On Einstein's explanation of the invariance of c

Discussion in 'Pseudoscience Archive' started by RJBeery, Dec 8, 2010.

  1. RJBeery Natural Philosopher Valued Senior Member

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    Equivalency doesn't demand that my inertial frame is "the" rest frame of my calculations, it simply allows for it. I can also consider myself to be moving without breaking physics. My point, though, is that I cannot consider myself to be moving relative to the beams of light without breaking SR.
    Yes, the space capsule dude, the train's passenger, and the embankment observer would all agree that the lights flashed simultaneously for the embankment observer. That is a lot different than saying they absolutely flashed simultaneously, period. In fact there are few things that could be more wrong when discussing relativity.
     
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  3. Motor Daddy Valued Senior Member

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    They flashed simultaneously for every observer in the universe, and every observer in the universe will agree. That is not to say the lights will impact each observer in the universe simultaneously, they won't, unless they are equal distance from both sources at time of emission, and they have an absolute zero velocity. When those conditions are met the lights will impact the observer simultaneously, because they were emitted simultaneously.

    Equal distance from emission points and an absolute zero velocity must be met in order to understand simultaneity.
     
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  5. Pete It's not rocket surgery Registered Senior Member

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    Yes, this is true.
    You've lost me somewhere. I think I'll have to read back through the thread to find out what you mean, and why.

    And good luck talking sense into MD. He has strong faith in the One True Rest Frame, no matter that no one can find it, and no matter that we happily use different reference frames all the time without even thinking about it.
     
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  7. Motor Daddy Valued Senior Member

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    Einstein found it, it is the frame of the embankment observer. He didn't realize it, but it's a fact, the embankment observer has a true zero velocity.
     
  8. AlexG Like nailing Jello to a tree Valued Senior Member

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    Compared to what?

    The embankment observer is whipping around in orbit and is rotating with the earth at 1100 mph. So how can you claim he has a zero velocity?

    on edit: Never mind. We've been over this numerous time, and there's no reason to suspect you'd understand it this time either.
     
  9. Motor Daddy Valued Senior Member

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    So are you saying Einstein's embankment observer has a velocity of 1100 MPH?

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    That's what I thought. You know better. lol
     
  10. AlexG Like nailing Jello to a tree Valued Senior Member

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    Do you deny the earth is rotating? Do you deny that the earth is in an orbit around the sun?

    I'm saying, and so is Einstein, that ALL motion is relative. There is no absolute frame of reference.

    Yes, there is no arguing with willfull ignorance.
     
  11. Motor Daddy Valued Senior Member

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    So let's just say you're right and give the embankment an 1100 MPH velocity. How's that working for ya?

    If the embankment were to have had a velocity, the lights couldn't have impacted the observer simultaneously. Ain't no way, Jose!
     
  12. Lady Historica Banned Banned

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    No the observer has a velocity of 1100mph East, as would your northbound train, as would the simultaneous light flashes veiwed by the central observer on the train. The speed of the train is not the only thing that changes our perspective. If the embankment observer is on the west side of the train, does the light move faster because of this velocity to reach the embankment observer?
     
  13. AlexG Like nailing Jello to a tree Valued Senior Member

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    So your position is that the earth does not orbit the sun? The earth does not rotate? If you are standing still in your living room, you have an absolute velocity of zero? :shrug:

    Nonsense.
     
  14. RJBeery Natural Philosopher Valued Senior Member

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    Even IF you wanted to assign some arbitrary frame as "the absolute rest frame", it is required to be inertial (i.e. not accelerating/spinning). Since the Earth is undeniably spinning, it is not an appropriate choice for an absolute reference frame. Otherwise the distant stars would be assigned velocities of WELL BEYOND c in their orbit path!

    Since some folks seem to have a problem understanding SR I don't expect the above point to be absorbed, either, but I thought I'd give it a shot.
     
  15. James R Just this guy, you know? Staff Member

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    Motor Daddy:

    Ok. Let's assume you're right and embankments on Earth are absolutely stationary.

    Now, you take your train track and train to Mars and set it up near an embankment on Mars. Do you now expect different results from the experiments?
     
  16. Neddy Bate Valued Senior Member

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    I think you nailed it pretty well right there.

    Except, as Pete said, you should probably change your word "frames" to something else, like "objects". It's a minor distinction, but you don't want to accidentally make it sound like some "frames" (reference frames) will not have invariance of c.


    Yes, but if you consider yourself moving, then you are sure to become confused about reference frames. I recommend that you never consider yourself moving. You won't really be in the reference frame you think you're in.

    If you want to switch to a different frame, that is fine. Do you want to consider what it is like to be the person on the train? You can put yourself in the train, and then consider yourself stationary.

    Do you want to consider what it is like to be the person on the embankment? Put yourself there, and then consider yourself stationary.


    If you ever think you are moving, then you are probably in the wrong frame, without realizing it. It messes things up, I tells ya.

