Re: Silly Einstein by Aardwolf » Thu Jul 07, 2011 5:56 am wrote:I'm afraid I can't accept that there will be any difference in either the time it takes light nor the shifting of the light between the 2 flashes observed by A or C. As a single flash of light at and only at point B there wouldn't be any shifting.
I wish there were an easy way to post newly drawn diagrams! Aardwolf , please hang in there; I can only get so many ideas into a post before it gets too confusing! Now, what I think you have overlooked is that a pulse of light has to have a duration. No duration; no light. At relativistic speeds by a source moving at one half foot per nanosecond, a nanosecond flash of light in that frame will be stretched over the distance of a half a foot in the opposite frame! Thus, from the beginning of the pulse to the end of it, while remaining at the same place within the frame, (if the pulse originating in X were to start one half a nanosecond before X reached point B in the opposite frame and end one half nanosecond after X past B) you can see that the time actually spent at point B is mind bogglingly short. Then there is the rest of the duration of the pulse as seen from the opposite frame as either approaching or leaving the mutual point of conjunction.
Aardwolf wrote:To me that means that both flashes propagated as spheres from point B. The momentum of ship X has no effect at all. Why would it?
Please remember, it was your idea to put one lamp in the X frame and one in the ABC frame. The two lamps have relative speed between them. The X frame sphere propagates from the X frame lamp at the center of X, the B frame lamp sends its sphere from a point centered at B. I picture each lamp “at rest” with its own frame. The light propagating from either lamp is spherically expanding at the speed of light in each respective frame. I give the aether the job of “keeping each lamp moving rectilinearly through space,” and keeping the sphere of each lamp centered on each respective lamp.
Aardwolf wrote:My point is that light doesn't propagate equally from all light sources if that source is moving through empty space.
Please remember that you are being ambiguous here: We just can't refer to “light propagating” per se. the question is always “relative to which observer; one at rest with the source, or one in motion that just happens to be at the same place as the at rest observer for an instant?
Aardwolf wrote:If moving at 0.5c it will track light ahead of it by 0.5c and move away from the light emitted behind by 1.5c.
I can't tell what “it” refers to in your sentence. Do you mean the source, or an observer? If you mean an observer; to which frame does the observer belong? An observer at the source, whether moving or not, can only observe the flash at the source the instant it originates. For observers to observe the expanding sphere at some given time and distance from the source, those observers have to be at the given time and distance from the source.
Aardwolf wrote:Now I understand that [consensus] relativists will be screaming at me that this is incorrect, but in my example it's the only answer. Light cannot reach points A & C from X at different times to light from B.
Please remember that you specified that X is receding from A and approaching C. When X is closer to A than C, (remember the “duration of the pulse” which I suggested we arbitrarily start just before X actually reaches B) (and the pulse is expanding in X frame at the speed of light in all directions from X in that frame, and is moving with that frame away from A and toward C)
Aardwolf wrote:I believe this partly stems from a misinterpretation of Einsteins 2nd postulate. If I am incorrect then why did Einstein say "...that is independent of the state of motion of the emitting body".
I believe it mainly stems from the fact that Einstein has pulled a slight of hand here. The truth is that logically; once the pulse is emitted, the state of motion of the source is no longer relevant for the next particular emission. The next pulse will be centered on where the source is when this new pulse is emitted.
We view light from stars light-years away. The truth is we have no idea where those stars are today. We only know that the light we see is centered upon the star where it was when the light was emitted! Einstein said what he did without thinking the whole situation completely through.
Re: Silly Einstein by Aardwolf » Thu Jul 07, 2011 6:32 am
wrote:For a bit more clarity (I hope!) I think I should point out a contradiction in what you have posted.
You state that I was correct in stating that the light received by observers at A & C from the flashes at X & B will be seen at the same time (notwithstanding the red/blue shifting disagreement which we'll leave for this example).
