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I must remind everyone here that i am no scientist or not even a student. i only found this matter interesting all of my life but always got put off by loads of 'shop talk'i cannot grasp.Tnx for your attempt.
It's simple really. The moment a photon leaves its source it starts traveling at lightspeed and because relative to this lightspeed this source is a point of origin that sits still and is actually static because the emmited photons speed is already the maximum and constant. there's is no acceleration. light emmision is instant. and there lies the clue.i think.
Only complication is that Doppler shift does apply to moving sources. Although the light has the constant speed once emitted, with a moving source the light waves are squished in the direction of motion, so the wavelength shortens, the frequency increases and the colour becomes bluer. Opposite if the source moves away from a receiver.
Quote from: Colin2B on 20/03/2016 13:19:23Only complication is that Doppler shift does apply to moving sources. Although the light has the constant speed once emitted, with a moving source the light waves are squished in the direction of motion, so the wavelength shortens, the frequency increases and the colour becomes bluer. Opposite if the source moves away from a receiver.However... The Pound Rebka experiment shows that a blueshift, and a redshift of lights wavelength occurs when the emitter, and the receiver of the light source are both held """static""" relative to each other!!!
Well yes - of course Colin!And isn't it interesting that a representation of Doppler shift can perhaps be found in the redshift, blueshift phenomenon between a light source emitter and receiver that are indeed held static relative to each other?
Quote from: timey on 20/03/2016 15:21:03Well yes - of course Colin!And isn't it interesting that a representation of Doppler shift can perhaps be found in the redshift, blueshift phenomenon between a light source emitter and receiver that are indeed held static relative to each other?Doppler shift doesn't occur when source/reception are static. That's not what the experiment showed, nor was it the intention. They were verifying Einstein / gravity shift. They used relative doppler motion/shift to cancel the effect of gravity shift.
Firstly, what an experiments intention is has no bearing on the use of its results.
You are forgetting that the Pound Rebka was initiated with a view to measuring gravitational shift with respect to time dilation considerations. The gravitational field itself experiences time dilation. It's not just a case of SR time dilation with regards to moving objects... you know!
Time will never run at full speed and neither will it completely stop as both states are absolutes that can never be reached.
What happens for the free falling observer Jeff? I assume time runs at 100%. As she falls (pushed off the tower by those who disagree with her theory) she looks up and sees the source receding- red shifted, looking down she realises the detector is moving up against the light waves - blue shifted. Her view is that there is no gravity, just acceleration and all effects at top and bottom of tower are due to doppler shift.
How can lights frequency be cancelled out by a Doppler shift between a light source emitter and a light source receiver that are both held static of motion relative to each other - and consist of a 'constant' distance apart?
Doppler shift and gravitational shift are not the same phenomenon but have the same effect on wavelength, so you can use one to measure the other
Yet - a Doppler shift cancelled the blueshift redshift frequencies between the 2 'static in motion' and 'constant in distance' locations... How did it do this?
.There was no relative speed between the top of tower and bottom of tower in either instance.
By vibrating the speaker cone the gamma ray source moved with varying speed, thus creating varying Doppler shifts. When the Doppler shift canceled out the gravitational blueshift, the receiving sample absorbed gamma rays and the number of gamma rays detected by the scintillation counter dropped accordingly. The variation in absorption could be correlated with the phase of the speaker vibration, hence with the speed of the emitting sample and therefore the Doppler shift.
I look forward to a proper physicists comments...
the gamma ray source moved
Colin - they created a Doppler shift by vibrating the speaker at frequencies between 10 and 50 hertz to cancel out the redshift blueshift frequencies. The distance between the speaker and the receiver remained at 22.5 metres.
Quote from: timey on 21/03/2016 23:49:57Colin - they created a Doppler shift by vibrating the speaker at frequencies between 10 and 50 hertz to cancel out the redshift blueshift frequencies. The distance between the speaker and the receiver remained at 22.5 metres. Either the speaker was vibrating, in which case the distance between source and detector was varying, or it wasn't vibrating and the distance was constant.Is that enough "proper physics"?
Is that enough "proper physics"?
I fear you are incorrect. You misunderstand what others comprehend, then argue a misguided point. That does not make for "proper" comment of physics or anything in general. Your posts are intentionally rude and ignorantly inappropriate.
Consider, as an analogy for a photon, a boat traveling on the water. The boat is analogous to the particle, while the wake created by the boat is analogous to the wave aspect of the photon. If we had two tunnels under the bridge, the boat; particle, can only go through one tunnel at a time, while the wake, if spread out, can go through both tunnels. The boat needs a constant supply of energy to keep moving at velocity V. This energy is needed to overcome friction between the boat and water. If the boat cuts the engines, the particle will slow, coast and then stop, while the wake will decay and finally stop. The speed of light is needed to maintain the wake/wave of the photon particles. The question becomes how does a photon move through the medium of space-time and not slow down or speed up? What is the source of the propulsion energy? If we assume the speed of light is the ground state of the universe, this implies all inertial references will be at higher potential. In this case, the constant speed of light would be connected to photons being constantly induced into the ground state ay C. The photons are constantly induced to higher potential; less than C by inertial. They cyclically drop back to the ground state; speed of light, while the energy differential is given off; motor that generates the wake/wave. One analogous way to look at this is connected to a house with a variety of electrical circuits, all using the same ground; earth. The ground is common to all the circuits and is at lower potential than any voltage/current configuration we may use. The potential difference between the inertial states, and the ground, is the energy potential used to drive the particle, which creates an analogous wake in space-time. This wake can become modified with the medium of space-time; red and blue shift, but the ground never changes, so the particles are always moving at C.
I learned that light travels at the same given speed no matter if a light source is static in a fixed place or the source is moving towards you in that same space.What is it that decelarates a photon that is emitted from an object moving toward you with say half the speed of light to come back to exactly the fixed speed of light.
That's called the invariance of the speed of light. It's the second postulate of special relativity. It's referred to as a postulate because nobody knows why the speed of light is independent of the speed of source.However you can think of the reason as due to the properties of spacetime. When you change from one frame of reference, e.g. the frame in which the source is at rest, to one in which the source is moving then you're changing to a frame where, as determined from the rest frame, distances parallel to the motion of the source are shorter and where time intervals are shorter, both in exact proportions so that the speed of light has the same speed in all inertial frames.
Now could you please tell me how, within the Pound Rebka experiment, a Doppler shift can be identified within the gravitational shift of light when there is no relative motion between the light source and the receiver other than the oscillations of the speaker cone... these oscillations of the speaker cone being the method of measuring the fact of the Doppler shift within the gravitational shift of light via cancellation of redshift blueshift frequencies...
The Pound Rebka experiment used MOTION produced by a speaker cone. The gamma ray light source was mounted on a MOVING speaker cone, which induced doppler shift.The argument that doppler shift occurred without motion is flawed. There was movement. It didn't require a lot of movement. Since the distance was in nearly constant flux. They recorded the phase of the speaker movement to account for doppler shift.--Now for my timely wizenhimer remark: DOH