Suppose you have a straight plank of wood which measures 1 metre long by 0.1 m wide (by 0.01 m deep). You also have a window which is 0.5 metres high and 2 metres wide. You want to pass your plank of wood through the window.

Holding you plank of wood with its long axis vertical, you look at the window in front of you. Comparing the length of the piece of wood to the height of the window you say "Oh dear! My piece of wood won't fit through the window! The wood is 1 metre long in the vertical direction, but the window is only 0.5 metres long in that direction!"

A small leprechaun called Albert lives on your plank of wood. The direction Albert refers to as "vertical" is always the direction along the long axis of the plank. "Horizontal" for Albert is the direction across the width of the wood.

Albert looks at the window, and at the plank, and says "Oh dear! The plank won't fit through the window! The plank is 1 metre long in the vertical direction, and the window is only 0.5 metres wide in that direction!"

You think about the problem for a while. Then, suddenly it hits you!
"Aha!" you think, "If I rotate the plank 90 degrees about an axis perpendicular to the plane of the window, then it will fit through."

You rotate the plank, and consider the result. The plank now measures 0.1 m in the vertical direction, and 1 m horizontally, while the window measures 0.5 m vertically by 2 m horizontally. "The plank has rotated," you say, "and now it will fit."

What happens from Albert's point of view? Albert sees the window rotate by 90 degrees, while his plank remains the same as ever (as he sits on it). After the rotation, Albert says "The window rotated, so that the window is now 2 m high (vertically) and 0.5 metres wide, while the plank is 1 m high by 0.1 metres wide, so it will now fit through!"

A keen observer and rotation skeptic standing watching all this suddenly says: "Wait a minute! There's something weird happening here!" He explains his puzzlement:

"From your point of view, the window stayed stationary, while the plank rotated. But from Albert the Leprechaun's point of view, the window rotated, while the plank remained stationary. It doesn't make sense! You and Albert disagree on what happened. You disagree on which object rotated, and (worse), you even disagree about the direction of rotation (whether it was clockwise or anticlockwise). That's not real physics! In reality, only one thing could really have rotated, and things can only ever rotate either clockwise or anticlockwise, but not both at once! Either the window or the plank rotated in reality. Since I'm not really sure, but I don't want to appear wishy-washy, from now on I'll say it must have been the window which rotated! And, what's more, I'm going to disagree with anybody who says the plank rotated.

So, my position from now on is that any theory of physics which can arbitrarily say that any one object remains stationary while all other objects rotate around it must be completely wrong. In reality, as we all know, only windows can rotate. Planks of wood can't rotate at all! It's impossible and it doesn't make sense. Anybody who disagrees with me is an idiot!

Only windows can rotate "in reality". All this talk of planks rotating is just the perception of an observer, and is completely wrong. No "real" physics happens in the reference frame of you, standing in front of the window. The only "real" physics happens in Albert the leprechaun's frame of reference. Albert sees the "true" situation of the window rotating. Isn't that far more "intuitive" than these silly ideas that planks can rotate? Who ever heard of a plank changing its vertical and horizontal measurements? Obviously, that's completely impossible - only windows can really change their vertical and horizontal measurements from one moment to the next."

Haha! Nice. What about the leprechaun who lives on the window-sill? You know, the one who declares the window-frame to be the one true frame? Got a name for him?

Humpty Dumpty. But he fell off and broke into a thousand pieces when his frame rotated. Or are these frames of reference not applicable on Earth due to gravity?

I was hoping to read a Relativity explanation for turning your head 90 degrees and seeing distant stars move at many times the speed of light.

Obviously it is good physics to take the G perspective and consider both points of view equally valid.......both rotated 45 degrees.......ha

Obviously it is good physics to take the G perspective and consider both points of view equally valid.......both rotated 45 degrees.......ha

It is even better to be pragmatic and realize that either the plank rotated or the entire universe was rotated withvery little physical effort or energy being expended.

