SR, LET, FTL & Causality Violation

[atyy]

LET means Lorentz Ether Theory.. or the Theory of Ethers by Lorentz. But if you would insist of your definition of LET as special relativity in a particular Lorentz inertial frame and then full stop. Note it's only your definition as you see fit. Also in the real world. Minkowski space is replaced by curved differential manifold in GR.. so SR and LET are not even large scale but only valid in very tiny local region. Some even thought of adding GR to LET. This means your definition of LET is not universal but only your own (and a few others).

The point is of course to use your definition. I only suggested a definition since you hadn't provided one. OK, I need more details - what is Lorentz Ether Theory or the Theory of Ethers by Lorentz. In particular, what papers of Lorentz are we discussing?

 

[stglyde]

The point is of course to use your definition. I only suggested a definition since you hadn't provided one. OK, I need more details - what is Lorentz Ether Theory or the Theory of Ethers by Lorentz. In particular, what papers of Lorentz are we discussing?

I don't know. Are you saying that there is no standard LET formalism. Meaning one can refer to a LET version with aether rest frame detected and the relativity principle still hold. And another LET version where it is defined to be one where the aether rest frame is impossible to determine? How many LET versions are there and what are they so we would know what versions whenever we hear people talking or discussing about them?

 

[PeterDonis]

There is something I can't understand fully. Why can't the aether being detected not live side by side with relativity?

Be specific. What, exactly, would constitute "the aether being detected"? What experimental result would indicate that? I gave an example in a earlier post: we could have detected a non-null result in the MMX. Of course we didn't. But can you come up with another *specific* experimental result that would enable us to say "This specific inertial frame is *the* aether frame"? If you can't, then how do you expect anyone to answer the question quoted above?

For example. If two ships in inertial motion with respect to each other measure each others' time slowing down and length contraction. We can say that this occur with respect to each other.

More or less, though I think your description is a bit sloppy; you haven't specified *how* they "measure each others' time slowing down and length contraction". To give any physical theory meaning, you have to be able to relate it to actual observations.

So even if they each can detect the aether rest frame.

How? What observations are they making that "detect the aether rest frame"?

They are not using it to time or sychronize each other... or their inertial frames are not with respect to the aether rest frame.

How can you be sure of this when you haven't specified what observations they make that tell them what the aether rest frame is?

But with respect to each other. So they should still experience time dilation and length contraction in default mode

How do you know this?

unless they synchronize to the aether rest frame in which their results would be different.

What does "synchronize to the aether rest frame" mean?

 

[atyy]

I don't know. Are you saying that there is no standard LET formalism. Meaning one can refer to a LET version with aether rest frame detected and the relativity principle still hold. And another LET version where it is defined to be one where the aether rest frame is impossible to determine? How many LET versions are there and what are they so we would know what versions whenever we hear people talking or discussing about them?

I don't know either. You really need to let people know what we are discussing, otherwise everyone will be talking about different things, and we'll be talking about nothing in particular. It's your thread. If you want to discuss several versions of what you call LET, make sure to define each version sharply and give them different names.

 

[stglyde]

Be specific. What, exactly, would constitute "the aether being detected"? What experimental result would indicate that? I gave an example in a earlier post: we could have detected a non-null result in the MMX. Of course we didn't. But can you come up with another *specific* experimental result that would enable us to say "This specific inertial frame is *the* aether frame"? If you can't, then how do you expect anyone to answer the question quoted above?

There is a Proper Time and Coordinate Time in SR. According to peer reviewed site:

http://www.iep.utm.edu/proper-t/#H1

"The essence of the Special Theory of Relativity (STR) is that it connects three distinct quantities to each other: space, time, and proper time. ‘Time’ is also called coordinate time or real time, to distinguish it from ‘proper time’. Proper time is also called clock time, or process time, and it is a measure of the amount of physical process that a system undergoes."

So Proper time could be time of object relative to aether
Coordinate time could be time of object relative to other object.

Why not? Can you give actual example in particle experiment in which the "time dilation" time is really with respect to other object and not with respect to any aether rest frame in conjunction with this concept of Proper time vs Coordinate time in SR? Does each case and scenerio has a unique prediction with different experimental outcome?

