Neddy Bate, What makes you think an 'interference pattern' is necessary? Surely you understand the interference pattern is just a primitive method of comparing transit times of the light travelling in counterclockwise vs. clockwise directions? That a GPS signal from a moving satellite will take longer to reach the receiver because the receiver has moved while the signal was in transit? The Sagnac effect, whether in rotating frames or linear frames, is a result of increasing or decreasing distance while the signal is in transit. An interference pattern is just a easy method of comparing transit times of counter-propagating signals in rotating frames. It is not a requirement for a Sagnac effect. The beam time-of-flight can be measured individually, or separately. Edit to include 'decreasing distance'.
Neddy, Dale, I just remembered an example of an interferometer that doesn't rotate. I was explaining how an interferometer doesn't need to rotate, but only to measure the transit time of light between two points, but didn't think about actual examples. The Laser Interferometer Gravitational-Wave Observatory (LIGO) is an example, or actually there are two of them, one in Washington and one in Louisiana. http://www.ligo-wa.caltech.edu/ligo_overview/ligo_overview.html Just as an interference pattern isn't necessary for an interferometer, an interference pattern itself has nothing to do with the Sagnac effect. Dale, I've tried to explain before, the Sagnac effect is a change in the distance a signal has to transit after it is emitted. You've got to give up the image of 'its the other guy moving' before you can visualize it. You have to depict the effect with moving diagrams, not stationary diagrams drawn on a sheet of paper. If the receiver is moving away from the emitter when the signal is sent, the distance between the two will increase while the signal is is transit. If, for instance, the receiver is moving away from the emitter at .5c and the EM signal was broadcast while they were 299,792,458 meters apart, the receiver will read the signal when they are 449,688,687 meters apart. It will take 1 1/2 seconds for the signal to reach the receiver, 1/2 seconds longer than what would be assumed if there were no movement by the receiver 'in its rest frame'. By asumming the receiver is at rest and the emitter sent the signal when they were 299,792,458 meters apart, the signal would be received one second after transmission, not 1 1/2 seconds. The timing is not symmetrical.
Yes, I know of many interferometers that do not rotate, I just don't know of any interferometers that are a straight line. The LIGO is no exception. To my knowledge all of Sagnac's work was related to interferometers and interference patterns, and until this conversation every time I heard about the "Sagnac effect" it was in reference to the interference patterns. It sounds like you are trying to describe this diagram I posted several months ago as a "linear Sagnac effect": Please Register or Log in to view the hidden image! Where the black lines are the worldlines of the two sides of a traditional "light clock" with the axis oriented parallel to the inertial motion and the red line is the worldline of the light pulse. -Dale
Why is frame of reference even argued in physics. Frame of reference is only as true as the frame referenced by an observer, only fooling an individual into thinking what he is experiencing is false. There is only one true truth, and that is there is only one frame of reference. A frame of reference attempts to decieve an individual in that he sees different than others. Doesn't matter. There is only one frame. One frame of time and one frame of space. No one owns either. There is only one time and one space which is observed by all. Frame of reference is the 'magic' in physics unless of course, you see that there is only one. But of course, everyone observes differently in a different time/space, we know that. It gives us self awareness to know where we are and how we play in the universe in relation to everything else. You may see different in your frame but in the total sum of frames, if you look outward to it, you will see, your frame isn't the only one and not "the" true frame.
There are problems with that perspective, some of which I mentioned earlier. The light comming from each side of an edge-on rotating galaxy would have to Doppler shift by different amounts to account for the increased rotational speed that was due to the observer's motion. It would create even more problems explaining why galaxies don't fly apart. Think of one receeding from us at near the speed of light. And you do realize astronomers and cosmologists are firm in their belief that all objects beyond the Hubble sphere are receeding from us faster than the speed of light? I think it is a mistaken belief because light itself is increasing in speed as it travels from the denser 'early condition' to the less-dense 'modern condition'. I speculate that the 'accelerating expansion' may disappear if the difference in the speed of light over time is considered. The universe may still be expanding, but not at an ever-increasing rate. Dark energy would no longer be required if my thinking is correct.
It is absolutely essential to SR, otherwise you have a violation of the first postulate. For example: you would have situations where co-located and co-moving light clocks and rotational clocks would tick at the same rate in one frame and different rates in another frame. The light coming from each side of an edge-on rotating galaxy has to be Doppler shifted by different amounts even for the classical Doppler shift. This sounds like a legitimate problem. I think it is addressed by GR, but I don't actually know. -Dale
DaleSpam, I think you failed to understand my point. Yes, light from each side is Doppler shifted, one side to the blue end of the spectrum, the other side to the red when compared to light from the center of the galaxy. Now, if the shift to the blue is not equal in magnitude to the shift to the red, something is wrong. One side of the galaxy would have to be moving faster than the other. If an observer moves toward the galaxy, the light from the center of the galaxy is shifted to the blue. The light from each side of the galaxy must shift to the blue by equal amounts due to the motion of the observer. The red shift will move towards the blue end of the spectrum, the blue shift will also move towards the blue end by an equal magnitude (getting 'bluer') and the light from the center of the galaxy will also shift to the blue by an equal magnitude. The galaxy as a whole will be 'bluer', but the rotational speed calculated by the difference in Doppler shifts at the edges will not change. The moving observer receives light from all locations on the galaxy simultaneously, all light must shift to the blue equally.
