I consistently see the phrase "in an inertial reference frame" or something
to that effect when I see statements about certain aspects of relativity
that are a little bit confusing for me. For example, "the speed of light is
the same in any inertial reference frame," or "nothing can go faster than
the speed of light in an inertial reference frame." Now, this seems to
imply that there are achievable situations where the speed of light is not
constant, or where there are one could measure something to be moving faster
than light. Now, naturally, in non-inertial reference frames, things can
get just a *little* bit more complex than in special relativity, but it was
my impression that the speed of light is *always* the same, and one can
*never* go past the speed of light, not just in the special case of an
inertial reference frame.

If I'm misunderstanding this, please help and tell me what I'm not getting.
Or, if I'm not, I'd love to learn some more about this! I have already
tried to research this some, but haven't found much. I would look more, but
the teachers here seem to think it's very important that we do lots of
needless work to take up time, and to make it nearly impossible to talk to
them. And I think all of the TAs have some kind of mental disorder here,
and I've had several, uhh, discussions, about who is right about certain
questions with one of them... (guess who won? It's a bad sign when a
freshman knows more about the subject than the grad students!) But that's a
whole 'nother topic...

Thanks!
Jeremy

"Jeremy Price" wrote in message
...
I consistently see the phrase "in an inertial reference frame" or
something
to that effect when I see statements about certain aspects of relativity
that are a little bit confusing for me. For example, "the speed of light
is
the same in any inertial reference frame," or "nothing can go faster than
the speed of light in an inertial reference frame." Now, this seems to
imply that there are achievable situations where the speed of light is not
constant, or where there are one could measure something to be moving
faster
than light. Now, naturally, in non-inertial reference frames, things can
get just a *little* bit more complex than in special relativity, but it
was
my impression that the speed of light is *always* the same, and one can
*never* go past the speed of light, not just in the special case of an
inertial reference frame.

If I'm misunderstanding this, please help and tell me what I'm not
getting.
Or, if I'm not, I'd love to learn some more about this! I have already
tried to research this some, but haven't found much. I would look more,
but
the teachers here seem to think it's very important that we do lots of
needless work to take up time, and to make it nearly impossible to talk to
them. And I think all of the TAs have some kind of mental disorder here,
and I've had several, uhh, discussions, about who is right about certain
questions with one of them... (guess who won? It's a bad sign when a
freshman knows more about the subject than the grad students!) But that's
a
whole 'nother topic...

Thanks!
Jeremy


Read the relativity FAQ's.
http://math.ucr.edu/home/baez/physics/

"Jeremy Price" wrote in message
...
I consistently see the phrase "in an inertial reference frame" or
something
to that effect when I see statements about certain aspects of relativity
that are a little bit confusing for me. For example, "the speed of light
is
the same in any inertial reference frame," or "nothing can go faster than
the speed of light in an inertial reference frame." Now, this seems to
imply that there are achievable situations where the speed of light is not
constant, or where there are one could measure something to be moving
faster
than light. Now, naturally, in non-inertial reference frames, things can
get just a *little* bit more complex than in special relativity, but it
was
my impression that the speed of light is *always* the same, and one can
*never* go past the speed of light, not just in the special case of an
inertial reference frame.

[...]
Thanks!
Jeremy

Yes, the speed of light is always the same. In a non-inertial frame, the
frequency of the light can change, and the direction of the velocity
within the non-inertial frame can change. Thus, the component of
velocity in the x direction, etc., of the frame can change, but the
magnitude of the resultant of the velocity remains the same. This
is what you are referring to, so you are correct in saying that the
speed of light is always the same.

Alen

Subject: Speed of light in non-inertial frames?
From: "Alen"
Date: 12/7/03 6:37 AM US Mountain Standard Time
Message-id:

"Jeremy Price" wrote in message
...
I consistently see the phrase "in an inertial reference frame" or
something
to that effect when I see statements about certain aspects of relativity
that are a little bit confusing for me. For example, "the speed of light
is
the same in any inertial reference frame," or "nothing can go faster than
the speed of light in an inertial reference frame." Now, this seems to
imply that there are achievable situations where the speed of light is not
constant, or where there are one could measure something to be moving
faster
than light. Now, naturally, in non-inertial reference frames, things can
get just a *little* bit more complex than in special relativity, but it
was
my impression that the speed of light is *always* the same, and one can
*never* go past the speed of light, not just in the special case of an
inertial reference frame.