 

[D H]

So Proper time could be time of object relative to aether
Coordinate time could be time of object relative to other object.

That is not proper time. That phrase has a well defined meaning. Proper time is what clocks measure. Moreover, your statement does not answer Peter's question.

This thread has gone on far too long already. stglyde, you are on an extremely short leash here. You need to

• Specify what you mean by Lorentz Ether Theory (reference some papers),
• Tell us how the ether in LET could ever be detectable,
• Tell us how LET is experimentally distinguishable from special relativity, and
• Tell us why LET is scientifically preferable to special relativity.

If you cannot do this there is no reason for this thread to continue.
Note very well: Everything I have read on LET says that (a) Lorentz' ether is inherently undetectable thanks to the Lorentz transformation and that (b) special relativity and LET are experimentally indistinguishable. While the two theories are indistinguishable in terms of predicted results, the theories are very distinguishable in terms of testable postulates. The postulates of special relativity are testable. Two of the postulates of LET are not. A theory with untestable hypotheses is not a scientific theory.

 

[stglyde]

That is not proper time. That phrase has a well defined meaning. Proper time is what clocks measure. Moreover, your statement does not answer Peter's question.

I will address the 4 things below but first let me defend on what I said about the Proper time.
In Wiki. It is said that:

"A Euclidean geometrical analogy is that coordinate time is like distance measured with a straight vertical ruler, whereas proper time is like distance measured with a tape measure. If the tape measure is taut and vertical it measures the same as the ruler, but if the tape measure is not taut, or taut but not vertical, it will not measure the same as the ruler."

Proper time is more precise as shown in the wiki graphics. And "In relativity, proper time is the elapsed time between two events as measured by a clock that passes through both events." versus that of "coordinate time is the time between two events as measured by a distant observer using that observer's own method of assigning a time to an event." Hence do you deny that the proper time is more accurate than coordinate time.

Now PeterDonis asked me "What does "synchronize to the aether rest frame" mean?".
And I answered that "synchronize to the aether rest frame" may be the proper time (the precise time) as I read in a LET paper I will try to find.

I know this thread needs to be locked.. but just give it a day more please to hear arguments and reasons why the the proper time can never be the actual aether rest frame time with respect to the object as some authors suggest. :) I will give the peer reviewed reference when I found it within the day (I know countdown to locking has started).

This thread has gone on far too long already. stglyde, you are on an extremely short leash here. You need to

• Specify what you mean by Lorentz Ether Theory (reference some papers),
• Tell us how the ether in LET could ever be detectable,
• Tell us how LET is experimentally distinguishable from special relativity, and
• Tell us why LET is scientifically preferable to special relativity.

If you cannot do this there is no reason for this thread to continue.



Note very well: Everything I have read on LET says that (a) Lorentz' ether is inherently undetectable thanks to the Lorentz transformation and that (b) special relativity and LET are experimentally indistinguishable. While the two theories are indistinguishable in terms of predicted results, the theories are very distinguishable in terms of testable postulates. The postulates of special relativity are testable. Two of the postulates of LET are not. A theory with untestable hypotheses is not a scientific theory.

 

[ghwellsjr]

How do you measure a high speed object?

One way to measure the relative constant speed between two objects where they are in line with each other, first traveling directly towards each other, then passing and finally traveling directly away from each other is Relativistic Doppler. This is observing a signal, such as a clock or timing signal or just the spectral characteristics of the moving object as compared to your own clock, timing signal or spectral characteristics. You divide your frequencies or periods and get the ratio R. Then you do this calculation:

β = |(1-R²)/(1+R²)|

There's no time delay in the measurement I described. There's also no need for either observer to establish any Frame of Reference or adhere to any developed theory such as LET or SR when making the measurement. There's no transformations, no coordinates, no offsets. Just measure how long it takes each ship to pass the other. They both get the same answer, even though one of them is stationary in the aether rest frame and one of them isn't (although they don't need to know that).

And how exactly does one do that?

Start your timer when the front of the other ship reaches you and stop it when the rear of the other ship reaches you. Multiply the time interval by the previously measured speed and you have the length of the other ship.

