Classical aberration of plane waves

Discussion in 'Physics & Math' started by tsmid, Apr 8, 2017.

  1. Write4U Valued Senior Member


    It occurred to me that there may be an assumption that an energy source emits via a wave function with a defined direction, such as in the double slit experiment, which is a controlled experiment.

    But what would be the implication in a case where the energy source spreads (emits) its wave function in 3 dimensional directions?

    Is this a valid question in context of the above illustrations?

    p.s. This reminds me of an Einstein lecture on the "man in the box", where an observer is inside a box which is travelling upward at near spead of light. When the box passes a ightsource outsde the box, a small hole in the box allows a beam of light to enter the box and travel to the opposite side. While the beam of light travels in a straight line, the box moves upward during the time it takes for the light to reach the opposite side of the box, to the observer the light beam will appear to bend and hit a lower target than if the box were stationary, but even though the beam appears to have travelled a greater curved distance, it will hit the opposite side at the same time as if the box were stationaryc, creating an illusion of.gravitational pull.
    I found this a fascinating observation.
    Last edited: Apr 13, 2017
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  3. Q-reeus Valued Senior Member

    ????? Most double slit experiments are inherently 3D! Water waves are a quasi-2D exception to that. The projected-onto-2D-screen interference fringes typically seen testify to a 3D spreading. They always have a height - thus 'spread in 3D' between slits and screen. One interesting property of surface i.e. 2D waves not shared by either 1D or 3D transmission is that there is always some continual reflection back to any point source. Thus partial standing waves are an inherent feature. Note the OP scenario is effectively 1D transmission and reflection/standing wave situation does not apply there.
    There is some confusion there. The light beam suffers aberration which is not a bending but a straight line propagation at an oblique angle - as discussed earlier in this thread. Perhaps you are confusing that with an accelerated box i.e. 'Einstein's elevator' which thought experiment was the genesis of equivalence principle.
    Last edited: Apr 13, 2017
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  5. Write4U Valued Senior Member

    Ah, yes, I had forgotten the "acceleration". Nevertheless, to my lay teenage mind it was a small revelation and helped me understand relativity better./.
    Thank you for responding.
    Q-reeus likes this.
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  7. tsmid Registered Senior Member

    Well, the 'tube' is actually not physically required here. You could just have a phase sensitive detector surface that will detect the orientation of the wave front. The point is that the lateral shear of the wave front due to the flow of the medium will not make any difference to what the detector sees: the wavefronts are still parallel to it and their frequency is still the same.

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    Even with an instrument like a telescope the tube is actually not required. You could just have the front lens fixed in place by some other means. What you see at the eyepiece of the telescope only depends on the light falling onto the front lens, and that isn't affected by the tube. And crucially, what is falling onto the front lens does not depend on v here.

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