That is a realist would realize that many things in relativity should (actually must) be viewe from more than two simple frames.

It is even better to be pragmatic and realize that either the plank rotated or the entire universe was rotated withvery little physical effort or energy being expended.

Wrong! To rotate the universe (including the window) required an immense amount of energy. Do the calculation (if you are capable)!

It is even better to be pragmatic and realize that either the plank rotated or the entire universe was rotated withvery little physical effort or energy being expended.

That is a realist would realize that many things in relativity should (actually must) be viewed from more than two simple frames.
MacM, I agree 100%.

James R,The Leprachaun can feel the rotation and the observer can (or could) see and hence knows the Leprachaun is rotating. The observer can, likewise, feel himself rotating the lumber and simutaneously notice that the Lerachaun is not subjected to any forces of rotation;or the observer can sense and observe both objects rotating and with her cleverly designed instrumentation package determine the rate of rotations of each.

Geistkiesel :cool:

Wrong! To rotate the universe (including the window) required an immense amount of energy. Do the calculation (if you are capable)!

Thank you for making my point. Your example sucks since you can't rotate the entire universe. Like the rest of relativity it is not based on sound physics but a mere word shell game.

MacM:

That is a realist would realize that many things in relativity should (actually must) be viewe from more than two simple frames.

You and geist want to view everything from just ONE frame. Two is far too many for you to cope with, let alone more than two.

geistkiesel:

James R,The Leprachaun can feel the rotation and the observer can (or could) see and hence knows the Leprachaun is rotating. The observer can, likewise, feel himself rotating the lumber and simutaneously notice that the Lerachaun is not subjected to any forces of rotation;or the observer can sense and observe both objects rotating and with her cleverly designed instrumentation package determine the rate of rotations of each.

Yes, Albert the leprechaun can feel mysterious forces as the window rotates around him, while the person holding the plank personally feels no unusual forces. Therefore, we conclude that there is something different about the two different reference frames. But what? Certainly, we can't conclude that one is "really" rotating and the other isn't.

why is it always one or the other ? why not both?

To me this is a perfect example of how there is no absolute frame of reference in an einstein universe.

Does it make logical sense? Not really. Does it make things more complicated? Yes, absolutely. Is it the way things are? Well until someone can prove otherwise...

Seriously, if one of you guys can actually prove GR and/or SR wrong (by proof, I mean backing up your math with current observations), please do so. If not then just drop it.

James is the only one that has continually put forward real answers/explanations with proof.

Regards,

UW :)

MacM:

You and geist want to view everything from just ONE frame. Two is far too many for you to cope with, let alone more than two.

You of course jest. Or are just full of it, which is it?

geistkiesel: Certainly, we can't conclude that one is "really" rotating and the other isn't.

It is unfortuante indeed that you cannot. You have the same problem understanding that onemust accelerate to have velocity and that relative velocity and relative motion are in fact two different physical principles.

The gamma function operates on actual physical motion caused by acceleration. Where two clocks are side by side at some unknown inertial velocity (or at rest), and only one accelerates, each does have a relative velocity but each does not have relative motion.

That is why the SRT view of reciprocity is invalid and not supported by observation , evidence or test data. It is why GPS works by relying on respective motion and not relative velocity.

...relative velocity and relative motion are in fact two different physical principles.


Yeah, sure they are.

each does have a relative velocity but each does not have relative motion.
MacM, care to elaborate on what you consider to be the distinction between relative velocity and relative motion?

wouldn't motion encompass both acceleration and velocity?

Yeah, sure they are.

You seem to have very little left in the way of physics to offer.

I think JamesR's analogy is simple and to the point. Very good. What is far more interesting to me is the psychology behind the various denials of such a simple observational analogy.

MacM, care to elaborate on what you consider to be the distinction between relative velocity and relative motion?

It is actually pretty obvious.

To have motion one must move. To move one must accelerate.