 

[ghwellsjr]

I will address the 4 things below but first let me defend on what I said about the Proper time.
In Wiki. It is said that:

"A Euclidean geometrical analogy is that coordinate time is like distance measured with a straight vertical ruler, whereas proper time is like distance measured with a tape measure. If the tape measure is taut and vertical it measures the same as the ruler, but if the tape measure is not taut, or taut but not vertical, it will not measure the same as the ruler."

Proper time is more precise as shown in the wiki graphics. And "In relativity, proper time is the elapsed time between two events as measured by a clock that passes through both events." versus that of "coordinate time is the time between two events as measured by a distant observer using that observer's own method of assigning a time to an event." Hence do you deny that the proper time is more accurate than coordinate time.

Now PeterDonis asked me "What does "synchronize to the aether rest frame" mean?".
And I answered that "synchronize to the aether rest frame" may be the proper time (the precise time) as I read in a LET paper I will try to find.

When Einstein said, "Time is what a clock measures", he was talking about proper time. Every clock keeps track of proper time, even clocks used to display coordinate time. The reason why we make a distinction is that proper time is what we use for clocks that can be accelerated and coordinate time is what we use for clocks that are not allowed to be accelerated. Einstein's convention for establishing synchronized clocks in order to build a coordinate system involves moving clocks to all locations and then synchronizing them and never allowing them to move again. It's because they are not allowed to be moved after they are synchronized that we can use them to display the same coordinate time at all locations throughout the coordinate system but they are still displaying proper time, just like any other clock. So we reserve the term "coordinate time" to refer to the clocks at fixed locations within our coordinate system and the term "proper time" to refer to the clocks that observers carry around with them when they do their interesting things.

 

[zonde]

Then perhaps Schmeltzer's GLET may be interesting to some people here. I think that his generic paper about it has not been published in a relevant journal (you can find it in Arxiv or on his web site); however, the following related paper (which regretfully is too technical for me) has been published in Foundations of Physics:
http://arxiv.org/abs/arXiv:0908.0591
Note: to see what the paper is really about, one should read its Introduction

Interesting indeed. I speak about this paper:
http://arxiv.org/abs/gr-qc/0205035

But rather technical so to say. I wonder how hi's $\Xi$ and $\Upsilon$ modify description of gravity. There should be differences for gravitating body at rest in aether frame and for gravitating body in motion relative to aether frame.
But I suppose that this question does not belong in this thread.

 

[Dale]

For Lorentz, there was only one frame in which light was isotropic c.

Thus, since the CMB IS light, and universally uniform, the rest frame for Lorentz's aether would be uniquely the one with no discernable Doppler. Agree?

No, I don't agree. Suppose we launch a satellite and put it at rest wrt the CMB. It would then measure isotropic c and approximately isotropic intensity. How do we know that the isotropy is real and not due to our measuring devices being distorted? Suppose that the CMB were moving at .6c through the aether, i.e. the whole universe has an average velocity, our measurements of the isotropy of the CMB frame would be the same, not because the CMB really is at rest, but because our measuring devices got distorted.

Similarly we can make artificial isotropic sources and we can measure the isotropy of c with versions of the MMX. All such experiments measure isotropy, so by your reasoning all such frames having isotropic c must be the rest frame for Lorentz' aether. The theory is designed to make it impossible to identify any specific frame as the aether frame.

 

[Dale]

Why not? Can you give actual example in particle experiment in which the "time dilation" time is really with respect to other object and not with respect to any aether rest frame in conjunction with this concept of Proper time vs Coordinate time in SR?

http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html#Twin_paradox

Bailey et al., “Measurements of relativistic time dilation for positive and negative muons in a circular orbit,” Nature 268 (July 28, 1977) pg 301.

Bailey et al., Nuclear Physics B 150 pg 1–79 (1979).

They stored muons in a storage ring and measured their lifetime. When combined with measurements of the muon lifetime at rest this becomes a highly relativistic twin scenario (v ~0.9994 c), for which the stored muons are the traveling twin and return to a given point in the lab every few microseconds. Muon lifetime at rest: Meyer et al., Physical Review 132, pg 2693; Balandin et al., JETP 40, pg 811 (1974); Bardin et al., Physics Letters 137B, pg 135 (1984).​

If you work out the math the experimental predictions are the same whether the lab is at rest wrt the aether or moving at any given v<c wrt the aether. So the measured time dilation and the measured proper time have nothing to do with the aether.

