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OK, he's using water here.There is still no Doppler effect in that picture. Both output beams shine with the same frequency as it would if the source was observed directly without the intervening apparatus. All it does is a phase shift on both sides.
The Doppler effect (or the Doppler shift) is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who described the phenomenon in 1842.
From the diagram, at the right end of water column, water velocity at light direction is 0, hence the Doppler effect is canceled at that points, and the light frequency and wavelength of the top light becomes the same as the bottom light as they come out of water before observed. But the Doppler effect has occured along the top and bottom horizontal columns by changing propagation speed, frequency, and wavelength, which generate changes in interference pattern at the detector. Hence the changes of each individual parameters can't be directly measured, but either frequency or wavelength must have been changed, thus Doppler effect must have happened.
Quote from: wikiThe Doppler effect (or the Doppler shift) is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who described the phenomenon in 1842.https://en.wikipedia.org/wiki/Doppler_effectFrom the definition above, Doppler effect can happen if wavelength changes even if the frequency stays the same, which means that the propagation speed also changes accordingly.
Quote from: hamdani yusuf on 15/10/2019 04:54:03Quote from: wikiThe Doppler effect (or the Doppler shift) is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who described the phenomenon in 1842.https://en.wikipedia.org/wiki/Doppler_effectFrom the definition above, Doppler effect can happen if wavelength changes even if the frequency stays the same, which means that the propagation speed also changes accordingly.I agree that the definition above says that, but it is wikipedia, and I think they mean frequency change and associated wavelength change and not the case of wavelength change associated only with refraction and not frequency change. I'm saying wiki is wrong here.From oxford dictionary (top of list if you google "what is doppler effect"):"[physics:] an increase (or decrease) in the frequency of sound, light, or other waves as the source and observer move toward (or away from) each other. The effect causes the sudden change in pitch noticeable in a passing siren, as well as the redshift seen by astronomers."Britanica: "Doppler effect, the apparent difference between the frequency at which sound or light waves leave a source and that at which they reach an observer, caused by relative motion of the observer and the wave source."webster:"a change in the frequency with which waves (as of sound or light) from a given source reach an observer when the source and the observer are in motion with respect to each other so that the frequency increases or decreases according to the speed at which the distance is decreasing or increasing"http://physics.bu.edu/~duffy/py105/Doppler.html"The Doppler effect describes the shift in the frequency of a wave sound when the wave source and/or the receiver is moving."Pretty much every place except wiki says it's a frequency shift and does not consider a wavelength change without frequency change to be an example of Doppler effect.
You are correct. In order to get frequency change, we have to change the number of waves in transit between source and observer, such as when distance between source and observer changes. This can also be done by accelerating medium.
Quote from: hamdani yusuf on 18/10/2019 04:18:22It makes me wonder if both source and observer accelerate uniformly. Does the light received by observer have the same frequency as the light emitted by the source? How much is the difference?The proper distance between them changes if one is in front of the other, but not side-by-side. So no redshift in the latter case.In the former case, the lead ship will outdistance the trailing one in the frame of either ship, so there will be a small Doppler effect as the proper distance between them grows.If, on the other hand, the two observers are in the same ship but opposite ends, the proper distance between the two would be fixed and the acceleration of each would not be the same and the one in front would see a red-shifted light from the rear and a blue shift looking the other way. This is a pure relativistic effect and not Doppler.
It makes me wonder if both source and observer accelerate uniformly. Does the light received by observer have the same frequency as the light emitted by the source? How much is the difference?
In the video at 18:00 timeline, you mentioned about group velocity. What if the light beam is continuous with constant amplitude? How do you define and measure its group velocity?