Observers at X and B will see their own light un-shifted, and for the tiniest instant the other's light un-shifted, at the same time. As they pass each other, they see the other's light will first be blue shifted, then red shifted.
Aardwolf wrote:However, you also say this "...all observers in the source inertial frame, fixed at a given distance from the source, will all see the flash at the same time."
Yes, I am correct on this: All the observers to which I refer here are on the “surface” of the expanding sphere, the diameter of which is determined by the duration of time the sphere has been expanding since the pulse was emitted. In addition, all observers in any frame, no matter the relative speed, who also happen to be at this time and place (on the sphere) in space will observe the pulse at this same time.
Aardwolf wrote:As you state, X is in its own frame. Let's say X was not alone, ahead of X is ship W and behind X is ship Y. Now they are 5ly ahead of and behind X respectively, and they are traveling at the same speed so are included in X's reference frame. Now, according to your statement the light from X will reach W & Y at at the same time. Relativity as currently interpreted says it must. So we have a problem. After 5 years has passed the light from point B will reach Point A & point C at the same time.
No problem here, except now we have two more observers! Keep in mind that the process of transmitting and receiving is asymmetrical.
Aardwolf wrote: So we have a problem. We know and you agreed that the light from X will also reach Point A & C (although shifted) at this time.
Did I say that? Spank me!
Aardwolf wrote:However, according to X's frame the light should also be reaching W which is 4.5ly past A and ship Y which is 4.5ly past C. How can this be possible?
Keep in mind that there is not “the light,” there are two “lights” and two expanding spheres in your scenario. Five years after the pulses have been emitted (in absolute time) each set of observers in their own respective frames will see the pulses from their own lamps at the same time. It is confusing to try to relate Y and W to A and C except to say that when B and X are aligned, Y and A are aligned and W and C are aligned. I wish I were adept at getting diagrams uploaded to the forum!
The proper process is to relate W and Y to B which is the source in the opposite frame; and A and C to X which is the source in the opposite frame. Which is to say that B is moving away from W and towards Y; and X is moving towards C and away from A.
After five years of separation, X and B will be 2.5 light-years apart (moving @ .5c), but the un-shifted opposite going light pulses from each source will reach their respective observers in each rest frame, simultaneously at the five year absolute time. (These observers being located on 5 light-year diameter spheres centered upon each source)
After five years of separation, X and B will be 2.5 light-years apart (moving @ .5c);
There is a sphere that has expanded to 5 light years in diameter and centered upon B. All observers in the B frame, located at this distance on the surface of the sphere will simultaneously see the pulse pass by them.
There is a group of observers moving along in the X frame: formed into an identical sphere to the five light-year sphere in B; only however, in the X frame, centered upon this 2.5 light-year point (2.5 light-years from X). When X passes the point 2.5 light-years from B, the center of this circle of observers in the X frame will, for a tiny instant, coincide with the observers who are on the sphere of B at 5 light-years from B, and the at same instant these X frame observers will see the pulse from B, along with the observers on the 5 light-year diameter sphere who are in the B frame! The difference in what the moving observers see is that the spectra they see of B's light in the B pulse is Doppler shifted accordingly, since the observers on the leading edge of the moving observers' sphere observe B's light red shifted, those on the trailing edge of the moving observers' sphere observe B's light blue-shifted.
If you have followed my reasoning so far, a repeat of the above paragraph happens for a group of observers moving along in the B frame: formed into an identical sphere to the five light-year sphere in X; only however, in the X frame, centered upon this 2.5 light-year point (2.5 light-years from B). and so on.
After five years of separation, B will be 2.5 light-years from Y and 5 light-years from W. Y will observe B's blue-shifted flash 2.5 years before A observes the same flash which will be un-shifted. W will observe B's red-shifted flash 7.5 years after the flash was emitted, and 2.5 years after C sees the un-shifted flash. Einstein is right about these points (Y and W) not seeing the pulse from the opposite frame simultaneously, however this is a bit disingenuous since there are points in space where observers in both frames do see the pulse simultaneously.