If you and I are setting side by side in cars at a red light and you go on green but my car stalls, we have relative velocity but I do not have any motion.

Relative motion means differance of motions. i.e. - you are now going 60 Mph and I am only going 30 Mpy because my car balked and I got a late acceleration.

MacM:

It is actually pretty obvious.

To have motion one must move. To move one must accelerate.

If you and I are setting side by side in cars at a red light and you go on green but my car stalls, we have relative velocity but I do not have any motion.

Relative motion means differance of motions. i.e. - you are now going 60 Mph and I am only going 30 Mpy because my car balked and I got a late acceleration.

-----------------------------------

It is actually pretty obvious.

To have a change in motion <strike>one must move. To move</strike> one must accelerate.

If you and I are setting side by side in cars at a red light and you go on green but my car stalls, we have relative velocity but I do not have any change in motion.

Relative motion means differance of motions. i.e. - you are now going 60 Mph and I am only going 30 Mph with respect to the ground because my car balked and I got a late acceleration.

-----------------------------------

There, I fixed it for you.

superluminal, that last post made my day.

:D

actually I thought that was what MacM meant.
It implies an absolute frame of reference. [the ground]

Now I have argued this point before and will try again.
I would contend that even relative velocity calculations must by their very nature employ an absolute frame of reference. It is implied in all SRT calculations yet SRT maintains non-simultaneity as an outcome.
On one hand SRT uses an absolute RF and yet refuses to accept that it does?

v= 10
v= 5
relative velocities by nature are RELATIVE and assume or imply an absolute reference. [even if it is just units of measurement] Other wise it would be impossible to calculate the difference.

Relative motion and relative velocity is always based on an absolute premise.
If time and distance are truely relative then their relationship IS RELATIVE to each other.

The transforms require absolute time to give a relative time result....

IMO

In other words the word relative is just as sound as the word reciprical or mutual or relationship. and implies an absolute [relative] relationship between at least two objects.

Relative motion and relative velocity is always based on an absolute premise.

Wrong. Have you read none of the previous discussions on this issue?

It implies an absolute frame of reference. [the ground]
No, the ground is just another FOR. Go into earth orbit and see how "absolute" the ground is as a reference.

Now I have argued this point before and will try again.
I would contend that even relative velocity calculations must by their very nature employ an absolute frame of reference.
Why?

It is implied in all SRT calculations yet SRT maintains non-simultaneity as an outcome.
No, it isn't.

On one hand SRT uses an absolute RF and yet refuses to accept that it does?
No, it dosen't.


v= 10
v= 5

relative velocities by nature are RELATIVE and assume or imply an absolute reference. [even if it is just units of measurement] Other wise it would be impossible to calculate the difference.

No.

v = 10 wrt the ground.
v = 5 wrt the ground.
relative velocity = 5

For true relative velocity (two objects in deep space for instance) no third frame is required.
v = 10
That's all.

Object A is moving at 10 wrt object B and vice versa. No other FOR's.

Relative motion and relative velocity is always based on an absolute premise.
No, it's not.

If time and distance are truely relative then their relationship IS RELATIVE to each other.
Yes.

The transforms require absolute time to give a relative time result....
No, they don't.

Wrong. Have you read none of the previous discussions on this issue?
I have followed some of the discussions...yes...
as you well know....
The point I am trying to make is suggested in the following question:

How can you tell if an object is contracted in length with our making a comparison to an absolute reference? [your rest frame]
How can you decide that time is relative [non-simultaneous] if you have no absolute time reference to compare it to?
How do you know something is relative and not absolute with out an implied reference to the Absolute?

Edit: Sorry SL I didn't see your post, it is just an issue of how we derive something is relative with out an absolute reference to compare to. This I think is underpinning MacMs Main contentions.....

How can you tell if an object is contracted in length with out making a comparison to an absolute reference? [your rest frame]

Your rest frame is just your rest frame. It's not absolute. It can be moving wrt anything else, and probably is.