 

[harrylin]

AFAICT from skimming the paper, this theory makes the same predictions regarding gravity as GR does; it just derives them by a different route. Also, I'm not sure whether this is actually an "LET" type theory; the paper does use the term "preferred frame" to describe the "unobservable" flat background spacetime that is used, but I'm not sure the theory actually requires that one particular "slicing" of the flat Minkowski background into space and time (i.e., one particular "frame") is privileged over all others as an "aether" frame. The theory may only require that the flat background is Minkowski, but still allow all inertial frames to be equivalent as ways of looking at that flat background.

It is definitely according to the author a "LET"-like theory, as he calls it "GLET" in another paper. And there seems to be a significant difference with GR for extreme cases... I quote:

"More details and consequences of this theory of gravity can be found in [25].
Especially, the gauge-breaking term stops (for the correct sign of the constants) the
black hole collapse and prevents the big bang singularity. The condensed matter
approach to gravity solves many quantization problems of canonical GR quantization:
The notorious "problem of time" [17] simply disappears. Together with the
black hole collapse the related information loss problem [23] disappears too."

PS: I agree with Zonde that this isn't the topic for a long discussion of his theory.

 

[harrylin]

I don't know. Are you saying that there is no standard LET formalism. Meaning one can refer to a LET version with aether rest frame detected and the relativity principle still hold. And another LET version where it is defined to be one where the aether rest frame is impossible to determine? How many LET versions are there and what are they so we would know what versions whenever we hear people talking or discussing about them?

Just check the papers of that time: no theory called "Lorentz Ether theory"; that's a later invention (and not well defined). Only "Lorentz Electron Theory" (which predated SR), and "relativity theory", which Einstein later renamed "Special relativity" (SR). SR was taught by both Einstein and Lorentz, although with different interpretations at the start.

 

[harrylin]

This is a different use of the term "aether"; it's what DaleSpam referred to as "Einstein aether" or "gravitational aether" a couple of posts back. The LET use of the term "aether" is more than just saying there has to be "something" to control the properties of spacetime; it is saying that one particular slicing of that "something" into space and time, i.e., one particular "frame", is the "true" one.

Indeed, Einstein disliked calling one particular "frame" the "true" one. However, the "Einstein ether" concept (should we call that "EET"?) is the same as the "Lorentz ether" concept, "if we substitute constants for the functions of space which describe [GR]" - Einstein 1920 (Leiden inauguration speech). Not sure however if "Einstein Ether Theory" belongs to this thread. :tongue2:

 

[Dale]

The "Einstein aether", as you call it, has no rest frame. That alone makes it quite different from any other concept associated with the term "aether". It can not be considered a "medium", regardless of if you randomly stick the label "aether" on it or not.

 

[PeterDonis]

It is definitely according to the author a "LET"-like theory, as he calls it "GLET" in another paper.

Yes, I see from the other paper zonde linked to that the author does mean the strong sense of "preferred frame".

PS: I agree with Zonde that this isn't the topic for a long discussion of his theory.

Agreed.

 

[PeterDonis]

According to peer reviewed site:

http://www.iep.utm.edu/proper-t/#H1

"The essence of the Special Theory of Relativity (STR) is that it connects three distinct quantities to each other: space, time, and proper time. ‘Time’ is also called coordinate time or real time, to distinguish it from ‘proper time’. Proper time is also called clock time, or process time, and it is a measure of the amount of physical process that a system undergoes."

I know this site says it's a "peer reviewed site", but I've never seen the term "real time" used for coordinate time before. IMO calling coordinate time "real time" is *not* appropriate. I note that, although there are references listed at the end of this article, there are no specific cites given for particular statements, such as the one quoted. Even Wikipedia does a better job of attribution than that.

 

[PeterDonis]

"A Euclidean geometrical analogy is that coordinate time is like distance measured with a straight vertical ruler, whereas proper time is like distance measured with a tape measure. If the tape measure is taut and vertical it measures the same as the ruler, but if the tape measure is not taut, or taut but not vertical, it will not measure the same as the ruler."