Quote from: Hal on 23/12/2020 09:09:07Suppose that an observer O is co-moving with absolute velocity V with a laser light source S, with O in front of S. The distance between S and O is D. Assume that the laser is switched ON at t = 0, and that O detects the leading edge of the continuous light at t = t1. The group velocity will be, Vg = D / t1 . It will take longer time for the leading edge to catch up with O than if the absolute velocity (V) was zero.That it will, but how is t1 measured? You seem to have two moving clocks separated by (presumably) proper distance D and have not given a convention to sync them, so they might read anything at all, giving some random value for 'group velocity'. You propose absolute velocity, so you must provide a method for absolute clock synchronization, else your argument is begging its own conclusion. Or you could think of a different experiment that doesn't presume the answer before taking the measurement.Relative (not absolute) sync can be accomplished by putting them in the same location (midpoint) and then starting (zeroing) them both with the same signal. Then carry them equal proper distance to opposite ends (separated by D) and then doing the measurement. This should also work according to the seemingly Newtonian physics you seem to suggest. But they will then measure the same duration for light to travel in either direction, regardless of absolute velocity of the setup, which contradicts said Newtonian physics. Your posts seem to predict that they will measure different times (from A to B, vs. B to A) depending on orientation of A and B relative to their absolute velocity, which would falsifies your proposal here.I'm just responding to posts. No, I've not bothered with watching the video, which just claims to be a simulation, not a real experiment. A simulation cannot disprove any theory. Only an empirical test which measures different results than that predicted by the theory can serve to falsify it.
Suppose that an observer O is co-moving with absolute velocity V with a laser light source S, with O in front of S. The distance between S and O is D. Assume that the laser is switched ON at t = 0, and that O detects the leading edge of the continuous light at t = t1. The group velocity will be, Vg = D / t1 . It will take longer time for the leading edge to catch up with O than if the absolute velocity (V) was zero.
Clock rates may change with absolute velocity.
For example, you take two identical clocks and synchronize them while they are at the same location A and both are at absolute rest.
Measuring absolute rest ( and absolute velocity ) can be done in several ways, for example by the Silvertooth experiment and other methods that do not require any clock synchronization.
In the case of the thought experiment of co-moving observer O and laser source S, two clocks, one at S and the other at O are used. Suppose that the whole experimental setup is at absolute rest at first. The clocks are first synchronized when they are at the same location, say both are at the location of the laser source S. Then the other clock is transported to O. Since each clock has an absolute velocity measuring device onboard, the moving clock will automatically correct/adjust its time so that the clocks will always be in sync.
So the moving clock will not be out of sync during transportation from S to O.Then imagine that the whole experimental setup starts moving with absolute velocity Vabs. The two clocks will always be in sync regardless of their absolute velocities because of automatic correction.
Quote from: Hal on 24/12/2020 09:57:26Clock rates may change with absolute velocity.Says the person in denial of relativity. So how do you know this?QuoteFor example, you take two identical clocks and synchronize them while they are at the same location A and both are at absolute rest.Except you have no way of knowing that they’re at absolute rest, so they’re simply given a completely arbitrary velocity and that velocity is defined to be the absolute rest velocity. That doesn’t make it absolutely at rest, it only makes it an arbitrary choice.QuoteMeasuring absolute rest ( and absolute velocity ) can be done in several ways, for example by the Silvertooth experiment and other methods that do not require any clock synchronization. No such device exists, and no experiment has ever defined a consistent rest frame in absence of selecting for a choice ahead of time. If it worked, it would work in a double blind test in properly controlled conditions, which of course was never done since it fails.I notice the guy measured almost exactly the peculiar velocity of the solar system despite Earth (his lab in particular) never being stationary relative to that frame, which means he already chose and answer and biased his finding to it. He’d do great in the Trump administration where they do science that way: working backwards from the result they’re expected to find.QuoteIn the case of the thought experiment of co-moving observer O and laser source S, two clocks, one at S and the other at O are used. Suppose that the whole experimental setup is at absolute rest at first. The clocks are first synchronized when they are at the same location, say both are at the location of the laser source S. Then the other clock is transported to O. Since each clock has an absolute velocity measuring device onboard, the moving clock will automatically correct/adjust its time so that the clocks will always be in sync.No such device exists, but assuming the absence of any gravitational field gradient, what you describe can be done with an inertial guidance system, and without the necessity of the tables you describe above. The devices are in use on Earth because they assume and adjust for a non-inertial reference frame implied by Earth's gravitational field. They're quite accurate over short periods of time.QuoteSo the moving clock will not be out of sync during transportation from S to O.Then imagine that the whole experimental setup starts moving with absolute velocity Vabs. The two clocks will always be in sync regardless of their absolute velocities because of automatic correction.OK, then what? No actual experiment with some finding is performed. SR isn’t invalidated since you’ve not actually done anything except declare two clocks to be in sync relative to the original arbitrary frame selected.
