Education and Crank Claims: Special Relativity

Discussion in 'Physics & Math' started by rpenner, Oct 5, 2011.

  1. OnlyMe Valued Senior Member

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    While it is true that to some extent light and sound were seen to be similar in how they propagate, that comparison was already coming into question prior to Einstein's 1905 paper. Sound could be experimentally shown to be velocity dependent on both the speed of the source and observer. Experimental observations and conclusions including the work of Fizeau did not show the same to be true of light.

    Einstein changed the analogy that sound and light were similar. Special Relativity presents a theoretical perspective that does not require the light medium, the aether to explain experience. (Without explicitly excluding the existence of the ether.)

    Yes, the constancy of the speed of light in vacuum was and is a fundamental requirement of much of the mathematics. At least within the context of SR and a flat space-time.
     
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  3. DonQuixote Registered Senior Member

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    Yes, I'm aware of that. I just wondered if specifically the independence of the motion of the light emitting source is fundamental. A light emitting source may emit a signal somewhere. Where it goes after that seems to be completely irrelevant...

    How is light speed meassured anyway? I should think that a light signal can be emitted at a point, and the signal concidered point-like, although it is actually a burst of light.

    Meassuring the speed of light (or anything) at a point is of course not possible. you need two points, a known distance between the two points, and a clock that is sync'ed between the two.
     
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  5. Tach Banned Banned

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    Because, if you read his paper, you will find out that he uses the second postulate in the derivation of the first equation of his paper. In turn, that leads him to the derivation of the Lorentz transforms.
     
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  7. DonQuixote Registered Senior Member

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    Thank you. Again, a good answer. Problem is, Il have to learn math now.
     
  8. OnlyMe Valued Senior Member

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    Within the context of laboratory experiment, the relative velocity of the source is does not affect the measured velocity, in vacuum. I am pretty sure even Fizeau demonstrated this. He did demonstrate that within a transparent medium where the speed of light is less than in vacuum (like a liquid), the velocity of both the source and the medium do affect the velocity of light. Never such that it's velocity is greater than "c.

    There are a number of ways that the speed of light is measured, in the laboratory. (I keep mentioning "in the laboratory" because the astronomical methods for measuring the speed of light are subject to significant margins of error or are theirselves dependent upon assumptions about the propagation of light.)

    Tach gave this link earlier (pointing to a specific section) and though at times it may be too technical it does provide some information that should not require the extra math.

    http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html
     
  9. Trooper Secular Sanity Valued Senior Member

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    Even if you do not understand the math, you should watch this video all the way through, and then look at RP’s post again. Professor Ramamurti Shankar gives enough commentary to make the equations comprehensible.

    Lorentz transformation


    RPenner’s Post
     
  10. Emil Valued Senior Member

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    The mathematics is correct.
     
  11. DonQuixote Registered Senior Member

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    Anyway, I am satisfied that both postulates are necessary for the theory. I won't be pursuing this particular line anymore. Get ready for more questions.
     
  12. Motor Daddy Valued Senior Member

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    All observers must acknowledge that light moves away from the point in space it was emitted at c. Just because a source emits light at a point doesn't mean the source will be at that point (center of the light sphere) some time later. The speed of light is independent of the source. Do you not understand what that means?
     
  13. wlminex Banned Banned

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    . . . . relativity of SOL . . . is kind of like discussions of "rainbows" on another Sciforums thread . . . kind of 'holographic'?
     
    Last edited: Oct 5, 2011
  14. CptBork Valued Senior Member

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    You know what's so badly missing from all these discussions on the Lorentz transformations? The web is flooded with Einstein's simple derivation in which the speed of light is the same in all inertial frames, and all inertial frames are equivalent. What's sorely missing, IMO, is the original derivation due to Lorentz & co. in which the goal is to find a set of linear transformations which preserve the form of Maxwell's equations in all reference frames.

    Granted, \(c\) being constant is a consequence of Maxwell's equations anyhow, but I find the derivation illuminating because it explicitly shows that Relativity is needed to preserve Maxwell's equations. Argue with Relativity and you're really arguing with Maxwell himself, unless you think Earth and any moving lab frames thereupon form magically special reference frames. I'm sure the derivation can be found in many books on advanced classical mechanics, probably Jackson Electrodynamics as well. I'll try to look into it and maybe post the original derivation if I find the spare time (if anyone knows a web link with the original derivation, that would be even better).
     
  15. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

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    This is a great idea of rpenner's, but is there some way of marking the crank claims and distinguishing them from the real science that is being outlined here?
    Those who don't know (and for whom it is therefore most useful) may have a hard time discerning the, er, validity, of posts from the likes of Motor Daddy.
    Any chance of hyper-strict moderation?
     
  16. CptBork Valued Senior Member

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    I think the lack of substance in MD's posts is self-evident, but yes at this point he's just throwing a temper tantrum without addressing any of the actual math arguments, so I too would like to see the mods step in and address it.
     
  17. DonQuixote Registered Senior Member

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    I had this paranoid thought: Maybe this thread is simply a ruse for attracting us cranks at one place? Then all you orthodox thinkers can have the other threads for yourselves? But then I thought: No. that's insane.

    Please Register or Log in to view the hidden image!

     
  18. AlphaNumeric Fully ionized Registered Senior Member

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    Different frames will say different points are at the centre of the light sphere. They will all say the light is expanding in a sphere at the speed of light but when you ask them to point to the centre of the sphere they will disagree.

    This is not a contradiction. This is something Jack_ whined about in multiple threads and was talked through again and again, pictures, equations, explanations and all that. Search for his threads and you'll find the explanations of why it isn't a problem.

    You seriously need to learn some relativity, rather than just whining it doesn't agree with your preconceptions.
     
  19. Emil Valued Senior Member

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    The camp crank increases and it will be increasingly higher.
    Think of CERN.
     
  20. AlexG Like nailing Jello to a tree Valued Senior Member

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    MD will never learn any relativity because he denies it's validity in the first place. He inhabits a universe of his own, where there is an absolute frame of reference, and nothing is relative.
     
  21. Motor Daddy Valued Senior Member

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    Lack of substance? The basis of all measures of light are:

    1. Light is emitted at a point in space at t=0.
    2. The source is at the point in space that light is emitted at t=0.
    3. Light travels away from the point at c.
    4. The source can travel away from the point, or it can stay at the point.
    5. If the source travels away from the point, the source has an absolute velocity relative to the point.
    6. If the source remains at the point, the source has an absolute zero velocity.
    7. ONLY if the source has an absolute zero velocity will the light be ct from the source a duration of time after emitting the light.
    8. If the source has an absolute velocity (not at the point after emitting light), the light will not be ct from the source a duration of time after emitting the light.
    9. In the source frame, light can only be MEASURED as c if the source has an absolute zero velocity.
    10 Einstein's second postulate is wrong because the only way light can be measured to be c is IF the source has an absolute zero velocity. If the source has an absolute velocity greater than zero, it is IMPOSSIBLE for light to be measured in that frame at c, in any direction. As a matter of fact, if the source frame has a velocity greater than zero, light will be measured at a different speed, depending on the direction you measure it.
     
    Last edited: Oct 5, 2011
  22. AlexG Like nailing Jello to a tree Valued Senior Member

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    When rpenner put the words 'Crank Claims: Special Relativity' in the title, he practically invited Motor Daddy to show up.
     
  23. Motor Daddy Valued Senior Member

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    The words "crank" and "SR" go hand and hand. That's because SR was authored by the super crank himself, Einstein.
     

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