A good illustration of why Wikipedia is not considered an authoritative source. In a curved spacetime, thinking of coordinate time as the "straight ruler" leads to confusion because in general coordinate systems are not rectilinear.

Proper time is more precise as shown in the wiki graphics. And "In relativity, proper time is the elapsed time between two events as measured by a clock that passes through both events." versus that of "coordinate time is the time between two events as measured by a distant observer using that observer's own method of assigning a time to an event." Hence do you deny that the proper time is more accurate than coordinate time.

It's not a question of "accuracy". Proper time is directly observable; you just described how to observe it. Coordinate time is an arbitrary label; it doesn't have to have *any* useful relationship to any physical observables, so the question of its "accuracy" isn't even meaningful. It's like saying that the number 3 is more "accurate" at describing how many marbles are in a bucket than the letter A.

Now PeterDonis asked me "What does "synchronize to the aether rest frame" mean?".
And I answered that "synchronize to the aether rest frame" may be the proper time (the precise time) as I read in a LET paper I will try to find.

DaleSpam has already explained repeatedly why measurements of proper time (or any other observable, for that matter) can't tell us anything about the aether frame. I'll be extremely surprised if you can find a credible reference that demonstrates a valid method of doing so.

 

[atyy]

I know this site says it's a "peer reviewed site", but I've never seen the term "real time" used for coordinate time before. IMO calling coordinate time "real time" is *not* appropriate. I note that, although there are references listed at the end of this article, there are no specific cites given for particular statements, such as the one quoted. Even Wikipedia does a better job of attribution than that.

It's unfortunately found in pop sci books that biologists like me read, eg. Rindler (p13): "Einstein was the first to derive the LT independently from the relativity principle ... as that which connects real space and real time in various inertial frames."

 

[ghwellsjr]

Einstein referred to LET in this talk delivered in 1920:

ETHER AND THE THEORY OF RELATIVITY

If you look down to part [11], you'll read these words:

As to the mechanical nature of the Lorentzian ether, it may be said of it, in a somewhat playful spirit, that immobility is the only mechanical property of which it has not been deprived by H. A. Lorentz. It may be added that the whole change in the conception of the ether which the special theory of relativity brought about, consisted in taking away from the ether its last mechanical quality, namely, its immobility. How this is to be understood will forthwith be expounded.

The space-time theory and the kinematics of the special theory of relativity were modeled on the Maxwell-Lorentz theory of the electromagnetic field. This theory therefore satisfies the conditions of the special theory of relativity, but when viewed from the latter it acquires a novel aspect. For if K be a system of co-ordinates relatively to which the Lorentzian ether is at rest, the Maxwell-Lorentz equations are valid primarily with reference to K. But by the special theory of relativity the same equations without any change of meaning also hold in relation to any new system of co-ordinates K' which is moving in uniform translation relatively to K.

Einstein makes it clear that the Lorentzian ether assumes a single rest state when he uses the word "immobility". However, everything continues to work just as well in Special Relativity with any rest state. That's the only difference between LET and SR.

 

[harrylin]

The "Einstein aether", as you call it, has no rest frame. That alone makes it quite different from any other concept associated with the term "aether". It can not be considered a "medium", regardless of if you randomly stick the label "aether" on it or not.

I cited Einstein's own clarification (nearly a definition) of how exactly his "GR ether" concept corresponds to the "Lorentz ether"; if you disagree with him about his own concept, the odds are in his favour.

Here is a more elaborate citation (from the same source as ghwellsjr):

The ether of the general theory of relativity is transmuted conceptually into the ether of Lorentz if we substitute constants for the functions of space which describe the former, disregarding the causes which condition its state.
[...]
Nor do we know whether it is only in the proximity of ponderable masses that [the new ether's] structure differs essentially from that of the Lorentzian ether; whether the geometry of spaces of cosmic extent is approximately Euclidean.

 

[stglyde]

Let's settle some loose issues before initializing lockdown.

No, I don't agree. Suppose we launch a satellite and put it at rest wrt the CMB. It would then measure isotropic c and approximately isotropic intensity.

iIsotropic intensity to at least 5 decimal places...

How do we know that the isotropy is real and not due to our measuring devices being distorted?