[...]
Thanks!
Jeremy

Yes, the speed of light is always the same.

The invariant speed c is the local vacuum speed of light. In SR it is the
vacuum speed of light according to an inertial frame. The remote coordinate
speed of light is not always c according to accelerated frames. See "light
speed" as indexed at
http://www.geocities.com/zcphysicsms/pageindex.htm

"Jeremy Price" wrote in message
...
I consistently see the phrase "in an inertial reference frame" or
something
to that effect when I see statements about certain aspects of relativity
that are a little bit confusing for me. For example, "the speed of light
is
the same in any inertial reference frame," or "nothing can go faster than
the speed of light in an inertial reference frame." Now, this seems to
imply that there are achievable situations where the speed of light is not
constant, or where there are one could measure something to be moving
faster
than light. Now, naturally, in non-inertial reference frames, things can
get just a *little* bit more complex than in special relativity, but it
was
my impression that the speed of light is *always* the same, and one can
*never* go past the speed of light, not just in the special case of an
inertial reference frame.

Its true. In non-inertial frames of referance the (coordinate) speed of
light will depend on the gravitational potential. Einstein realized this
when he discovered the equivalence principle in 1907. However the locally
measured speed of light is always 2.998 x 10^8 m/s. If you have a copy of
"The Principle of Relativity" Dover Pub then you can read a paper he wrote
regarding, in part, this topic. The paper is on page 99 of that book and is
entitled "On the Influence of Gravitation on the Propagation of Light"

He refers to "gravitation" since in Einstein's general theory of relativity
a non-inertial frame of referance has a gravitational field even though the
original frame had no such field.


If I'm misunderstanding this, please help and tell me what I'm not
getting.
Or, if I'm not, I'd love to learn some more about this! I have already
tried to research this some, but haven't found much. I would look more,
but
the teachers here seem to think it's very important that we do lots of
needless work to take up time, and to make it nearly impossible to talk to
them.

Really??? This is an important point! Its not that hard to prove once you
have know that time slows down/speeds up in a g-field then the speed of
light must change as well. If you get that book I mentioned Einstein will
explain it to you.

A modern discussion can be found in "Exploring Black Holes" by Taylor and
Wheeler

Pmb

Pmb

"Androcles" wrote

If the ridiculous assertion that the speed of light was "always the same",
in other words depended on the observer, .

What are you talking about? The speed of light does *not* depend on the
inertial observer. Its the same for all inertial observers (in flat
spacetime)

...it would be impossible for me to
model these light curves, which are real and taken by thousands of amateur
astronomers.

Then define your quantities. All I see are diagarms with no labels on the
axes to tell what quantities are being plotted.

Pmb

Subject: Speed of light in non-inertial frames?
From: "Pmb"
Date: 12/7/03 9:46 AM US Mountain Standard Time
Message-id:


"Jeremy Price" wrote in message
...
I consistently see the phrase "in an inertial reference frame" or
something
to that effect when I see statements about certain aspects of relativity
that are a little bit confusing for me. For example, "the speed of light
is
the same in any inertial reference frame," or "nothing can go faster than
the speed of light in an inertial reference frame." Now, this seems to
imply that there are achievable situations where the speed of light is not
constant, or where there are one could measure something to be moving
faster
than light. Now, naturally, in non-inertial reference frames, things can
get just a *little* bit more complex than in special relativity, but it
was
my impression that the speed of light is *always* the same, and one can
*never* go past the speed of light, not just in the special case of an
inertial reference frame.

Its true. In non-inertial frames of referance the (coordinate) speed of
light will depend on the gravitational potential. ...