How can you decide that time is relative [non-simultaneous] if you have no absolute time reference to compare it to?

Because it is RELATIVE to your frame. Don't understand the question...

How do you know something is relative and not absolute with out an implied reference to the Absolute?

How do you know something is green without a reference to something that is not green? Does that make sense?

All you have to do is put yourself in deep space on one object (in uniform motion) with another object receeding from you (in uniform motion). Then switch places.

the thing that intrigues me is the circularity of the reasoning....

To decide that something is non-silmultaneous we must compare this to what would be simultaneous. Thus the observation is grounded with an absolute reference.

SRT will show that time is relative, but how is this arrived at?

Given that time is the most fundamental attribute of physics.

To arrive at the result we have to at first assume an absolute 1=1 relationship. And then we use the math to arrive at 1=2 relationship but in arriving at a 1=2 relationship we can only recognise it as relative by referring to our 1=1 relationship.

So SRT takes the absolute and declares it as relative but it requires the absolute to begin with.

The flow of reasoning I see is this:

Absolute time is used to show relative time, however if relative time is correct then [I]how can absolute time be used in the first place?
[keeping in mind that we are talking about the very premise of space time....]
so even though we declare a relative relationship it is still premised on an absolute relationship. Otherwise all the math is meaningless.....

it really isn't an awfully important point to me but I think this is what MacM is attempting to confront.
The duality of absolute relativity.......

QQ:

How can you tell if an object is contracted in length with our making a comparison to an absolute reference? [your rest frame]

Your rest frame is not absolute. If you move, all velocities with respect to your rest frame change.

How can you decide that time is relative [non-simultaneous] if you have no absolute time reference to compare it to?

Why would you need an absolute reference to measure a relative quantity?

How do you know something is relative and not absolute with out an implied reference to the Absolute?

Is that a philosophical question?

James is the only one that has continually put forward real answers/explanations with proof.

Regards,

UW :)

You have to be kidding. All James R knows how to do is cite the theory. Physics be damned.

How much did you get paid for this endorsement? :D

wouldn't motion encompass both acceleration and velocity?

Yep. You got it. If you don't accelerate you don't have any motion. Two clocks at rest side by side (of course they may already have some absolute velocity but who knows). One accelerates away. They have "relative velocity" but not motions. The only motion and and velocity are in the one that accelerated.

Your rest frame is not absolute. If you move, all velocities with respect to your rest frame change.

How do you know this if not for an absolute reference?
How can you determine the amount of change?

I think JamesR's analogy is simple and to the point. Very good. What is far more interesting to me is the psychology behind the various denials of such a simple observational analogy.


Anytime something is OVER simplified one gets invalid results.

-----------------------------------

It is actually pretty obvious.

To have a change in motion <strike>one must move. To move</strike> one must accelerate.

If you and I are setting side by side in cars at a red light and you go on green but my car stalls, we have relative velocity but I do not have any change in motion.

Relative motion means differance of motions. i.e. - you are now going 60 Mph and I am only going 30 Mph with respect to the ground because my car balked and I got a late acceleration.

-----------------------------------

There, I fixed it for you.

Thank you. BTW our relative velocity to each other is still 30 Mph but you are (by energy change -i.e. physics conservation) going 60 Mph and I only 30 Mph. Any physics i.e. gamma functions, would be based on your 60 Mph not or relative velocity of 30 Mph. :D

All James R knows how to do is cite the theory. Physics be damned.

Our best understanding of the physics is the theory.

Without theory, we wouldn't have physics. We'd have stamp collecting.

No, the ground is just another FOR. Go into earth orbit and see how "absolute" the ground is as a reference.

QQ meant well but the ground is not viewed as an absolute. Only values or absolute and that means they are not reversable. It is merely the common inertial rest from which each has deviated and the only FOR from which any relavistic calculations will be valid. (i.e. - eliminates reciprocity and yields a correct gamma.