By Lorentz's definition, light is only isotropic in the aether's background, or, as Einstein called it, 'empty space'... Doppler IS! a measure of motion wrt to a light source. In the case of the
CMBR that source is space itself. Thus by any 'reasonable' definition the CMBR illuminates Lorentz's aether frame.

Suppose that the CMB were moving at .6c through the aether, i.e. the whole universe has an average velocity, our measurements of the isotropy of the CMB frame would be the same, not because the CMB really is at rest, but because our measuring devices got distorted.

The only thing that Lorentzian 'distortion' does to Doppler is to alter the Doppler expression to what we call the relativistic Doppler equation. You still measure Doppler with any motion relative to the source.

Similarly we can make artificial isotropic sources and we can measure the isotropy of c with versions of the MMX. All such experiments measure isotropy, so by your reasoning all such frames having isotropic c must be the rest frame for Lorentz' aether. The theory is designed to make it impossible to identify any specific frame as the aether frame.

Look c IS locally isotropic and independent of the motion of the source/receiver JUST! as both Lorentz and Einstein indicated. Both took advantage of the fact that for any closed path (Two way) the anisotropic aspects factor out which is why the LT is based upon c +/- v. Therefore the MMX and all such does exactly what mediums do and sonic fields behave in exactly the same fashion. The ONLY reason we 'measure' them differently is because the instruments we
utilize are not subject to the stress/strain effects of the mediums being measured. If matter had been 'ponderable' plowing through the aether and not part of it we'd have seen what Michelson expected.

 

[stglyde]

When Einstein said, "Time is what a clock measures", he was talking about proper time. Every clock keeps track of proper time, even clocks used to display coordinate time. The reason why we make a distinction is that proper time is what we use for clocks that can be accelerated and coordinate time is what we use for clocks that are not allowed to be accelerated. Einstein's convention for establishing synchronized clocks in order to build a coordinate system involves moving clocks to all locations and then synchronizing them and never allowing them to move again. It's because they are not allowed to be moved after they are synchronized that we can use them to display the same coordinate time at all locations throughout the coordinate system but they are still displaying proper time, just like any other clock. So we reserve the term "coordinate time" to refer to the clocks at fixed locations within our coordinate system and the term "proper time" to refer to the clocks that observers carry around with them when they do their interesting things.

Proper time and length is alway defined in the rest frame of the object...

One way to measure the relative constant speed between two objects where they are in line with each other, first traveling directly towards each other, then passing and finally traveling directly away from each other is Relativistic Doppler. This is observing a signal, such as a clock or timing signal or just the spectral characteristics of the moving object as compared to your own clock, timing signal or spectral characteristics. You divide your frequencies or periods and get the ratio R. Then you do this calculation:

β = |(1-R²)/(1+R²)|

Ah, by light signals coming to & from both systems, right?

Start your timer when the front of the other ship reaches you and stop it when the rear of the other ship reaches you. Multiply the time interval by the previously measured speed and you have the length of the other ship.

And how do you know exactly when the ship reaches you? By light signals right? Do these travel at infinite speed?

 

[ghwellsjr]

When Einstein said, "Time is what a clock measures", he was talking about proper time. Every clock keeps track of proper time, even clocks used to display coordinate time. The reason why we make a distinction is that proper time is what we use for clocks that can be accelerated and coordinate time is what we use for clocks that are not allowed to be accelerated. Einstein's convention for establishing synchronized clocks in order to build a coordinate system involves moving clocks to all locations and then synchronizing them and never allowing them to move again. It's because they are not allowed to be moved after they are synchronized that we can use them to display the same coordinate time at all locations throughout the coordinate system but they are still displaying proper time, just like any other clock. So we reserve the term "coordinate time" to refer to the clocks at fixed locations within our coordinate system and the term "proper time" to refer to the clocks that observers carry around with them when they do their interesting things.

Proper time and length is alway defined in the rest frame of the object...

No, you have it backwards. Proper time (the time that a clock measures) and proper length (the length that a ruler measures) are used to define a frame, along with the one-way speed of light to synchronize remote clocks to the local clock. After you define the frame, then, of course you can say that a clock at rest in that frame will exhibit the same time as the proper time on the original clock. Every clock always displays proper time. You don't need to define any frame in order to define proper time. It's real simple. It's the time on every clock.