To the Newtonian pmb, You have said asserted inappropriately that this
"potential" is given by
Phi = (c^2 / 2)(g_0_0 - 1)
In fact the expression for the remote coordinate speed of light is more
complicated than this. See equation 13.1.2 at
http://www.geocities.com/zcphysicsms/chap13.htm

"Jeremy Price" wrote in message
...
I consistently see the phrase "in an inertial reference frame" or
something
to that effect when I see statements about certain aspects of relativity
that are a little bit confusing for me. For example, "the speed of light
is
the same in any inertial reference frame," or "nothing can go faster than
the speed of light in an inertial reference frame." Now, this seems to
imply that there are achievable situations where the speed of light is not
constant, or where there are one could measure something to be moving
faster
than light. Now, naturally, in non-inertial reference frames, things can
get just a *little* bit more complex than in special relativity, but it
was
my impression that the speed of light is *always* the same, and one can
*never* go past the speed of light, not just in the special case of an
inertial reference frame.

If I'm misunderstanding this, please help and tell me what I'm not
getting.
Or, if I'm not, I'd love to learn some more about this! I have already
tried to research this some, but haven't found much. I would look more,
but
the teachers here seem to think it's very important that we do lots of
needless work to take up time, and to make it nearly impossible to talk to
them. And I think all of the TAs have some kind of mental disorder here,
and I've had several, uhh, discussions, about who is right about certain
questions with one of them... (guess who won? It's a bad sign when a
freshman knows more about the subject than the grad students!) But that's
a
whole 'nother topic...

Thanks!
Jeremy


It can be a bit confusing. Inertial frames of reference are by definition
frames of reference where causality is obeyed - the things that need causal
relationships can never be operating in reference frames where they can be
observed to be violating causality. You will never see a beam of light in
any reference frame where it hasn't yet been emmitted. Relativity is a
time-dependent way of defining the operation of energetic exchanges and
describing how they will look to an observer. Are these the only reference
frames? No. EPR entangled systems exchange information non-energetically and
instantly in a time independent way. Entangled systems operate faster than
light and therefore are in non inertial fames of reference. Relativity has
nothing to say about non inertial reference frames and anything that may
operate non inertially. Faster than Light communicators do not neeed to obey
any of the laws of relativity, but it also means they do not operate in a
causal manner. The FTL communicator I developed in 1999 is instantaneous,
globally acausal, and nonrelativistic. But it doesn't violate any of the
precepts of Quantum Mechanics.

Greysky
www.allocations.cc
Learn how to build a FTL radio.

"Greysky" wrote

It can be a bit confusing. Inertial frames of reference are by definition
frames of reference where causality is obeyed

That is not the definition of "inertial frame." Causality is obeyed in all
frames of referance or in no frame of referance

Pmb

Jeremy Price wrote:
I consistently see the phrase "in an inertial reference frame" or something
to that effect when I see statements about certain aspects of relativity
that are a little bit confusing for me. For example, "the speed of light is
the same in any inertial reference frame," or "nothing can go faster than
the speed of light in an inertial reference frame." Now, this seems to
imply that there are achievable situations where the speed of light is not
constant, or where there are one could measure something to be moving faster
than light.

Yes. This is so because in an accelerated system most of our common
notions about how clocks and rulers behave are invalid. In particular,
clocks at different locations along the acceleration axis cannot remain
in synch, even though they are both at rest in the accelerated system.
This directly implies that if one uses a given pair of standard clocks
and set of rulers to measure the speed of light (along the acceleration
axis), the value will change over time.


Now, naturally, in non-inertial reference frames, things can
get just a *little* bit more complex than in special relativity, but it was
my impression that the speed of light is *always* the same, and one can
*never* go past the speed of light, not just in the special case of an
inertial reference frame.

Your impression is wrong.

Here's a simple explanation: for accelerated motion, the front and back
of an accelerating system are not ever at rest in the same inertial
frame[#]. It should be obvious that attempts to "measure" the speed of
light using clocks in different inertial frames yields only nonsense.

For a more detailed discussion, see my post from 12/13/1998 with Subject
"The Speed of Light in an Accelerated System"
http://www.google.com/groups?as_umsg...ucent.com %3E

[#} This is strictly true only for Born rigid motion. For an
arbitrary nonzero acceleration they can indeed be at rest
in the same inertial frame for isolated instants of time,
but not continuously, and so not for the duration of the
measurement.


Tom Roberts