear what we mean by constancy of the speed of light before we answer our
question. We have to state what we are going to use as our standard ruler
and our standard clock when we measure c. In principle we could get a very
different answer using measurements based on laboratory experiments from
the one we get using astronomical observations. (One of the first
measurement of the speed of light was derived from observed changes in the
length of the eclipses of Jupiter's moons by Olaus Roemer in 1676.) We
could, for example, take the definitions of the units as they stood between
1967 and 1983. Then the metre was defined as 1,650,763.73 wavelengths of
the reddish-orange light from a krypton-86 source, and the second was
defined (then as now) as 9,192,631,770 periods of the radiation
corresponding to the transition between the two hyperfine levels of cesium-
133. Unlike the previous definitions these depend on absolute physical
quantities which apply everywhere and at any time. Can we tell if the
speed of light is constant in those units?
From the quantum theory of the atom we know that these frequencies and
wavelengths depend chiefly on the values of Planck's constant, the
electronic charge and the masses of the electron and nucleons as well as
the speed of light. By eliminating the dimensions of units from the
parameters we can derive a few dimensionless quantities such as the fine
structure constant and the electron to proton mass ratio. These values are
independent of the definition of units so it makes much more sense to ask
if these values change. If they did change it would not just be the speed
of light which was affected. The whole of chemistry is dependent on their
values and significant changes would alter the chemical and mechanical
properties of all substances. Furthermore, the speed of light itself would
change by different amounts according to which definition of units you
used. In that case it would make more sense to attribute the changes to
variations in the charge on the electron or the particle masses than to
changes in the speed of light.
In any case, there is good observational evidence to indicate that those
parameters have not changed over most of the lifetime of the universe. See
the FAQ article Have physical constants changed with time?
[Note that the fine structure constant does change with energy scale but I
am referring to the constancy of its low energy limit.]
Special Relativity
Another assumption on the laws of physics made by the SI definition of the
metre is that the theory of relativity is correct. It is a basic postulate
of the theory of relativity that the speed of light is constant. This can
be broken down into two parts:
The speed of light is independent of the motion of the observer.
The speed of light does not vary with time or place.
To state that the speed of light is independent of the velocity of the
observer is very counterintuitive. Some people even refuse to accept this
as a logically consistent possibility but in 1905 Einstein was able to show
that it is perfectly consistent if you are prepared to give up assumptions
about the absolute nature of space and time.
In 1879 it was thought that light must propagate through a medium in space
just as sound propagates through the air and other substances. Two
scientists Michelson and Morley set up an experiment to attempt to detect
the ether by observing relative changes in the speed of light as the Earth
changed its direction of travel relative to the sun during the year. To
their surprise they failed to detect any change in the speed of light.
Fitzgerald then suggested that this might be because the experimental
apparatus contracted as it passed through the ether in such a way as to
countermand the attempt to detect the change in velocity. Lorentz extended
this to changes in the rates of clocks to ensure complete undetectability
of the ether. Einstein then argued that those transformations should be
understood as transformation of space and time rather than physical objects
and that the absoluteness of space and time introduced by Newton should be
discarded. Just after that Minkowski, a mathematician showed that
Einstein's theory of relativity could be understood in terms of a 4
dimensional non-euclidean geometry of space-time.
The theory is not only mathematically consistent, it is in agreement with
countless direct experiments. The Michelson-Morley experiment was repeated
with greater accuracy in the years that followed. In 1925 Dayton Miller
announced that he had detected a change in velocity of the speed of light
and was even awarded prizes for the discovery, but a 1950's appraisal of
his work indicated that the most likely origin of his erroneous results lay
with diurnal and seasonal variations in the temperature of his equipment.
Modern instruments could easily detect any ether drift if it existed. The
Earth moves around the sun at a speed of about 30 km/sec so if velocities
added vectorially as Newtonian mechanics requires, the last 5 digits in the
value of the speed of light now used in the SI definition of the metre
would be meaningless. Today high energy physicists at CERN and Fermilab
routinely accelerate particles to within a whisper of the speed of light.
A dependence of the speed of light on reference frames would have shown up
long ago unless it is very slight indeed.
But what if we pursued the original theory of Fitzgerald and Lorentz who
proposed that the ether is there but undetectable because of physical
changes in the lengths of material objects and the rates of clocks, rather
than transformations of space-time? For such a theory to be consistent with
observation the ether would have to be completely undetectable using clocks
and rulers. Everything, including the observer, would have to contract and
slow down by the right amounts. Such a theory could make exactly the same
prediction in all experiments as the theory of relativity but in that case
the ether would be no more than a meta-physical construct unless there was
some other way of seeing it which nobody has found. Such a construct would
be an unnecessary complication to be eliminated from the theory in the view
of Einstein.
General Relativity
Einstein went on to discover a more general theory of relativity which
explained gravity in terms of curved space-time and he talked about the
speed of light changing in this new theory. In the 1920 book "Relativity:
the special and general theory" he wrote: . . . according to the general
theory of relativity, the law of the constancy of the velocity of light in
vacuo, which constitutes one of the two fundamental assumptions in the
special theory of relativity . . . cannot claim any unlimited validity. A
curvature of rays of light can only take place when the velocity of
propagation of light varies with position. Since Einstein talks of velocity
(a vector quantity) rather than speed it is not clear that he meant the
speed will change but the reference to special relativity suggests he did
mean so. This interpretation is perfectly valid but a more modern
interpretation is that the speed of light is constant in general
relativity.
The problem here comes from the fact that speed is a coordinate-dependent
quantity, and is therefore somewhat ambiguous. To determine speed
(distance/time) you must first choose some standards of distance and time,
and different choices can give different answers. This is already true in
special relativity: if you measure the speed of light in an accelerating
reference frame, the answer will, in general, differ from c.