Thank you. BTW our relative velocity to each other is still 30 Mph but you are (by energy change -i.e. physics conservation) going 60 Mph and I only 30 Mph. Any physics i.e. gamma functions, would be based on your 60 Mph not or relative velocity of 30 Mph. :D

I would and have been arguning that all calculations are based on the assumption of zero whether relative or absolute..... :)

Our best understanding of the physics is the theory.

Please, do not include me in your "Our". Our is a clkck of hard headed individuals that refuse to consider actual physics and consequences and ignores the obvious.

Without theory, we wouldn't have physics.

Without correct theories (or the willingness to amend theories, we have crap.


We'd have stamp collecting.

Perhaps you should give that a try. Might be more successful.

Please, do not include me in your "Our".

Don't worry, MacM. I wouldn't include you in my group of hard-headed individuals.

Now, do you have any comments on the thread topic, or are you going to continue acting like a child?

Don't worry, MacM. I wouldn't include you in my group of hard-headed individuals.

Now, do you have any comments on the thread topic, or are you going to continue acting like a child?

I do say it is your post that seems childish. Just how do you see this as responding to a physics issue?

say for exaqmple we have two objects and one "appears" to be approaching you at lets say 0.2c

How do you know whether that iobject which appears to be travelling towards you is in fact not travelling 0.2c slower than you are?

If we hold to relativity fully then to declare yourself at v=zero IMO immediately contradicts the notion of relativity.

IN srt all other frames of v are alwas faster than the RF you choose never slower.....how can this be seen as a valid premise. If all velocities are relative. [including your own]
I woudl contend that to arbitarilly declare yourself at zero velocity is placing an abitary error of observation given that absolute rest is unable to be determined.

Question:
In relativity can another object have a velocity that is slower than your own?

And I don't mean a negative velocity as used to describe vector...

QQ,

Use the words "with respect to" anytime you mention a velocity. See what happens. It is an unstated assumption every time you mention velocity.

I am driving 60mph WRT the ground, etc.

QQ:

I woudl contend that to arbitarilly declare yourself at zero velocity is placing an abitary error of observation given that absolute rest is unable to be determined.

Declaring yourself at v = 0 is completely arbitrary and is completely valid BECAUSE there is no absolute reference.

Me at v = 0 only means that anything travelling with me has zero velocity WRT me. That's all.

You can assume that you are moving at any v you want, it just complicates a simple calculation, and gives the same results.

An error of observation by whom? How fast are you moving wrt yourself? Zero. No error. A completely accurate observation.

Declaring yourself at v = 0 is completely arbitrary and is completely valid BECAUSE there is no absolute reference.

Me at v = 0 only means that anything travelling with me has zero velocity WRT me. That's all.

You can assume that you are moving at any v you want, it just complicates a simple calculation, and gives the same results.

An error of observation by whom? How fast are you moving wrt yourself? Zero. No error. A completely accurate observation.

Actually this is merely rhetorical. QQ is more correct from a physics view. You won't agree but so be it.

Mierda de vaca.

MacM:

You ceased discussing physics issues some time ago on this forum. Now you just whinge and whine and make totally unsupported statements. And whenever you're confronted by an actual physical or mathematical demonstration that your claims are false, you claim that whoever posted it is "not addressing the issue" or "simply citing rhetoric" or "not taking a physics view". But your claims are empty, because you do not refute any of the information presented. Instead, you attempt proof by bludgeoning repetition - a tactic which is easily seen through. You refer to no data, theory or authority other than yourself. Nobody agrees with you. And you dance around and deflect conversation and avoid answering questions. You're like a spoilt child whose mummy has told him whatever he says is right, no matter what. Well, we're not your mummy, MacM. We call you on wrong claims. And whinging won't help you wriggle out of your mistakes.

