# Time Dilation and Relativistic Doppler

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When we are stationary relative to each other, I see a (very) distant beacon flashing once per second.

Is it correct please that if I move towards this source at high speed (say 1/2c) I perceive the flashes to be faster ; and that this a consequence of both TD and RD ?

Conversely, moving away the beacon appears to slow down ?

I would like then to envisage a scenario (gedankexperiment) where TD only comes into play - if this is possible ?

Thank you

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It is the Doppler effect.

As a side note there is only one imaginary time at the moment which is the day and while a mechanical clock may make mistakes in measuring time the day stays the same. Therefore a satellite in geostationary orbit completes one orbit of the earth in a day.

Now if I am in a satellite looking at the earth rotate while moving away from the earth the earth will appear to rotate slower because of the Doppler effect.

Edited by fiveworlds
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" Now for light,traveling in a vacuum which does not require a medium and adjusting for Relativity, we use

where v/c is the relative speed of source and receiver measured as a fraction of the speed of light and is positive when they are approaching each other.

With this formula, it doesn't matter which(source or receiver), is considered to be moving."

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Interesting repies - thank you. But none offer what I ask for viz. a minimal scenario where Time Dilation operates, but Doppler does not.

As I suggested, it may be impossible to have such a situation.

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You may need to reverse engineer this to infer a scenario. The experiment requires only time dilation in space-time, To do this we need to add extra time to space-time, which implies an acceleration d/t/t. As we accelerate in space-time, we have velocity d/t incrementally increasing; space-time changes, as a function of time.

Edited by puppypower
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You may need to reverse engineer this to infer a scenario. The experiment requires only time dilation in space-time, To do this we need to add extra time to space-time, which implies an acceleration d/t/t. As we accelerate in space-time, we have velocity d/t incrementally increasing; space-time changes, as a function of time.

Neither time dilation nor Doppler shift require acceleration. They are functions of relative speed.

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Interesting repies - thank you. But none offer what I ask for viz. a minimal scenario where Time Dilation operates, but Doppler does not.

As I suggested, it may be impossible to have such a situation.

Doppler depends on the changing distance between the observer and beacon. So if you and the beacon pass each other at some distance, then the light that leaves the beacon at the moment of closest approach will be seen as you shifted by exactly an amount equal to time dilation.

Or you can have the situation where the beacon is circling you at a constant distance, and again you will see the beacon blink at the time dilation rate for its speed.

Edited by Janus
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I found this post #8 of Janus58 explaining it very well:

Special relativity is about Relativity of Simultaneity which results in time dilation and length contraction.

Visual Doppler effect is about an optical effect. SR is not.

Relativistic doppler effect takes care of the time dilation and length contraction of SR.

Edited by VandD

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