In special relativity, the speed of light is constant when measured in any
inertial frame. In general relativity, the appropriate generalization is
that the speed of light is constant in any freely falling reference frame
(in a region small enough that tidal effects can be neglected). In this
passage, Einstein is not talking about a freely falling frame, but rather
about a frame at rest relative to a source of gravity. In such a frame,
the speed of light can differ from c, basically because of the effect of
gravity (spacetime curvature) on clocks and rulers.
If general relativity is correct then the constancy of the speed of light,
in inertial frames is a tautology from the geometry of space-time. The
causal structure of the universe is determined by the geometry of null
vectors. Travelling at the speed c means following world-lines tangent to
these null vectors. The use of c as a conversion between units of metres
and seconds, as in the SI definition of the metre, is fully justified on
theoretical grounds as well as practical terms because c is not merely the
speed of light, it is a fundamental feature of the geometry of space-time.
Like special relativity, the predictions of general relativity have been
confirmed in many different observations. The book by Clifford Will is an
excellent reference for further details.
Finally we come to the conclusion that the speed of light is not only
observed to be constant; in the light of well tested theories of physics,
it does not even make any sense to say that it varies.
Reference:
C.M. Will, "Was Einstein Right?" (Basic Books, 1986)
--
-=oc=-
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| User: "=?ISO-8859-1?Q?10=A2_punk?=" |
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| Title: Re: Taglines |
21 Nov 2003 08:29:11 AM |
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Indigo Moon Man wrote:
What can we do about ignorance and apathy? Who knows? Who cares?
my fav!
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| User: "harakiri" |
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| Title: Re: Taglines |
21 Nov 2003 06:26:03 PM |
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i dont understand this one?
"Indigo Moon Man" <indigomoon@bonbon.net> wrote:
186,000 miles/sec. It's not just a good idea, it's the law.
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| User: "Indigo Moon Man" |
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| Title: Re: Taglines |
21 Nov 2003 06:38:59 PM |
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harakiri <m.d.wittenberg@att.net> spake thusly:
i dont understand this one?
"Indigo Moon Man" <indigomoon@bonbon.net> wrote:
186,000 miles/sec. It's not just a good idea, it's the law.
186,000 miles/sec is the speed of light. This tagline parodies an old ad
campaign from the 70s about the national 55 mph speed limit in which the ads
touted slowing down as a way to save gas and that it was safer. The the
commercial would end with the line, "55 miles per hour. It's not just a
good idea, it's the law."
--
Our Daily Bread Devotional:
http://www.gospelcom.net/rbc/odb/odb.shtml
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| User: "harakiri" |
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| Title: Re: Taglines |
21 Nov 2003 06:55:22 PM |
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too cute!
"Indigo Moon Man" <indigomoon@bonbon.net> wrote in message
news:bpmb8k$1qo4ht$1@ID-70710.news.uni-berlin.de...
harakiri <m.d.wittenberg@att.net> spake thusly:
i dont understand this one?
"Indigo Moon Man" <indigomoon@bonbon.net> wrote:
186,000 miles/sec. It's not just a good idea, it's the law.
186,000 miles/sec is the speed of light. This tagline parodies an old ad
campaign from the 70s about the national 55 mph speed limit in which the
ads
touted slowing down as a way to save gas and that it was safer. The the
commercial would end with the line, "55 miles per hour. It's not just a
good idea, it's the law."
--
Our Daily Bread Devotional:
http://www.gospelcom.net/rbc/odb/odb.shtml
.
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| User: "Indigo Moon Man" |
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| Title: Re: Taglines |
21 Nov 2003 07:04:41 PM |
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harakiri <m.d.wittenberg@att.net> spake thusly:
too cute!
:-)
--
Our Daily Bread Devotional:
http://www.gospelcom.net/rbc/odb/odb.shtml
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| User: "Tracy Barber" |
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| Title: Re: Taglines |
21 Nov 2003 09:35:25 PM |
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On Fri, 21 Nov 2003 18:04:41 -0700, "Indigo Moon Man"
<indigomoon@bonbon.net> wrote:
harakiri <m.d.wittenberg@att.net> spake thusly:
too cute!
:-)
They be farm out man, and right arm! I must be getting too old for
this, eh? :^)
Tracy Barber
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| User: "Indigo Moon Man" |
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| Title: Re: Taglines |
21 Nov 2003 09:40:36 PM |
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Tracy Barber <Mohawky@adirondack-pc.com> spake thusly:
On Fri, 21 Nov 2003 18:04:41 -0700, "Indigo Moon Man"
<indigomoon@bonbon.net> wrote:
harakiri <m.d.wittenberg@att.net> spake thusly:
too cute!
:-)
They be farm out man, and right arm! I must be getting too old for
this, eh? :^)
I haven't heard those expressions in a while. :-)
--
Our Daily Bread Devotional:
http://www.gospelcom.net/rbc/odb/odb.shtml
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| User: "Tracy Barber" |
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| Title: Re: Taglines |
21 Nov 2003 10:10:47 PM |
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On Fri, 21 Nov 2003 20:40:36 -0700, "Indigo Moon Man"
<indigomoon@bonbon.net> wrote:
Tracy Barber <Mohawky@adirondack-pc.com> spake thusly:
On Fri, 21 Nov 2003 18:04:41 -0700, "Indigo Moon Man"
<indigomoon@bonbon.net> wrote:
harakiri <m.d.wittenberg@att.net> spake thusly:
too cute!
:-)
They be farm out man, and right arm! I must be getting too old for
this, eh? :^)
I haven't heard those expressions in a while. :-)
Outta state and like on Thursday - gravy, man, gravy... :^P
Tracy Barber
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