Thanks SuperL and JamesR, just that every now and then I get this bizzare urge to get involved in pointless SRT discussions....hmmmmm....

can I please repeat this one question I asked earlier as I see it hasn't been addressed directly?
Question:
In relativity can another object have a velocity that is slower than your own?

In relativity can another object have a velocity that is slower than your own?

When you walk down the street, does your house have a velocity slower than your own?

Do you think relativity can cope with a problem as complex as you walking down the street?

Now, what do you think the answer is?

You can assume that you are moving at any v you want, it just complicates a simple calculation, and gives the same results.
actually come to think of it this is I think not quite right, although I am sure JamesR will correct me if I am wrong.

The need to declare yourself at rest is due to the invariance factor of light. [ I think ]
If you assume you have a velocity then how do you calculate lights velocity to be invariant with out reducing your v to zero.....?

The invariance of light locks us into the position of declaring ourselves at rest when measuring 'c' thus d/t equations of lights v are maintained as invariant.

Another issue which borders on philosophy is that if you are on a ship with no meaningful way of measuring your motion why would you assume anything as to that motion.

A simple "unknown" would be a more reasonable postion than to arbitarilly declare that you were stationary.....[stepping out of the SRT box for a second] Even though you are always stationary to lights movement.....[invariance again!!]
and
being stationary as regards to lights v doesn't necessarilly extend to be stationary wrt an object of masses v. Although I am aware that SRT will disagree.
Given the difference in dimension between light and an object of mass.....


Just thoughts.....

When you walk down the street, does your house have a velocity slower than your own?

Do you think relativity can cope with a problem as complex as you walking down the street?

Now, what do you think the answer is?

according to SRT if I am walking down the street the house has a greater v than my own [ being zero ]
And no I don't think SRT can handle the complexity of this simple study of motion. [my opinion]
Because I can only consider myself at rest wrt to lights velocity and not the house......

QQ:

according to SRT if I am walking down the street the house has a greater v than my own [ being zero ]

Only in your rest frame. In the street frame, the house has a lower v than you do.

And no I don't think SRT can handle the complexity of this simple study of motion. [my opinion]

Well, you're wrong, then.

Because I can only consider myself at rest wrt to lights velocity and not the house......

Huh? What has light got to do with this problem?

The need to declare yourself at rest is due to the invariance factor of light. [ I think ]

No. You don't ever need to declare yourself at rest. That's just a choice, which may or may not be useful.

If you assume you have a velocity then how do you calculate lights velocity to be invariant with out reducing your v to zero.....?

Light's velocity is always c, in every inertial frame.

The invariance of light locks us into the position of declaring ourselves at rest when measuring 'c' thus d/t equations of lights v are maintained as invariant.

Not at all. Measure the speed of light in any frame and it comes out as c. No declaration of rest needed.

Yep. You got it. If you don't accelerate you don't have any motion.
MacM, you do know that you are advocating a viewpoint that went out of fashion when Newton came along, don't you?

Not at all. Measure the speed of light in any frame and it comes out as c. No declaration of rest needed.

So If I am travelling at v=0.8c and length is contracted and time is dillated 'c' will still measure 'c' in my frame.....hmmmmmm.....this is so contrary to normal SRT reasoning.....If dilation and length contraction are a product of relative velocity, how does my reality change just by declaring what ever velocity I arbitarilly chooose to declare.....


I would have thought that it would be essential for 'c' to be invariant that when measuring 'c' you must assume a postion of zero velocity thus length and time are deemed to be neither contracted nor dilated....

Hi QQ,

So If I am travelling at v=0.8c and length is contracted and time is dillated 'c' will still measure 'c' in my frame.....hmmmmmm.....this is so contrary to normal SRT reasoning.....If dilation and length contraction are a product of relative velocity, how does my reality change just by declaring what ever velocity I arbitarilly chooose to declare.....