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  17. AlphaNumeric Fully ionized Registered Senior Member

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    Do you not realise the daftness of what you just said? If there's one and only one 'true' zero velocity frame than doesn't it strike you as odd that it's precisely the platform? These sorts of experiments have been done and thus by your logic Earth, specifically the apparatus used, is at just the right velocity to have 'zero' velocity. In all the universe, of all the objects which are moving (all of them at some relative velocity compared to Earth) it just so happens we inhabit the special planet where zero absolute velocity occurs when objects are nailed to the ground? There's terribly egocentric of you, to think Earth is so special, as you must conclude given your 'logic' and the experiments done.

    Of course your logic gets worse, as something nailed to the ground cannot be in a true inertial frame because the Earth revolves and rotational motion can be measured. And it goes around the Sun, which goes around the galactic core, which moves in our local cluster etc. So for any experiment which lasts more than a single instant in time its impossible to measure a result of zero absolute velocity since every such train embankment is experiencing accelerations due to rotational motion and thus at some point is definitely not at absolute rest. That also means that if you do exactly the same experiment later you should get a different 'absolute velocity' reading due to the time summed accelerations altering the velocity of the system.

    This is not the case and thus your conclusion that such outcomes imply the embankment is at absolute rest are incompatible with reality. This isn't to say that the notion of absolute rest is proven false but its enough to show your assertions about the physics of said systems is wrong.
     
  18. Motor Daddy Valued Senior Member

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    You guys don't understand the theoretical zero velocity embankment, do you???

    Do I really believe the Earth doesn't orbit the Sun? NO, of course not, as the earth came from the sun, and continues to get further away. Mass evolves to space!

    There is only one velocity the embankment in Einstein's thought experiment could have, and that is zero velocity. Any other velocity and the thought experiment doesn't work, as light traveled the same time and distance to reach the midpoint observer, and arrived simultaneously. That can only happen if the embankment observer had a true zero velocity.

    NO, I'm not saying an embankment on Earth has zero velocity, I am saying in Einstein's thought experiment in chapter 9, there is only one possibility, and that is a zero velocity. If you don't like the fact that he proposed a zero velocity embankment, presumably located on Earth, take issue with him, not me. He said it, I didn't. I'm just telling you that in order for light to travel equal distance and equal time to a midpoint observer, and the lights impacting that midpoint observer simultaneously, it MUST have been a zero velocity. MUST HAVE BEEN!!!
     
    Last edited: Dec 12, 2010
  19. Motor Daddy Valued Senior Member

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    If you are standing in your living room at the midpoint between two synchronized clocks, and you see both clocks as reading the same time, then you have an absolute zero velocity. If one clocks reads different to you than the other does, then you have a velocity. It's just as simple as that. Light travels independently of frames!

    Am I saying which will happen? NO, I'm just telling you what each result means, and in Einstein's chapter 9, the result of the embankment observer being at the midpoint, and light traveling the same distance and time, and arriving at the midpoint simultaneously can only mean one thing, that the embankment observer had a true zero velocity. It's not even debatable! Don't believe me? Then give the embankment a velocity and see what happens.
     
    Last edited: Dec 12, 2010
  20. Motor Daddy Valued Senior Member

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    1. Light is inertial, it doesn't accelerate. It travels at c, which is an absolute velocity.

    2. 100 RPM is inertial, and it is "spinning." Do you understand that?
     
  21. arfa brane call me arf Valued Senior Member

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    If you just edit M.D.'s thesis slightly:

    "There is only one [relative] velocity the embankment in Einstein's thought experiment could have, and that is zero [relative] velocity. Any other velocity and the thought experiment doesn't work, as light traveled the same time and distance to reach the midpoint observer, and arrived simultaneously. That can only happen if the embankment observer had a true zero [relative] velocity.

    ...I'm just telling you that in order for light to travel equal distance and equal time to a midpoint observer, and the lights impacting that midpoint observer simultaneously, [they] MUST have been at zero velocity [relative to the places the lights are emitted from]."

    Note that being at a midpoint of emission of two sources of light is a very artificial situation, and doesn't occur very often in the real world. But the point is that the thought experiment is meant to illustrate the independence of the velocity of light from the velocities of moving or 'stationary' objects.
     
  22. RJBeery Natural Philosopher Valued Senior Member

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    It's circular logic here. "The midpoint" between two events is determined by viewing them simultaneously. If you, the clocks, and the living room were spinning in a large circle at over 1000 MPH (which you are), you could still observe both clocks retaining their synchronicity (wow, The Police just stormed my brain!).
     
  23. Motor Daddy Valued Senior Member

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    It's not circular logic, the midpoint of a length is a point centered between the ends. It is timeless.


    Wrong, as light takes time to travel. You can remain centered between the clocks the entire time, but light emitted simultaneously from each clock has to travel a different distance to reach you if you were in motion after the lights were emitted.
     

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