4. Silvertooth was a pioneer in the field and I don't think he is capable of doing such outright scientific fraud.
Quote from: Hal on 26/12/2020 08:50:44So your question about clock synchronization comes down to a question about the existence ( or non- existence) of absolute motion.No, not at all. I was wondering what your point was, but reading more carefully, you seem to be attempting to make an absolute clock.Suppose Bob has such a magical device that detects absolute motion which does so instantly (not over weeks), and to at least 16 digits of precision needed to be used as a navigation device. Bob thus makes himself stationary, and sends this second clock way out by say Pluto. The clocks will not be in sync by your method, and if they are synced by a better convention, they will not stay in sync since the distant one runs faster. They are both kept absolutely stationary because both have this magical device.So one of my points is, since the clocks don't stay in sync, which (if either) is correct? Probably not Bob's clock since dilation always slows a clock, never speeds it up. So how does Bob's clock adjust for this absolute dilation of its measurement? You seem to be attempting to define an absolute time device using the magical absolute motion device, but it doesn't work.
So your question about clock synchronization comes down to a question about the existence ( or non- existence) of absolute motion.
Quote from: Halc on 26/12/2020 16:29:16Quote from: Hal on 26/12/2020 08:50:44So your question about clock synchronization comes down to a question about the existence ( or non- existence) of absolute motion.No, not at all. I was wondering what your point was, but reading more carefully, you seem to be attempting to make an absolute clock.Suppose Bob has such a magical device that detects absolute motion which does so instantly (not over weeks), and to at least 16 digits of precision needed to be used as a navigation device. Bob thus makes himself stationary, and sends this second clock way out by say Pluto. The clocks will not be in sync by your method, and if they are synced by a better convention, they will not stay in sync since the distant one runs faster. They are both kept absolutely stationary because both have this magical device.So one of my points is, since the clocks don't stay in sync, which (if either) is correct? Probably not Bob's clock since dilation always slows a clock, never speeds it up. So how does Bob's clock adjust for this absolute dilation of its measurement? You seem to be attempting to define an absolute time device using the magical absolute motion device, but it doesn't work.If I have understood your argument, Bob has an absolute velocity measuring device and two clocks A and B. Each clock also has an absolute velocity measuring device integral with it. Each clock uses a clock rate correction table to continuously, automatically correct it's time depending on absolute velocity. The table gives the correction needed ( nanoseconds per second) for each absolute velocity. Clocks at rest do not need any correction.At first Bob comes to absolute rest and synchronized the two clocks. Then he sends clock B towards Pluto. Clock B will then be in absolute motion and then come to rest on Pluto.Because of the continuous, automatic correction, clock B will always be in synch with clock A, both when it is in motion and after coming to rest.
At first Bob comes to absolute rest and synchronized the two clocks. Then he sends clock B towards Pluto. Clock B will then be in absolute motion and then come to rest on Pluto.
Because of the continuous, automatic correction, clock B will always be in synch with clock A, both when it is in motion and after coming to rest.
Let me clarify what I actually mean by : ' Clocks at rest do not need any correction'Suppose that it takes 1 day = 24 x 3600 seconds for clock B to reach Pluto. Assume that clock B travels with such constant absolute velocity that it needs a correction of + 10 ns/s. Therefore, once clock B comes to rest and remains at rest on Pluto, the difference between the times of clock A and the UNCORRECTED time of clock B will remain constant: 10ns/s x 24x3600 s = 864 micro seconds.But as soon as clock B starts moving again this difference will start to change.( the assumption of a clock being at rest on a moving planet is not good, but let us ignore it)
This implies that if we want to make an absolute clock we need 1. an accurate clock2. that always remains at rest once its time is set.For this, an absolute motion detecting device must be integral with the absolute clock, so that any possible small motions of the clock will be detected, so that the clock is brought to rest automatically.That is, an absolute clock is one that has no history of motion once it's time is set while at absolute rest.
Relative motion and the Doppler shift can also be explained with changes in entropy.
What is absolute motion? Velocity = (x-x0)/Δt. Where is x0?