First, the measurement of the speed of light being 'c' in all frames is not the product of SRT reasoning. It is a postulate based on an experiment. It's the way nature is. From this and one or two other postulates, SRT "reasoning" is constructed. For you to measure 'c' as 'c' no matter what your state of motion, time and length must change in such a way as to explain the observation that in your frame you always measure light speed as 'c'.

Now, declaring your own velocity arbitrarily does nothing to change the relative velocities of other objects. If you measure a car going by at 30mph, you say his velocity wrt you is 30mph. If you want to say your velocity is 1000mph (wrt what?), that's fine. His relative velocity to you is still 30mph and he will outpace you at 30mph no matter what.

30mph - 0mph = 30mph
1030mph - 1000mph = 30mph
4567330mph - 4567300mph = 30mph

I would have thought that it would be essential for 'c' to be invariant that when measuring 'c' you must assume a postion of zero velocity thus length and time are deemed to be neither contracted nor dilated....

I measure 'c' by seeing how long it takes a beam of light to cross 1meter (about 3.33ns) I do that here on earth and get 'c' (no suprise there). Now, I blast up to 0.866c wrt the earth (remember, all velocities are relative) and I do the experiment again. While sipping tea in the lab I measure a beam of light to cross 1meter in 3.33ns. That's 'c'.

From the earth I appear to be moving just behind the light beam. So what must have happened to my length and time for me to still be able to measure 'c'?

Hi QQ,



First, the measurement of the speed of light being 'c' in all frames is not the product of SRT reasoning. It is a postulate based on an experiment. It's the way nature is. From this and one or two other postulates, SRT "reasoning" is constructed. For you to measure 'c' as 'c' no matter what your state of motion, time and length must change in such a way as to explain the observation that in your frame you always measure light speed as 'c'.

Now, declaring your own velocity arbitrarily does nothing to change the relative velocities of other objects. If you measure a car going by at 30mph, you say his velocity wrt you is 30mph. If you want to say your velocity is 1000mph (wrt what?), that's fine. His relative velocity to you is still 30mph and he will outpace you at 30mph no matter what.

30mph - 0mph = 30mph
1030mph - 1000mph = 30mph
4567330mph - 4567300mph = 30mph



I measure 'c' by seeing how long it takes a beam of light to cross 1meter (about 3.33ns) I do that here on earth and get 'c' (no suprise there). Now, I blast up to 0.866c wrt the earth (remember, all velocities are relative) and I do the experiment again. While sipping tea in the lab I measure a beam of light to cross 1meter in 3.33ns. That's 'c'.

From the earth I appear to be moving just behind the light beam. So what must have happened to my length and time for me to still be able to measure 'c'?
check my answer and counter response:
obviously they are contracted and dilated but not to your obsevation but only to earths. If you declare your own velocity as .8c and apply length and contraction to your measurment you would not get 'c' because your length and time are already contracted and dilated but appear as normal.....so therefore you must consider your v as zero when measuring 'c'.
Does that make sense?

Sure. At classical speeds, it's no problem, but at relativistic speeds, it just becomes a mess. You are at rest (v = 0) in your rest frame. Right.

MacM:

You ceased discussing physics issues some time ago on this forum. Now you just whinge and whine and make totally unsupported statements. And whenever you're confronted by an actual physical or mathematical demonstration that your claims are false, you claim that whoever posted it is "not addressing the issue" or "simply citing rhetoric" or "not taking a physics view". But your claims are empty, because you do not refute any of the information presented. Instead, you attempt proof by bludgeoning repetition - a tactic which is easily seen through. You refer to no data, theory or authority other than yourself. Nobody agrees with you. And you dance around and deflect conversation and avoid answering questions. You're like a spoilt child whose mummy has told him whatever he says is right, no matter what. Well, we're not your mummy, MacM. We call you on wrong claims. And whinging won't help you wriggle out of your mistakes.

Funny. You continue to post these selfserving disclaimers but choose not to address the issue. Do you really think others are buying it?

MacM: You're wasting everybody's time here. Give it a rest.