One way to measure the relative constant speed between two objects where they are in line with each other, first traveling directly towards each other, then passing and finally traveling directly away from each other is Relativistic Doppler. This is observing a signal, such as a clock or timing signal or just the spectral characteristics of the moving object as compared to your own clock, timing signal or spectral characteristics. You divide your frequencies or periods and get the ratio R. Then you do this calculation:

β = |(1-R²)/(1+R²)|

Ah, by light signals coming to & from both systems, right?

Of course, that's what Relativistic Doppler is all about. Why did you need to ask?

Start your timer when the front of the other ship reaches you and stop it when the rear of the other ship reaches you. Multiply the time interval by the previously measured speed and you have the length of the other ship.

And how do you know exactly when the ship reaches you? By light signals right? Do these travel at infinite speed?

No, the light signals don't travel at infinite speed but since the ships are directly in line with each other, there is no distance between them as they pass and so there is no time delay.

 

[Dale]

By Lorentz's definition, light is only isotropic in the aether's background,

Sure, light is isotropic only in the aether frame but according to LET light is measured to be isotropic in all frames. Therefore, the fact that the CMB is measured to be isotropic to 5 decimal places is not evidence that the CMB is Lorentz's aether.

Doppler IS! a measure of motion wrt to a light source. In the case of the
CMBR that source is space itself.

:rofl: Your ignorance is amusing at times. The source of the CMBR is called the surface of last scattering. It is a piece of matter (not space) that had just cooled to the point where protons and electrons bound into hydrogen and the matter became transparent. That is why it has a black body spectrum and is evidence for the big bang theory.

 

[stglyde]

now the finale...

Sure, light is isotropic only in the aether frame but according to LET light is measured to be isotropic in all frames.

Sure, light is 'measured' as isotropic from any inertial frame due to the artifact of:

c = dg/tg -> (d/t)(g/g)


BUT any school child knows that while


2 = 2/1

and

2 = 12/6

these ARE NOT! the same values. Likewise, light is ONLY! measured as isotropic (i.e. without Doppler shifts) if AND ONLY IF! the source is stationary to the frame.

Therefore, the fact that the CMB is measured to be isotropic to 5 decimal places is not evidence that the CMB is Lorentz's aether.

I see d'nile isn't just a river in Egypt... It meets Lorentz's (and Einstein's) original definition for such. This is why its used in GR-aether...

 

[atyy]

I see d'nile isn't just a river in Egypt... It meets Lorentz's (and Einstein's) original definition for such. This is why its used in GR-aether...

But you still haven't said what LET is. Even without going beyond the standard model, there are many concepts including the http://www.tu-harburg.de/rzt/rzt/it/Ether.html, the http://www.nobelprize.org/nobel_prizes/physics/laureates/2006/smoot_lecture.pdf, or the quantum vacuum which have been called "aethers" because they have some relationship to Lorentz's. That is not contested (by me). However, to have a good discussion of the similarities and differences between these different things, we need a sharp definition of LET, and give each of these aethers different names. For example, if one includes that the aether of LET is undetectable, then we can straightaway say that the CMB as a preferred frame does not have that property, since it is detectable. So could we please have your precise definition of LET, along the lines suggested by D H?

 

[Dale]

light is ONLY! measured as isotropic (i.e. without Doppler shifts) if AND ONLY IF! the source is stationary to the frame..

True. But the source of the CMB is the surface of last scattering, not the aether. So again, the fact that it is measured to be isotropic provides no evidence about the velocity wrt the aether.

I encourage you to work through the math. According to LET, what would a detector measure for the radiation in each direction along the x and y axes for the case where the surface of last scattering and the detector are both moving at v=0 and both moving at v=.6c wrt the aether?

I see d'nile isn't just a river in Egypt... It meets Lorentz's (and Einstein's) original definition for such. This is why its used in GR-aether...

:rofl: OK then, do the math I suggested above and prove me wrong.

 

[TrickyDicky]

True. But the source of the CMB is the surface of last scattering, not the aether. So again, the fact that it is measured to be isotropic provides no evidence about the velocity wrt the aether.