Huh? I'm not clear what you are concerned about here. Are you worried that you cannot have a rigid rotation? You can have a state of Born-rigid rotational motion with a given angular velocity, you just can't have Born-rigid angular acceleration. -Dale
No, I am not talking about rigid discs. You stated the rocket observer would see both the pulsar and the galaxy change rotational velocity. That is not possible. Rotational velocity is determined by comparing the Doppler shift of the right side vs. the left side. A moving observer would see BOTH sides blue shift by the same amount. There would be no net difference to indicate a change in rotational velocity of the galaxy. The rocket observer is located 5 billion light years from the galaxy, so we are not concerned about an observer located on the circumference a rotating disc.
Dale, most objections to my little hypothesis have been directed against accepted cosmology. About the only thing different that I hypothesized was the speed of light based on a varying permittivity & permeability of the vacuum over time. You need to read some modern General Relativity and cosmology. One of the most accepted models used today has the speed of light as being a negative velocity at some points early in its travels to us. You will see that I am really pretty conservative. Here is some excerpts and a link to a site I just found. Modern cosmology is explained in a compact format, along with problems with some basic models such as you were using. http://www.cosmologymodels.com/index2.html
Is it safe to assume that all of us have heard the old news that astronomers have determined an asymetrical blue/red shift in the CBR showing the solar system to have an absolute velocity of several hundred MPS in the direction of Leo?
The above calculation method for rotation rate of galaxies actually measures the rate in it's own frame (at least classically). The majority of the relative motion effects have been factored out by the "right side vs. left side" comparison. Overall, classical Doppler effects are negated. If we had been discussing a pulsar, instead of a galaxy, we might not have used this method of measuring the rotation rate. We might have just looked at the frequency of the wave generated by the pulsar. But that's okay, I like galaxies too! Anyway, the "right side vs. left side" comparison method remains very intriguing from a relativity perspective. I think that relativity predicts that the the galaxy still must change rotaton rate due to relative motion, despite the above worrisome concerns about symmetry of left/right. Would anyone care to offer ideas about how the "right side" might Doppler shift differently than the "left side"? I think I know but I don't want to spoil a pretty neat idea before it's been rehashed (thank you 2inquisitive)!
Neddy Bate, The pulses observed from pulsars have nothing to do with a 'frequency of the wave generated' by the pulsar. I pointed this out to you before, Neddy. The hypothetical pulsar I used rotated at 60 revolutions per second. There are 100's of pulsars that rotate much faster, some up to 1000 times per second. Explain what you mean by the frequency of the wave, please.
Wait, you're missing the most interesting part. I agree with you that galactic rotation rates are extremely interesting, especially considering the methodology of measurement. If we put the pulsars on hold for now, we can learn about the weirdness of 'the edges of rotation' of galaxies -- which I am trying to visualize relativistically.
Pulsar rotation rates are very interesting, too. They are the result of conservation of angular momentum. They are directly related to the mass of the star that collapsed to form the pulsar, its rotational rate, and the final diameter of the pulsar. You can't just change their rotational velocities willy-nilly because of relative velocity. You do realize a pulsar is just a neutron star in which the 'beam' ejected from its magnetic pole happens to sweep past our line of sight as it rotates. Again, the jet (the lighthouse-type beam) is not emitted from its rotational axis (the north/south poles), but from a magnetic axis which does not align with the rotational axis. Much like Earth's magnetic pole does not align with its rotational axis (north/south poles).
Personally I am not very interested in cosmology. I tend to look to science for prediction and not for explanation and since nobody here is in the business of building universes the need for cosomological predictions is fairly minimal. I am not going to argue for the mainstream view of cosmology because I don't even know what it is, I don't know the evidence that supports or contradicts it, and I am not interested enough in the subject to find out. Sorry. The part of your comments that I am interested in are regarding the SR understanding of rotational motion. You seem to think that the time dilation of rotational motion leads to some sort of internal inconsistency in SR. It does not. I suggest you do the math so that you can see that clearly. For example, take your pulsar scenario and put your pulsar near a comoving galaxy. In B's rest frame (a rest frame of the center of the galaxy) the left edge of the galaxy is moving away from B at .3c and the right edge is moving toward B at .3c. Determine the Doppler shifts for B, the motion in Fa, and the Doppler shifts for A. -Dale
Interesting. You seem to be stating that conservation of angular momentum is an invalid law in Special Theory.
