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Relativity, speed of light and stuff... 
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#73
Aug3108, 02:11 PM

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now, inversesquare laws regarding radiant intensity (E&M or acoustic) do necessarily follow from a combination hypotheses of conservation of energy and 3dim space (both reasonable). the radiant energy (or power) comprises a natural form of "flux", which is conserved. BTW, it is because of this concept of flux in inversesquare laws that make me wish that Planck units had originally normalized [itex]4 \pi G[/itex] and [itex]\epsilon_0[/itex] rather than normalizing [itex]G[/itex] and [itex]4 \pi \epsilon_0[/itex] as was done. i believe these rationalized Planck units are a little more natural (yielding simpler field equations) than the existing definitions. with any extraneous constants removed from the field equations, i think that might lead to insight to what might be behind such. we know that Nature isn't really performing a multiplication in her head to convert a particle wave frequency to its energy. that multiplication is necessary only because of the anthropocentric units we arbitrarily chose to use. and Nature doesn't give a rat's as$ what units humans (or some alien race) chose to use. i think that Einstein first, from pure thought experiments with just a few really reasonable postulates (like the laws of physics are invariant for every inertial observer and that a freefalling observer cannot differentiate his or her state from being inertial  the equivalence principle), came up with SR, and with a little mathematical help from folks like Mercel Grossman, the GR. there is no evidence that Einstein ever drew on or referred to the MichaelsonMorley experiment and the null result, and i am convinced that it made little difference to him ("as if God had any choice in the matter"). assuming he knew of the experiment and result, Einstein was likely utterly not surprized. it's amazing what you can cook up from a very few extremely reasonable postulates, thought experiments, and math (all from pure thought). that is, if your brain is the size of a small planet and you have truly historical levels of insight. such persons are rare in history. 


#74
Aug3108, 02:43 PM

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#75
Aug3108, 03:24 PM

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thanks for the reference to the original 1905 paper. i stand corrected about that. he clearly indicates he knew of the MM experiment and result (but he should have cited it).



#76
Aug3108, 03:48 PM

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edit: also, note that the quote is listed in the "misattributed" section of this page. On the other hand, this page claims that he said it to his assistant, Ernst Straus, but doesn't give a reference. 


#77
Aug3108, 04:47 PM

P: 2,258

if light is thought of as a KIND OF sound wave in the aether then I believe it follows naturally that electric fields must follow an inverse square law. there is no difference between the electric field in a light wave and the electric field from an electron.



#78
Aug3108, 06:24 PM

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A wave which propagates through a medium has a propagation velocity that depends on the medium and is relative to that medium. If, by some coincidence, the propagation velocity of a wave in some medium were equal to the invariant speed then all observers would measure the propagation velocity to be the invariant speed regardless of what they measure the velocity of the medium to be.
However, a wave that does require a medium must propagate at the invariant speed. Since light does not require a medium it propagates at the invariant speed, which is how we originally discovered the invariant speed and its implications for the geometry of spacetime. Since the aether is otherwise undetectable, and since it would be an enormous coincidence if the propagation of light through the aether were equal to the invariant speed, and since the speed of light is more simply explained by assuming it does not require a medium, what is the value of the concept of aether? 


#79
Aug3108, 06:28 PM

P: 2,258

your second paragraph is unclear.
it might be an enormous coincidence or it might indicate the existence of an underlying symmetry that we havent been smart enough to figure out yet. why should light alone of all known waves not require a medium? it is much simpler to just take its wave nature as evidence of the existence of such a medium. in any event, relativity doesnt entirely eliminate the aether. it just renames it 'space'. according to relativity even empty space has properties. 


#80
Aug3108, 06:33 PM

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If a wave does not propagate in a medium then what other speed could it possibly propagate at besides the invariant speed?



#81
Aug3108, 06:37 PM

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zero



#82
Aug3108, 06:40 PM

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Then it wouldn't be a wave



#83
Aug3108, 06:44 PM

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exactly



#84
Aug3108, 06:45 PM

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#85
Aug3108, 06:55 PM

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#86
Aug3108, 06:57 PM

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granpa, you are not making any sense



#87
Aug3108, 07:10 PM

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it does not follow that a wave without a medium would travel at c. it follows that a wave without a medium would not travel at all and if it did it wouldnt be a wave.



#88
Aug3108, 07:29 PM

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granpa, first, even a propagation velocity of 0 wouldn't work, because 0 in one frame is nonzero in another frame. Second, what you are really saying is that it is not possible for any wave to propagate without a medium, do you have any logical reason to think that?
None of the four fundamental forces have a medium in which they propagate. 


#89
Aug3108, 07:34 PM

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none of the forces have a medium? what do you think the aether is?
do you have any reason to think that a wave can propagate without a medium? I've never seen one do so. 


#90
Aug3108, 07:48 PM

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Yes, I have a reason to think that a wave can propagate without a medium, and if you have never seen one do so then you must be blind.
[tex]\nabla \cdot \mathbf{E} = 0[/tex] [tex]\nabla \cdot \mathbf{B} = 0[/tex] [tex]\nabla \times \mathbf{E} =  \frac{\partial\mathbf{B}} {\partial t}[/tex] [tex]\nabla \times \mathbf{B} = \mu_0\varepsilon_0 \ \ \frac{\partial \mathbf{E}} {\partial t}[/tex] So according to you, all four fundamental forces require a medium in which to propagate, they all share the same medium, it is completely undetectable, it just happens that all four forces have the same propagation speed in this medium, and that propagation speed also happens to be the invariant speed. Have you even one piece of evidence to support this rather long list of coincidences? 


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