I encourage you to work through the math. According to LET, what would a detector measure for the radiation in each direction along the x and y axes for the case where the surface of last scattering and the detector are both moving at v=0 and both moving at v=.6c wrt the aether?

But aren't you confusing here the source of the CMB with the CMB radiation itself? If I understand correctly styglide is identifying the aether frame with the frame at which no doppler shift is detected from the CMB, what does this have to do with the surface of last scattering as an object? BTW there is a thread in the QP subforum about the CMB that might interest you: "does CMBR include free photons?"

 

[TrickyDicky]

What I mean (for some reason DaleSpam deleted his answer to my last post) is that I think stglyde is referring to the observed doppler dipole that is observed by COBE and WMAP and the fact that according to current mainstream knowledge this doppler shift would not be expected to be observed in the cosmological comoving frame, how is that doppler shift related to the last scattering surface source that is supposed to be taken care of by the fact the CMB photons are redshifted to microwave wavelengths?, seems to me a different altogether issue than what stglyde is referring to.

 

[PeterDonis]

the observed doppler dipole that is observed by COBE and WMAP and the fact that according to current mainstream knowledge this doppler shift would not be expected to be observed in the cosmological comoving frame

Yes (meaning the dipole, not the shift as a whole).

how is that doppler shift related to the last scattering surface source that is supposed to be taken care of by the fact the CMB photons are redshifted to microwave wavelengths?, seems to me a different altogether issue than what stglyde is referring to.

Because the process of the universe becoming transparent to photons took place homogeneously and isotropically throughout the universe. The "last scattering surface" marks the place (and time) where that process happened, and the CMB photons are the photons that have been traveling freely since the last scattering.

Put another way, in the "comoving" frame the process of "last scattering" took place at the same time everywhere (more precisely, since the process was not instantaneous, it started and ended at the same times everywhere). So the CMB photons coming from every direction have been traveling freely for (on average) the same amount of time. Since their redshift depends on how long they have been traveling freely (because it depends on how much the universe has expanded since they were emitted), the redshift will be (on average) isotropic in the "comoving" frame. In other words, no dipole is equivalent to saying that the "comoving" frame is the frame in which the last scattering was isotropic.

 

[TrickyDicky]

Hi, Peter, always glad to read your knowledgeable answers.

Yes (meaning the dipole, not the shift as a whole).

Sure, that was my meaning too, the dipole anisotropy from the Doppler shift of the background radiation due to the Earth's motion wrt the CMB frame as we both know.

In other words, no dipole is equivalent to saying that the "comoving" frame is the frame in which the last scattering was isotropic.

Oh, I think there's been some sort of misunderstanding. The dipole has nothing to do with the last scattering, it only reflects the relative motion of the Earth wrt CMB comoving frame.
I was merely trying to clarify that IMO the discussion in this thread was not related to the redshift of the CMB photons due to the cooling expansion, but that when stglyde talks about isotropy (he probably made a bad choice of words) he is not referring to the last scattering surface isotropy that is observed in the CMB maps after the dipole and the local sources have been cleaned off, but to the fact that an observer comoving with the CMB is not supposed to observe any dipole.
I thought Dalespam was mixing these and that's why i pointed it out.

 

[Dale]

for some reason DaleSpam deleted his answer to my last post

Sorry, I just decided I didn't want to get sidetracked and start a new chain of arguments.

 

[PeterDonis]

The dipole has nothing to do with the last scattering, it only reflects the relative motion of the Earth wrt CMB comoving frame.

Yes, but the fact that the CMB is isotropic in the comoving frame is due to the fact that the surface of last scattering is a surface of constant comoving time. And *that* fact is due to the fact that the process of "last scattering" occurred homogeneously and isotropically throughout the universe, which is a *physical* property of that process, and therefore of the surface in spacetime on which it took place. So the dipole we observe *is* connected to the actual physical process of last scattering.

I thought Dalespam was mixing these and that's why i pointed it out.

If he was, he was justified, IMO, because as I just noted, the two are connected. The CMB is not isotropic in the comoving frame by magic; it's that way *because* of a particular physical process that produced the CMB, and that process started at the surface of last scattering.